Mono, di and polynuclear Cu(II)–azido complexes incorporating N, N, N reduced schiff base: syntheses, structure and magnetic behavior

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Inorganica Chimica Acta 358 (2005) 641–649

Mono, di and polynuclear Cu(II)–azido complexes incorporatingN,N,N reduced schiff base: syntheses, structure

and magnetic behavior

Sumana Sarkar a, Amrita Mondal a, Joan Ribas b, M.G.B. Drew c,Kausikisankar Pramanik a, Kajal Krishna Rajak a,*

a Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata 700 032, Indiab Department de Quımica Inorganica, Universitat de Barcelona, Diagonal 6487, 08028 Barcelona, Spainc School of Chemistry, The University of Reading, PO Box 224, Whiteknights, Reading, RG6 6AD, UK

Received 18 June 2004; accepted 28 September 2004

Available online 21 November 2004

Abstract

Three kinds of copper(II) azide complexes have been synthesised in excellent yields by reacting Cu(ClO4)2 Æ 6H2O with N,N-bis(2-

pyridylmethyl)amine (L1); N-(2-pyridylmethyl)-N 0,N 0-dimethylethylenediamine (L2); and N-(2-pyridylmethyl)-N 0,N 0-diethylethylen-

ediamine (L3), respectively, in the presence of slight excess of sodium azide. They are the monomeric Cu(L1)(N3)(ClO4) (1), the end-

to-end diazido-bridged Cu2(L2)2(l-1,3-N3)2(ClO4)2 (2) and the single azido-bridged (l-1,3-) 1D chain [Cu(L3)(l-1,3-N3)]n(ClO4)n (3).

The crystal and molecular structures of these complexes have been solved. The variable temperature magnetic moments of type 2

and type 3 complexes were studied. Temperature dependent susceptibility for 2 was fitted using the Bleaney–Bowers expression

which led to the parameters J = �3.43 cm�1 and R = 1 · 10�5. The magnetic data for 3 were fitted to Baker�s expression for

S = 1/2 and the parameters obtained were J = 1.6 cm�1 and R = 3.2 · 10�4. Crystal data are as follows. Cu(L1)(N3)(ClO4): Chemical

formula, C12H13ClN6O4Cu; crystal system, monoclinic; space group, P21/c; a = 8.788(12), b = 13.045(15), c = 14.213(15) A;

b = 102.960(10)�; Z = 4. Cu(L2)(l-N3)(ClO4): Chemical formula, C10H17ClN6O4Cu: crystal system, monoclinic; space group, P21/c;

a = 10.790(12), b = 8.568(9), c = 16.651(17) A; b = 102.360(10)�; Z = 4. [Cu(L3)(l-N3)](ClO4): Chemical formula, C12H21ClN6O4Cu;

crystal system, monoclinic; space group, P21/c; a = 12.331(14), b = 7.804(9), c = 18.64(2) A; b = 103.405(10)�; Z = 4.

� 2004 Elsevier B.V. All rights reserved.

Keywords: Copper; Reduced Schiff base ligands; Azido bridge; Magnetic properties

1. Introduction

The coordination chemistry of copper is of consider-

able interest as the copper ions are found in the active

sites of a large number of metalloproteins such as hemo-

cyanin, tyrosinase, laccase and ascorbate oxidase [1–4].

These proteins are involved in various biological pro-cesses such as biological electron-transfer reaction, oxy-

0020-1693/$ - see front matter � 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2004.09.055

* Corresponding author. Tel.: +24146666; fax: +91 33 2414 6584.

E-mail addresses: [email protected] (J. Ribas), kajalrajak@

hotmail.com (K.K. Rajak).

gen atom insertion into substrates, dioxygen reduction

to hydrogen peroxide or water and hydrolytic reactions

[5,6]. These proteins are inhibited by the azide ion

[1c,d,e,3e,7], and hence the met-azido complexes of such

proteins were studied extensively [8] in order to under-

stand the electronic nature, geometrical properties as

well as the role of the metal in those processes. Besidessuch studies, the chemistry of azido-bridged cop-

per(II)complexes has also received great deal of atten-

tion to enhance the fundamental knowledge about the

magnetic interactions between the paramagnetic centres

642 S. Sarkar et al. / Inorganica Chimica Acta 358 (2005) 641–649

and for developing new functional molecule-based mate-

rials [9].

Among the bridging ligands, the azide ion can act not

only as a monodentate ligand [10] but also link the metal

ions in l-1,1 (end-on) or l-1,3 (end-to-end) bridging

coordination modes, depending on the steric and elec-tronic demands of the coligand. It has been widely sta-

ted that the end-to-end (EE) bridging mode

predominantly leads to antiferromagnetic coupling [11]

and the end-on (EO) mode to ferromagnetic exchange

[12]. However, the instances of ferromagnetic coupling

in the case of end-to-end azido-bridged complexes are

rare [13]. Though several correlations have been pro-

posed to explain the influence of structural parameters,such as the Cu–N3–Cu torsion angle and the distortion

of copper(II) coordination geometry on the magnetic

parameter, J, but they were restricted to a limited num-

ber of data and are not applicable in a general sense.

This has prompted us to search a new family of

Cu(II)-azido bridged complexes in order to investigate

how a ligand environment modulates the details of

nuclearity, molecular geometry, Cu(II)/Cu(I) redoxproperties, copper(II) spectral features and their mag-

netic behavior.

Here, we describe the synthesis and properties of sin-

gle and double asymmetric-bridged l-1,3-copper(II)-azide complexes incorporating conformationally flexible

N,N,N-coordinating reduced Schiff base ligands. The

complexes were characterised by elemental analysis, cyc-

lic voltammetry, IR, UV–Vis, EPR spectra and singlecrystal X-ray diffraction analysis. The variable tempera-

ture magnetic moments were studied in case of dinuclear

and polynuclear complexes.

2. Results and discussion

2.1. Syntheses

In this present work, three tridentate reduced Schiff

bases L1–L3 (general abbreviation, L) have been used

as coligand to block three coordination sites leaving the

other positions for possible azide binding (see Chart 1).

The reduced Schiff bases were prepared by general

procedure [14]. The stoichiometric reaction of copper(II)

perchlorate hexahydrate with L in methanol in air in the

N

L1 R = CH3 : L2

R = C2H5 : L3

N

CH2 NH

NR2N

CH2 NH

Chart 1.

presence of excess azide ion afforded the dark blue col-

oured complex, [CuLN3]ClO4, in excellent yields.

The IR spectra of the complexes show a strong dou-

blet near 2080 and 2065 cm�1, which is consistent with

the asymmetric stretching of the azide ion for Cu–N3

bonding [6c]. The perchlorate stretches occur at 640and 1100 cm�1, respectively.

In UV–Vis spectra, the compounds display a weak

band at �620 nm. This transition is logically assigned

as ligand field excitation (d–d transition) [15]. The al-

lowed intense band near 380 nm is due to the

N�3 ! CuII LMCT [16].

2.2. Crystal structure

The crystal structures of Cu(L1)(N3)(ClO4), 1,

Cu(L2)2(l-1,3-N3)2(ClO4)2, 2, and [Cu(L3)(l-1,3-N3)]n(ClO4)n, 3, have been determined. Molecular views

are shown in Figs. 1–3 and the selected bond parameters

are given in Tables 1 and 2, respectively.

Cu(L1)(N3)(ClO4), 1. The structure of complex 1 con-

sists of a monomeric Cu(L1)(N3)(ClO4) unit and thecopper ion is coordinated to four nitrogen and one oxy-

gen atom. The gross geometry of 1 appears to be dis-

torted square-pyramid (s = 0.23) [17a] and is

characterised by trans N–Cu–N and O–Cu–N bond an-

gles (see Table 1) that deviate significantly from their

ideal values of 180� and 90�, respectively. In a distorted

CuN4O square-pyramidal environment, three nitrogen

atoms [N(11), N(18) and N(21)] of the ligand and onenitrogen atom [N(1)] of the azide ion lie in the equatorial

Fig. 1. Perspective view and atom-labelling scheme for Cu(L1)(N3)(-

ClO4), 1. All non-hydrogen atoms are represented by their 20%

thermal probability ellipsoids.

Fig. 2. Perspective view and atom-labelling scheme of Cu2(L2)2(l-1,3-

N3)2(ClO4)2, 2. All non-hydrogen atoms are represented by their 20%

thermal probability ellipsoids.

Fig. 3. Perspective view and atom-labeling scheme of [Cu(L3)(l-1,3-N3)]n(ClO4)n. All non-hydrogen atoms are represented by their 20%

thermal probability ellipsoids.

Table 1

Selected bond distances (A) and angles (�) for complex 1

Bond distances

Cu(1)–N(1) 1.944(7)

Cu(1)–N(11) 1.986(7)

Cu(1)–N(18) 2.016(6)

Cu(1)–N(21) 1.995(6)

Cu(1)–O(11) 2.559(10)

N(1)–N(2) 1.193(9)

N(2)–N(3) 1.144(10)

Bond angles

N(1)–Cu(1)–N(11) 96.9(3)

N(1)–Cu(1)–N(18) 178.5(3)

N(1)–Cu(1)–N(21) 98.1(3)

N(11)–Cu(1)–N(18) 82.2(2)

N(11)–Cu(1)–N(21) 164.6(2)

N(18)–Cu(1)–N(21) 82.7(2)

O(11)–Cu(1)–N(1) 88.84(9)

O(11)–Cu(1)–N(11) 88.67(9)

O(11)–Cu(1)–N(18) 92.36(10)

O(11)–Cu(1)–N(21) 95.0(10)

N(2)–N(1)–Cu(1) 124.0(6)

N(3)–N(2)–N(1) 176.5(8)

Table 2

Selected bond distances (A) and angles (�) for complexes 2 and 3

2 3

Bond distances

Cu(1)–N(1) 1.955(4) 1.967(4)

Cu(1)–N(11) 2.026(3) 2.026(4)

Cu(1)–N(18) 2.008(3) 2.002(4)

Cu(1)–N(21) 2.070(3) 2.069(4)

Cu(1)–N(3A) 2.880(4) 2.448(5)

Cu(1)–O(14) 2.495(10)

N(1)–N(2) 1.189(5) 1.174(5)

N(2)–N(3) 1.162(5) 1.154(5)

Cu� � �Cu 5.248(8) 6.086(7)

Bond angles

N(1)–Cu(1)–N(11) 102.54(15) 98.31(18)

N(1)–Cu(1)–N(18) 174.52(14) 168.21(18)

N(1)–Cu(1)–N(21) 91.67(15) 93.95(17)

N(11)–Cu(1)–N(21) 164.94(13) 165.20(14)

N(18)–Cu(1)–N(11) 80.66(14) 81.31(16)

N(18)–Cu(1)–N(21) 84.79(15) 84.99(15)

N(1)–Cu(1)–N(3A) 84.78(12) 102.70(2)

N(11)–Cu(1)–N(3A) 78.85(14) 85.91(16)

N(18)–Cu(1)–N(3A) 91.54(15) 89.08(18)

N(21)–Cu(1)–N(3A) 97.78(12) 99.50(15)

O(14)–Cu(1)–N(1) 99.38(10)

O(14)–Cu(1)–N(11) 88.19(9)

O(14)–Cu(1)–N(18) 85.10(12)

O(14)–Cu(1)–N(21) 94.43(10)

N(3)–N(2)–N(1) 175.5(4) 174.60(5)

N(2)–N(1)–Cu(1) 133.5(3) 136.40(4)

N(2)–N(3)–Cu(1A) 100.27(4) 141.20(4)

S. Sarkar et al. / Inorganica Chimica Acta 358 (2005) 641–649 643

plane, whereas the axial position is occupied by oxygen

atom of the perchlorate ion. The copper atom is dis-

placed by 0.0392 A towards the oxygen atom from equa-

torial plane (mean deviation 0.0163 A). The azide ion is

coordinated in a monodentate fashion and the Cu–N–N

angle is 124.0(6)�. The N–N bond distances within

the azide ion are not equal [N(1)–N(2) 1.193(9) and

N(2)–N(3) 1.144(10) A]. The large difference [�0.05 A]between the N–N bond lengths can be attributed to

the terminal bonding of the azide ion. The four Cu–N

bond lengths span in the range of 1.944(7) and

2.016(6) A and the shortest distance is the bond with

the azide nitrogen and the longest is that with the amine

nitrogen.

Cu2(L2)2(l-1,3-N3)2(ClO4)2, 2. Two centrosymmetri-

cally related Cu(L2)(l-1,3-N3)(ClO4) units are linkedby the azide ion in an end-to-end fashion forming a diaz-

ido-bridged dimeric complex. The coordination geome-

try around the copper ion is a distorted octahedron.

Four nitrogen atoms (the pyridine, the tertiary amine,

the secondary amine and the azide ion) form the square

plane (mean deviation 0.0018 A). The Cu–N bond

lengths and the N–Cu–N bond angles in the basal plane

644 S. Sarkar et al. / Inorganica Chimica Acta 358 (2005) 641–649

range from 1.955(4) to 2.070(3) A and 80.66(14)� to

102.54(15)�, respectively, and the copper atom is dis-

placed by 0.0766 A from this plane towards the oxygen

atom of the coordinated perchlorate ion. The perchlo-

rate oxygen atom of one unit and the azide nitrogen

atom from the other unit occupy the axial positions.The long axial Cu–O [2.495(10) A] and the Cu–N

[2.88(4) A] bond distances are due to pseudo Jahn–Tell-

er distortion [17b]. The intra dimer Cu� � �Cu distance is

5.248(8) A. The EE bridging azide is quasilinear with N–

N–N bond angle of 175.5(4)� and the N–N bond lengths

in the azide ion are 1.162(5) and 1.189(5) A, respectively.

In the end-to-end bridging moiety, the Cu–N–N bond

angles are 100.27(4)� for Cu–N(axial)–N and 133.5(3)�for Cu–N(equatorial)–N.

[Cu(L3)(l-1,3-N3)]n(ClO4)n, 3. The crystal structure

consists of infinite one dimensional copper(II)–azido

chains and each copper centre is in a (4 + 1) distorted

square-pyramidal environment. In CuN5 coordination

sphere, the apical position is occupied by one nitrogen

of the azide ion and the metal atom is displaced by

0.17 A towards the apical nitrogen atom, away fromthe equatorial plane defined by N(1), N(18), N(11)

and N(21) atoms (mean deviation 0.04 A). The four

equatorial Cu–N bond distances are not equal

[1.969(5) to 2.070(4) A]. The azide ion is almost linear

[N(1)–N(2)–N(3), 174.6(5)�] and the N–N bond

lengths are 1.174(5) and 1.154(5) A, respectively. The

bridging Cu(1)–N(1)–N(2) and Cu(1A)–N(3)–N(2)

angles are 136.4(4)� and 141.2(4)�, respectively,whereas the torsional angle of Cu–NNN–Cu moiety

is 92�. Here, the Cu� � �Cu distance is 6.086(7) A . In

the lattice, the perchlorate ion is strongly hydro-

gen bonded with the amine nitrogen atom

[O� � �N � 2.216 A].

2.3. EPR spectra

The X-band EPR spectra of the complexes were re-

corded at 77 K for polycrystalline samples in frozen

solution (DMF/toluene). The spectral data are listed in

Table 3. Complexes 1 and 2 show axial features in the

Table 3

X-band EPR data for complexes 1, 2 and 3

Complex Matrix gav Aav (G)

1 DMF/toluene, 300 K 2.122 120

DMF/toluene, 77 K

solid, 300 K

2 DMF/toluene, 300 K 2.125 120

DMF/toluene, 77 K

solid, 300 K

3 DMF/toluene, 300 K 2.131 126

DMF/toluene, 77 K

solid, 300 K

polycrystalline solid state, indicating no significant inter-

action between the neighbouring copper centres (Fig. 4).

The spectrum of complex 3 is considerably different

from that of 1 and 2 revealing the presence of strong

interaction within and between the chains in the solid

state (Fig. 4).All the complexes exhibit axial EPR spectrum typical

for monomeric tetragonal copper(II) species with dx2�y2

ground state (gi > g^ > 2.0) [18] (Fig. 4). From the spec-

trum of 3, it is clear that the polymeric chain dissociates

in solution.

2.4. Magnetic studies

Variable temperature magnetic susceptibility mea-

surements were performed in the range 2–300 K. Plots

of vM and vM T versus T of complexes 2 and 3 are shown

in Figs. 5 and 6, respectively.

In 2, the magnetic data are for two copper(II) ions,

the complex being a dinuclear system. The vMT at 300

K is 0.86 emu cm�1 K which remains almost constant

upto 50 K, decreasing rapidly to 0.27 emu cm�1 K at2 K, suggesting weak antiferromagnetic interaction.

The vMT data were fitted by employing the Bleaney-

Bowers formula for dimer of S = 1/2 with Hamiltonian

[11b].

H ¼ �JS1 � S2:

The best-fit parameters are J = �3.43 ± 0.008 cm�1,g = 2.15 ± 0.0006 with R = 1 · 10�5.

The plot of the reduced magnetisation (Fig. 7), which

tends to 1.6 Nb, is also clearly indicative of the weak

antiferromagnetic character.

The experimental vMT per copper(II) ion at 300 K

is 0.434 emu cm�1 K for 3. This value is almost con-

stant to 50 K but increases rapidly to 0.67

emu cm�1 K at 2 K. Such magnetic behavior is char-acteristic of ferromagnetic interaction. The magnetic

susceptibility data were fitted to Baker�s expression

[19] for S = 1/2 in a uniformly spaced chain with a

Hamiltonian

gi g^ Ai (G) g1 g2

2.215 2.030 178

2.18 2.07

2.215 2.033 176

2.21 2.06

2.215 2.039 170

2.19 2.07

Fig. 4. X-band EPR spectra of: (a) Cu2(L2)2(l-1,3-N3)2(ClO4)2 in solid

state at 300 K, (b) [Cu(L3)(l-1,3-N3)]n(ClO4)n in solid state at 300K and

(c) [Cu(L3)(l-1,3-N3)]n(ClO4)n in DMF: toluene at 77 K. Instrument

settings: power, 30 dB; modulation, 100 kHz; sweep centre, 3200 G.

Fig. 5. Plot of vM (inset) and vMT versus T for 2. Open points are the

experimental data and solid line represents the best fit obtained.

Fig. 6. Plot of vM (inset) and vMT versus T for 3. Open points are the

experimental data and solid line represents the best fit obtained.

S. Sarkar et al. / Inorganica Chimica Acta 358 (2005) 641–649 645

H ¼ �JXn�1

i¼1

SiSiþ1:

The best-fit parameters are J = 1.6 ± 0.02 cm�1,

g = 2.14 ± 0.01 with R = 3.2 · 10�4. Such behavior isalso supported from the field-dependent magnetisation

measurement at 2 K (Fig. 8). The reduced magnetisation

saturates rapidly tending to 1.0 Nb and the shape of the

curve does not follow the Brillouin formula for S = 1/2

and g = 2.14 (experimental value). The experimental val-

ues exceed the theoretical ones, which clearly suggest the

ferromagnetic interaction in the chain.

The Addison parameter, s, [17a] plays an important

role in the determination of magnetic interaction and

it has been pointed out that the greater is this parameter

the higher is the spin delocalisation on the bridge, con-

sequently the stronger is the antiferromagnetic couplingand vice-versa [11a,20]. These interactions also depend

on structural parameters such as Cu–N(azide) distance,

Cu–N–N angle, the Cu–NNN–Cu torsion angle and the

dihedral angle, d, between the N(azido)–M–N(azido)

plane and the mean plane defined by the two parallel

azido bridges [21]. For the double EE bridged complex,

the dihedral angle, d, defines the distortion of the

Cu–(NNN)2–Cu ring from planarity towards the chair

Fig. 8. Plot of the reduced magnetisation (M/Nb) versus T at 2 K for

3. Open points are the experimental values and the solid line is the

representation of the Brillouin formula for S = 1/2 and g = 2.14.

Fig. 7. Plot of the reduced magnetisation (M/Nb) versus T at 2 K for

2. Open points are the experimental values and the solid line indicates

the best fit obtained.

646 S. Sarkar et al. / Inorganica Chimica Acta 358 (2005) 641–649

conformation. It has been well established from EHMO

and DFT calculations that the antiferromagnetic inter-

action between the two paramagnetic centres decreases

with increase in distortion. Cano-Boquera [22] demon-

strated that for single asymmetric end-to-end azido-

bridged complexes, the ferromagnetic contribution in-

creases for Cu–N(ap)–N angles close to 90� and, onthe contrary, Cu–N(eq)–N angles close to 180� favour

the ferromagnetism while for angles close to 90� this fer-romagnetism will be minimum.

In complex 2, the weak antiferromagnetic coupling

can be attributed to the large dihedral angle, d, and

the long Cu–N(apical) distance. The low Cu–N(eq)–N

and the large Cu–N(ap)–N angles also prefer antiferro-

magnetic coupling.

In complex 3, the azide group is quasilinear and the

rx and the pz azide orbitals are strictly orthogonal.

The rx and pz orbitals overlap with dx2�y2 and d2z

orbitals of two bridged copper(II) ions, respectively.

Thus, the magnetic orbitals of the two nearest

neighbours are strictly orthogonal leading to ferro-magnetic interaction. It is believed that the short

Cu–N(equatorial) and the long Cu–N(apical) bond

distances are responsible for the weak ferromagnetic

coupling.

3. Experimental

3.1. Materials

All the starting chemicals were analytically pure

and used without further purification. The ligandswere prepared according to the literature procedure

[14]. Caution: Perchlorate salts are highly explosive,

and should be handled with care and in small

amounts.

3.2. Physical measurements

UV–Vis spectra were recorded on a Perkin–ElmerLAMBDA EZ-301 spectrophotometer and IR spectra

were measured with Perkin–Elmer L-0100 spectrometer.

EPR spectra were recorded on a Varian E-109C X-band

spectrometer. Magnetic measurements were carried out

on polycrystalline samples with a Quantum Design

MPMS XL SQUID susceptometer operating at a mag-

netic field of 0.1 T between 2 and 300 K. The diamag-

netic corrections were evaluated from Pascal�sconstants. Elemental analyses (C, H and N) were per-

formed on a Perkin–Elmer 2400 Series II elemental

analyser.

3.3. Synthesis of complexes

The complexes were prepared by the same general

methods. Details are given here for a representative case.

3.3.1. Cu(L1)(N3)(ClO4), 1To a methanolic solution (10 mL) of copper(II) per-

chlorate hexahydrate (0.186 g, 0.5 mmol), sodium azide

(0.046 g, 0.8 mmol) and L1 (0.100 g, 0.5 mmol) were

added. The resulting blue solution was stirred for about

0.5 h at room temperature. Slow evaporation of the

solution yielded blue crystalline product. Yield: 0.140 g(70%). Anal. Calc. for C12H13N6ClO4Cu: C, 35.64; H,

3.22; N, 20.79. Found: C, 35.86; H, 3.20; N, 20.94%.

UV–Vis (kmax/nm (e/M�1 cm�1) CH3CN solution):

385(3463); 617(355). IR (KBr, cm�1): mðN�3 Þ 2080,

2064; mðCLO�4 Þ 1100, 620.

Table 4

Crystal data and structure refinement parameters for 1, 2 and 3

1 2 3

Formula C10H17ClN6O4Cu C12H21ClN6O4Cu C12H13ClN6O4Cu

Formula weight 384.28 412.34 404.27

Cryst system monoclinic monoclinic monoclinic

Space group P21/c P21/c P21/c

Unit cell dimensions

a (A) 10.790(12) 12.331(14) 8.788(12)

b (A) 8.568(9) 7.804(9) 13.045(15)

c (A) 16.651(17) 18.64(2) 14.213(15)

b (�) 102(8) 108.633(8) 104.32(3)

V (A3) 1588(3) 1504(3) 1745(3)

Z 4 4 4

Dcalc (mg m�3) 1.691 1.697 1.569

l (mm�1) 1.575 1.658 1.434

h (�) 2.14–25.78 2.50–25.75 1.70–25.70

Measured reflection 9972 9179 6178

Unique reflection/Rint 2901/0.0579 2722/0.0334 3214/0.0446

T (K) 293 293 293

R1a,wR2

b (I > 2r(I)) 0.0790,0.1581 0.0501,0.1132 0.0553,0.1218

Goodness-of-fit on F2 1.044 1.169 1.145

a R1 ¼P

j F o j � j F c jP

j F o j= .b wR2 ¼

PwðF 2

o � F 2cÞ

2 PwðF 2

oÞ2

.h i1=2.

S. Sarkar et al. / Inorganica Chimica Acta 358 (2005) 641–649 647

3.3.2. [Cu(L2)(l-1,3-N3)(ClO4)]2, 2Yield: 0.145g (75%). Anal. Calc. for C10H17N6ClO4-

Cu: C, 31.25; H, 4.43; N, 21.87%. Found: C, 31.46; H,

4.43; N, 22.02. UV–Vis (kmax/nm (e/M�1 cm�1) CH3CN

solution): 383(2287); 616(244). IR (KBr, cm�1): mðN�3 Þ

2083, 2062; mðCLO�4 Þ 1120, 640.

3.3.3. [Cu(L3)(l-1,3-N3)]n(ClO4)n, 3Yield: 0.150g (72%). Anal. Calc. for C12H21N6ClO4-

Cu: C, 34.95; H, 5.09; N, 20.38. Found: C, 35.20; H,

4.95; N, 20.58%. UV–Vis (kmax/nm (e/M�1cm�1)

CH3CN solution): 388(3158); 631(347). IR (KBr,

cm�1): mðN�3 Þ 2078, 2068; mðCLO

�4 Þ 1118, 645.

3.4. Crystallographic studies

Single crystals were obtained by recrystallisation of

the crystalline products in methanol. Data were mea-

sured with Mo Ka radiation using the MA Research Im-

age Plate System. The crystals were positioned at 70 mm

from the Image Plate. 100 frames were measured at 2�intervals with a counting time of 5 min. Data analyses

were carried out with the XDSXDS program [23] and the

structures were solved using direct methods with theSHELXSHELX 86 program [24]; non hydrogen atoms were re-

fined with anisotropic thermal parameters. The hydro-

gen atoms bonded to carbon were included in

geometric positions and given thermal parameters

equivalent to 1.2 times those of the atom to which they

were attached. Empirical absorption corrections were

applied using DIFABSDIFABS [25] and the stuctures were refined

on F2 using SHELXLSHELXL [26]. Significant crystal data are gi-

ven in Table 4.

4. Concluding remarks

The main findings of this work can now be sum-marised. Three N,N,N-coordinating reduced Schiff

bases, namely, N,N-bis(2-pyridylmethyl)amine (L1);

N-(2-pyridylmethyl)-N 0,N 0-dimethylethylenediamine

(L2) and N-(2-pyridylmethyl)-N 0,N 0-diethylethylenedi-

amine (L3), have been successfully utilised as coligands

to generate copper(II) azide complexes. Here, L1 af-

fords the mononuclear species whereas L2 and L3 fur-

nish the di and polynulear complexes, respectively.The species represent the first examples of structurally

characterised Cu(II) azide complexes incorporating re-

duced Schiff base as coligands. The nuclearity of the

complexes plausibly arises due to slight modification

of the ligand architecture. These were also character-

ised by spectroscopic techniques. The magnetic behav-

ior of the complexes is quite different from the

analogous Schiff base complexes. This difference be-tween Schiff bases and reduced Schiff bases is a new

demonstration of the remarkable versatility of the

azido ion in building new magnetic materials and

illustrates the great challenges and opportunities in

the fields of coordination chemistry and molecular

magnetism.

648 S. Sarkar et al. / Inorganica Chimica Acta 358 (2005) 641–649

5. Supporting information

CIF files of [Cu(L1)(N3)(ClO4)], (1), [Cu(L2)(N3)

(ClO4)]2, (2) and [Cu(L3)(N3)]n(ClO4)n, (3), are depos-

ited. The CCDC Nos. are CCDC-237589, -237590 and

-237591, respectively.

Acknowledgements

Financial supports from the Department of Science

and Technology, New Delhi, India and from the Coun-

cil of Scientific and Industrial Research, New Delhi, In-

dia are gratefully acknowledged. Joan Ribasacknowledges the financial support from the Spanish

Government (Grant BQU2000/0791).

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