Crystal structure of nonadentate tricompartmental ligand derived from pyridine-2,6-dicarboxylic acid: Spectroscopic, electrochemical and thermal investigations of its transition metal(II) complexes

Article abstract of DOI:10.1016/j.saa.2011.03.011

The coordinating behavior of a new dihydrazone ligand, 2,6-bis[(3- methoxysalicylidene)hydrazinocarbonyl]pyridine towards manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been described. The metal complexes were characterize

Full text of DOI:10.1016/j.saa.2011.03.011

Spectrochimica Acta Part A 79 (2011) 348–355
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Crystal structure of nonadentate tricompartmental ligand derived from
pyridine-2,6-dicarboxylic acid: Spectroscopic, electrochemical and thermal
investigations of its transition metal(II) complexes
Ramesh S. Vadavia, Rashmi V. Shenoya, Dayananda S. Badigera, Kalagouda B. Gudasia,∗
,
L. Gomathi Devib, Munirathinam Nethajic
a Department of Chemistry, Karnatak University, Dharwad 580 003, India
b Department of Post Graduate Studies in Chemistry, Central College Campus, Ambedkar Veedi, Bangalore University, Bangalore 560 001, India
c Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The coordinating behavior of
a
new dihydrazone ligand, 2,6-bis[(3-methoxysalicylidene)
Received 3 December 2009
Received in revised form
19 December 2010
hydrazinocarbonyl]pyridine towards manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and
cadmium(II) has been described. The metal complexes were characterized by magnetic moments,
conductivity measurements, spectral (IR, NMR, UV–Vis, FAB-Mass and EPR) and thermal studies.
The ligand crystallizes in triclinic system, space group P-1, with ˛ = 98.491(10)◦, ˇ = 110.820(10)◦
Accepted 10 March 2011
◦
˚
˚
˚
and ꢀ = 92.228(10) . The cell dimensions are a = 10.196(7) A, b = 10.814(7) A, c = 10.017(7) A, Z = 2 and
V = 1117.4(12). IR spectral studies reveal the nonadentate behavior of the ligand. All the complexes
are neutral in nature and possess six-coordinate geometry around each metal center. The X-band EPR
spectra of copper(II) complex at both room temperature and liquid nitrogen temperature showed
unresolved broad signals with giso = 2.106. Cyclic voltametric studies of copper(II) complex at different
scan rates reveal that all the reaction occurring are irreversible.
Keywords:
Nonadentate ligand
Dihydrazone
Pyridine-2,6-dicarboxylic acid
Transition metal complexes
Single crystal X-ray diffraction
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
The ligating diversity of such ligands has prompted us
to design and synthesize 2,6-bis[(3-methoxysalicylidene)
In the recent past, multi functional dihydrazones contain-
ing amide, azomethine and phenolic functions in duplicate have
attracted a lot of attention, mainly due to their potentiality to yield
homo- and hetero-polynuclear complexes [1]. The dihydrazones
can act as good precursors for macrocyclic systems having avail-
able adjacent, similar or dissimilar coordination compartments,
which are potential mono, bi and trinucleating ligands. The polynu-
clear complexes are of interest in the areas such as multimetallic
enzymes, and homogeneous and heterogeneous catalysis [1].
Polynuclear uranyl complexes of bissalicylaldehyde-2,6-
dipicolinoyl-hydrazone have been reported by Paolucci et al. [2].
Chen et al. [3] have reported a series of trinuclear copper(II) com-
plexes of 2,6-bis[[5-substituted salicylidine]hydrazinocarbonyl]
pyridine and also reported the crystal structure of copper(II)
complex of the bissalicylaldehyde-2,6-dipicolinoyl-hydrazone [2].
The crystal structure of the complex reveals the tricompartmental
nature of the ligand. However, no structural study is reported for
the free dihydrazone derived from pyridine-2,6-dicarboxylic acid.
hydrazinocarbonyl]pyridine [BMSHCPH4] and to study its chelating
behavior towards different transition metal ions such as man-
ganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II).
It has shown binucleating behavior towards lanthanide(III) ions
[4].
2. Experimental
2.1. Materials
Pyridine-2,6-dicarboxylic acid (Spectrochem) and 3-methoxy
salicylaldehyde (Fluka) were used without further purification and
all other solvents were distilled before use.
2.2. Measurements
Elemental analyses were carried out on a Thermoquest CHN
analyzer and metal complexes were analyzed for their metal con-
tents by EDTA titration after decomposition with a mixture of
HCl and HClO4 [5]. The chloride content of the complexes was
determined as silver chloride gravimetrically after decomposing
the complexes with HNO3 [5]. The IR spectra were recorded on a
∗
Corresponding author. Tel.: +91 836 2460129/2215286; fax: +91 836 27712275.
E-mail address: kbgudasi@rediffmail.com (K.B. Gudasi).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.03.011

R.S. Vadavi et al. / Spectrochimica Acta Part A 79 (2011) 348–355
349
Nicolet 170 SX FT-IR spectrometer in the region 4000–400 cm−1
using KBr discs. The 1H NMR spectra were recorded in DMSO-d6
on Bruker Avance 300 MHz spectrometer. Magnetic susceptibility
of the metal complexes were measured at room temperature on a
Gouy balance using Hg[Co(SCN)4] as the calibrant and diamagnetic
corrections were made by direct weighing of the ligand for dia-
magnetic pull. Electronic spectra were recorded on a Carry-Bio-50
spectrophotometer in the range 200–1100 nm. The EPR spectrum
of a polycrystalline sample was recorded at room temperature and
also at liquid nitrogen temperature on a Varian E-4-X-band spec-
trometer using TCNE as a “g” marker. Conductance measurements
were recorded in DMSO (10−3M) using ELICO-CM-82 conductivity
bridge with the cell type CC-01 and cell constant 0.53. Electro-
chemical measurements were performed at room temperature in
DMF using Optoprecission potentiostat. A three electrode assem-
bly comprising a glassy carbon working electrode, a platinum
auxillary electrode and a saturated Ag/AgCl electrode were used.
The supporting electrolyte was 0.1 M TBAP (tetrabutyl ammonium
perchlorate). The sample concentration was 0.002 M. Ferrocene
was used as a standard showing the Fe(III)/Fe(II) couple at 0.38 V
(versus Ag/AgCl electrode) under similar experimental conditions
containing 0.1 M TBAP. TGA–DTA studies were carried out in the
temperature range 25–1000 ◦C using TGA7 analyzer, Perkin Elmer,
US with a heating rate of 10 ◦C per minute in nitrogen atmosphere.
FAB mass spectra of the complexes were recorded on a JEOL SX
102/DA-6000 mass spectrometer/data system using Argon/Xenon
(6 kV, 10 mA) as the FAB gas.
The
crystal
structure
BMSHCPH4
was
determined
by single crystal X-ray diffraction with dimensions of
0.35 mm × 0.30 mm × 0.30 mm. Data were collected at Department
of Inorganic and Physical Chemistry, Indian Institute of Science,
Bangalore on a BRUKER SMART APEX- CCD diffractometer with
˚
MoK␣ radiation (ꢁ = 0.71073 A) at 293 K and scan mode in the
range of 1.91 < ꢂ < 27.45◦. The structure was solved by direct
methods and refined by Full-matrix least squares on F2. All of the
non-hydrogen atoms were refined with anisotropic temperature
factors. The calculations were performed with the SHELXTL pro-
gramme [6]. The crystallographic data (CIF file) of BMSHCPH4 have
been deposited at Cambridge Crystallographic Data Center (CCDC),
12 Union Road, Cambridge CBZ 1EZ, UK. Copies of the data can be
obtained free of charge by quoting the deposition number 256324.
2.3. Syntheses of ligand and complexes
2.3.1. Synthesis of
2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine
[BMSHCPH4] [Scheme 1]
A mixture of pyridine-2,6-dicarboxylic acid (1) (1.67 g, 10 mmol)
and thionyl chloride (2) (10 cm3) was refluxed for 5 h main-
taining anhydrous conditions. Excess thionyl chloride was then
removed under reduced pressure and further cooled in ice bath
for 15 min to get (3). 15 cm3 of super dry ethanol was added
and refluxed for 3 h to obtain 2,6-diethylcarboxylatopyridine (4).
This was further treated with hydrazine hydrate (5) (0.02 mol,
1 cm3) in absolute ethanol (20 cm3) and refluxed for 2–3 h to obtain
2,6-bis[hydrazinocarbonyl]pyridine (6), which was washed with
distilled water and recrystallized from hot water to give colorless
silky needles.
Yield : 1.336 g, 80%; m.p.285–286 ◦C.
2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine
(BMSHCPH4) was synthesized by the literature method [2] with a
slight modification. To a hot suspension of (6) (1.95 g, 10 mmol) in
absolute ethanol (20 cm3), a solution of 3-methoxy salicylaldehyde
(7) (3.04 g, 20 mmol) in the same solvent (20 cm3) was added, and

350
R.S. Vadavi et al. / Spectrochimica Acta Part A 79 (2011) 348–355
Dry C2H5OH
Reflux, 3h
Reflux
5h
O
O
O
O
O
O
+ SOCl2
N
N
N
OH
OH
C2H5
O
O C2H5
Cl
Cl
(1)
(3)
(4)
(2)
4
3
NH2NH2.H2O (5)
5
Reflux, 2 - 3h
2
6
O
N
O
N
O
N
1
(a)
8
(c)
NH
HN
(b)
OH
CH3 OH
OH
9'
CH3
O
O
C2H5OH
O
N
+
9
2
O
7
7'
Reflux, 4h
10
10'
11'
8'
13'
H2N NH
HN NH2
O CH3
11
12
13
12'
BMSHCPH4
(6)
(7)
Scheme 1. Synthetic route for BMSHCPH4.
Table 2
refluxed for 4 h. The yellow microcrystalline product (BMSHCPH4)
obtained was filtered, washed with hot water followed by hot
ethanol, air dried and recrystallized from 2-ethoxyethanol to get
crystals suitable for X-ray diffraction studies.
Crystal data and structure refinement of BMSHCPH4.
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C23 H23 N5 O7
481.46
Triclinic
P-1
Yield : 1.365 g, 70%; m.p.270–272 ◦C.
10.196(7)
b (Å)
10.814(7)
c (Å)
11.017(7)
98.491(10)
110.820(10)
92.228(10)
1117.4(12)
2
293(2) K
0.108
˛ (◦)
2.3.2. Syntheses of manganese(II), cobalt(II), nickel(II), copper(II),
zinc(II) and cadmium(II) complexes [M3(BMSHCP)·Cl2·7H2O]
BMSHCPH4 (0.481 g, 1 mmol) was boiled under reflux with
sodium hydroxide (0.080 g, 2 mmol) in 75% aqueous ethanol
(10 cm3) for 30 min. The metal(II) chloride (Mn, Co, Ni, Cu, Zn and
Cd) (3 mmol) dissolved in EtOH (10 cm3) was added and the mix-
ture was refluxed further for 4–5 h. The precipitate obtained was
filtered, washed with distilled water and dried in air. Attempts to
grow single crystals were unsuccessful.
ˇ (◦)
ꢀ (◦)
V (Å 3
Z
)
T (K)
Absorption coefficient (mm−1
ꢁ(MoK␣) (Å)
)
0.71073
F (0 0 0)
ꢂ range
Limiting indices
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2ꢆ(I)]
504
1.91–27.45◦
−13 ≤ h ≤ 13, −13 ≤ k ≤ 13, −13 ≤ l ≤ 14
11906
Yield : 65–76%.
4604 [Rint = 0.0164]
4604/0/408
1.052
R1 = 0.0467, wR2 = 0.1240
3. Results and discussion
Analytical data are presented in Table 1. All the complexes have
3:1 (M:L) stoichiometry. They are soluble to a limited extent in
EtOH, MeOH, DMF and DMSO, but insoluble in H2O, CHCl3 and C6H6.
The molar conductance values of the complexes ranging from 0.43
to 0.71 Ohm−1 cm2 mol−1 suggest their non-electrolytic nature [7].
The manganese(II), cobalt(II), nickel(II) and copper(II) complexes
showed the magnetic moments of 4.82, 3.72, 2.23 and 1.47 B.M. per
atom, respectively. These values are less than the high spin metal
octahedral complexes probably due to metal-metal interaction in
the complexes [8]. Zn(II) and Cd(II) complexes are diamagnetic.
−antiperiplanar across N(4)–C(15) and N(1)–C(7), and +synperipla-
nar across N(3)–C(14) and N(2)–C(8) and the corresponding torsion
angles are, −179.71(14)◦ [N(3)–N(4)–C(15)–C(16)], −176.69(15)◦
[N(2)–N(1)–C(7)–C(6)], 2.5(2)◦ [N(4)–N(3)–C(14)–O(4)] and
11.6(3)◦ [N(1)–N(2)–C(8)–O(3)], and these angles indicate that
N(3) and N(2) are in trans position to the C(16) and C(6), respectively
whereas carbonyl oxygens [O(4) and O(3)] are cis to azomethine
3.1. Crystallographic studies of BMSHCPH4
Crystallographic parameters, selected bond lengths, bond angles
and hydrogen bonds in the structure are given in Tables 2–4.
The ORTEP [9] and molecular packing diagrams are shown in
Figs. 1 and 2, respectively.
Crystal structure of BMSHCPH4 reveals that the whole molecule
is coplanar. The plane I [C(1), C(2), C(3), C(4), C(5), C(6), O(1), O(2)
and C(23)] make dihedral angles 17.87 (5)◦ and 33.28 (4)◦ with the
plane II [N(5), C(9), C(10), C(4), C(12) and C(13)] and plane III [C(16),
C(17), C(15), C(19), C(20), C(21), O(5), C(6) and C(22)], respectively.
The dihedral angle between plane II and plane III is 17.08(5)◦.
The bond distances and bond angles are in good agreement with
the reported ones [10–12]. The conformational designations are
Fig. 1. ORTEP diagram of BMSHCPH4.

R.S. Vadavi et al. / Spectrochimica Acta Part A 79 (2011) 348–355
351
Table 3
Selected bond lengths (Å) and angles (◦) for BMSHCPH4.
Bond lengths
O(3)–C(8)
O(4)–C(14)
O(5)–C(17)
O(6)–C(18)
O(6)–C(22)
N(1)–C(7)
N(3)–C(14)
N(3)–N(4)
1.220(2)
N(4)–C(15)
N(5)–C(13)
N(5)–C(9)
C(12)–C(13)
C(13)–C(14)
C(15)–C(16)
C(16)–C(17)
C(17)–C(18)
1.279(2)
1.333(2)
1.323(2)
1.380(3)
1.491(2)
1.441(2)
1.392(2)
1.396(2)
1.223(2)
1.352(2)
1.361(2)
1.415(3)
1.278(2)
1.338(2)
1.367(2)
Bond angles
C(18)–O(6)–C(22)
C(15)–N(4)–N(3)
C(9)–N(5)–C(13)
O(4)–C(14)–N(3)
O(4)–C(14)–C(13)
N(3)–C(14)–C(13)
117.15(19)
116.89(15)
117.30(14)
124.41(16)
121.38(16)
114.20(14)
C(17)–C(16)–C(15)
C(21)–C(16)–C(15)
O(5)–C(17)–C(16)
O(5)–C(17)–C(18)
O(6)–C(18)–C(19)
O(6)–C(18)–C(17)
121.31(16)
119.51(17)
117.55(16)
117.55(16)
125.78(17)
114.15(16)
nitrogens [N(4) and N(1)]. The torsion angles, N(1)–C(7)–C(6)–C(1)
[7.1(3)◦], C(7)–C(6)–C(1)–O(2) [−1.1(3)◦] and O(2)–C(1)–C(2)–O(1)
[0.5(2)◦] reveals that N(1), O(2) and O(1) are cis to one another and
in the similar way O(4), N(4) and O(5) are also in cis fashion.
The molecular packing [Fig. 2] shows the existence of
intramolecular and intermolecular hydrogen bonds. The distances,
to the stretching frequency of newly formed C N–N C azine
moiety indicating the coordination of amide oxygen and nitro-
gen through enolization and deprotonation [3]. This was further
supported by the disappearance of amide II and III bands. The
azomethine vibration has shifted to lower wave number in all the
complexes by 5–8 cm−1 indicating the coordination of azomethine
nitrogen to the metal. The band at 1368 cm−1 due to v(C–O), phe-
nolic stretching has shifted to higher wave number by 6–18 cm−1
in all the complexes. The 1590 and 1573 cm−1 bands of pyri-
dine moiety were not distinctly observed and probably might
have merged with the azomethine vibration. The other two vibra-
tions [1461 and 1446 cm−1] have shifted to higher frequency by
6–7 cm−1 indicating the coordination of pyridine nitrogen to the
metal.
˚
O(2)–H(O2)· · ·N(1) and O(5)–H(O5)· · ·N(4) are 2.573 and 2.597 A.
These values indicate the existence of strong intramolecular hydro-
gen bonding comparable with the earlier report [12].
The oxygen [O(7)] of water molecule in the crystal lat-
tice is intramolecularly hydrogen bonded to carbonyl oxygen,
O(4) [O(7)–H(7A)· · ·O(4) = 2.845(3) Å] and intermolecularly hydro-
gen bonded to O(3) [O(7)–H(7B)· · ·O(3) = 2.874(2) Å] and N(3)
[N(3)–H(N3)· · ·O(7) = 3.045(3) Å] of the two different adjacent
molecules. Thus water molecule is involved in trifurcate hydrogen
bonding.
The C–H in plane bend and out of plane bend vibrations showed
considerable shift to the higher frequency by 20–22 and 8–12 cm−1
,
respectively indicating clearly the coordination of pyridine nitro-
gen to the metal [15].
3.2. IR spectra
The presence of a broad band in the region 3434–3470 cm−1
was attributed to the v(O–H) of coordinated water [15]. This was
further confirmed by the appearance of a weak non-ligand band in
the region 831–856 cm−1, in all the complexes assignable to rocking
mode of coordinated water [16]. The presence of coordinated water
molecules was further confirmed by TG studies
The diagnostic IR bands are listed in Table 5. The IR spec-
trum of BMSHCPH4 showed a series of broad and weak absorption
bands extending from 3246 to 2936 cm−1 due to intramolecular
hydrogen bonding [OH· · ·N C] [13] and it was confirmed by the
crystal studies. In all the complexes, the bands due to v(OH) and
v(NH) were absent, indicating the complex formation through phe-
nolic oxygen and amide nitrogen via deprotonation [14,15]. The
absence of amide I band and presence of a new strong and broad
band centered at 1615 cm−1 in all the complexes was assigned
Looking into the position of coordinating sites in the crystal
structure of BMSHCPH4 and bonding sites as suggested by the IR
observations, it can be concluded that the ligand behaves as tri-
compartmental (a, b and c) ligand as shown in Scheme 1.
Table 4
Hydrogen bonds (Å) and angles (◦) for BMSHCPH4.
D–H· · ·A
D–H
D· · ·A
H· · ·A
<D–H· · ·A
O2–H2O· · ·O3a
O2–H2O· · ·N1a
O2–H2O· · ·N2a
O5–H5O· · ·N3a
O5–H5O· · ·N4a
O7–H7A· · ·O4a
N3–H3N· · ·O7b
C7–H7· · ·O7b
1.094(3)
1.094(3)
1.094(3)
0.933(2)
0.933(2)
0.779(2)
0.846(2)
0.944(2)
0.813(2)
0.965(2)
0.993(2)
0.947(2)
0.974(3)
0.821(2)
3.934(3)
2.573(2)
3.831(3)
3.871(3)
2.597(2)
2.845(3)
3.045(3)
3.401(3)
3.086(3)
3.550(3)
3.251(4)
3.654(4)
3.729(5)
0.874(2)
2.992(3)
1.563(3)
2.751(3)
2.957(2)
1.743(2)
2.071(2)
2.333(2)
2.593(2)
2.338(2)
2.624(2)
2.520(2)
2.719(2)
2.952(3)
2.069(2)
144.42(2.07)
150.63(2.55)
169.36(2.16)
166.67(1.92)
150.81(2.17)
172.87(2.60)
142.10(1.74)
143.86(1.60)
153.17(2.08)
160.84(1.87)
130.25(2.33)
169.40(1.77)
137.52(2.48)
166.52(2.66)
N2–H2N· · ·O7b
C19-H19· · ·O1c
C22–H222· · ·O2c
C3–H3· · ·O5d
C23H231· · ·O7d
O7–H7B· · ·O3e
a
Symmetry transformations used to generate equivalent atoms: x, y, z.
b
c
Symmetry transformations used to generate equivalent atoms: x + 2, −y + 2, −z.
Symmetry transformations used to generate equivalent atoms: x − 1, +y + 1, −z + 1.
Symmetry transformations used to generate equivalent atoms: x, −y − 1, +z + 1.
Symmetry transformations used to generate equivalent atoms: x, +y + 1, +z.
d
e

352
R.S. Vadavi et al. / Spectrochimica Acta Part A 79 (2011) 348–355
Fig. 2. Molecular packing diagram of BMSHCPH4 showing hydrogen bonds.
at 7.08 [H13 and H13ꢀ, J = 7.8 Hz], 7.30 [H11 and H11ꢀ, J = 7.6 Hz]
3.3. 1H NMR spectra
and 8.38 ppm [H5 and H3, J = 7.2 Hz] corresponds to six aromatic
protons. A sharp singlet in the up field region at 3.85 ppm was
attributed to six protons of methoxy group. These assignments have
been done by comparing the 1H NMR of title compound with the
2,6-pyridinedicarboxylic acid and o-vanillin [17,18]. In the 1H NMR
spectrum of zinc(II) complex, some of the signals were doubled
indicating the magnetically non equivalence nature of the com-
plex in solution. The absence of OH and NH signals clearly indicate
the deprotonation during complex formation. The signals due to
azomethine protons [H7 and H7ꢀ] have been shifted to down field by
0.24 ppm clearly indicating the coordination of azomethine nitro-
gen to the metal [2]. The signals due to the protons of the pyridine
ring [H3, H4 and H5] observed as a broad multiplet in the range from
8.37 to 8.43 ppm suggest the coordination of pyridine nitrogen.
The signals due to H12 and H12ꢀ, and H11 and H11ꢀ were dou-
The numbering scheme for the assignments of the protons is
given in Scheme 1. The 1H NMR spectrum of BMSHCPH4 in DMSO-
d6 shows only one set of signals indicating the two pendant arms of
the pyridine moiety are magnetically equivalentonthe correspond-
ing nmr time scale. Two broad singlets at 10.66 and 12.41 ppm
are assigned to two NH and two OH protons, respectively [2],
and are exchanged by D2O. The presence of these signals in the
downfield region in comparison with aromatic protons was due
to the involvement of both the phenolic oxygens and amide nitro-
gens in intramolecular hydrogen bonding which was confirmed by
the crystal structure. A sharp singlet at 8.97 ppm was ascribed to
two azomethine protons [H7 and H7ꢀ] [2]. A multiplet at 8.30 ppm
[H4] and a triplet at 6.91 ppm [H12 and H12ꢀ, J = 7.9 Hz] accounts
for one and two aromatic protons, respectively. Three doublets
Fig. 3. Electronic spectra of representative complexes; (a) [Co3(BMSHCP)(H2O)7Cl2], (b) [Ni3(BMSHCP)(H2O)7Cl2].

R.S. Vadavi et al. / Spectrochimica Acta Part A 79 (2011) 348–355
353
bled and observed in the up field region at 6.80 and 6.70 and 6.41
and 6.14 ppm. Another signal due to H13 and H13ꢀhas also shifted
up field by 0.45 ppm. These changes indicate the coordination of
phenolic oxygen to the metal [2]. The signal due to methoxy group
shifted up field and appeared as two singlets at 3.73 and 3.62 ppm,
which clearly supports the non-equivalence of the two pendant
arms upon complexation.
3.4. EPR spectra
The EPR spectrum of the present copper(II) complex at room
temperature as well as at LNT exhibit unresolved broad signals
giving only one ‘g’ value, i.e., giso = 2.106. Such isotropic spectra,
consisting of a broad signal and hence only one g-value, arise from
extensive exchange coupling through misalignment of the local
molecular axes between different molecules in unit cell (dipolar
broadening) and enhanced spin lattice relaxation. This type of spec-
tra unfortunately give no information on the electronic state of the
Cu(II) ion present in the complex.
3.5. Electronic spectra
The electronic spectrum of BMSHCPH4 showed three bands in
the UV region at 314, 308 and 304 nm. The former two bands were
assigned to ␲–␲* transitions and latter to n–␲* transition. In the
electronic spectrum of the cobalt(II) complex [Fig. 3(a)], two spin
allowed transitions at 560 and 441 nm were observed, assignable
4
4
4
4
to T1g → A2g(F) and T1g(F) → T1g(P), indicating an octahedral
geometry around the metal center [19,20]. A broad band at 510 nm
3
3
in the nickel(II) complex [Fig. 3(b)] was due to the A2g → T1g(P)
transition, indicating an octahedral geometry for the nickel(II) com-
plex [19,21]. In addition to this band, nickel(II) complex showed
two broad bands centered at 437 and 329 nm, which are probably
due to the charge transfer transitions. A broad band centered at
610 nm, observed as an envelope in copper(II) complex, assigned
to the 2Eg → T2g reveals the octahedral geometry [19] and another
2
broad band at 442 nm was due to charge transfer transition. The
manganese(II), zinc(II) and cadmium(II) complexes did not show
any bands.
3.6. Electrochemistry
The effect of ligands on oxidation-reduction potential and of
central metal ion in copper(II) complex, which is a multinuclear
cluster, was studied by the cyclic voltammetry. The cyclic voltam-
mograms are scanned at different rates (0.025 V/s, 0.05 V/s and
0.1 V/s) in different potential ranges (+1.2 V to −2.0 V and 1.2 V to
−1.6 V).
In general the cyclic voltammograms [Fig. 4] show that all the
reaction occurring are irreversible. This irreversibility increases
with increase in the sweep rate. Since this system has trinu-
clear copper, various voltametric peaks appear. The peak at −1.4 V
[Fig. 4(b)] is due to the intermediate formed in the reduction reac-
tion, which disappears at high scan rates [Fig. 4(b) and (c)]. The
peak at −1.0 V is due to the reduction of CuII CuII CuII–CuI CuI CuI
[Fig. 4(a) and (b)]. The peak at −0.6 V [appear only in Fig. 4(a)] is due
to the reduction of CuII CuII CuII–CuI CuIICuI. This is because; the cur-
rent continues to be cathodic even when the scan is reversed. The
potential is still negative, which is enough to cause reduction. Once
the potential becomes positive, reduction of electro active species
can no longer occur and the current becomes anodic. The peak at
0.45 V [Fig. 4(b)] corresponds to one electron oxidation of CuII CuII
CuII–CuII CuIII CuII. This occurs only at higher potential, which is
due to satiric effect experienced by central copper. The observed
peak shift further apart with increasing scan rates, which further
confirms the irreversibility of the system. Moreover the peaks are

354
R.S. Vadavi et al. / Spectrochimica Acta Part A 79 (2011) 348–355
Fig. 4. Cyclic voltammogram of [Cu3(BMSHCP)(H2O)7Cl2] at different scan rates; (a) 0.05 V/s, (b) 0.025 V/s, (c) 0.1 V/s.
widely separated that no parts of two peaks overlap on the potential
axis. Therefore this system can be classified as totally irreversible
system. Electrochemical irreversibility is caused by slow electron
exchange of redox species with the working electrodes; in this case,
at very high scan rate [Fig. 4(c)] since the system is completely
irreversible, no oxidation or reduction takes place.
3.7. FAB mass and thermal studies
The FAB mass spectra were obtained for the trinuclear com-
plexes [Zn3(BMSHCP)·Cl2·7H2O] and [Cd3(BMSHCP)·Cl2·7H2O]. The
spectra show the presence of three Zn and three Cd atoms in the
complexes with the molecular ion peaks at m/z = 852 and 993,
Fig. 5. FAB mass spectra of representative complexes; [Zn3(BMSHCP)(H2O)7Cl2], (b) [Cd3(BMSHCP)(H2O)7Cl2].

R.S. Vadavi et al. / Spectrochimica Acta Part A 79 (2011) 348–355
355
Fig. 6. Thermograms of representative complexes; (a) [Mn3(BMSHCP)(H2O)7Cl2] (b) [Cu3(BMSHCP)(H2O)7Cl2].
oxygen [in the two side compartments (a and c)] and through
pyridyl nitrogen and two hydrazonic nitrogens [in the central com-
partment (b)] as shown in the Scheme 1. The proposed structure
for the all the complexes is depicted in Fig. 7.
OH2
OH2
O
O
H2O
H2O
H2O
N
M
M
N
N
M
OH2
Cl
Cl
N
N
O
Acknowledgements
O
H2O
HC
O
CH
O
Thanks are due to S.I.F., I.I.Sc., Bangalore, I.I.T Bombay, C.D.R.I
Lucknow and U.S.I.C. Karnatak University, Dharwad for recording
NMR, EPR and UV–vis spectra. Authors are thankful to Prof. S.B. Pad-
hye, University of Pune, India for magnetic measurement facilities.
CH3
H3C
Fig. 7. The proposed structure for all the complexes.
Appendix A. Supplementary data
respectively. The m/z values agreed well with the molecular weight
of the species and also confirmed the molecular structure of the
complex. Spectra are reproduced in the Fig. 5(a) and (b), respec-
tively.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.03.011.
References
Thermal study reveals, the manganese(II) and copper(II) com-
plexes decompose in three stages. The manganese(II) complex
[Fig. 6(a)] loses a weight of 15.28% (calcd. 15.35%) in the range
140–210 ◦C and copper(II) complex [Fig. 6(b)] showed a weight loss
of 14.80% (calcd. 14.88%) in the range 150–237 ◦C. The observed
weight loss in the first step for both the complexes corresponds
to the loss of seven coordinated water molecules. The tempera-
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second step two coordinated chlorides were lost in the temper-
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correspond to the formation of stable MnO and CuO. The weight of
MnO and CuO corresponds to 25.95 and 28.12%, respectively and
tallies with the metal analysis.
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