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STUDIES ON THE METAL COMPLEXES OF FIRST
AND SECOND TRANSITION SERIES
A
THESIS SUBMITTED
BY
VANDANA PANDEY (Regn. No. 2K05-NITK-1075)
FOR THE AWARD OF DEGREE OF
DOCTOR OF PHILOSOPHY
IN
CHEMISTRY
UNDER THE SUPERVISION OF
Dr. DINESH KUMAR
DEPARTMENT OF CHEMISTRY
NATIONAL INSTITUTE OF TECHNOLOGY
KURUKSHETRA-136119
HARYANA, INDIA
2011
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CONTENTS Foreword i- iv
INTRODUCTION 1-116
Chapter 1 Coordination compounds of Schiff base containing urea
moiety
117-124
Chapter 2
Ligational behavior of the azetidin-2-one derived from
salicylaldehyde and o-hydroxyphenylurea towards some di-, tri-
and hexavalent metal ions
125-129
Chapter 3 Physico-chemical studies on the coordination compounds
of thiazolidin-4-one derived from salicylaldehyde and
o-hydroxyphenylurea
130-135
Chapter 4 Studies on the coordination compounds of the
polystyrene-anchored Schiff base obtained from the condensation of
chloromethylated polystyrene, 3-formylsalicylic acid and o-
hydroxyphenylurea
136-141
Appendix-1 Abbreviations 142-143
Appendix-2 Materials and sources 144-145
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Appendix-3 Analyses and physical measurements 146-147
Appendix-4
Tables at a glance 148-156
Appendix-5 Figures at a glance
157-196
References 197-215
Summary 216-217
Future scope 218-218
List of published papers and their reprints
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i
FOREWORD The Thesis contains General Introduction, four Chapters
dealing with the syntheses, elemental analyses, spectral studies
and the magnetic susceptibility measurements on the coordination
compounds of Schiff base, azetidin-2-one, thiazolidin-4-one,
polystyrene-anchored Schiff base. The organization of the Thesis is
such that each
Chapter consists of Abstract, Introduction, Experimental,
Results and Discussion and Conclusion. The Appendicies 1, 2, 3, 4
and 5 have been used for the Abbreviations for the chemical
entities, Materials and sources, Analyses and physical
measurements, Tables and Figures respectively used elsewhere. The
Synopsis of each Chapter is presented below:
Chapter 1 This Chapter describes the syntheses and
characterization of the Schiff base, LH3 (1) derived from the
condensation of salicylaldehyde and o-hydroxyphenylurea and its
coordination compounds with Zn(II), Co(II), Ni(II), Fe(III) and
Zr(OH)2(IV) ions. The nucleophilic addition reaction followed by
the elimination of one H2O molecule between salicylaldehyde and
o-hydroxyphenylurea in equimolar ratio in MeOH results in the
formation of 1. A MeOH solution of the latter reacts with a MeOH
solution of Zn(II), Co(II), Ni(II), Fe(III) and Zr(OH)2(IV) ions in
equimolar ratio and forms [Zn(LH)(MeOH)] (2), [M(LH)(MeOH)2]2 (3, M
= Co, Ni), [FeCl(LH)(MeOH)]2 (4) and [Zr(OH)2(LH)(MeOH)2] (5)
respectively. The coordination compounds are insoluble in H2O, MeOH
and EtOH but soluble in DMF and DMSO. They have been characterized
on the basis of elemental analyses, molecular weight, spectral (IR,
reflectance, 1H NMR) studies, thermo-gravimetric analyses and the
magnetic susceptibility measurements. Their
molar conductance values (M = 4.58.2 mho cm2 mol-1 in DMF) show
that they are non-electrolytes. The molecular weight measurements
indicate a monomeric structure of 2 and 5, while a dimeric
structure of 3 (M = Co, Ni)
and 4. The loss of the coordinated MeOH molecule(s) occur
between 80-120 oC in 2-5. LH3 acts as a dibasic tridentate ONO
donor ligand. The (MO) and (MN) stretches occur between 540-570 and
420-450 cm-1
respectively. The reduction of Racah parameter [from the free
ion values: 971 cm-1 to 780.7 cm-1 for Co(II) and from 1030 cm-1 to
799.8 cm-1 for Ni(II)] and the values of % covalency in 3 [19.5
when M = Co(II) and 23.0 when M = Ni(II)] are indicative of
covalent nature of these coordination compounds. 1 exhibits
multiplet at 6.82-8.00 ppm
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ii
due to the aromatic protons, a singlet at 7.32 ppm due to the
azomethine proton, a broad signal at 10.91 ppm due to the phenolic
proton and a singlet at 11.73 ppm due to the NH proton. The
appearance of alcoholic proton (singlet, 1H) at 2.74 ppm and methyl
protons at 3.58 ppm in 2 confirms the presence of coordinated MeOH.
The reduced magnetic moments of 3 (M = Co, Ni) and 4 may be due to
the magnetic interaction between the two metal ions connected by
phenoxo bridge. A tetrahedral geometry to 2, an octahedral geometry
to 3 (M = Co, Ni) and 4 and a pentagonal-bipyramidal geometry to 5
have been assigned. The energy optimized structures, 6 and 7 for 1
and 2 respectively are proposed using the semiempirical ZINDO/1
quantum mechanical calculations.
Chapter 2 This Chapter describes the syntheses of the
azetidin-2-one, L'H3 (8) [obtained by
the cyclocondensation of 1 with chloroacetyl chloride
(ClCH2COCl, CAC) in the presence of triethylamine (Et3N) in
dioxane]. A MeOH solution of Cu(II), Cd(II), Mn(II), Fe(III) and
MoO2(VI) ions reacts with 8 in 1:1 molar ratio and forms the
monomeric coordination compounds, [Cu(OAc)(L'H2)] (9),
[Cd(OAc)(L'H2)] (10), [Mn(OAc)(L'H2)(MeOH)2] (11),
[FeCl2(L'H2)(MeOH)] (12) and [MoO2(acac)(L'H2)(MeOH)] (13)
respectively. The coordination compounds have been characterized on
the basis of elemental analyses, molar conductance, molecular
weight, spectral (IR, reflectance and ESR) studies and magnetic
susceptibility measurements. They are insoluble in H2O, MeOH, EtOH
but
soluble in DMSO and DMF. They are non-electrolytes in DMF (M =
5.3-8.3 mho cm2 mol-1). 8 behaves as a monobasic tridentate ONO
donor ligand. The acetato ligands are bonded to the central metal
ions in a monodentate fashion in 9, 10 and 11. The ESR
spectral parameters of 9 [g|| (2.8) > g (2.08) > 2.0), A||
(1.50 10-2 cm-1, A = 3.0 10-3 cm-1) and G (3.50)] are typical of a
tetragonal type geometry. The magnetic moments, 1.87, 5.81 and 5.78
B.M. for 9, 11 and 12 respectively account for their magnetically
dilute nature. A square-planar structure for 9, a tetrahedral
structure for 10, the octahedral structures for 11 and 12 are
proposed. The coordination number of Mo is eight in 13. Chapter
3
This Chapter deals with the syntheses and characterization of a
thiazolidin-4-one, L'H3 (14) [obtained by the cycloaddition
reaction of LH3 (1) with mercaptoacetic acid (HSCH2COOH) in dry
C6H6] and its coordination compounds with Cu(II), Co(II),
Ni(II),
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iii
MoO2(VI) and Zr(OH)2(IV) ions. 14 reacts with appropriate metal
ions in 1:1 molar ratio in MeOH and produces the compounds,
[Cu(OAc)(L'H2)] (15), [M(OAc)(L'H2)(MeOH)2] (16, M = Co, Ni),
[MoO2(acac)(L'H2)(MeOH)] (17) and [Zr(OH)3(L'H2)] (18). The
coordination compounds are air-stable, insoluble in H2O, MeOH, EtOH
and soluble in
DMSO and DMF. They are non-electrolytes (M = 4.3-9.6 mho cm2
mol-1) in DMF. 14 behaves as a monobasic tridentate ONO donor
ligand coordinating through its phenolic O (o-aminophenol moiety),
N (o-aminophenol moiety) and O (thiazolidin-4-one moiety) atoms.
The phenolic O (aldehydic moiety), N and S atoms (thiazolidin-4-one
moiety) are not involved in coordination. The appearance of two new
bands between 1564-1572 cm-1
[as(OAc)] and 1340-1352 cm-1 [s(OAc)] stretches indicates the
presence of the coordinated acetato group in 15 and 16 (M = Co,
Ni). The presence of coordinated MeOH molecule(s) in 16 (M = Co,
Ni) and 17 is proposed on the basis of IR spectral studies. The
reflectance spectra of 15 and 16 (M = Co, Ni) are consistent with
square-planar and octahedral environment around metal ions. 14
exhibits the signals at 6.82-8.00, 7.32, 10.91 and 11.7 ppm due to
the aromatic, azomethine, OH protons, andNH protons respectively. A
square-planar structure for 15, an octahedral structure for 16 (M =
Co, Ni) and 18 are proposed. Mo assumes a coordination number of
eight in 17.
Chapter 4 This Chapter deals with the syntheses and
characterization of polystyrene-anchored
Schiff base, PSCH2LH3 (19) and its coordination compounds. The
nucleophilic addition reaction followed by the elimination of one
H2O molecule between
polystyrene-3-formylsalicylate and o-hydroxyphenylurea in DMF in
the presence o f ethyl acetate results in the format ion o f 19 .
The lat ter reacts with a DMF swollen suspension of Cu(II), Cd(II),
Mn(II), Fe(III) and MoO2(VI) ions and forms the corresponding
polystyrene-anchored coordination compounds, [PSCH2LH2Cu(OAc)(DMF)]
(20), [PSCH2LH2 Cd(OAc)(DMF)] (21), [PSCH2LH2Mn(OAc)(DMF)3] (22),
[PSCH2LH2 FeCl2(DMF)2] (23) and [PSCH2LH2MoO2(acac)] (24 , acacH =
pentane-2,4-dione) respect ively. The polystyrene-anchored
coordination compounds (20-24) have been characterized on the basis
of elemental analyses, spectral (IR, reflectance, ESR) studies and
magnetic susceptibility measurements. The per cent reaction
conversion (PRC) of the compounds
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iv
lies between 44.8-81.3 and the metal binding capacity (MBC) of
the ligand between 0.32-0.60 mmol of metal per g of the resin. The
coordinated DMF molecules are completely lost from the
polystyrene-anchored coordination compounds by heat ing them at
a
definite temperature in an air-oven for 3 h . 19
acts as a monobasic bidentate ON donor ligand in these
compounds. 20 shows usual anisotropic pattern with two g values,
which are characteristic of axial symmetry. 20 , 22 and 23 are
paramagnetic and magnetically dilute. A square-planar structure for
20 , a tetrahedral structure for 21and the octahedral structures
for 22, 23 and 24 are proposed.
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IINNTTRROODDUUCCTTIIOONN
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1
The Introductory Part of the Thesis entitled Studies on the
Metal Complexes of First and Second Transition Series consists the
Literature Survey on the coordination compounds of Mn(II), Fe(III),
Co(II), Ni(II), Cu(II), Zn(II), Zr(OH)2(IV), MoO2(VI) and Cd(II)
ions. A metal coordination compound is the aggregate of Lewis acid
(electron pair acceptor central metal atom or metal ion having
vacant d- or f- orbitals) and Lewis base(s) (electron pair donor
anion, cation or neutral entity). A brief summary of the
coordination compounds of the above metal ions with monodentate,
bidentate, tridentate, tetradentate
and polydentate ligands are presented here.
Coordination compounds of manganese(II) Mangnese (Mn) is a
greyish-white transition metal belonging to Group 7 and
Period IV of the Periodic Table. Its atomic number, atomic
weight and the electronic configurations are 25, 54.93 amu and [Ar]
4s23d5 respectively. Its common oxidation states are +2, +3, +4, +6
and +7. Mn ions have various colours depending upon their oxidation
state and they are generally paramagnetic. The most stable
oxidation state of Mn
is +2, which has pink to red colour. Mn(II) ion acts as a
cofactor for a number of enzymes in higher organisms, where they
are essential in detoxification of superoxide free radicals. It is
an essential trace nutrient in all forms of life. The ability of
Mn(II) ion to form the coordination compounds with a wide range of
ligands has been reported. These ligands are
coordinated to Mn(II) ion in a monodentate, bidentate,
tridentate, tetradentate, pentadentate and hexadentate fashion. We
present here a brief survey of the Chemistry of coordination
compounds of Mn(II) ion. A. With monodentate ligands:
The synthesis of centrosymmetric compound,
bis[-(E)-1,5-dimethyl-2-phenyl-4-(3-pyridylmethyleneamino)pyrazol-3(2H)-one]bis{dibromido[(E)-1,5-dimethyl-2-phenyl-4-(3-pyridylmethyleneamino)pyrazol-3(2H)-one]manganese(II)},
[Mn2Br4(C17H16N4O)4] has been reported[1]. In the crystal
structure, the Mn atom adopts a trigonal-bipyramidal
geometry and the ligand adopts two coordination modes,
monodentate and bidentate bridging.
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2
B. With bidentate ligands:
Maurya et al.[2] have synthesized a reddish-brown,
non-electrolyte (M = 10.5 mho cm2 mol-1), four-coordinate compound,
[Mn(OAc)L(H2O)] (where LH = 25; R = 3-OMe, R' = OH, R'' = H) by
refluxing a mixture of an EtOH solution of Mn(OAc)24H2O and a DMF
solution of LH in 1:1 molar ratio for 4 h. It decomposes at 260 oC.
It is soluble in DMF and DMSO. LH behaves as a monobasic bidentate
ON donor ligand coordinating through its phenolic O and azomethine
N atoms. The acetato ligand is coordinated to the metal ion in a
monodentate fashion. The (MnO) and the (MnN) vibrations occur at
510 an 435 cm-1 respectively. Its magnetic moment is 5.94 B.M.
The six-coordinate heterochelate, [MnL2L'] [here LH = 25, R =
5-Cl, 5-Br; R' = OH; R'' = H; L' = 26, R = R' = H; R'' = Me; R''' =
(CH2)2] has been synthesized[3]. LH acts as a monobasic bidentate
ON donor ligand coordinating through its phenolic O and
azomethine N atoms, whereas L'
acts as a neutral NN donor ligand coordinating through its
azomethine N atoms. The heterochelates exhibit three weak bands at
~15000, ~19000 and ~25500 cm-1 due to the 6A1g 4T1g(G)(1), 6A1g
4T2g(G)(2) and 6A1g 4A1g(G)(3) transitions respectively for
octahedral geometry. The magnetic moments of the
heterochelates are 6.00 and 6.01 BM.respectively. The
heterochelates show higher antimicrobial activity against S. typhi,
F. oxysporum, S. cereusisae and L. theobromae than LH. The enhanced
antimicrobial activity of the heterochelates against these microbes
is due to the presence of two halogen and four azomethine groups.
An octahedral structure (27, R = 5-Cl, 5-Br; M = Mn) has been
suggested for the heterochelates.
The reaction of 2-aminophenol with Mn(II) ions in 1:1 molar
ratio produces the aminophenolate compound as precipitate (in
solution), which on further treatment with 4-benzyloxybenzaldehyde
or but-2-enal in the above molar ratio yields the six-coordinate,
orange-yellow compound, [MnL2(H2O)2] or brown compound,
[MnL'2(H2O)2] respectively (where LH and L'H = 28 and 29
respectively)[4]. They melt at 180 and 200 oC respectively. They
display two bands one at 16667, 16393 cm-1 and another at 20704,
20000 cm-1 respectively indicating the presence of an octahedral
environment around the metal ion. They exhibit the magnetic moments
5.94 and 5.78 B.M. respectively, corresponding to high-spin
octahedral symmetry due to five unpaired electrons. The
coordination compounds are more biologically active against S.
dysenteria, E. coli (responsible for
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3
diarrhoea), P. aeruginosa, B. subtilis (responsible for
contamination), S. lutea and S. aureus (responsible for wound
infection) than 2-aminophenol.
Due to the formation of stable coordination compounds with heavy
metal ions,
aroylhydrazones have been employed as specific reagents in
analytical and extraction chemistry[5]. A red, four-coordinate
compound, [Mn(LH)2] (where LH2 = 30, R = H) is obtained when an
EtOH solution of LH2 and Mn(OAc)24H2O in 2:1 molar ratio are
refluxed in the presence of TEM[6]. It decomposes at 274 oC and its
molar conductance is
43 mho cm2 mol-1. LH2 acts as a monobasic bidentate ON donor
ligand coordinating through its enolic O and azomethine N atoms. C.
With tridentate ligands:
A monomeric, dark-brown, six-coordinate, polystyrene-anchored
coordination
compound, [PSLMn(DMF)3] (here PSLH2 = 31) is obtained[7] by
refluxing a DMF swollen suspension of Mn(OAc)24H2O and PSLH2 for 8
h. The Schiff base acts as a dibasic tridentate ONO donor ligand.
The DMF molecules are coordinated to the metal ion. The PRC of the
compound is 78.6. The MBC of the ligand is 0.60 mmol of metal per g
of it. Its magnetic moment is 5.92 B.M. It displays three bands at
18440, 22980 and 25220 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G)
and 6A1g 4A1g(G) spin-forbidden transitions respectively.
The heterochelates containing O and N atoms are important owing
to their
significant antifungal, antibacterial and anticancer activity.
The pale-brown compound, [Mn5Cl10(LH2)(H2O)9] and the black
heterochelate, [Mn2Cl3(LH2)(acac)(H2O)] (where LH2 = 32) have been
synthesized[8]. They are non-electrolytes. The ligand acts as a
neutral tridentate ONO donor. The central Mn(II) ions in both the
cases are held together by bridged chloro ligands and the remaining
coordination sites are occupied by O atom of water molecules. The
appearance of three bands at 25640, 22222, 17240 and 25315, 20833,
16805 cm-1 and the low magnetic moments (2.5 and 3.1 BM)
respectively of the compound/ heterochelate due to super-exchange
suggest their octahedral geometry around
the metal ions.
A dark-brown, six-coordinate, polystyrene-anchored compound,
[PSCH2LMn(DMF)3] (where PSCH2LH2 = 33; R = 3-PSCH2OCO, X = O)
has been synthesized by refluxing Mn(OAc)24H2O and the ligand in
2:1 molar ratio in DMF[9]. The
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4
Schiff base acts as a dibasic tridentate ONO donor ligand
coordinating through its phenolic O, azomethine N and enolic O
atoms. The furanoic O atom does not participate towards
coordination as evident by the unaltered (COC) stretch (1080 cm-1)
both in ligand and the compound. Its magnetic moment is 5.85 B.M.
The appearance of two bands one at 16395 cm-1 and another at 24600
cm-1 due to the 6A1g 4T1g(G) and 6A1g 4T2g(G) transitions is
indicative of an octahedral environment around the metal ion.
Kumar et al.[10]
have synthesized a dark-brown, polystyrene-anchored six-
coordinate compound, [PSCH2LHMn(DMF)3] (where PSCH2LH3 = 34) by
refluxing a DMF swollen suspension of PSCH2LH3 and a DMF solution
of Mn(OAc)24H2O. The PRC of the compound is 93.3 and the MBC of
PSCH2LH3 is 0.58 mmol of Mn per g of the ligand. PSCH2LH3 behaves
as a dibasic tridentate ONO donor ligand. The magnetic
moment (5.9 B.M.) and the appearance of two bands one at 16000
and another at 22500 cm-1 due to the 6A1g 4T1g(G) and 6A1g 4T2g(G)
transitions respectively indicate an octahedral environment around
the metal ion.
A deep-brown, binuclear, six-coordinate compound, [Mn2L2(H2O)4]
is obtained by stirring an EtOH solution of Mn(OAc)24H2O and LH2
(35A-35C) in 1:1 molar ratio in the presence of LiOH for 4 h[11].
It melts at 198 oC. It is soluble in Me2CO but insoluble in MeOH.
The ligand behaves as a dibasic tridentate OON donor. The lower
value of the magnetic moment (5.39 B.M.) indicates the presence of
an anti-ferromagnetic interaction between the adjacent metal
cations. An octahedral geometry 36 (M = Mn; A = H2O) has been
suggested for the compound.
The synthesis of a light-yellow, four-coordinate,
non-electrolyte (in DMSO), [MnCl(LH)]3H2O (where LH2 = cephalexin,
37) has been reported[12]. It is air-stable, soluble in DMSO and
DMF, slightly soluble in MeCN. The coordination of the ligand
occurs through the carboxylato O, carbonyl O (-lactam) and N
atom of NH2 group. The carboxylato group is coordinated in a
monodentate mode ( = 235 cm-1). A mass loss equivalent to three
water molecules in the 90-110 oC range suggests that these
molecules are not coordinated to the metal ion. The magnetic moment
(5.6 B.M.) indicates the presence of five unpaired electrons. A
tetrahedral structure (38, M = Mn) has been assigned to it.
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5
A four-coordinate compound, [MnCl(LH)]3H2O (here LH2 = 39) has
been synthesized by stirring a MeOH solution of NaHL and MnCl24H2O
in 2:1 molar ratio
for 8 h at room temperature[13]. It is air-stable, soluble in
DMSO and DMF and slightly soluble in MeCN. The (C==O)(-lactam)
stretch of the ligand occurring at 1780 cm-1 shifts to 1720 cm-1 in
the coordination compound indicating the involvement of carbonyl O
atom towards coordination. The overlapped (C==O)(amide) and
(C==O)(ester) bands in LH2 appears at 1640 cm-1. These bands remain
unchanged in the compound suggesting that coordination of the
ligand occurs through the O atom from the lactam carbonyl group
rather than the amide and ester carbonyl groups. The carboxylato
group is coordinated in a monodentate mode ( = 240 cm-1). The amino
group of LH2 is coordinated to the metal ion as evident by the
presence of the (MnN) stretch at 450 cm-1. Thus, LH2 behaves as a
monobasic tridentate OON donor ligand. The compound has a magnetic
moment of 5.4 B.M. It shows higher activity than LH2 against P.
mirabilis, K. pneumoniae, S. enteriditis and E. coli, while it
remains inactive towards S. aureus and P. aeruginosa. A tetrahedral
structure (40, M = Mn) has been assigned to it.
Hankare et al.[14] have synthesized a brown, dimeric,
four-coordinate, non-
electrolyte, high-spin compound, [Mn2Cl2L2] [here LH = 41, the
Schiff base obtained from the condensation of
5-(2'-thiazolylazo)salicylaldehyde and 4-methoxyaniline] by
refluxing an EtOH solution of MnCl24H2O and LH in 1:1 molar ratio.
It is soluble in DMSO. The Schiff base acts as an ONN donor ligand
coordinating through its phenolic O and azomethine N to one Mn(II)
ion and through azo N atom to another Mn(II) ion.
Upon digesting an aqueous solution of Mn(OAc)24H2O and a DMF
solution of LH (42; R = Me, R' = Ph) in 1:1 molar ratio for h, a
six-coordinate compound, [MnL2] is obtained[15]. It is insoluble in
common organic solvents but sparingly soluble in dioxane and DMF.
The monobasic ligand coordinates to the metal ion through its
pyrazolinic O,
azomethine N and thiazolic N atoms. The (MnO) and (MnN)
vibrations occur at 460 and 390 cm-1 respectively in the
coordination compound. Due to their doubly forbidden nature, it
exhibits three very low intense bands at 16667, 23256 and 26316
cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4Eg(G)/4A1g(G)
transitions respectively indicating the octahedral environment
around metal ions. The magnetic moment (6.05 B.M.) suggests its
distorted octahedral geometry alongwith high-spin 3d5
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6
configuration of the metal ion. The ligand and the coordination
compound show antibacterial activity against E. coli, B. subtilis
and S. aureus.
Chandole et al.[16] have synthesized the air-stable,
non-hygroscopic, non-
electrolyte, dimeric, six-coordinate compound, [MnClL(H2O)]2
(here LH = 43; R = Me, Et, propyl) and [MnCl(L'H)(H2O)]2 (here L'H2
= 43; R = CH2CH2OH) by refluxing a MeOH solution of MnCl22H2O and
LH or L'H2 in 1:1 molar ratio for 4 h. They are soluble in DMF and
DMSO. The coordinated water molecules are lost between 190-200 oC.
Although L'H2 is potentially a dibasic tetradentate NONO donor
ligand but similar to LH, it also behaves as a monobasic tridentate
NON donor ligand bridging through its enolic O atom. The
coordination compounds display three bands between 16835-16949,
~23584 and ~26385 cm-1 due to the 6A1g 4T1g(G)(1), 6A1g 4T2g(G)(2)
and 6A1g 4Eg(G)(3) transitions respectively indicating the
octahedral environment around the metal ion. Their magnetic moments
lie between 4.88-5.07 B.M. The compound (when R = Me) crystallizes
in a monoclinic fashion with a = b = 4.92 , c = 5.41 , = = 90, =
120. They exhibit higher antifungal activity against A. niger than
the corresponding ligands. A distorted octahedral structure (44, M
= Mn) has been suggested for them.
On refluxing an hot MeOH solution of Mn(NO3)26H2O and LH (45) in
1:2 molar ratio at pH = 7.5-8.5, a brown, six-coordinate complex,
[MnL2] is obtained[17]. The complex is non-electrolyte (M = 10.02
mho cm2 mol-1 in DMSO). LH acts as a monobasic tridentate ONN donor
ligand coordinating through its phenolic O and both azomethine N
atoms. The magnetic moment (5.7 B.M.) and the appearance of the
bands at 16611, 24390 and 26881 cm-1 due to the 6A1g 4T1g(G), 6A1g
4T2g(G) and 6A1g 4Eg transitions respectively indicate the presence
of an octahedral environment around the metal ion. The complex
crystallizes in monoclinic fashion with a = 14.223 , b = 5.196 , c
= 7.754 . The compound shows higher antimicrobial activity against
Gram-negative E. coli, Gram-positive S. aureus and LH.
The coordination compounds of Schiff bases containing S atom
have received considerable attention during recent past, primarily
due to the remarkable antitumor, antibacterial and antiviral
properties[18,19]. The complexation of yellow colored
benzothiazoline derivative,
3-(2,3-dihydro-1,3-benzothiazole-2-yl)quinoxalin-2(1H)-one (LH2 =
46A, 46B) with Mn(II) ion proceeds with the rearrangement of
benzothiazoline
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7
ring to form the corresponding red colored, non-electrolyte,
[Mn(LH)(OAc)(H2O)2][20]. In the presence of Mn(II) ion, the
benzothiazoline rearranges to form the Schiff base (LH2). The
latter coordinates in keto form as monobasic tridentate ONS donor.
The magnetic
moment (5.80 B. M.) and the existence of the bands at 24814,
23529 and 21413 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g
4Eg transitions respectively, are indicative of an octahedral
environment around the Mn(II) ion. The loss of coordinated water
molecules occurs between
150-200 oC. Makode et al.[21] have synthesized a light-green,
dimeric, six-coordinate
compound, [MnL(H2O)2]2 (where LH2 = 47) by refluxing
Mn(OAc)24H2O and LH2 in EtOH. Although LH2 is potentially a dibasic
pentadentate ONNSS donor ligand, but
behaves as a dibasic tridentate ONS donor ligand. The phenolic
O, azomethine N and the thioenolic S afford the coordination sites
of the octahedron. The value of magnetic
moment (5.14 B.M.) and the appearance of three bands due to the
6A1g 4T1g, 6A1g 4T2g and
6A1g 4A1g transitions indicate its octahedral stereochemistry.
Both the coordinated
H2O molecules are lost between 160-210 oC. It shows activity
against E. aureus, P. mirabilis and S. typhi.
An aqueous solution of Mn(OAc)24H2O reacts with an EtOH solution
of LH2 (48) in 1:2 molar ratio and forms[22] a yellow compound,
[Mn(LH)2]. It is stable in air, decomposes at 201 oC, insoluble in
EtOH, C6H6 and CHCl3 but soluble in Me2CO, DMF and DMSO. It is
non-electrolyte in DMSO and Me2CO. LH2 acts as a monobasic
tridentate ONS donor ligand. The (MnN) vibrations occur at 565 cm-1
in the compound. The magnetic moment (5.9 B.M.) indicates the
presence of high-spin octahedral environment around the metal ion.
The compound assumes a six-coordinate structure (49, M = Mn).
A four-coordinate, air-stable, non-electrolyte (in DMSO),
[MnCl(LH)] (where LH2 = cephalothin, 50; R = H, R' = Me) has been
synthesized by stirring a MeOH solution of MnCl24H2O and LH2 in 1:2
molar ratio[23]. It is soluble in DMSO and DMF, slightly soluble in
MeCN and insoluble in MeOH and H2O. The (C==O)(-lactam) stretch of
LH2 shifts from 1730 to 1690 cm-1 in the compound indicating the
involvement of O atom towards coordination. The (C==O)(amide)
stretch of LH2 occuring at 1650 cm-1 remains unchanged in the
compound indicating its non-involvement towards coordination.
The
-
8
as(COO) and s(COO) stretches of LH2 occurring at 1620 and 1400
cm-1 shift to 1615 and 1380 cm-1 respectively in the compound
indicating monodentate behaviour of the carboxylato group ( = 235
cm-1). LH2 acts as a monobasic tridentate OOS donor ligand. The
presence of MS stretch indicates the coordination through thiophene
S atom. The value of magnetic moment (5.5 B.M.) indicates the
presence of five unpaired electrons. It shows a very weak
absorption band at 25640 cm-1 due to a spin-orbit forbidden
transition. It shows antibacterial activity higher than the ligand
against S. aureus, E. coli, S.
enteriditis and P. mirabilis, while it shows no activity against
K. pneumoniae. A tetrahedral structure (51; R = H, R' = Me, M = Mn,
A = nil) has been assigned to it.
An EtOH solution of MnCl24H2O and LH [here LH = 52, R =
(C5H4N)CH, R' = NH C6H4(4-OMe); L'H = 52, R = (C5H4N)CH, R' =
NHCH2CH2C6H5; L''H = 52, R = (C5H4N)CH, R' = N(Me)C6H5; X = S] in
1:2 molar ratio upon refluxing[24] produce brown-orange,
six-coordinate, non-electrolyte, [MnL2]H2OEtOH, [MnL'2]3H2O,
[MnL''2]3H2O; brown, six-coordinate, 1:1 electrolyte,
[MnL(LH)](OAc) and brown, six-coordinate, 1:2 electrolyte,
[Mn(L''H)2](SCN)2MeOH. The ligands behave as a monobasic tridentate
NNS donors in [MnL2]H2OEtOH, [MnL'2]3H2O, [MnL''2]3H2O; neutral
tridentate NNS donor in [Mn(L''H)2](SCN)2MeOH and neutral as well
as monobasic tridentate NNS donor in [MnL(LH)](OAc). The magnetic
moments are 6.02, 5.33, 5.56, 5.62 and 5.81 B.M. for [MnL2]H2OEtOH,
[MnL'2]3H2O, [MnL''2]3H2O, [MnL(LH)](OAc) and [Mn(L''H)2](SCN)2MeOH
respectively. A broad band at 22936, 23419, 23148, 23810 and 23542
cm-1 due to the 6A1g 4T2g(G) transition and a very week band at
18248, 18903, 18867, 18051 and 18478 cm-1 due to the 6A1g
4T1g(G)(2) transition respectively occur in [MnL2]H2OEtOH,
[MnL'2]3H2O, [MnL''2]3H2O, [MnL(LH)](OAc) and [Mn(L''H)2](SCN)2MeOH
respectively. [MnL2]H2OEtOH crystallizes in a monoclinic fashion
with a = 15.164 , b = 18.793 , c = 11.896 ; = = 90.0o, = 109.31o
and Z = 8. An octahedral geometry is assigned to them. D. With
tetradentate ligands:
Kumar et al.[25] have become the first to synthesize a
polystyrene-anchored asymmetric Schiff base, PSCH2LH2 [53; R = R' =
Me, R'' = (CH2)2] and its brown, six-coordinate compound,
[PSCH2LMn(DMF)2]. The Schiff base acts as a dibasic tetradentate
ONNO donor ligand. The magnetic moment of the compound (5.92 B.M.)
and
-
9
the occurrence of two bands one at 16950 cm-1 and other at 24400
cm-1 are characteristic of its octahedral geometry around Mn(II)
ion.
Hasnain et al.[26] have reported the two step syntheses of Mn
chelated
polyurethane containing LH2
(54) as the Schiff base. In the first step, a DMSO solution of
LH2 refluxed with Mn(OAc)24H2O in DMSO forms a mustard coloured
complex, [MnL(H2O)2]. In the second step, the polyaddition of
toluene-2,4-diisocyanate with [MnL(H2O)2] is carried out in the
presence of di-n-butyltindilaurate. The ligand behaves as a
tetradentate ONNO donor in both the compounds coordinating through
its phenolic O and N atoms of thiosemicarbazide moieties. The
high-spin octahedral polymeric complex
(5.68 B.M.) displays three bands at 16200, 19400 and 22980 cm-1
due to the 6A1g 4T1g, 6A1g 4T2g and 6A1g 4A1g spin-forbidden
transitions respectively. The antimicrobial
studies show that metal chelated polyurathane is more active
than [MnL(H2O)2]. A four-coordinate, air-stable compound, [MnL]
(where LH2 = 55) has been
synthesized by refluxing a MeOH solution of Mn(OAc)24H2O and a
CH2Cl2 solution of LH2 in 1:1 molar ratio for 17 h[27]. It is
readily soluble in DMF, DMSO and CHCl3, sparingly soluble in MeOH
and EtOH and insoluble in non-polar solvents. The IR data are
indicative of the dibasic tetradentate ONNO donor nature of the
ligand. The compound shows magnetic moment of 1.9 B.M. indicating
the presence of one unpaired electron.
A brown, six-coordinate, monomeric compound, [Mn(LH2)(H2O)2]
(where LH4 = 56) has been synthesized[28]. LH4 acts as a dibasic
tetradentate ONNO donor ligand. The coordinated H2O molecules are
lost at about 170 oC. The magnetic moment of the compound is 5.62
B.M.
A brown, low-spin, six-coordinate compound, [Mn(LH2)(H2O)2]
(where LH4 = 57) is obtained by stirring MnSO4H2O and LH4 in
H2O-EtOH solution[29]. Interestingly, a yellow, high-spin,
six-coordinate compound, [Mn(LH2)(H2O)2] is obtained by stirring
MnCl24H2O and ligand in EtOH. The Schiff base behaves as a dibasic
tetradentate ONNO donor ligand in both the compounds. The magnetic
moment of the low-spin compound is 1.85 B.M. and it exhibits two
ESR signals one at g = 2.03 and another at g = 4.4 at LNT. The
high-spin compound affords the magnetic moment of 5.90 B.M.
A brown, four-coordinate, thermally-stable, binuclear compound,
[MnL]2 (where LH2 = 58) has been synthesized by Maurya et al.[30].
LH2 behaves as a dibasic tetradentate
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10
ONNO donor ligand. The magnetic moment (5.74 BM) of the compound
is indicative of high-spin, tetrahedral environment around both
Mn(II) ions.
A six-coordinate, non-electrolyte compound, [MnL(H2O)2] [where
LH2 = 59) has been synthesized[31]. LH2 behaves as a dibasic
tetradentate ONOO donor ligand coordinating through its phenolic O,
azomethine N, carbonyl O and nitroso O atoms. The magnetic moment
of the compound is 4.30 B.M.
Manjunathan et al.[32] have synthesized a four-coordinate, 1:1
electrolyte, [MnL]Cl (where LH = 60) by refluxing LH and MnCl24H2O
in EtOH for 1.5 h. LH acts as a monobasic tetradentate ONNN donor
ligand coordinating through its phenolic O, both azomethine N and
anilinic N atoms. The compound shows six hyperfine lines with g||
=
2.0236 and g = 2.004. A square-planar geometry has been
suggested to it.
An air-stable, six-coordinate, slightly ionized (M =13.0 mho cm2
mol-1 in DMF) complex, [MnLCl2]H2O (here L = 61) is obtained by
reacting MnCl2 and L in EtOH[33]. L behaves as a neutral
tetradentate N4 donor ligand coordinating through its both
azomethine and pyridyl ring N atoms. The (MCl)
vibration occurs at 224 cm-1. The chloro ligands occupy the
axial coordination sites.
The light-brown, cube-shaped crystalline, seven-coordinate
dinuclear Mn(II) complex, [Mn2L2(1,5-dca)2(dca)2]H2O [L =
N,N'-ethylenebis(2-benzoylpyridineimine), dca = dicyanamide] is
obtained by refluxing an equimolar mixture of Mn(NO3)2, L and dca
in EtOH[34]. The molar conductances of the complex are 246 and 212
mho cm2 mol-1 in MeOH and MeCN respectively indicating its
existence as a 1:2 electrolytes in these
solvents. The complete loss of H2O molecule occurs at ~175 oC
and [Mn2L2(1,5-dca)2(dca)2] is obtained. Mn2O3 is the end product
at 480 oC. L behaves as a neutral tetradentate N4 donor ligand. The
effective magnetic moment of the complex is 8.36 B.M. The complex
crystallizes in an orthorhombic fashion. Two [Mn(II)L] units are
doubly bridged by dicyanamide ligands in a 1,5 pattern. The
molecule of the complex possesses a centre of inversion at the mid
point of the line bisecting the adjacent metal centers of the
dimeric unit. The dca ligands are involved in coordination with the
metal center via monodentate and 1,5 bridging patterns. The
pentagonal base is provided by five N atoms,
four from L and one from one of the bridging dca moieties. The
axial positions are occupied by a terminal dca and other by the
bidging dca moiety. The axial MnN bonds
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11
are shorter than the basal MnN bonds. A distorted
pentagonal-bipyramidal structure has been assigned to the complex.
The complex is an efficient catalyst for the oxidation of
3,5-di-tert-butylcatechol to 3,5-di-tert-butylbenzo- quinone under
air in MeOH solution, but is inactive in MeCN. E. With pentadentate
ligands:
A five-coordinate compound, [Mn(LH)]2H2O (here Na2LH =
ceftriaxone, 62) has been synthesized by stirring a MeOH solution
of Na2LH and MnCl24H2O in 1:1 molar
ratio for 1 h at room temperature[35]. It is air-stable and
insoluble in H2O and EtOH, C6H6,
Me2CO, MeCN, Et2O, py, DMF and DMSO suggesting its polymeric
nature. Na2LH behaves as a dibasic pentadentate ONOON donor ligand.
The non-coordinated H2O molecules are lost between 80-110 oC. The
magnetic moment of the compound is 6.1 B.M. It shows higher
bactericidal activity than Na2LH against S. sonnei, P. mirabilis
and P.
aeruginosa; lesser activity than Na2LH against S. aureus and S.
enteritidis. A five-coordinate structure (63, M = Mn) has been
assigned to it.
The synthesis of a monomeric, seven-coordinate compound,
[Mn(LH2)(H2O)2](ClO4)2 (here LH2 = 64; R = R' = H) has been
reported[36]. The Schiff base acts as a neutral pentadentate SNNNS
donor ligand. The Mn ion is ligated to three N and two S atoms of
the ligand forming the pentagonal girdle and O atoms of the water
molecules occupying the apical positions. The ClO4 ions are
involved in hydrogen bonding with the H2O molecules and with the
terminal amino groups of the ligand. A distorted
pentagonal-bipyramidal structure [65; M = Mn, A = H2O] has been
suggested to it.
F. With hexadentate ligands: Salehzadeh et al.[37] have reported
the synthesis of a monomeric, seven-coordinate,
1:1 electrolyte, [MnClL](ClO4) [here L = 66; R = 2-C5H4N]. L
acts as a neutral hexadentate N6 donor ligand. The Mn(II) ion is
coordinated to three py and three asymmetric tripodal amine N
atoms. The environment around the Mn(II) ion is distorted
pentagonal-bipyramid.
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12
Coordination compounds of iron(III) Iron (Fe) is a greyish
transition metal of Group 8 and Period IV of the Periodic
Table. Its atomic number, atomic weight and the electronic
configurations are 26, 55.84 amu and [Ar] 3d64s2 respectively. It
is associated with ferromagnetic properties. Its common oxidation
states are +2 and +3. Ferrous ion (Fe2+) is necessary trace element
in living organisms. It is present in hemoglobin, myoglobin,
cytochrome system. Iron containing enzymes usually containing heme
prosthetic groups participate in catalysis of
oxidation reactions in biology. The ability of Fe(III) ion to
form the coordination compounds with a wide range of ligands has
been reported. These ligands are coordinated to Fe(III) ion in a
bidentate, tridentate, tetradentate, pentadentate and hexadentate
fashions. We present here a brief survey of the Chemistry of
coordination compounds of Fe(III) ion. A. With bidentate
ligands:
The synthesis of a brown, high-spin, six-coordinate compound,
[FeCl2L(PPh3)2] (where LH = 25, R = H, C4H4; R' = OH; R'' = H, Cl,
Me, OMe) has been reported[38]. The IR data indicate the monobasic
bidentate ON donor behaviour of LH. The compounds
have been used as catalysts in aryl-aryl coupling reactions
between phenylmagnesium bromide and phenyl bromide to yield
biphenyl.
The reaction of 2-aminophenol with Fe(III) ions produces the
aminophenolate coordination compound as precipitate (in solution),
which on further treatment with 4-benzyloxybenzaldehyde or
but-2-enal in 1:1:1 molar ratios yields[4] the deep-brown,
six-coordinate compounds, [FeClL2(H2O)] or [FeClL'2(H2O)] (where LH
and L'H = 28 and 29 respectively). They melt at 290 and 190 oC
respectively. Both LH and L'H act as the monobasic bidentate ON
donor ligands. The former displays the (FeO) and (FeN) vibrations
at 600 and 508 cm-1 respectively, while the latter displays these
vibrations at 582 and 428 cm-1 respectively. Their magnetic moments
(5.97 and 6.00 B.M. respectively) correspond to the presence of
five unpaired electrons in a high-spin octahedral Fe(III) compound.
These values are very close to the spin-only value (5.90 B.M.)
since the ground state (derived from 5S state of free ion) has no
orbital angular momentum. [FeClL2(H2O)] displays the molecular ion
peak at 713 (M+) and 302 (100%, C6H5CH2OC6H4CN==C6H4O)+. Another
compound, [FeClL'2(H2O)] displays the molecular ion peak at 429
(M+) and 160 (100%, CH3CHCHCHNC6H4O)+. They are
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13
biologically more active against S. dysenteria, E. coli, P.
aeruginosa, B. subtilis, S. lutea and S. aureus than
2-aminophenol.
On refluxing an EtOH solution of FeCl3 (anhydrous) and LH (67)
in 1:2 molar ratio for 2 h, a black dimeric coordination compound,
[FeClL2]2 is obtained[39]. It is non-hygroscopic, air-stable,
decomposes above 230 oC, soluble in DMF and DMSO but partially
soluble in MeOH, EtOH, MeCN, PhNO2 and CHCl3. It is non-electrolyte
in MeOH and PhNO2. The ligand is coordinated to the metal ion
through its phenolic O and
azomethine N atoms. The low value of the magnetic moment (5.3
B.M.) indicates the bridged structure involving an
anti-ferromagnetic exchange interaction. A dimeric octahedral
structure has been suggested for it.
The synthesis of a brown, six-coordinate, polystyrene-anchored
coordination
compound, [PSCH2LFeCl2(DMF)2] (here PSCH2LH = 68) has been
reported[25]. The ligand acts as a monobasic bidentate ON donor
ligand. The magnetic moment (6.00 B.M.) and the appearance of three
bands at 12200, 15500 and 19000 cm-1 suggest an octahedral geometry
around Fe(III) ion. B. With tridentate ligands:
The dark-brown, six-coordinate, polystyrene-anchored
coordination compound, [PSLFeCl(DMF)2] (where PSLH2 = 31) is
obtained by refluxing a DMF swollen suspension of PSLH2 and
anhydrous FeCl3 for 6 h[7]. Its PRC is 93.7. The MBC of the ligand
is 0.73 mmol of metal per g of it. The dibasic tridentate ligand
coordinates through its phenolic O, azomethine N and alcoholic O
atoms. The magnetic moment of the compound is 5.87 B.M. The latter
displays three bands at 12720, 19600 and 25000 cm-1 due to the 6A1g
4T1g(G), 6A1g 4T2g(G), 6A1g 4A1g(G) spin-forbidden transitions
respectively suggesting its octahedral geometry.
The brown coloured compound, [Fe3Cl8(LH)(H2O)3]2H2O and the red
coloured [FeL(acac)(H2O)]H2O have been synthesized by reacting
FeCl3 and LH2 (32) in the presence and absence of Et3N
respectively[8]. LH2 acts as a monobasic tridentate ONO
donor ligand in the former and as a dibasic tridentate ONO donor
ligand in the latter. The lower value of magnetic moment (3.7 B.M.)
for the brown compound is due to the spin-density exchange between
the iron(III) centers. The value of magnetic moment (5.9 B.M.) for
the red compound indicates its octahedral geometry. They are more
potent fungicides
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14
and bactericides than the ligand. A chloro-bridged structure has
been suggested for the brown compound.
A DMF swollen suspension of PSCH2LH2 (33; R = 3-PSCH2OCO, X = O)
upon refluxing with anhydrous FeCl3 produces[9] a brown,
six-coordinate compound,
[PSCH2LFeCl(DMF)2]. The Schiff base acts as a dibasic tridentate
ONO donor ligand coordinating through its phenolic O, azomethine N
and enolic O atoms. The furanoic O atom does not participate
towards coordination. The magnetic moment (5.98 B.M.) and the
appearance of three bands at 12500, 17420 and 25000 cm-1 due to the
6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4A1g(G) transitions are
indicative of an octahedral environment around the metal ion.
Kumar et al.[10]
have synthesized a reddish-brown, polystyrene-anchored,
six-coordinate compound, [PSCH2LHFeCl(DMF)2] (where PSCH2LH3 = 34)
by refluxing a DMF swollen suspension of PSCH2LH3 and a DMF
solution of anhydrous FeCl3 The
PRC of the compound is 64.2 and the MBC of PSCH2LH3 is 0.41 mmol
of Fe per g of the ligand. The ligand behaves as a dibasic
tridentate ONO donor. The magnetic moment (5.96 B.M.) and the
appearance of three bands at 13000, 17100 and 25100 cm-1 due to the
6A1g 4T1g (G), 6A1g 4T2g (G), 6A1g 4A1g (G) indicate an octahedral
environment around the metal ion.
The synthesis of a six-coordinate compound, [FeX2L(H2O)]2H2O
(here LH = 69, X = Cl, NO3) has been reported[40]. LH acts as a
monobasic tridentate ONO donor ligand. [FeCl2L(H2O)]2H2O shows
three bands due to the presence of both high-spin Fe(III) (S = 5/2)
and low-spin Fe(III) (S = 1/2) ions within the same crystal lattice
indicating its octahedral geometry.
The synthesis of a brown, dinuclear coordination compound,
[Fe2L2(NO3)2]H2O (here LH2 = 70, X = NH2) has been reported[41]. It
melts above 280 oC and is soluble in common organic solvents but
partially soluble in DMF and DMSO. LH2 behaves as a bis(monobasic
tridentate) ONN donor ligand. The appearance of two new bands at
1384 and 856 cm-1 indicates the presence of coordinated nitrato
group in the compound. The (FeO) and the (FeN) vibrations occur at
580 and 454 cm-1 respectively. The low value of magnetic moment
(4.95 B.M.) of the compound suggests the presence of an anti-
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15
ferromagnetic interaction acting between the neighbouring
Fe(III) ions. The lattice H2O molecules are lost by heating the
compound between 40-97 oC.
The brown, six-coordinate complex, [FeL2](NO3) (here LH = 45) is
obtained[17] on refluxing an hot MeOH solution of Fe(NO3)39H2O and
LH in 1:2 molar ratio at pH = 7.5-8.5. LH
acts as a monobasic tridentate ONN donor ligand coordinating
through phenolic O and both azomethine N atoms. The magnetic moment
(5.85 B.M.) and the appearance of three bands at 12658, 18940 and
30864 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4A1g(G)
transitions respectively indicate the presence of an octahedral
environment around the metal ions. The compound shows higher
antimicrobial activity against Gram-negative E. coli, Gram-positive
S. aureus and LH.
A reddish-brown, six-coordinate, dinuclear compound,
[Fe2Cl4(LH)2]2EtOH (here LH2 = 35A-35C) is obtained by stirring an
EtOH solution of FeCl36H2O and LH2 in 1:2 molar ratio for 4 h[11].
It melts at 160 oC. It is soluble in MeOH but insoluble in H2O
and
Et2O. The rather higher value of molar conductance (M = 58.0 mho
cm2 mol-1) in DMF is due to the partial replacement of the chloro
ligands with DMF molecules. The IR data are indicative of the
monobasic tridentate OON donor behaviour of the ligand. The
compound
shows two broad bands one at 18797 cm-1 and other at 25510 cm-1
due to the spin-forbidden 6A1 4T2(G) and 6A1 4A1, 4E(G) transitions
respectively. Its magnetic moment is 5.94 B.M. and that of a single
Fe(III) ion is 4.20 B.M. Thus, there occurs an anti-ferromagnetic
interaction between the adjacent Fe(III) ions. The unsymmetrical
broad band at g = 1.827 indicates a distorted octahedral geometry
around the Fe(III) ions. The compound consists of two mononuclear
units, where the cations in each unit are coordinated to OON sites
of a ligand and are linked together by Cl atoms. An octahedral
structure (71) has been assigned to it.
A non-electrolyte, five-coordinate compound, [FeCl2(LH)]3H2O
(72) (here LH2 = 39) has been synthesized by stirring a MeOH
solution of NaHL and FeCl36H2O in 2:1 molar ratio for 8 h at room
temperature[42]. It is air-stable, soluble in DMSO and DMF and
slightly soluble in MeCN. NaHL behaves as a monobasic tridentate
OON donor ligand. The carboxylato group coordinates in a
monodentate fashion. The compound has a
magnetic moment of 4.6 B.M. which lies between the values
expected for the Fe(III) coordination compounds with S = 5/2 and S
= 1/2 suggesting the possibility of spin-state
-
16
equilibrium between 6A2 and 2T2 states respectively. It shows
weak absorption at 23810 cm-1 due to the spin-orbit forbidden
transitions. The latter shows higher bactericidal activity than LH2
against P. mirabilis, K. pneumoniae, S. enteriditis and E. coli,
while it
remains inactive towards S. aureus and P. aeruginosa. A
four-coordinate, 1:1 electrolyte (in DMSO), [FeCl(LH)]Cl (where LH2
=
cefoxitin, 50; R = OMe, R' = NH2) has been synthesized by
stirring a MeOH solution of NaHL and FeCl36H2O in 1:1 molar ratio
for 8 h in N2 atmosphere at room temperature[43].
It is air-stable, soluble in DMF and DMSO but slightly soluble
in MeCN. NaHL behaves
as a monobasic tridentate OOS donor ligand. The carboxylato
group coordinates in a monodentate mode. The presence of (MS)
stretch at 300 cm-1 indicates coordination through S atom of
thiophene moiety. Its magnetic moment is 6.1 B.M. It shows lesser
bactericidal activity than LH2 against S. aureus, E. faecalis, E.
coli, P. mirabilis, S. sonnei and S. enteritidis.
El-Sawaf et al.[44] have reported the synthesis of a brown,
five-coordinate compound, [Fe(ClO4)2L] [where LH = 73]. LH
coordinates through carbonyl O (pyrazolone ring), thiolato S and
azomethine N atoms. The chlorato group coordinates in a monodentate
fashion. The magnetic moment of the compound is 3.7 B.M. A
square-pyramidal structure has been suggested for the latter. C.
With tetradentate ligands:
Kumar et al.[25] have synthesized a reddish-brown,
six-coordinate polystyrene-anchored coordination compound,
[PSCH2LFeCl(DMF)] by refluxing a DMF swollen suspension of PSCH2LH2
[53; R = R' = Me, R'' = (CH2)2] and a DMF solution of anhydrous
FeCl3 in 2:1 molar ratio in the presence of ethyl acetate and Et3N.
Its PRC is 49.2. The MBC of the ligand is 0.34 mmol of metal per g
of it. The Schiff base acts as a dibasic tetradentate ONNO donor
ligand. The magnetic moment of the compound is 5.94 B.M. The three
bands at 12650, 16970 and 25000 cm-1 in the latter are
characteristic of octahedral geometry around Fe(III) ion.
Although LH2 (74) and L'H2 (75) are potentially the dibasic
hexadentate NONNON donor and the dibasic heptadentate NONNNON donor
ligands respectively,
they act as a dibasic tetradentate ONNO donors[45] in the black,
mononuclear compound, [FeL1.5]3H2O and another black, binuclear
compound, [Fe2L'3]. The former shows a
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17
narrow band at 14493 cm-1 in nujol and a broad band at 15748
cm-1 in DMSO, while the latter shows a narrow band at 14493 cm-1 in
nujol and a broad band at 16367 cm-1 in DMSO due to the
spin-forbidden, 6A1g 4T2g(G) transition indicating the distorted
octahedral environment due to the polymerization around the metal
ion. Their magnetic moments are 3.86 and 3.38 B.M. respectively.
The former displays gx, gy and gz signals at 2.216, 2.109 and 1.959
respectively, while these signals appear at 2.224, 2.115 and 1.959
respectively in the latter indicating severe distortion of the
octahedral geometry in the
array in the solid state.
Saghatforoush et al.[46] have synthesized the six-coordinate,
1:2 electrolyte (M = 196-233 mho cm2 mol-1 in MeCN), [FeL(H2O)2]Cl2
[where LH = 5-R-N-(2-pyridylethylsulphanylethyl)salicylideneimine;
R = OMe, N2Ph, I, NO2] (76) by refluxing a MeOH solution of
FeCl36H2O and LH in 1:1 molar ratio in the presence of NaOH. They
are light-brown to dark-brown crystalline solids, fairly soluble in
MeOH, MeCN, DMF, DMSO and melt between 173-201 oC. LH coordinates
through deprotonated phenolic O, imine N, thioether S and py N
atoms and affording an octahedral geometry around the Fe(III) ion
in the compounds. It decomposes (when R = I) before melting at 209
oC. The others melt before undergoing exothermic decomposition.
They undergo two-step degradation reactions. The first step occurs
at 127, 130, 134 and 135 oC (when R = I, OMe, NO2, N2Ph)
respectively corresponding to the loss of two water molecules. The
second step occurs at 210, 231, 235, 218 oC corresponding to the
loss of organic ligand moiety. The compound (when R = NO2) has got
the highest thermal stability. The Schiff base is more potent
antibacterial than the compounds. The antibacterial data indicate
high activity of the ligand (when R = I) against S. pyogenes, S.
agalaciae, S. aureus, P. anthracis, K. pneumoniae and P.
aeruginosa.
D. With pentadentate ligands: Relatively little work has been
reported on Fe(III) coordination compounds with
pentadentate ligands. A six-coordinate compound, [FeCl(LH)]2H2O
(where Na2LH = 62) has been synthesized by stirring a MeOH solution
of Na2LH and FeCl36H2O in 1:1 molar ratio for 1 h at room
temperature[35]. It is air-stable and insoluble in H2O, EtOH,
C6H6,
Me2CO, MeCN, Et2O, py, DMF and DMSO. The energy difference ( =
240 cm-1) between as(COO) and s(COO) stretches suggests the
monodentate coordinating
-
18
behaviour of carboxylato group. Na2HL behaves as a dibasic
pentadentate ONOON donor ligand. The non-coordinated H2O molecules
are lost between 80-110 oC. The magnetic moment of the compound is
5.9 B.M. The latter shows higher bactericidal activity than Na2LH
against P. mirabilis however, it is less active than Na2LH against
E. coli, S. aureus, S. enteritidis and S. sonnei. An octahedral
structure (77) has been assigned to it. E. With hexadentate
ligands:
Tweedle et al.[47] have synthesized a monomeric, six-coordinate,
1:1 electrolyte,
[Fe(LH2)]Y (here LH4 = 78, R = H, OMe, NO2; Y = PF6, NO3, BF4,
I, Cl). LH4 acts as a dibasic hexadentate ONNNNO donor ligand. A
distorted octahedral geometry has been suggested for the
compounds.
Kannappan et al.[48] have synthesized the monomeric, low-spin,
six-coordinate
compounds, [FeL](ClO4), [FeL'](ClO4), [FeL](BF4) and [FeL'](BF4)
(here LH2 =
N,N',N'',N'''-1,5,8,12-tetraazadodecanebis(salicylaldiminato) and
L'H2 =
N,N',N'',N'''-1,5,8,12-tetraazadodecanebis(3-methoxysalicylaldiminato).
LH2 and L'H2 act as the dibasic hexadentate ONNONN donor ligands.
The coordination geometry around Fe(III) ion is distorted
octahedral with the iron to phenoxo O bonds being trans to each
other. In the crystal lattice, the mononuclear entities are
organized into infinite 1D chains due to H-bonding interactions
involving the secondary amine residue and one O or F atom of a
counter anion respectively.
Sarkar et al.[49] have reported the synthesis of a monomeric,
six-coordinate, 1:1 electrolyte, [Fe(LH2)](ClO4) [here LH4 = 79].
LH4 acts as a dibasic hexadentate ONSSNO donor ligand.
The syntheses of two monomeric, dark-green, ion-pair
coordination compounds,
[FeL][FeCl4] [here LH2 =
1,3-di-(o-salicylaldiminophenylthio)propane] and [FeL'][FeCl4]
[here L'H2 = 1,2-di(o-salicylaldiminophenylthio)xylene] have been
reported[50]. Each Fe(III) ion has a distorted octahedral geometry
in the cationic part and a distorted tetrahedral in the anionic
part. The Fe(III) centre in the cationic species is low-spin.
Fe(ClO4)36H2O on reacting with above ligands forms the monomeric,
six-coordinate, 1:1 electrolyte, [FeL](ClO4) or [FeL'](ClO4)
respectively. The Fe(III) centres in both cationic species are
high-spin. LH2 and L'H2 act as the dibasic hexadentate N2S2O2 donor
ligands.
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19
Coordination compounds of cobalt(II) Cobalt (Co) is a hard,
grey, d-block transition metal belonging to the Group 9 and
Period IV of the Periodic Table. Its atomic number, atomic
weight and electronic
configurations are 27, 58.93 amu and [Ar] 3d74s2 respectively.
Its common oxidation states are +2 and +3. The Co(II) has a d7
system and its coordination compounds show the paramagnetism either
equivalent to three unpaired electrons (Oh or Td ) or equivalent to
one unpaired electron (square-planar). Since the orbital
contribution of tetrahedral Co(II) is much less than that of
octahedral coordination compounds, the former have generally lower
values than octahedral compounds This high degree of orbital
contribution for octahedral compounds is due to the three-fold
degeneracy of 4T1g ground state. The metal is the central component
of the vitamin B12 (cobalmin) and is associated with some proteins
such as methionine and aminopeptidase. 60Co is used in
radiotherapy. The ability of Co(II) ion to form the coordination
compounds with a wide range of ligands is well known. These ligands
coordinate to Co(II) ion in a bidentate, tridentate, tetradentate,
pentadentate and hexadentate fashion. We present here a brief
survey of the Chemistry of
coordination compounds of Co(II) ion. A. With bidentate
ligands:
The synthesis of a brown, four-coordinate non-electrolyte (M =
6.9 mho cm2 mol-1), [Co(OAc)L(H2O)] (where LH = 25; R = 3-OMe, R' =
OH, R'' = H) has been reported[2]. It decomposes at 270 oC. It is
soluble in DMF and DMSO. LH acts as a monobasic bidentate ON donor
ligand. The presence of coordinated H2O molecule is indicated by
the
presence of a broad band at 3400 cm-1 in the above coordination
compound. The acetato ligand is coordinated in a monodentate
fashion. It shows the (CoO) and (CoN) vibrations at 510 and 435
cm-1 respectively. The magnetic moment (4.30 B.M.) of the compound
indicates a tetrahedral environment around the metal ion.
The synthesis of a green, high-spin, four-coordinate compound,
[CoClL(PPh3)] (where LH = 25; R = H, C4H4; R' = OH, R'' = H, Cl,
Me, OMe) has been reported[38]. The IR data are indicative of the
monobasic bidentate ON donor behaviour of LH. The magnetic moments
of the coordination compounds lie between 1.8-2.3 B.M. in
square-
planar environment. They have been used as catalysts in
aryl-aryl coupling reactions between C6H5MgBr and C6H5Br to yield
biphenyl.
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20
An EtOH solution of CoCl26H2O and LH (80) on refluxing for 2 h
in 1:2 molar ratio, a four-coordinate compound, [CoL2] is
obtained[51]. LH acts as a monobasic bidentate ON donor ligand. The
magnetic moment (3.58 B.M.) of the compound and the occurrence of a
band at 16366 cm-1 due to the 1A1g 1B1g transition support its
square-planar geometry. Its antibacterial activity against bacteria
like S. aureus, B. subtilis, E. coli and the fungus A. niger is
higher than LH.
A MeOH solution of Co(OAc)24H2O and LH3 (81; R = OH, R' = H) or
L'H4 (81; R = R' = OH) in 1:2 molar ratio on refluxing for 1 h
produce a brown, four-coordinate, non-electrolyte (M = 8.7 mho cm2
mol-1), [Co(LH2)2]3H2O and another red non-electrolyte (M = 7.6 mho
cm2 mol-1), [Co(L'H3)2]3H2O respectively[52]. Both the coordination
compounds are soluble in DMF, DMSO and THF. The former melts at 295
oC, while the latter at >300 oC. Both the Schiff bases act as
monobasic bidentate ON donor ligands. The (CoO) and the (CoN)
vibrations occur at 475 and 455 cm-1 in [Co(LH2)2]3H2O, while these
occur at 480 and 445 cm-1 in [Co(L'H3)2]3H2O respectively. The
magnetic moments of [Co(LH2)2]3H2O and [Co(L'H3)2]3H2O are 4.38 and
4.33 B.M. respectively suggesting their tetrahedral geometries
around the metal ion.
Tumer et al.[53] have observed that an EtOH solution of
Co(OAc)24H2O and LH2 (82; R = H, R' = 2-OH, R'' = 3-OMe) or L'H
(82; R = R' = H, R'' = 4-NMe2) or L''H2 (82; R = 3-CMe3, R' = 4-OH,
R'' = 5-CMe3) on refluxing in 1:2 molar ratio produce the
compounds, [Co(LH)2]H2O (red-brown), [CoL'2]H2O (dark-red) and
[Co(L''H)2]H2O (red) respectively. They are monomeric, air-stable,
non-electrolytes and are soluble in common polar solvents. Although
LH2 and L''H2 are potentially the dibasic tridentate
ONO donor ligands, but similar to L'H, they also act as the
monobasic bidentate ON donor ligands in the respective compounds.
The NH and pyridine N atoms do not participate towards the
coordination. These tetrahedral coordination compounds have
magnetic moments 4.13, 4.23 and 4.50 B.M. respectively.
The brown compound, [CoL2(H2O)2] (here LH = 28) and the
reddish-brown compound, [CoL'2(H2O)2] (L'H = 29) have been
synthesized by template method[4]. The reaction of 2-aminophenol
with Co(II) ions produces the aminophenolate coordination compound
as precipitate (in solution), which on further treatment with
4-benzyloxybenzaldehyde or but-2-enal in 1:1:1 molar ratios yields
the desired compounds.
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21
[CoL2(H2O)2] and [CoL'2(H2O)2] melt at 245 and 225 oC
respectively. Both LH and L'H act as monobasic bidentate ON donor
ligands. [CoL2(H2O)2] displays the (CoO) and (CoN) vibrations at
596 and 450 cm-1 respectively, while [CoL'2(H2O)2] displays these
vibrations at 580 and 460 cm-1 respectively. [CoL2(H2O)2] exhibits
two bands, one at 14577 cm-1 and another at 17094 cm-1, while
[CoL'2(H2O)2] exhibits these bands at 14815 and 17241 cm-1
respectively due to the 4T1g(F) 4A2g(2) and 4T1g(F) 4T1g(P)(3)
transitions respectively indicating the octahedral environment
around the metal ion. The
magnetic moments of [CoL2(H2O)2] and [CoL'2(H2O)2] are 4.97 and
4.95 B.M. respectively favouring the presence of three unpaired
electrons of Co(II) ion in a high-spin octahedral compound. The
higher values than the spin-only value (3.89 B.M.) is due to the
orbital contribution. Their biologically activity against S.
dysenteria, E. coli, P.
aeruginosa, B. subtilis, S. lutea and S. aureus is more than
2-aminophenol. The monomeric, four-coordinate compound, [CoL2]
(here LH = Schiff base
obtained from the condensation of cinnamaldehyde and
2-aminophenol) has been synthesized by refluxing an EtOH solution
of Co(OAc)24H2O and LH in 1:2 molar ratio[54]. LH acts as a
monobasic bidentate ON donor ligand. The magnetic moment of the
compound is 5.50 B.M. A tetrahedral structure has been assigned to
it.
The blue, six-coordinate compound, [Co(LH)2(H2O)2] (83; M = Co,
Y = O, COO) has been synthesized[55] by refluxing a MeOH solution
of LH2 [here LH2 = Schiff base obtained from the condensation of
1,2,3,5,6,7,8,8a-octahydro-3-oxo-N-1-diphenyl-5-(phenylmethylene)-2-naphthalenecarboxamide
and 2-aminophenol/2-aminobenzoic acid] and Co(OAc)24H2O in 1:2
molar ratio for 2 h followed by adjusting the pH to 7.0 using 3%
NaOH solution. It is soluble in DMF and DMSO, partially soluble in
MeCN and
CHCl3 but insoluble in H2O. The complete loss of coordinated
water molecules occurs at 130 oC. The IR data are indicative of the
monobasic bidentate ON donor behaviour of the Schiff base. The
carboxylato group is coordinated in a monodentate fashion. The
compound (when Y = O) shows two intense bands one at 13900 cm-1 and
another at 18800 cm-1 due to the 4T1g(F) 4A2g(F)(2) and 4T1g(F)
4T1g(P) transitions in an octahedral environment. These bands occur
at 14100 and 18900 cm-1 in the compound (when Y = COO)
respectively. Their magnetic moments (4.86 and 3.18 B.M., when Y =
O, COO
-
22
respectively) indicate a high-spin octahedral environment around
Co(II) ion. A trans-octahedral structure (83; M = Co, Y = O, COO)
has been suggested for them.
A light-brown, four-coordinate, polystyrene-anchored
coordination compound,
[PSCH2L(OAc)Co(DMF)] (here PSCH2LH = 68) has been synthesized by
refluxing Co(OAc)24H2O and PSCH2LH in 2:1 molar ratio in N2
atmosphere[25]. The PRC of the compound is 34.6. The MBC of the
ligand is 0.53 mmol of metal per g of it. The coordinated DMF
molecules are coordinated to the metal ion through O atom. The
acetato
ligand is coordinated in a monodentate fashion. The Schiff base
acts as a monobasic bidentate ON donor ligand. The magnetic moment
(2.40 B.M.) of the compound suggests a square-planar geometry
around the metal ion.
A four-coordinate, non-electrolyte, [Co2(OH)(Cl)(LH)2]H2O (where
LH2 = 32) has been synthesized[8] by mixing CoCl26H2O and LH2 in
the presence of Et3N. The ligand coordinates in a monobasic
bidentate ON donor fashion. The magnetic moment of the compound is
3.4 B.M. A tetrahedral structure has been assigned to it.
A violet, six-coordinate, non-electrolyte (M = 10.6 mho cm2
mol-1 in DMSO), [CoCl2(LH2)2] (here LH2 = 84; R = 4-OH, R' = Me) is
obtained by refluxing an H2O/EtOH solution of CoCl26H2O and LH2 in
1:1 molar ratio for 8 h[56]. It is insoluble in Me2CO, CHCl3 and
C6H6 but is fairly soluble in DMF and DMSO. It decomposes between
245-247 oC. LH2 acts as a neutral bidentate ON donor ligand. The
coordination compound displays two bands one at 16338 cm-1 and
other at 19330 cm-1 due to the 4T1g(F) 4A2g(F)(2) and 4T1g(F)
4T1g(P)(3) transitions. The spectral parameters [10Dq (8602 cm-1),
B' (860 cm-1), (0.88), 0 (11.4), LFSE (81.9 kJ mol-1)] and the
magnetic moment (5.16 B.M.) support its octahedral geometry. The
latter shows higher antibacterial activity against E. coli than
LH2, whereas its antifungal activity against A. niger is less than
LH2. An octahedral structure (85, M = Co) has been assigned to the
compound.
Although, LH2 (86) is potentially a dibasic pentadentate O2N3
ligand, it acts as a monobasic bidentate ligand[57] in the brown,
six-coordinate compound, [Co(OAc)(LH)(H2O)2]. The bonding takes
place through the enolic O and the azomethine N atoms. The acetato
group is coordinated in a bidentate fashion. The OH and NH2
groups
do not participate in the coordination. The magnetic moment
(4.71 B.M.) and the appearance of two bands (17360 and 20964 cm-1)
suggest its high-spin octahedral
-
23
geometry. The ligand has been used for the micro-determination
of Co(II) ion within metal concentration up to 46.3 ppm.
An EtOH solution of Co(OAc)24H2O and LH2 (30, R = H) in 1:2
molar ratio upon refluxing in the presence of TEM produce[6] a
brown-red compound, [Co(LH)2]. It is non-electrolyte (M = 16 mho
cm2 mol-1) and decomposes at 268 oC. LH2 acts as a monobasic
bidentate ON donor ligand.
An EtOH solution of LH2 (87; R = H, 5,6-benzo) reacts with a
warmed EtOH solution of CoCl26H2O in 1:1 molar ratio at pH ~7 and
forms[58] the six-coordinate, non-electrolyte, dinuclear compound,
[Co2L2(H2O)4]. It is pink (when R = H) and red (when R =
5,6-benzo). They are amorphous in nature, having high melting
points and are feebly soluble in DMF and dioxane. The IR data are
indicative of the monobasic bidentate ON donor nature of the ligand
per metal ion coordinating through its phenolic O and
azomethine N atoms. The as(O==S==O) and the s(O==S==O) stretches
of LH2 occurring at 1150-1155 and 1320-1330 cm-1 respectively
remain at the same energy in the coordination compounds indicating
the non-involvement of sulphone O atom(s) towards coordination. The
(CoO) and the (CoN) vibrations occur at 500, 355 and 505, 350 cm-1
(when R = H, 5,6-benzo respectively). They display the absorption
bands at ~8955, ~18125, ~20800 and 32500 cm-1 due to the 4T1g(F)
4T2g(F)(1), 4T1g(F) 4A2g(F)(2), 4T1g(F) 4T1g(P)(3) and charge
transfer transitions respectively indicating the octahedral
environment around the metal ion. The spectral parameters: [10Dq
(9170, 8775 cm-1), B' (809.3, 795.1 cm-1), 2/1 (2.02. 2.00),
(0.883, 0.81) and (20.48, 23.45)] further lend support for their
octahedral geometry. Their sub-normal magnetic moments (2.7 and 2.6
B.M.) indicate MM interactions in a polymeric structure. The
unpaired electron of the d-orbital of the metal ion overlaps with
the -orbital of the N atom of the azomethine moiety of the ligands.
Due to the high electron density of the N atoms, an electron from
N
moves to partially occupied d-orbital of the metal ion with
antiparallel spin to the original d-electron. Thus, the magnetic
moments are aligned antiparallel and are responsible for partial
quenching of paramagnetism due to the super-exchange phenomenon. A
dinuclear, octahedral structure (88, R = H, 5,6-benzo; M = Co, A =
H2O) has been suggested to it.
Chohan et al.[59]
have observed that on refluxing an EtOH solution of CoCl26H2O
and an H2O/EtOH solution of cloxacillin (NaLH, 89) in 1:1 and 1:2
molar ratios, air and
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24
moisture-stable, intense-coloured, amorphous, six-coordinate
compounds, [CoCl(LH)(H2O)3] and [Co(LH)2(H2O)2] respectively are
obtained. They are insoluble in common organic solvents and soluble
in H2O, DMF and DMSO. NaLH behaves as a
monobasic bidentate ON donor (carboxylic O and endocyclic N of
-lactam ring) ligand. The carboxylato group is coordinated in a
monodentate mode. The presence of the (CoO) stretch at 525 cm-1 and
(CoN) stretch at 410 cm-1 indicates the bonding through O and N
atoms. The presence of the (CoCl) stretch in the former at 320 cm-1
supports the presence of coordinated chloro group to the metal ion.
The former shows the 4T1g(F) 4T2g(F), 4T1g(F) 4A2g(F) and 4T1g(F)
4T2g(P) transitions at 7375, 17280 and 20595 cm-1 and the latter at
7225, 17165 and 20380 cm-1 respectively, for octahedral
configuration.
They show antibacterial activities against E. coli, K.
pneumoniae, P. mirabilis, P.
aeruginosa, S. typhi, S. dysentriae, B. cereus, C. diphtheriae,
S. pyogenes and S. aureous. The structures, 90 (M = Co) for
[CoCl(LH)(H2O)3] and 91 (M = Co) for [Co(LH)2(H2O)2] have been
assigned.
Amirnasr et al.[60] have synthesized a four-coordinate compound,
[CoX2L] [here L =
N,N'-bis(-phenylcinnamaldehyde)-1,2-diaminoethane, X = Cl, Br] by
refluxing CoX26H2O and L in CH2Cl2 in 1:1 molar ratio under N2
atmosphere. It has a distorted tetrahedral structure.
Upon refluxing an EtOH solution of CoCl26H2O and LH2 (92) in 1:2
molar ratio for 1 h at pH = 6, a six-coordinate compound,
[Co(LH)2(H2O)2] is obtained[61]. It is soluble in common organic
solvents. It is non-electrolyte (M = 11.5 mho cm2 mol-1) in Me2CO.
The (CoN) vibrations occur at 440 cm-1. The Schiff base acts as a
bidentate NN donor ligand. The appearance of two spin-allowed
transitions at 17856 and 21734 cm-1 due to the 4T1g(F) 4A2g(F) and
4T1g(F) 4T1g(P) transitions respectively and the value of magnetic
moment (4.81 B.M.) suggest the high-spin, distorted octahedral
geometry around the metal ion.
The synthesis of a bluish-green, six-coordinate,
non-electrolyte, [Co(LH)2(H2O)2] (83; M = Co, Y = S) has been
reported[55]. It is soluble in DMF and DMSO, partially soluble in
MeCN and CHCl3 but insoluble in H2O. The complete loss of the
coordinated
H2O molecules occurs at 130 oC. The IR data are indicative of
the monobasic bidentate NS donor behaviour of the Schiff base. The
appearance of two intense bands (14000 and
-
25
19000 cm-1) due to the 4T1g(F) 4A2g(F)(2) and 4T1g(F) 4T1g(P)
transitions respectively and the magnetic moment (4.90 B.M.)
suggest an octahedral environment around the metal ion.
B. With tridentate ligands: Sallam et al.[62] have reported the
synthesis of a yellow coordination compound,
[Co(LH)2]2H2O [where LH2 = 93; R' = R'' = Ph, A = (CH2)2] and
two brown compounds, [Co(L'H)2]H2O [here L'H2 = 93; R' = Ph, R'' =
Me, A = (CH2)2] and [Co(L''H)(OH)] [here L''H2 = 93; R' = R'' = Me,
A = (CH2)2]. They are insoluble in EtOH, Me2CO, C6H6, CHCl3 and
partially soluble in DMF and DMSO. They are non-electrolytes (M =
7.7-9.0 mho cm2 mol-1) in DMSO. The IR data are indicative of the
monobasic tridentate ONO donor behaviour of these Schiff bases. The
(CoO) and the (CoN) vibrations occur between 519-659 cm-1 and
394-565 cm-1. The octahedral compounds, [Co(LH)2]2H2O and
[Co(L'H)2]H2O exhibit three bands at 17667, 19880 and 22222; 18587,
20833 and 23752 cm-1 due to the 4T1g(F) 4A2g(F) and 4T1g(F) 4T1g(P)
and intra-ligand transitions respectively. The appearance of a band
at 18691 cm-1 due to the 4A2 4T2(F) transition in [Co(L''H)(OH)]
suggests its tetrahedral structure. The magnetic moments of
[Co(LH)2]2H2O and [Co(L'H)2]H2O are 5.3 and 5.2 B.M. respectively
indicating the presence of high-spin six-coordinate geometry around
the metal ion. The magnetic moment (3.2 B.M.) of [Co(L''H)(OH)] is
intermediate between the values for tetrahedral and square-planar
structures and results from a spin-equilibrium between low- and
high-spin states. [Co(L'H)2]H2O has an endothermic peak between
46-130 oC indicating the loss of lattice water molecule. The
existence of two exothermic peaks between 156-260 and 370-480 oC
indicates the loss of side chain and ligand moieties respectively.
CoO is the final product formed.
A brown, monomeric, six-coordinate, polystyrene-anchored
coordination
compound, [PSLCo(DMF)3] (where PSLH2 = 31) is obtained by
refluxing a DMF swollen suspension of PSLH2 and Co(OAc)24H2O in 1:2
molar ratio for 8 h[7]. The PRC of the compound is 68.5. The MBC of
the ligand is 0.53 mmol of metal per g of it. The Schiff base acts
as a dibasic tridentate ONO donor ligand. DMF molecules are
coordinated
to the metal ion. The magnetic moment (4.80 B.M.) and the
appearance of three bands at 8300, 12500 and 17860 cm-1 due to the
4T1g 4T2g(1), 4T1g 4A2g(2) and 4T1g(F)
-
26
4T1g(P)(3) spin-allowed transitions respectively suggest an
octahedral environment around the metal ion.
Sallam et al.[62] have also reported the syntheses of two brown,
four-coordinate
compounds, [Co(OH)(LH)] (where LH2 = 93; R' = R'' = Ph, A =
1,2-C6H4) and [Co(OH)(L'H)] (here L'H2 = 93; R' = CF3, R'' =
thienyl, A = 1,2-C6H4). They are non-electrolytes (M = 7.3-9.6 mho
cm2 mol-1) in DMSO. The IR data are indicative of the monobasic
tridentate ONO donor behaviour of these Schiff bases. The (C==S)
stretch (1264 cm-1) of L'H2 remains at the same energy in
[Co(OH)(L'H)] indicating the non-coordinating behaviour of S atom
of thienyl moiety. The (CoO) and the (CoN) vibrations occur between
647-687 cm-1 and 536-580 cm-1. The appearance of two bands at
12269, 16000 and 11111, 16313 cm-1 due to the 2B2g 2Eg and 2B2g 2Ag
in [Co(OH)(LH)] and [Co(OH)(L'H)] respectively is indicative of
their square-planar geometry. The magnetic moments of [Co(OH)(LH)]
and [Co(OH)(L'H)] are 1.74 and 1.89 B.M. respectively indicating a
low-spin square-planar geometry around the metal ion.
Emara et al.[41] have synthesized a yellowish-blue,
four-coordinate compound, [Co2L(MeOH)2]2MeOH (where LH4 = 70, X =
OH) by refluxing a MeOH solution of LH4 and Co(NO3)26H2O in 1:2
molar ratio for 3 h. It is soluble in common organic solvents but
partially soluble in DMF and DMSO. The (C==N)(azomethine) stretch
of the ligand occurring at 1642 cm-1 shifts to lower energy by 12
cm-1 in the compound. The IR data are indicative of bis(dibasic
tridentate) ONO donor nature of LH4. The (CoO) and the (CoN)
vibrations occur at 608 and 524 cm-1 respectively. The magnetic
moment (4.41 B.M.) and the appearance of three bands at 21834,
20450 and 16420 cm-1 due to the 4A2(F) 4T2(F), 4A2(F) 4T1(F) and
4A2(F) 4T1(P) transitions in the compound suggest the tetrahedral
environment around the metal ion. Both the uncoordinated and
coordinated MeOH molecules are lost by heating the coordination
compound between 35-85 and 85-127 oC respectively. Tuncel et
al.[63] have synthesized a brown, four-coordinate compound,
[CoL(H2O)]
(where Na2LH2 = 94, R = H) and another black, four-coordinate
compound, [CoL'(H2O)] (here Na2L'H2 = 94, R = 3-OMe) by refluxing
an EtOH solution of CoCl26H2O and an aqueous solution of LH2 or
L'H2 respectively in 1:1 molar ratio. They are soluble in DMF,
DMSO. They are non-electrolytes (M = 15.3 and 13.3 mho cm2
mol-1) in aqueous
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27
solution and melt at 203 and 245 oC respectively. The IR data
indicate a dibasic tridentate ONO donor behaviour of the ligands.
Their magnetic moments (3.8 and 3.3 B.M. respectively) indicate a
tetrahedral environment around the metal ion. [CoL(H2O)] remains
stable up to 130 oC. The loss of coordinated H2O molecule and the
decomposition of organic skeleton occur between 130-190 oC and
341-585 oC respectively. In case of [CoL'(H2O)], the above
phenomena occurs between 120-185 oC and 338-557 oC respectively. In
both the cases, Co3O4 is the final product.
The synthesis of a four-coordinate, high-spin compound,
[Co(LH3)(H2O)]nH2O (where LH5 = 95; R = H, Cl) has been
reported[64]. Although the Schiff base is potentially a pentabasic
heptadentate ligand, but acts as a dibasic tridentate ONO donor
ligand. A tetrahedral structure has been suggested for the
coordination compound.
An EtOH solution of CoCl26H2O and LH2 [96; R = 3-OMe, R' = OH,
R'' = H, R''' = Me] on stirring forms[65] a light-brown,
non-electrolyte, air-stable, four-coordinate compound, [CoL(H2O)].
The Schiff base coordinates through its phenolic O, azomethine N
and carboxylato O atoms. The band at 16103 cm-1 due to the 4A2
4T1(F) transition indicates a tetrahedral environment around the
metal ion. The compound shows the
ferromagnetic behavior. The syntheses of a dark-brown compound,
[Co(NO3)(LH)(H2O)2]2H2O and
another violet compound, [Co2(OAc)2L(H2O)]2H2O (where LH2 = 32)
have been reported[8]. Both the coordination compounds are
non-electrolytes. The ligand is coordinated in a monobasic
tridentate ONO donor fashion. The nitrato group is
coordinated as a monodentate mode in the dark-brown compound,
whereas, the acetato group is coordinated as a monodentate mode as
well as bridged-bidentate ligand in the violet compound. The
magnetic moments of the dark-brown and the violet compounds are 4.1
and 2.9 B.M. indicating their high-spin octahedral and tetrahedral
geometries
respectively. The occurrence of a band at 16667 cm-1 due to the
4T1g(P) 4A2g transition in the former and the appearance of two
bands one at 18018 cm-1 and other at 15385 cm-1
due to the 4T1g(F) 4A2g(F) and 4T1g 4T2g(F) transitions in the
latter also indicate the same.
Kumar et al.[10] have reported the synthesis of a brown,
six-coordinate, polystyrene-anchored compound, [PSCH2LHCo(DMF)3]
(where PSCH2LH3 = 34). The
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28
PRC of the compound is 35.4 and the MBC of PSCH2LH3 is 0.22 mmol
of Co per g of the ligand. PSCH2LH3 behaves as a dibasic tridentate
ONO donor ligand. The magnetic moment (4.89 B.M.) and the
appearance of three bands at 9100, 13000 and 18800 cm-1 due to the
4T1g 4T2g(1), 4T1g 4A2g(2) and 4T1g(F) 4T1g(P)(3) spin-allowed
transitions respectively are indicative of an octahedral
environment around the metal ion.
A brown, six-coordinate, binuclear compound, [Co2L2(H2O)4]
[where LH2 = 35A-35C] is obtained by stirring an EtOH solution of
Co(OAc)24H2O and LH2 in 1:2 molar ratio for 12 h[11]. It melts at
150 oC. It is soluble in most common solvents except ether. The
ligand acts as a dibasic tridentate OON donor ligand. An octahedral
geometry [36; M = Co, A = H2O] has been suggested for it.
The air-stable, non-hygroscopic, non-electrolyte, dimeric,
six-coordinate
compounds, [CoClL(H2O)]2 (here LH = 43; R = Me, Et, propyl) and
[CoCl(L'H)(H2O)]2 (here L'H2 = 43; R = CH2CH2OH) have been
synthesized by refluxing a MeOH solution of CoCl26H2O and LH or
L'H2 in 1:1 molar ratio for 4 h[16]. They are soluble in DMF and
DMSO. The coordinated water molecules are lost between 190-200 oC.
Although L'H2 is potentially a dibasic tetradentate NONO donor
ligand but similar to LH, it also behaves as a monobasic tridentate
NON donor ligand bridging through its enolic O atom. The
coordination compounds display three bands between 10952-10989,
16806-16949 and 23584 cm-1 due to the 4T1g(F) 4T2g(F)(1), 4T1g(F)
4A2g(F)(2) and 4T1g(F) 4T1g(P)(3) transitions respectively
indicating the octahedral environment around the metal ion. The
magnetic moment (4.54-4.70 B.M.) support the weak
anti-ferromagnetic spin-exchange interaction between the two Co(II)
ions. They exhibit higher antifungal activity against A. niger than
the corresponding ligands. A distorted octahedral structure (44; M
= Co) has been suggested for them.
A violet, nano-crystalline, four-coordinate compound,
[CoL(H2O)]Cl (where LH = 97) has been synthesized by refluxing a
MeOH solution of CoCl2xH2O and LH in 1:1 molar ratio for 2 h[66].
The complex is 1:1 electrolyte (M = 85 mho cm2 mol-1 in MeOH). It
is soluble in DMF and DMSO. The ligand behaves as a monobasic
tridentate NON donor coordinating through its azomethine N,
carboxylato O and imidazole N atoms. The
magnetic moment (4.21 B.M.) and the existence of a band at 17857
cm-1 due to the 4A2(F) 4T1(P) transition indicate a tetrahedral
environment around the metal ion. The loss of
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29
coordinated H2O molecule, Cl- ion (as HCl gas) and the organic
skeleton occur between 210-230, 250-270 and 400-550 oC
respectively. Finally CoO is obtained as residue.
A brown, six-coordinate compound, [CoL2] (here LH = 45) is
obtained[17] on refluxing an hot MeOH solution of Co(NO3)26H2O and
LH in 1:2 molar ratio at pH = 7.5-8.5. The compound is
non-electrolyte (M = 15.03 mho cm2 mol-1 in DMSO). LH acts as a
monobasic tridentate ONN donor ligand coordinating through its
phenolic O and both azomethine N atoms. The magnetic moment (4.7
B.M.) and the appearance of three bands at 10162, 18621 and 25575
cm-1 due to the 4T1g(F) 4T1g(P), 4T1g(F) 4A2g and 4T1g(F) 4T1g
transitions respectively indicate the presence of high-spin
octahedral environment around the metal ions. The compound
crystallizes in a monoclinic fashion with a = 16.038 , b =4.285 and
c = 10.692 . The compound shows low antimicrobial activity against
E. coli than S. aureus, however, it shows moderate antimicrobial
activity against E. coli
than S. aureus.
The synthesis of a brown, trinuclear compound,
[Co3(NO3)2L2(H2O)2]2H2O (LH2 = 70; X = NH2) has been reported[41].
It is soluble in common organic solvents but partially soluble in
DMF and DMSO. The IR data are indicative of bis(monobasic
tridentate) ONN donor nature of LH2. The appearance of four new
bands at 1548, 1384, 1302 and 1058 cm-1 indicates the presence of
bidentate nitrato group in the compound. The (CoO) and the (CoN)
vibrations occur at 606 and 542 cm-1 respectively. The magnetic
moment (3.20 B.M.) and the appearance of one band at 18868 cm-1 due
to the 4T1g 4T2g transition suggest the low-spin octahedral
environment around the metal ion.
A yellowish, four-coordinate, non-electrolyte, [CoL(H2O)] (where
LH = 98) has been synthesized[67]. It is soluble in DMSO. The
monobasic tridentate Schiff base coordinates through its
carboxylate O, azomethine N and amino N atoms. The magnetic moment
of the compound is 4.61 B.M. The appearance of a band at 22026 cm-1
due to the 4A2 4T1(P) transition indicates the tetrahedral geometry
around the metal ion. The compound crystallizes in a monoclinic
fashion.
A purple, six-coordinate, non-electrolyte (M = 9.9 mho cm2 mol-1
in DMSO), [CoCl2(LH)(H2O)]n (here LH = 84; R = H, R' = Me) has been
synthesized by refluxing an H2O/EtOH solution of CoCl26H2O and LH
in 1:1 molar ratio for 1 h[56]. The compound is insoluble in Me2CO,
CHCl3 and C6H6 but is fairly soluble in DMF and DMSO. It melts
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30
between 240-242 oC. The coordinated H2O molecule is lost at 130
oC. LH acts as a neutral tridentate ONN donor ligand. The compound
displays two bands one at 16130 cm-1 and other at 19230 cm-1 due to
the 4T1g(F) 4A2g(F)(2) and 4T1g(F) 4T1g(P)(3) transitions
respectively. The spectral parameters [10Dq (8558 cm-1), B' (855
cm-1), (0.88), 0 (11.9%) and LFSE (81.4 kJ mol-1)] and the magnetic
moment (4.96 B.M.) lend support for its octahedral geometry. The
compound shows higher antibacterial activity against E. coli than
LH, whereas its antifungal activity against A. niger is less than
LH. An
octahedral polymeric structure (99, M = Co) has been assigned to
the compound. The synthesis of a green, monomeric, four-coordinate
compound,
[Co(LH)(H2O)]Cl (where LH2 = 86) has been reported[57]. The
ligand is linked through its enolic O, azomethine N and amino N
atoms. The phenolic OH group does not participate
in the coordination. The magnetic moment (4.42 B.M.) and the
occurrence of two bands at 14749 and 20921 cm-1 suggest a
tetrahedral geometry of the compound.
Sebastian et al.[20] have observed that the complexation of the
yellow coloured Schiff base, (LH2 = 46A, 46B) with Co(II) ion
proceeds with the rearrangement of benzothiazoline ring to form the
corresponding brown colored, non-electrolyte, [CoL(H2O)3]H2O. The
Schiff base coordinates in enolic form as dibasic tridentate ONS
donor ligand. The magnetic moment (5.18 B. M.) suggests a high-spin
octahedral geometry for the complex. The lattice water molecule and
three coordinated water
molecules are lost between 90-120 oC and 150-200 oC
respectively. A brown, mononuclear, six-coordinate compound,
[Co(LH2)(H2O)3] (where LH4 =
100) has been synthesized[42]. The Schiff base behaves as a
dibasic tridentate ONS donor ligand coordinating through its enolic
O, azomethine N and thiolato S atoms. The oxime
group does not participate in coordination. A pink,
non-electrolyte, [CoL(H2O)2]2, (where LH2 = 47) has been
synthesized[21].
The Schiff base acts as a dibasic tridentate ONS donor ligand.
The bands at 8728 and
19200 cm-1 due to the 4T1g 4T2g(F) and 4T1g 4T1g(P) transitions
respectively and the magnetic moment (4.86 B.M.) are indicative of
the octahedral environment around the metal ion. Here two cobalt
ions are bridged through phenolic O atoms resulting in a dimer.
An aqueous solution of Co(OAc)24H2O reacts[22] with an EtOH
solution of LH2 (48) in 1:2 molar ratio in N2 atmosphere and forms
an air-stable, reddish-brown
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31
compound, [Co(LH)2]. It decomposes at 186 oC and is soluble in
Me2CO, DMF and DMSO. It is non-electrolyte (M = 12.3 mho cm2 mol-1
in DMSO and 3.1 mho cm2 mol-1 in Me2CO). The Schiff base acts as a
monobasic tridentate ONS donor ligand and coordinates to the metal
ion through its hydroxylic O, azomethine N and thiolato S
atoms.
The (CoN) vibrations occur at 565 cm-1 in the compound. The
magnetic moment (4.9 B.M.), the appearance of a broad band (7700
cm-1) and two shoulders (13500 and 20500 cm-1) due to the 4T1g
4T2g(1), 4T1g 4A2g(2) and 4T1g 4T1g(P)(3) transitions respectively
indicate the presence of high-spin octahedral environment around
the metal
ion. A distorted octahedral structure, 49 (M = Co) has been
suggested for it. An air-stable, four-coordinate compound,
[CoCl(LH)]3H2O (here LH2 = 37) has
been obtained by stirring a MeOH solution of LH2 and CoCl26H2O
in 2:1 ratio at pH 8.0 for 8 h[68]. It is soluble in DMSO and DMF,
slightly soluble in MeCN and insoluble in
MeOH and H2O. It behaves as non-electrolyte in DMSO. It shows a
mass loss equivalent to three H2O molecules in the 90-110 oC range,
suggesting that these molecules are not coordinated to the metal
ion. The carboxylato group is coordinated in a monodentate mode.
The low value of the magnetic moment (4.1 B.M) of the compound
indicates its distorted tetrahedral geometry.
The synthesis of an air-stable, four-coordinate compound,
[CoCl(LH)]2H2O (here LH2 = 39) has been reported[13]. The compound
is soluble in DMSO and DMF and slightly soluble in MeCN. It
exhibits the non-electrolytic behavior in DMSO. NaLH behaves as a
monobasic tridentate OON donor ligand. The carboxylato group is
coordinated in a
monodentate fashion. The (CoN) stretch occurs at 450 cm-1. The
compound shows a broad band centered at 25640 cm-1 due to Td
symmetry around the metal ion. Its magnetic moment is 3.8 B.M. The
compound shows higher activity than NaLH against P. mirabilis, K.
pneumoniae, S. enteriditis and E. coli, while it remains inactive
towards S. aureus and
P. aeruginosa. A tetrahedral structure (40, M = Co) has been
assigned to it. A four-coordinate compound, [CoCl(LH)] (here LH2 =
50; R = OMe, R' =
NH2) has been synthesized by stirring a MeOH solution of NaLH
and CoCl2.6H2O in 2:1 molar ratio for 8 h at room temperature[43].
It is air-stable and soluble in DMF and
DMSO and is slightly soluble in MeCN. It is non-electrolyte in
DMSO. The carboxylato group is coordinated in a monodentate
fashion. The presence of the (CoS) stretch at
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32
300 cm-1 indicates the coordination through S atom of thiophene
moiety. LH2 behaves as a monobasic tridentate OOS donor. The
magnetic moment of the compound is 4.2 B.M. The compound is
inactive towards S. aureus, E. faecalis, E. coli and P. mirabilis,
while it shows lesser antibactericidal activity than the ligand
against S. sonnei and S. enteritidis. A distorted tetrahedral
structure (51; R = OMe, R' = NH2, A = nil; M = Co) has been
assigned to it.
Suni et al.[69] have noticed that upon refluxing an EtOH
solution of
Co(OAc)24H2O, LH (52; R = (C5H4N)2C, R' = NHC6H11, X = S) and
KSCN in 1:1:1 molar ratios, a brown, four-coordinate compound,
[Co(NCS)L]2H2O is obtained. On the other hand, on refluxing an EtOH
solution of CoCl26H2O and L'H (52; R = (C5H4N)2C, R' = NHC6H5, X =
S) in 1:1 molar ratio, another brown, four-coordinate compound,
[CoClL']2H2O is obtained. Both the ligands behave as the monobasic
tridentate NNS do