JJC Volume 14, Number 2, June 2019 Pages 81-87 * Corresponding Author: Taghreed M. A. Jazzazi Email: [email protected]Jordan Journal of Chemistry ARTICLE Zinc(II) Complexes of Symmetrical Tetradentate Schiff Base Ligands Derived From 2,2'-Diamino-6,6'-dibromo-4,4'-dimethyl-1,1'- biphenyl-salicylaldehyde: Synthesis, Characterization and Computational Study Taghreed M. A. Jazzazi a* , Taher S. Ababneh b and Eman K. Abboushi a a Department of Chemistry, Yarmouk University, Irbid 21163, Jordan. b Department of Chemistry and Chemical Technology, Tafila Technical University, Tafila, Jordan. Received on: 6 th Aug. 2019; Accepted on: 9 th Sep. 2019 Abstract: Five new complexes (1-5) of the general formula ZnL were prepared by refluxing the new Schiff base ligands (L1-L5) with Et 2 Zn in THF. The new ligands (L1-L5) were prepared by reacting two equivalents of salicyladehyde derivatives (3,5-ditert-butyl-, 3-tert-butyl-, 5-tert-butyl-, 3,5-dinitro- and 3,5-dibromo-salicylaldehyde) with 2,2'-di- amino-6,6'-dibromo-4,4'-dimethyl-1,1'-biphenyl. The new Schiff base ligands and their zinc complexes were characterized by 1 H-, 13 C-NMR and IR spectroscopy as well as elemental analysis. Additionally, the molecular geometries of all prepared zinc complexes were fully optimized and examined using density functional theory (DFT) calculations at the B3LYP/6-31G(d) level of theory. Infrared vibrational analysis was conducted, and the results are in good agreement with the experimental data. Keywords Schiff base ligands, Synthesis, Computational study, Zinc complexes, DFT. Introduction Schiff bases are compounds with a functional group that contains a carbon-nitrogen double bond [1] . These ligands can coordinate and stabilize metal ions with different oxidation states through imine nitrogen and other groups. Schiff base ligands and their complexes have many interesting applications. For instance, several of them have been used in medicinal and pharmaceutical chemistry with significant bio- logical activities [2-7] . Moreover, they are used as catalysts in various biological systems [8,9] , in polymers [10] , dyes [11] and as effective corrosion inhibitors [12] . They are also used in optical computers to measure and control the intensity of radiation in imaging systems [13,14] . Further- more, Schiff base metal complexes are used as catalysts in many chemical reactions [15] . For example, divalent metal Schiff base complexes of Fe(II), Ru(II) and Cu(II) have been used in the oxidation of alcohols, cyclopropanation and base hydrolysis of amino acid esters [16] . In addition, Zn(II) complexes derived from acetylacetone and p-anisidine have displayed antimicrobial activity [17] . Zinc(II) complexes have also shown promising applications in organic light-emitting devices OLEDS [18,19] . In this study, five new Schiff base tetradentate ligands (L1-L5) derived from two equivalents of salicylaldehyde derivatives with 2,2'-diamino-6,6'-dibromo-4,4'-dimethyl-1,1'-bi- phenyl and their complexes (1-5) have been prepared (Figure 1). Experimental Section General Remarks CHN elemental analysis was carried out on a Perkin Elmer 240 elemental analyzer. 1 H- and 13 C-NMR spectra were recorded on a Bruker AC 400 spectrometer in CDCl 3 . Infrared spectra were recorded using KBr on Bruker FT-IR-4100
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JJC
Volume 14, Number 2, June 2019
Pages 81-87
*Corresponding Author: Taghreed M. A. Jazzazi Email: [email protected]
Jordan Journal of Chemistry
ARTICLE
Zinc(II) Complexes of Symmetrical Tetradentate Schiff Base Ligands
Derived From 2,2'-Diamino-6,6'-dibromo-4,4'-dimethyl-1,1'-
biphenyl-salicylaldehyde: Synthesis, Characterization and
Computational Study
Taghreed M. A. Jazzazi
a*, Taher S. Ababneh
b and Eman K. Abboushi
a
a Department of Chemistry, Yarmouk University, Irbid 21163, Jordan.
b Department of Chemistry and Chemical Technology, Tafila Technical University, Tafila,
Jordan.
Received on: 6th
Aug. 2019; Accepted on: 9th
Sep. 2019
Abstract: Five new complexes (1-5) of the general formula ZnL were prepared by
refluxing the new Schiff base ligands (L1-L5) with Et2Zn in THF. The new ligands (L1-L5)
were prepared by reacting two equivalents of salicyladehyde derivatives (3,5-ditert-butyl-,
3-tert-butyl-, 5-tert-butyl-, 3,5-dinitro- and 3,5-dibromo-salicylaldehyde) with 2,2'-di-
amino-6,6'-dibromo-4,4'-dimethyl-1,1'-biphenyl. The new Schiff base ligands and their zinc
complexes were characterized by 1H-,
13C-NMR and IR spectroscopy as well as elemental
analysis. Additionally, the molecular geometries of all prepared zinc complexes were fully
optimized and examined using density functional theory (DFT) calculations at the
B3LYP/6-31G(d) level of theory. Infrared vibrational analysis was conducted, and the
results are in good agreement with the experimental data.
Keywords Schiff base ligands, Synthesis, Computational study, Zinc complexes, DFT.
Introduction
Schiff bases are compounds with a functional
group that contains a carbon-nitrogen double
bond[1]
. These ligands can coordinate and
stabilize metal ions with different oxidation
states through imine nitrogen and other groups.
Schiff base ligands and their complexes have
many interesting applications. For instance,
several of them have been used in medicinal and
pharmaceutical chemistry with significant bio-
logical activities[2-7]
. Moreover, they are used as
catalysts in various biological systems[8,9]
, in
polymers[10]
, dyes[11]
and as effective corrosion
inhibitors[12]
. They are also used in optical
computers to measure and control the intensity
of radiation in imaging systems[13,14]
. Further-
more, Schiff base metal complexes are used as
catalysts in many chemical reactions[15]
. For
example, divalent metal Schiff base complexes
of Fe(II), Ru(II) and Cu(II) have been used in the
oxidation of alcohols, cyclopropanation and base
hydrolysis of amino acid esters[16]
. In addition,
Zn(II) complexes derived from acetylacetone
and p-anisidine have displayed antimicrobial
activity[17]
. Zinc(II) complexes have also shown
promising applications in organic light-emitting
devices OLEDS[18,19]
.
In this study, five new Schiff base
tetradentate ligands (L1-L5) derived from two
equivalents of salicylaldehyde derivatives with
2,2'-diamino-6,6'-dibromo-4,4'-dimethyl-1,1'-bi-
phenyl and their complexes (1-5) have been
prepared (Figure 1).
Experimental Section
General Remarks
CHN elemental analysis was carried out on a
Perkin Elmer 240 elemental analyzer. 1H- and
13C-NMR spectra were recorded on a Bruker AC
400 spectrometer in CDCl3. Infrared spectra
were recorded using KBr on Bruker FT-IR-4100
Jazzazi et al.
28
N
N
O
OZn
Br
Br
X
X
Y
Y
(X,Y)=
(tert-Butyl, tert-Butyl)(L1) (1);
(tert-Butyl, H)(L2) (2); (H, tert-Butyl)(L3) (3);
(NO2, NO2)(L4) (4); (Br, Br)(L5) (5)
Figure 1. Structure of ligands (L1-L5) and
their zinc complexes (1-5).
spectrometer over the range 4000-400 cm-1
. All
commercially available substrates were
purchased from Sigma Aldrich or Alfa Aesar and
used without further purification. Solvents were
purified and dried according to standard
procedures followed by distillation under nitro-
gen. 2,2'-diamino-6,6'-dibromo-4,4'-dimethyl-
1,1'-biphenyl was prepared according to a
literature procedure[20]
.
General Synthesis of Schiff Bases (L1-L5)
A mixture of 0.81 mmol 2,2'-diamino-6,6'-
dibromo-4,4'-dimethyl-1,1'-biphenyl and 1.62
mmol salicylaldehyde derivatives in absolute
ethanol (10 ml) was stirred and refluxed for 3 hr.
During the reaction, the corresponding Schiff
base was precipitated as a colored solid. The
solid was collected by filtration, washed with
cold ethanol and dried under vacuum.
L1: Yield 0.45 g, 69.2%. Elemental analysis
for C44H54Br2N2O2 calculated (found): %C =
65.84 (65.98), %H = 6.78 (6.76), %N = 3.49
(3.54). MS (EI, m/z): 802 [M]+. IR/cm−1
: 2995
(w, OH), 2867 (s, t-Bu), 1613 (s, C=N).
1H NMR
(400 MHz, CDCl3, 298 K): δ 1.29 (s, 18H,
C(CH3)3), 1.38 (s, 18H, C(CH3)3), 2.42 (s, 6H,
(CH3), 7.04-7.44 (m, 8H, aromatic-H), 8.52 (s,
2H, N=CH), 12.81 (s, 2H, OH). 13
C NMR (400
MHz, CDCl3, 298 K): δ 163.6 (N=CH), 158.4,
148.5, 140.5, 140.1, 136.8, 131.9, 130.7, 128.0,
126.7, 124.5, 118.0, 117.8 (aromatic-C), 35.0,
34.1 (CMe3), 31.4, 29.2 (CMe3) and 21.0 (Me).
L2: Yield 0.36 g, 64.4%. Elemental analysis
for C36H38Br2N2O2 calculated (found): %C =
62.62 (62.59), %H = 5.55 (5.53), %N = 4.06
(4.01). MS (EI, m/z): 690 [M]+. IR/cm−1
: 3010
(m, OH), 2935 (w, t-Bu), 1619 (s, C=N).
1H
NMR (400 MHz, CDCl3, 298 K): δ 1.32 (s, 18H,
C(CH3)3), 2.39 (s, 6H, (CH3), 6.71-7.28 (m, 10H,
aromatic), 8.44 (s, 2H, N=CH), 12.70 (s, 2H,
OH). 13
C NMR (400 MHz, CDCl3, 298 K): δ
165.4 (N=CH), 156.8, 150.5, 144.2, 142.3,
138.5, 131.7, 129.8, 128.4, 126.2, 123.8, 118.4,
116.5 (aromatic-C), 34.8, 33.9 (CMe3), and 21.5
(Me).
L3: Yield 0.37 g, 66.2%. Elemental analysis
for C36H38Br2N2O2 calculated (found): %C =
62.62 (62.61), %H = 5.55 (5.52), %N = 4.06
(3.98). MS (EI, m/z): 690 [M]+. IR/cm−1
: 2958
(m, OH), 2863 (w, t-Bu), 1618 (s, C=N).
1H
NMR (400 MHz, CDCl3, 298 K): δ 1.34 (s, 18H,
C(CH3)3), 2.40 (s, 6H, (CH3), 6.69-7.31 (m, 10H,
aromatic), 8.41 (s, 2H, N=CH), 12.78 (s, 2H,
OH). 13
C NMR (400 MHz, CDCl3, 298 K): δ
164.2 (N=CH), 158.6, 153.5, 146.3, 143.4,
135.9, 133.2, 128.2, 128.0, 125.8, 124.1, 117.8,
116.1 (aromatic-C), 32.7, 31.6 (CMe3), and 21.3
(Me).
L4: Yield 0.46 g, 74.9%. Elemental analysis
for C28H18Br2N6O10 calculated (found): %C =
44.35 (44.32), %H = 2.39 (2.36), %N = 11.08
(11.06). MS (EI, m/z): 758 [M]+. IR/cm−1
:
IR/cm−1
: 2991 (m, OH), 1620 (s, C=N), 1524 (s,
NO2), 1341 (s, NO2), 1H NMR (400 MHz,
CDCl3, 298 K): δ 2.41 (s, 6H, (CH3), 6.64-7.29
(m, 8H, aromatic), 8.57 (s, 2H, N=CH), 13.02 (s,
2H, OH). 13
C NMR (400 MHz, CDCl3, 298 K): δ
163.1 (N=CH), 155.6, 152.7, 144.1, 142.4,
138.9, 131.2, 129.4, 127.6, 126.3, 125.8, 116.9,
115.7 (aromatic-C), and 21.0 (Me).
L5: Yield 0.51 g, 70.4%. Elemental analysis
for C28H18Br6N2O2 calculated (found): %C =
37.62 (37.55), %H = 2.03 (2.00), %N = 3.13
(3.14). MS (EI, m/z): 894 [M]+. IR/cm−1
: 2996
(w, OH), 1615 (s, C=N). 1H NMR (400 MHz,
CDCl3, 298 K): δ 2.40 (s, 6H, (CH3), 6.35-7.41
(m, 8H, aromatic), 8.36 (s, 2H, N=CH), 12.88 (s,
2H, OH). 13
C NMR (400 MHz, CDCl3, 298 K): δ
162.7 (N=CH), 157.2, 157.5, 147.5, 146.1,
136.8, 133.5, 127.8, 126.5, 124.8, 124.3, 116.4,
115.0 (aromatic-C), and 21.4 (Me).
General Synthesis of Complexes 1-5
To a stirred solution of 0.62 mmol Schiff
base in 20 ml THF, Et2Zn (0.62 ml, 1.0 M
solution in hexane) was added at room
temperature under inert atmosphere. The mixture
was stirred at room temperature overnight. The
Zinc(II) Complexes of Symmetrical Tetradentate Schiff Base Ligands …