Synthesis, spectroscopy and electrochemical behaviors of nickel(II) complexes with tetradentate shiff bases derived from 3,5-Bu2 t-salicylaldehyde

Article abstract of DOI:10.1016/j.saa.2005.02.041

Nickel(II) complexes of a series of N,N′-polymethylenebis(3,5-Bu2t- salicylaldimine) ligands containing 2,4-di-Bu2t-phenol arms, NiL_x, were synthesized and their spectroscopic and redox properties were examined. The UV-vis, ¹H NMR sp

Full text of DOI:10.1016/j.saa.2005.02.041

Spectrochimica Acta Part A 62 (2005) 716–720
Synthesis, spectroscopy and electrochemical behaviors of nickel(II)
complexes with tetradentate shiff bases derived from
3,5-But2-salicylaldehyde
Veli T. Kasumova,∗, S¸eniz Ozalp-Yaman , Es¸ref Tas¸
b
a
¨
a
Chemistry Department, Harran University, 63200 S¸anlıurfa, Turkey
b
Chemistry group of Faculty of Engineering, Atilim University, 06836 Ankara, Turkey
Received 19 November 2004; accepted 24 February 2005
Abstract
Nickel(II) complexes of a series of N,Nꢀ-polymethylenebis(3,5-Bu2t -salicylaldimine) ligands containing 2,4-di-Bu2t -phenol arms, NiLx, were
synthesized and their spectroscopic and redox properties were examined. The UV–vis, 1H NMR spectroscopic and magnetic results indicate
that complexes NiL1–NiL4 unlike NiL5 and NiL6 have a square-planar structure in the solid state and in solution. Cyclic voltammograms of
NiLx (x = 1–4) complexes displayed two-step oxidation processes. The first oxidation peak potentials of all Ni(II) complexes corresponds to
the reversible one-electron oxidation process of the metal center, yielding Ni(III) species. The second oxidation peak of the complexes was
assigned as the ligand based oxidation generating a coordinated phenoxyl radical species.
© 2005 Elsevier B.V. All rights reserved.
Keywords: N,Nꢀ-polymethylenebis(3,5-But2-salicylaldiminato)nickel(II); Spectroscopy; Electrochemistry
1. Introduction
from ethylenediamine and 3,5-di-tert-butylsalicylaldehyde
[10]. In this study, we present the synthesis, spectroscopic
and electrochemical behavior of a new series of N,Nꢀ-
polymethylenebis(3,5-di-t-butylsalicylaldiminato)nickel(II)
complexes, Ni(Lx) [H2Lx = N,Nꢀ-bis(3,5-But2-salicylidene)-
polymethylenediamines] (Fig. 1).
The coordination chemistry of transition metal complexes
with salen-type ligands has achieved a special status in
the last decades [1–3], because of their very interesting
O2-binding reactivity, redox chemistry, unusual magnetic
and structural properties, as well as their usage as models
for metalloproteins [5], as catalysts for the oxidation and
epoxidation reactions [1,4,6], and as “metalloligands”
for the design and the syntheses of a various heteronu-
clear complexes [7]. Salen complexes have also been
recently used as catalytically active materials to develop
surface-modified electrodes for sensoring applications
and as sources of planar supramolecular building blocks
[8,9].
2. Experimental
2.1. Materials and physical measurements
All chemicals and solvents were reagent grade and
used without further purification. Ni(AcO)2·4H2O, 2,4-di-
tert-butylphenol, all diamines, NH2 (CH2)n NH2, where
n = 2–4, were obtained from Aldrich Chemical Co. The
reagent 3,5-di-tert-butylsalicylaldehyde was prepared from
2,4-di-tert-butylphenol according to literature [4b].
Previously, one of us (V.T.K.) has reported the prop-
erties and spectroscopic characterization of some metal
complexes with salen- and salan-type ligands prepared
IR spectra were recorded in KBr using a Perkin-Elmer
spectrophotometer. Electronic absorption spectra of the
complexes measured by Hewlett Packard UV-VIS HP 8453A
∗
Corresponding author. Tel.: +90 4143128456; fax: +90 4143121998.
E-mail address: vkasumov@harran.edu.tr (V.T. Kasumov).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.02.041

V.T. Kasumov et al. / Spectrochimica Acta Part A 62 (2005) 716–720
717
Fig. 1.
Diode Array and by a Shimadzu 1601 UV–vis Spectropho-
tometers in several solvents. A Bruker Spectro spin Avance
DPX400 Ultra Shield Model NMR was used to obtain H
solution (50–55 ◦C) of H2L4 (0.26 g, 0.5 mmol) and Et3N
(0.05 g, 0.53 mmol) dissolved in methanol/CHCl3 (v/v = 3:1)
mixture by stirring. A green precipitate formed immediately.
After refluxing for 30 min, the volume of the solution
was reduced to 20 ml by evaporation and then allowed to
cool to room temperature. The precipitated green crystals
were collected by filtration, then washed with methanol,
CHCl3 and dried at 70 ◦C in air for 4 h. The precipitate was
recrystallised from CHCl3/methanol (v/v = 1:2).
Other NiLx complexes were prepared in a similar manner.
ItshouldbenotedthattheNiL5 andNiL6 complexescouldnot
be prepared in the absence of Et3N. NiL1 complex reported
in [10], for electrochemical characterization and comparative
purposes, also was prepared. The analytical and spectral data
of the complexes are presented in Tables 1, 3 and 4.
1
NMR of the diamagnetic compounds. Room temperature
solid-state magnetic susceptibilities were measured by using
a Sherwood Scientific magnetic susceptibility balance.
The effective magnetic moment, µeff, per nickel atom was
calculated from the expression µeff = 2.83(χMT)1/2 B.M,
where χM is the molar susceptibility corrected using Pascal’s
constants [11] for diamagnetism for all the atoms in the
compounds. The temperature-independent paramagnetism
associated with nickel ions was not included in the calcula-
tions of µeff. Voltammetric recordings were made by using
Volta Lab PGZ 301 Dynamic Voltammetry. A platinum-bead
working, a platinum-coil counter electrode and saturated
calomel reference electrode (SCE) were used for CV
measurements. Cyclic voltammograms (CV) were recorded
under N2 gas atmosphere in DMF at room temperature. Con-
centration of the complexes was 0.001 M in the electrolyte
solution where commercially obtained [n-(C4H9)4N]BF4
was used as a supporting electrolyte. The voltage scan rate
during the CV measurements was 100 mV/s.
3. Results and discussion
The analytical data of the NiLx complexes indicate 1:1
metal to ligand stoichiometry. All the isolated complexes are
soluble in CHCl3, CH2Cl2, DMF, DMSO and partially solu-
ble in alcohols, THF, acetonitrile.
2.2. Synthesis of H2Lx ligands
3.1. IR spectra
The tetradentate Schiff base ligands used in this work,
N,Nꢀ-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminoethane
(H2L1), N,Nꢀ-bis(3,5-di-tert-butylsalicylidene)-1,2-diami-
nopropane (H2L2), N,Nꢀ-bis(3,5-di-tert-butylsalicylidene)-
1,3-diaminopropane (H2L3) and N,Nꢀ-bis(3,5-di-tert-
butylsalicylidene)-1,4-diaminobutane (H2L4) and other
ligands were prepared by refluxing 0.02 mol of 3,5-di-tert-
butylsalicylaldehyde and 0.011 mol of the appropriate di-
amine in 60 ml of methanol/ethanol mixture (v/v = 3:1) for ca.
1 h. The products were recrystallised from methanol/CHCl3
mixture (v/v = 5:1) and dried in air (Yield: 92–95%). The
analytical and spectral data of the ligands are presented in
Tables 1–3.
The IR spectra of the complexes were interpreted by com-
paring the spectra with that of the free ligands. The absence
of the broad band at 2500–3100 cm−1 due to ν(OH) of the in-
tramolecularly bonded N HO in the spectra of the complexes
indicates the deprotonation of the salicylaldimine moiety of
H2Lx in the complexation. The shift of the characteristic
imine (>CH N) band from 1629–1634 to 1615–1622 cm−1
,
demonstrates the coordination of the azomethine nitrogen
to the nickel atom. Furthermore, the bands observed at
450–650 cm−1 assigned to Ni O and Ni N bending vibra-
tions, supporting the ligand and Ni(II) ion coordination [12].
2.3. Synthesis of NiLx complexes
3.2. 1H NMR spectra
2.3.1. Synthesis of [N,Nꢀ-bis(3,5-di-tert-
butylsalicylaldiminato)-1,4-butylene]nickel(II)
[Ni(L4)]
All H2Lx tetradentate Schiff bases show a narrow intense
singlet in the region of δ 13.64–13.99 ppm assigned to hy-
drogen bonded salicylic proton. The CH N imine, protons
except H2L2 exhibit a singlet resonance in δ 8.16–8.37 ppm
region. The presence of a doublet signal at δ 8.16 and
A solution of Ni(AcO)2·4H2O (0.125 g, 0.5 mmol)
dissolved in 5 ml warm methanol was added to the hot

718
V.T. Kasumov et al. / Spectrochimica Acta Part A 62 (2005) 716–720
Table 1
The melting points, yields and analytical data for H2Lx and NiLx compounds
H2Lx
Colour
T (◦C)
Yield (%)
Elemental analyses (%) (Found/Calcd.)
C
H
N
H2L2
H2L3
H2L4
H2L5
H2L6
NiL2
NiL3
NiL4
NiL5
NiL6
Yellow
Yellow
Yellow
Yellow
Yellow
Green
Green
Brown green
Dark green
Dark green
138
144
154
134
121
95
92
92
94
95
83
93
88
60
74
79.12/78.20
79.24/78.20
79.18/78.42
78.34/78.60
79.34/78.78
71.35/70.33
71.45/70.33
69.78/70.70
70.16/71.06
71.89/71.39
9.86/9.94
6.34/5.53
6.14/5.53
5.78/5.37
5.45/5.24
4.92/5.10
5.34/4.97
5.59/4.97
5.75/4.85
4.68/4.73
4.58/4.62
9.21/9.94
11.45/10.06
9.85/10.17
9.89/10.28
7.87/8.58
9.38/8.58
9.56/8.73
9.12/8.86
8.75/8.98
>270
>270
>270
Dec > 160
236
Table 2
IR and electronic absorption spectral data for the H2Lx
Ligand
IR spectra (cm−1), νCH
N
Electronic spectra λmax (nm) (log ε M−1 L−1
)
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
a
1629
1629
1633
1634
1631
1634
1595
215 (4.86), 235a, 264 (4.22), 328 (3.81), 420 (2.29)
219 (4.86), 263 (4.82), 330 (4.41), 428 (2.59)
1594
1594
1595
1592
1597
222 (4.85), 262 (4.58), 328 (4.13), 416 (2.61)
218 (4.56), 240a, 264 (4.13), 328 (4.11), 416 (2.82)
219 (4.89), 235 (4.76), 264 (3.89) 331 (3.88) 416 (2.67)
217 (486), 238a, 261 (3.97), 330 (3.97), 416 (2.75)
Shoulder.
Table 3
1H NMR spectral data for the H2Lx and NiLx (δ ppm) compounds
Compound
δOH
δCH
N
δSal.H
Others
δC(CH3)3
H2L1
NiL1
H2L2
NiL2
H2L3
NiL3
H2L4
H2L6
13.70
–
13.64
–
13.80
–
13.89
13.99
8.16 s, 1 H; 8.37 s, 1 H
7.23 s, 2 H
8.38 s, 2 H
7.42 s, 2 H
8.38 s, 2 H
7.1 s, 2 H
8.36 s, 2 H
8.34 s, 2 H
7.05 d, J = 2.1 Hz; 7.35 d, J = 2.4 Hz
6.81 d, J = 2.5 Hz; 7.38 d, J = 2.4 Hz
7.07 d, J = 2.4 Hz; 7.36 d, J = 2.4 Hz
6.81 d, J = 2.3 Hz 7.23 d, J = 2.6 Hz
7.07 d, J = 1.7 Hz 7.37 d, J = 2.4 Hz
6.75 d, J = 2.5 Hz 7.17 d, J = 2.6 Hz
7.08 d, J = 1.4 Hz 7.37 d, J = 2.2 Hz
7.07 d, J = 2.2 Hz 7.36 d, J = 2.4 Hz
3.34 t, N CH2, 3.75 m, N CH
2.72 d, N CH2, 3.52 m, N CH
3.91 t, N CH2
1.29 s, 1.45 s
1.17 s, 1.33 s
1.28 s, 144 s
1.17 s, 1.33 s 1.47 s
1.29 s, 1.45 s
1.17 s, 1.32 s
1.30 s, 1.46 s
1.30 s, 1.45 s
3.23 s, N CH2
2.14 qw, CH2, 3.65 t, N CH2
1.74 qw CH2−, 3.47 t, N CH2
3.61 m, CH2−,1.97 t, N CH2
3.57 t, 4 H, 1.72 m, CH2−, 8 H
Table 4
IR (cm−1), electronic absorption spectral data and magnetic moments for NiLx complexes
Compound
NiL1
IR spectra, νC
N
µeff, BM
Solvent
Electronic spectra λmax (nm) (log ε M−1 L−1
)
1615
Diamagnetic
CHCl3
DMF
Dioxan
CHCl3
DMF
Dioxan
CHCl3
DMF
Dioxan
CHCl3
DMF
Dioxan
CHCl3
DMF
Dioxan
CHCl3
DMF
258 (4.47), 320a, 347 (4.21), 428 (4.09), 650a (2.33)
320a, 346 (3.93), 420 (3.82), 460a, 570 (2.30)
341, 425, 556
257 (4.67), 340a, 350 (4.17), 428 (3.07), 460a, 650a (2.63)
340 (4.04), 400a, 419 (3.93), 466a, 570a (2.31)
331, 425, 470a, 570a
270 (4.37), 330 (3.98), 407 (3.80), 648 (2.19)
355 (3.35), 426 (3.28), 500a, 600a (2.12)
358, 432, 500a, 628
261 (4.41), 321 (3.99), 446 (3.87), 630 (2.02)
372 (3.88), 437 (3.69), 500a (2.67), 640 (1.97)
364, 441, 500a 630a
260 (3.02), 331 (3.96), 399 (3.75), 510 (2.91)a, 642 (2.15)
328 (3.93), 389 (3.82), 638 (2.19)
NiL2
NiL3
NiL4
NiL5
NiL6
1622
1620
1615
1622
1621
Diamagnetic
Diamagnetic
1.71
1.56
259, 407, 633
Diamagnetic
267 (4.32), 360 (4.06), 433 (3.98), 510 (2.85)a, 618 (2.09)
330 (3.50), 398 (3.84), 642 (2.18)
Dioxan
322, 408, 456, 530a, 647
a
Shoulder.

V.T. Kasumov et al. / Spectrochimica Acta Part A 62 (2005) 716–720
719
Table 5
8.37 ppm for the azomethine protons in the spectra of H2L2
Cyclic voltammetry data (VSR = 100 mV/s) for H2Lx and NiLx in DMF
indicates, as it would be expected, the nonequivalent nature
of the azomethine protons. Protons of the bridging methylene
groups attached to a nitrogen atom, N CH2−, resonances in
the region of δ 3.57–3.91 ppm as a triplet pattern. Salicylic
protons at 4 and 6 positions appeared as meta-coupled dou-
blets from ring protons on salicylic moiety at δ 7.05–7.08 (d, 1
H, J = 1.4–2.4 Hz) and δ 7.35–7.37 (d, 1 H, J = 2.41 Hz) ppm.
The spectra of H2Lx contains only two a single resonances
at δ 1.28–1.30 and at δ 1.44–1.46 ppm corresponding to each
of the unique t-Bu groups. As can be examined from Table 3,
along with the disappearance of NH/OH resonance, the high
Compound
Ea (V)
Ec (V)
NiL1
NiL2
NiL3
NiL4
NiL5
NiL6
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
0.90a, 1.20
0.84a, 0.96
0.74a, 1.00
0.68a, 0.96
0.84, 1.11
0.83, 1.16
0.98
1.10
1.10
1.06
1.12
1.10b
1.10b
0.93b
0.80b
–
–
–
–
–
–
–
–
1
field shifts for all proton resonance signals in the H NMR
1.17
spectra for diamagnetic NiL1–NiL3 complexes compared to
those of free L1H2–L3H2 ligands in CDCl3 were observed.
Ea represents the oxidation peak potential. Ec represents the reduction peak
potential.
a
Reversible peak potential.
Dependence on the second oxidation peak potential.
b
3.3. Electronic spectra
Electronic absorption spectral data of H2Lx are very
similar to each other because of their structural identity
(Table 2). The strong absorption band observed below
300 nm is assigned to intraligand π → π* transitions of the
phenolic chromophores. The absorption band observed in
all ligand spectra within the range of 328–331 nm is most
probably due to the transition of n → π* of imine group [13].
The bands appeared in the range of 414–428 nm in ethanol
solutions are attributed to n → π* transition of dipolar
zwitterionic keto-amine tautomeric structures of H2Lx [14].
Electronic absorption spectral data of NiLx complexes
in CHCl3, DMF and dioxan are presented in Table 3. The
weak d d transitions (ε = 50–500 M−1 cm−1) of square pla-
nar nickel(II) complex in D4h symmetry observed in the
regions of 370–430 and 430–670 nm [15]. More intense
charge transfer bands obscure the third and second d d bands
at high-energy region (λ < 450 nm) in many cases. These
literature [16–18]. Our magnetic moment measurements
(Table 4) carried out at room temperature reveals that NiL1,
NiL2, NiL3 and NiL6 complexes are diamagnetic, indicating
the low spin (S = 0) square planar d8-systems, as its expected.
The magnetic moments for NiL4 and NiL5 complexes were
1.70 and 1.56 BM, respectively. For these complexes it would
be suggested that there should be two chemically unequiva-
lent Ni+2 sites: low-spin (S = 0) square planar Nickel(II) and
high spin (S = 1) octahedral (II) in ca. 1:2 ratio.
3.5. Electrochemical oxidation of NiLx complexes
The electrochemical data for all Ni(II)-complexes
obtained in this study are presented in Table 5. The voltam-
mograms of all Ni(II)-complexes show two step oxidation
processes in DMF at room temperature under N2-gas
atmosphere. As seen in Fig. 2 or Table 5, the first oxidation
peak potential of all Ni(II)-complexes, reveals a reversible
electron transfer with slight differences from 0.68 to 0.90 V
versus SCE. The anodic potential of NiL2 is more positive
than of that for NiL1 complex, most likely due to the steric
effect of methyl group on the ethylene bridge, which header
the axial coordination of the DMF molecules to the Ni(II) ion.
bands are usually assigned to the 1A1g → A2g A1g → B1g
1
1
1
1
1
and A1g → E1g transition [16], respectively. The bands
observed in the 570–660 nm (ε ≈ 100–420 M−1 cm−1) and
460–510 nm (ε ≈ 460–820 M−1 cm−1) regions (Table 4) can
1
1
be assigned to the 1A1g → A2g and 1A1g → B1g transitions,
respectively. As can be seen from Table 4, the electronic
absorption bands of the presented complexes in the visible
region exhibit solvent dependence behaviour. The observed
red shifts in the low-energy d-d band of NiLx complexes in
DMF can be interpreted in terms of weaking of ligand field
strength [17]. In a general, as the number of methylene group
increased in the bridge from 2 to 4, a decrease in the ligand
field energies is expected. It is interesting that the same trend
is not observed in the electronic absorption spectra of our
bulky tert-butylated Ni(Lx) complexes in CHCl3 (Table 4).
3.4. Magnetic moments
There is still much controversy present on the magnetism
of the Ni(II) complexes with salen type ligands, containing
Fig. 2. Cyclic voltammogram of 0.001 M NiL3 in DMF at room temperature
vs. SCE (VSR = 100 mV/s).
diamine bridges, N (CH2)n
N
with n = 3–12, in the

720
V.T. Kasumov et al. / Spectrochimica Acta Part A 62 (2005) 716–720
[2] (a) R.D. Jones, D.A. Summerville, F. Basolo, Chem. Rev. 79 (1979)
We found one-electron transfer for the first oxidation peak
139;
by using a digital coulometer. Since the integrated area under
the second oxidation peak is two times larger than the area
under the fist anodic peak, 2-e− transfer was assigned for the
second anodic peak, as well. This experimental fact indicates
that the ligand-localized oxidation takes place in both coor-
dinated salicylaldimine fragments. More positive potentials
are obtained as the methylene group chain decreased from 4
to 2. This is in well agreement with the observed a red shift in
the electronic spectra of NiLx in DMF (Table 4). It is known
that in increasing length of the bridging N (CH2)x N chain
(x = 2–4) is expected initially to increase steric strain in the
ligand ring, resulting in distortion from planarity toward a
tetrahedral geometry [7a]. For NiLx, increasing n (n = 2–4)
causes a red shift in the absorption band near 600 nm, inter-
preted in terms of effective weakening of ligand field strength
[16].
(b) E.C. Niederhoffer, J.H. Timmons, A.E. Martel, Chem. Rev. 84
(1984) 137.
[3] (a) L.J. Klein, K.S. Alleman, D.G. Peters, J.A. Karty, J.P. Reilly, J.
Electroanal. Chem. 481 (2000) 24;
(b) A.A. Isse, A. Cenno, E. Vianello, Electrochim. Acta. 47 (1992)
113.
[4] (a) W. Zhang, J.L. Loebach, S.R. Wilson, E.N. Jacobsen, J. Am.
Chem. Soc. 112 (1990) 2801;
(b) R.G. Konsler, J. Karl, E.N. Jacobsen, J. Am. Chem. Soc. 120
(1998) 10780;
(c) L. Canali, D.C. Sherrington, Chem. Soc. Rev. 28 (1998) 85;
(d) T. Katsuki, Coord. Chem. Rev. 140 (1995) 159.
[5] A. Berkessel, M. Bolte, C. Griesinger, G. Huttner, T. Neumann, H.
Schwalbe, T. Schwenkeris, Angew. Chem. Int. Ed. Engl. 32 (1993)
1777.
[6] R. Irie, K. Noda, Y. Ito, N. Matsumoto, T. Katsuki, Tetrahedron Lett.
31 (1990) 7345.
[7] (a) S.J. Gruber, C.M. Harris, E. Sinn, J. Inorg. Nucl. Chem. 30
(1968) 1805;
(b) E. Sinn, Coord. Chem. Rev. 5 (1970) 313;
(c) J.P. Costes, F. Dahan, A. Dupuis, Inorg. Chem. 39 (2000) 165,
and references cited therein.
4. Conclusion
[8] (a) P.H. Aubert, A. Neudeck, L. Dunsch, P. Audebert, P. Capdevielle,
M. Maumy, J. Electroanal. Chem. 470 (1999) 77;
(b) L. Mao, K. Yamamato, W. Zhou, L. Jin, Electroanalysis 12 (2000)
72.
[9] (a) E.G. Ja¨ger, K. Schunmann, H. Go¨rls, Inorg. Chim. Acta 255
(1997) 295;
The reactivity and coordination modes of H2Lx are simi-
lar to those exhibited by non-tertbutylated salen type ligands
when they are treated with Ni(acet)2 in the presence of Et3N.
TheelectrochemicalbehavioursofNiLx aresubsequentlydif-
ferent from those reported for analogous salen type Ni(II)
complexes with polymethylene bridges. This features seems
to be due to the steric requirements of the tert-butyl groups
on the 3,3ꢀ-positions of the salisylic fragments.
(b) K. Chichak, U. Jacquemard, N.R. Branda, Eur. J. Inorg. Chem.
(2002) 357.
˙
[10] V.T. Kasumov, A.A. Medjidov, I.A. Golubeva, O.V. Shubina, R.Z.
Rzaev, Russ. J. Coord. Chem. 17 (1991) 1698.
[11] P.W. Selwood, Magnetochemistry, Interscience Publishers, New
York, 1956.
[12] G.C. Percy, D.A. Thornton, J. Inorg. Nucl. Chem. 34 (1972)
3357.
Acknowledgement
[13] C. Fraser, B. Bosnich, Inorg. Chem. 33 (1994) 338.
[14] P.W. Alexander, R.J. Sleet, Aust. J. Chem. 23 (1970) 1183.
[15] (a) G. Maki, J. Phys. Chem. 28 (1958) 651;
(b) H. Gary, C.J. Ballhausen, J. Am. Chem. Soc. 85 (1963) 260.
[16] (a) R.H. Holm, J. Am. Chem. Soc. 82 (1960) 5632;
(b) W.C. Hoyt, G.W. Everett, J. Inorg. Chem. 8 (1969) 2013.
[17] (a) J. Csaszar, J. Balog, Acta Chim. Acad. Sci. Hung. 87 (1975)
331;
Financial support by the Harran University Research Fund
is gratefully acknowledged.
References
(b) M. Calvin, C.H. Barkelew, J. Am. Chem. Soc. 68 (1946)
2267.
[18] A.E.M.M. Ramadan, W. Sawodny, H.Y.F. El-Baradie, M. Gaber,
Trans. Met. Chem. 22 (1997) 211.
[1] (a) R.H. Holm, G.W. Everett, A. Chakravorty, Prog. Inorg. Chem. 7
(1966) 83;
(b) M.D. Hobday, T.D. Smith, Coord. Chem. Rev. 9 (1972) 311.