Synthesis and characterization of some Thiocyanato Complexes of Ni(II), Cu(II), Pd(II), Pt(II), Au(III), Ti(III), and V(IV) containing a tridentate Schiff base ligand

Article abstract of DOI:10.1081/SIM-120016468

A tridentate ligand HL having a ONN donor sequence has been synthesised by the condensation of ethylenediamine with salicylaldehyde. The ligand undergoes deprotonation during complexation and forms complexes of the compositions, [M(L)(SCN)], [M = Ni(II), Cu(II), Pd(II) and Pt(II), L = deprotonated Schiff base], K[Ti(L)(SCN)₃], [Au(L)(SCN)]C1 and K[V(O)(L)(SCN)₂]. These complexes were characterized on the basis of elemental analyses, conductivity and magnetic measurements, NMR, infrared and electronic spectral studies. The magnetic and spectral data are consistent with square-planar stereochemistry for the Ni(II), Cu(II), Pd(II), Pt(II) and Au(III) complex while the Ti(III) and V(IV) complexes are octahedral in nature.

Full text of DOI:10.1081/SIM-120016468

Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry
ISSN: 0094-5714 (Print) 1532-2440 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt19
SYNTHESIS AND CHARACTERIZATION OF SOME
THIOCYANATO COMPLEXES OF Ni(II), Cu(II), Pd(II),
Pt(II), Au(III), Ti(III), AND V(IV) CONTAINING A
TRIDENTATE SCHIFF BASE LIGAND
M. Saidul Islam , M. Akhter Farooque & M. A. K. Bodruddoza
To cite this article: M. Saidul Islam , M. Akhter Farooque & M. A. K. Bodruddoza (2002)
SYNTHESIS AND CHARACTERIZATION OF SOME THIOCYANATO COMPLEXES OF Ni(II), Cu(II),
Pd(II), Pt(II), Au(III), Ti(III), AND V(IV) CONTAINING A TRIDENTATE SCHIFF BASE LIGAND, Synthesis
and Reactivity in Inorganic and Metal-Organic Chemistry, 32:10, 1811-1823, DOI: 10.1081/
SIM-120016468
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 32, No. 10, pp. 1811–1823, 2002
SYNTHESIS AND CHARACTERIZATION
OF SOME THIOCYANATO COMPLEXES
OF Ni(II), Cu(II), Pd(II), Pt(II), Au(III), Ti(III),
AND V(IV) CONTAINING A TRIDENTATE
SCHIFF BASE LIGAND
M. Saidul Islam,* M. Akhter Farooque, and
M. A. K. Bodruddoza
Department of Chemistry, Rajshahi University,
Rajshahi 6205, Bangladesh
ABSTRACT
A tridentate ligand HL having a ONN donor sequence has
been synthesised by the condensation of ethylenediamine with
salicylaldehyde. The ligand undergoes deprotonation during
complexation and forms complexes of the compositions,
[M(L)(SCN)], [M ¼ Ni(II), Cu(II), Pd(II) and Pt(II),
L ¼ deprotonated Schiff base], K[Ti(L)(SCN)3], [Au(L)-
(SCN)]Cl and K[V(O)(L)(SCN)2]. These complexes were
characterized on the basis of elemental analyses, conductivity
and magnetic measurements, NMR, infrared and electronic
spectral studies. The magnetic and spectral data are consistent
with square-planar stereochemistry for the Ni(II), Cu(II),
*Corresponding author. E-mail: rajucc@citechco.net
1811
DOI: 10.1081=SIM-120016468
Copyright # 2002 by Marcel Dekker, Inc.
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com

1812
ISLAM, FAROOQUE, AND BODRUDDOZA
Pd(II), Pt(II) and Au(III) complexes while the Ti(III) and
V(IV) complexes are octahedral in nature.
INTRODUCTION
Many complexes of different Schiff bases have been reported by a
number of authors.[1710] These kinds of Schiff base ligands provide intri-
guing chemistry with both the lighter and heavier transition metals. We have
extended our studies to a simple tridentate ONN ligand resulting from the
condensation of ethylenediamine and salicylaldehyde.[9710] In this paper we
report the synthesis and characterization of thiocyanato complexes of
Ni(II), Cu(II), Pd(II), Pt(II), Au(III), Ti(III) and V(IV) containing the tri-
dentate ONN ligand. The structure of the Schiff base is shown in Fig. 1.
EXPERIMENTAL
Reagents
All chemicals used were of reagent grade and were used as supplied by
E. Merck or BDH Ltd. Ethanol was purified by refluxing the 99% com-
mercially available product with magnesium turnings and iodine.
Physical Measurements
Microanalyses for carbon, hydrogen and nitrogen were performed by
the microanalytical services of the Department of Chemistry, University of
St. Andrews, Scotland. The metals were determined by the standard lit-
erature procedures.[11] The IR spectra (KBr discs) were recorded on Shi-
madzu IR-470, Shimadzu FTIR-8400 and Perkin Elmer IR-470
1
spectrophotometers. H NMR spectra in DMSO-d6 were obtained with a
Bruker DRX-400 (400.13 MHz) NMR spectrometer. Conductivities of
Figure 1. 4-(2-Hydroxy-phenyl)-3-aza-1-amino-3-butene.

THIOCYANATO COMPLEXES
1813
10ꢀ3 M solutions in DMSO were measured at room temperature using a
WPA CM 35 conductometer and a dip-type cell with platinized electrodes.
Magnetic measurements have been carried out in a Johnson Mathey mag-
netic susceptibility balance at room temperature. Electronic spectra in
DMSO were obtained on a LKB-Ultrospec K4053 spectrophotometer.
Melting and decomposition points of the complexes have been determined
on an electrothermal melting point apparatus.
Preparation of Schiff Base
Salicylaldehyde (0.61 g, 0.005 mol) in absolute ethanol (15 mL) was
added to a solution of ethylenediamine (0.3 g, 0.005 mol) in the same solvent
(20 mL). The mixture was heated on a water bath to reduce the volume of
the solution to ca. 15 mL. The solution was then cooled to room tempera-
ture when yellow crystals were formed. These were separated and washed
throughly with ethanol and dried in vacuo over P4O10. Yield, 0.7 g, (76%)
m.p. 1047106 ꢁC. Anal. Calc. for C9H12N2O (MW 164): C, 65.8; H, 7.3; N,
17.1. Found: C, 65.7; H, 7.3; N, 16.7%.
General Method for the Preparation of [M(L)(SCN)] [M ¼ Cu(II),
Ni(II), Pd(II), and Pt(II), HL ¼ Schiff Base]
An appropriate solution of 0.005 mol of the metal salt (CuCl2ꢂH2O,
NiCl2ꢂ6H2O, PdCl2, PtCl2) in absolute ethanol (25 mL) was added to an
ethanolic solution (30 mL) of potassium thiocyanate (0.48 g, 0.005 mol). The
solution was filtered and an ethanolic solution (80 mL) of HL (Schiff base)
(0.82 g, 0.005 mol) was added to the filtrate. The resulting mixture was
heated on a water bath for 5 min and cooled in an ice-bath. The complexes
separated, were washed with hot ethanol and dried in vacuo over P4O10.
Preparation of K[Ti(L)(SCN)3]
This complex was prepared by adding an ethanolic solution (15 mL) of
TiCl3 (0.77 g, 0.005 mol) to a solution of potassium thiocyanate (1.45 g,
0.015 mol) in the same solvent (45 mL). The solution was filtered and an
ethanolic solution (60 mL) of HL (0.82 g, 0.005 mol) was added to the fil-
trate. The resulting mixture was boiled on a water-bath for 5 min and then
cooled in an ice bath. The complex separated, was washed with hot ethanol
and dried in vacuo over P4O10.

1814
ISLAM, FAROOQUE, AND BODRUDDOZA
Preparation of [Au(L)(SCN)]Cl
A solution of HAuCl4 (1.7 g, 0.005 mol) in ethanol (25 mL) was added
to a solution of potassium thiocyanate (0.48 g, 0.005 mol) in the same solvent
(30 mL). The solution was filtered and to the filtrate was added an ethanolic
solution (50 mL) of HL (0.82 g, 0.005 mol). The complex separated and was
washed successively with ethanol and ether and dried in vacuo over P4O10.
Preparation of K[V(O)(L)(SCN)2]
A solution of VO(SO4)ꢂ5H2O (1.26 g, 0.005 mol) in ethanol (25 mL) was
added to a solution of potassium thiocyanate (0.97 g, 0.01 mol) in the same
solvent (40 mL). The solution was filtered and to the filtrate was added an
ethanolic solution (70 mL) of HL (0.82 g, 0.005 mol). The complex separated
and was washed successively with ethanol and ether and dried as above.
RESULTS AND DISCUSSION
During the course of the reactions the Ni(II), Cu(II), Pd(II), Pt(II),
Au(III), Ti(III) and V(IV) thiocyanates were first formed, and then coor-
dinated to the Schiff base.
MCl2 þ 4KSCN ! K2½MðSCNÞ4ꢃ þ 2Kþ þ 2Clꢀ
ð1Þ
ð2Þ
K2½MðSCNÞ4ꢃ þ HL ! ½MðLÞðSCNÞꢃ þ Hþ þ 2Kþ þ 3SCNꢀ
M ¼ Ni(II) (1), Cu(II) (2), Pd(II) (3) and Pt(II) (4), HL ¼ Schiff base.
Reaction Steps of Au(III) (6) Complex
HAuCl4 þ 4KSCN ! K2½AuðSCNÞ4ꢃCl þ Hþ þ 2Kþ þ 3Clꢀ
ð3Þ
K2½AuðSCNÞ4ꢃCl þ HL ! ½AuðSCNÞꢃCl þ Hþ þ 2Kþ þ 3SCNꢀ ð4Þ

THIOCYANATO COMPLEXES
1815
Reaction Steps of Ti(III) (5) Complex
TiCl3 þ 6KSCN ! K3½TiðSCNÞ6ꢃ þ 3Kþ þ 3Clꢀ
ð5Þ
K3½TiðSCNÞ6ꢃ þ HL ! K½TiðLÞðSCNÞ3ꢃ þ 2Kþ þ Hþ þ 3SCNꢀ ð6Þ
Reaction Steps of V(IV) (7) Complex
2ꢀ
VOðSO4Þ þ 5KSCN ! K3½VOðSCNÞ5ꢃ þ 2Kþ þ SO4
ð7Þ
ð8Þ
K3½VOðSCNÞ5ꢃ þ HL ! K½VOðLÞðSCNÞ2ꢃ þ Hþ þ 3SCNꢀ þ Kþ
Elemental Analyses and Conductivity
The analytical data and conductivity of the complexes are given in
Tables I and II. All of the complexes are soluble in dimethyl sulfoxide but
insoluble in water. The conductance values indicate that the complexes (1),
(2), (3), (4) and (6) are all 1:1 electrolytes while the complexes (5) and (7) are
2:1 electrolytes.[12]
IR Studies
The infrared spectral data are shown in Table III. The Schiff base
ligand is potentially tridentate, the available coordination sites being the
amino nitrogen, methine nitrogen and the oxo anion. The free Schiff base
shows characteristic bands at 3550 [n(OH)], 3480, 3420 [n(NH2)] and 1615
cmꢀ1, [n(C¼N)]. In all of the complexes, a broad band appears at
330073600 cmꢀ1, in which n(NH2) bands of the complexes are probably
hidden. The NH2 complexation is inferred from the appearance of n(M7N)
modes at 4307472 cmꢀ1 in the complexes.[2,13,14] We believe that the ligand
deprotonates at the OH end providing oxo coordination, as is evident
from the n(M7O) bands at 4807542 cmꢀ1 in the complexes. The n(C¼N)
band observed at 1615 cmꢀ1 in the free Schiff base ligand is shifted to
157771602 cmꢀ1, indicating coordination by the methine nitrogen.

1816
ISLAM, FAROOQUE, AND BODRUDDOZA

THIOCYANATO COMPLEXES
Table II. Physical Properties
1817
S. No.
Complex
Molar Conductance
(Ohmꢀ1cm2 molꢀ1
Magnetic Moment
meff (B.M.)
Complex
)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
[Ni(L)(SCN)]
29
32
34
35
62
30
65
Dia.
1.95
Dia.
Dia.
1.89
Dia.
1.69
[Cu(L)(SCN)]
[Pd(L)(SCN)]
[Pt(L)(SCN)]
K[Ti(L)(SCN)3]
[Au(L)(SCN)]Cl
K[V(O)(L)(SCN)2]
The ambidentate thiocyanate ligand can coordinate either through the
nitrogen or through the sulfur depending on the size of the metal ions. In
general, the n(CN) modes appear at lower frequencies in M7N¼C¼S
complexes than those in M7S7CꢄN complexes.[15,16] The complexes also
display n(CN) at 207772100 cmꢀ1 characteristic of S-bonded thiocyanato
moieties.[15,17,18] In Pearson’s terminology, these are soft acids. The n(CS)
modes appear at lower frequencies in the M7S7CꢄN complexes than those
in the M7N¼C¼S complexes.[15,16]
Complexes (1)7(7) exhibit n(CS) at 7357754 cmꢀ1, characteristic of
a M7S7CꢄN bonding sequence. This is further apparent from the
n(M7S) modes at 4007425 cmꢀ1 in the far-IR spectra of the com-
plexes.[2,13,19] The vanadium complex (7) displays a n(V¼O) mode[20,21]
at 954 cmꢀ1
.
Magnetic Moments and Electronic Spectra
The effective magnetic moments of the complexes are shown in Table II.
The Cu(II), Ti(III) and V(IV) complexes are paramagnetic and show mag-
netic moments (1.6971.95 B.M.) corresponding to one unpaired electron.
The Ni(II), Pd(II), Pt(II) and Au(III) complexes are diamagnetic.
In the UV spectra three bands were observed at 15,350, 19,500 and
2
2
22,180 cmꢀ1, corresponding to the transitions B1g?2A1g , B1g?2Eg and
charge transfer, respectively, for the Cu(II) complex. These bands are con-
sistent with a square-planar structure.[22] The titanium(III) complex exhibits
one characteristic d-d band at 19,550 cmꢀ1 which corresponds to the tran-
sition 2T2g?2Eg. This suggests an octahedral geometry with Oh symmetry of
the Ti(III) complex.[23]

1818
ISLAM, FAROOQUE, AND BODRUDDOZA

THIOCYANATO COMPLEXES
1819
Table IV. Electronic Spectral Data of the Complexes (Band Maxima in cmꢀ1
)
Compound
No.
Band I
Band II
Band III
Band IV
Band V
(1)
(2)
(3)
(4)
(5)
(6)
(7)
21,114 (121)
7
7
15,350 (90) 19,500 (120) 22,180 (45)
7
7
7
7
22,155 (47) 28,170 (130) 31,115 (352) 35,000 (340) 40,150 (380)
36,075 (320) 39,510 (360) 41,112 (375)
19,550 (120) 7
33,885 (345) 40,220 (385)
7
7
7
7
7
7
7
7
7
17,825 (74) 22,124 (45) 33,112 (345) 39,200 (370)
Extinction coefficients in dm3 molꢀ1 cmꢀ1 are given in parentheses.
The vanadium(IV) complex shows four bands at 17,825, 22,124,
33,112 and 39,200 cmꢀ1. The first two bands correspond to the transitions
2
2B2?2B1 and B2?2A1, respectively, whereas the last two absorptions are
caused by metal to ligand charge transfer. All of these bands are char-
acteristic of an octahedral vanadium(IV) complex.[24,25] The Ni(II) complex
displays a broad band at 21,114 cmꢀ1 characteristic of a d-d transition
(1A1g?1B1g) for a singlet ground state of square-planar geometry.[26,27] The
spectra of the Pd(II) complex in DMSO shows three spin-allowed d-d
transitions and two charge transfer transitions. The bands were obtained at
22,155, 28,170, 31,115, 35,000 and 40,150 cmꢀ1 corresponding to the tran-
1
1
1
1
1
sitions A1g?1A2g, A1g?1B1g, A1g ?1Eg, A1g?1A2u and A1g?1Eu,
respectively, which indicates square-planar stereochemistry.[28] The Pt(II)
complex gave three bands at 36,075, 39,510 and 41,112 cmꢀ1 corresponding
to the transitions A1g?1B1u, A1g?1Eu and A1g?1A2u, respectively. All
of these bands are characteristic of a square-planar Pt(II) complex. The
Au(III) complex gave two bands at 33,885 and 40,220 cmꢀ1 corresponding
to the transitions A1g?1Eu and A1g?1A2u, respectively, which indicates
1
1
1
1
1
square-planar geometry.
1H NMR Spectra
1
The H NMR spectra of the Schiff base ligand and complex (3) were
recorded in DMSO-d6 solution at room temperature. All of these data are
summarized in Table V.
1H NMR spectra of the Schiff base ligand showed resonances corre-
sponding to CH2, NH2, CH¼N and OH protons, respectively. A singlet at

1820
ISLAM, FAROOQUE, AND BODRUDDOZA
Table V. Proton NMR Spectral Data of the Schiff Base and Its Pd Complex
(in ppm)
Compound
N¼CH
OH Proton
13.33
NH2
CH2
Schiff base
Complex (3)
8.54
8.56
6.83
6.86
3.87
3.87
3.87 ppm corresponds to the four protons of the two CH2 groups in
diaminoethane. The CH¼N proton resonance of the Schiff base ligand
occurs as singlet at 8.54 ppm. For the NH2 and OH group were singlets were
observed at 6.83 and 13.33 ppm, respectively.
The 1H NMR spectrum of (3) showed a downfield shift of the
CH¼N-azomethine hydrogen signal to 8.56 ppm compared to the free Schiff
base ligand which supports the coordination of the azomethine nitrogen to
the Pd(II) centre. Although the chemical shift difference between the ligand
and the complex is not large, but all other supporting data e.g., IR support
the coordination of the ligand. The NH2 protons resonance of complex (3)
experienced a downfield shift to 6.86 ppm which also supports the coordi-
nation of the NH2 group nitrogen to the Pd(II) centre. Coordination of the
oxyanion (Oꢀ) to the Pd(II) centre is suggested in the complex (3) on the
basis of the disappearance of the OH proton signal. Thus, we assume that
the disappearance of the OH proton resonance signal in complex (3) clearly
indicates the coordination of the oxyanion (Oꢀ) to the Pd(II) centre. This
1
result is also supported by the IR data. The H NMR spectra of the other
complexes can also be explained in the same way.
Figure 2. Proposed structure of the complex [Pd(L)(SCN)] (3).

THIOCYANATO COMPLEXES
1821
The IR and 1H NMR evidence allow us to construct a probable
structure which is given in Fig. 2.
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Received September 4, 2001
Accepted August 20, 2002
Referee I: P. J. Toscano
Referee II: Y. Tor