R. Dulare et al. / Journal of Molecular Structure 984 (2010) 96–101
97
DMSO-d6 on a JEOL AL300 FT NMR spectrometer using TMS as
2.4.3. Synthesis of complex 2
internal reference.
A solution of ppt (0.5 g, 2 mmol) in MeOH (15 mL) was added to
a solution of Zn(OAc)2ꢀ2H2O (0.219 g, 1 mmol) in MeOH (15 mL)
and the mixture was stirred for 4 h at room temperature. The
resulting clear solution was filtered off and kept for crystallization.
Colorless crystals of 2 suitable for X-ray analyses were obtained by
slow evaporation of its solution over a period of 21 days. Yield:
57%.
2.3. X-ray crystallography
The X-ray data collection for 1 and 2 were performed on Oxford
Xcaliber diffractometer equipped with a Crys Alis Pro, using graph-
ite monochromated Mo K
a radiation (k = 0.71073 Å) source. The
Anal. Found: C, 49.72; H, 3.59; N, 15.43; S, 8.82; Zn, 8.97%. Calc.
for C30H26N8O6S2Zn (724.10): C, 49.76; H, 3.62; N, 15.47; S, 8.86;
structures were solved by direct methods (SHELXL-2008) and re-
fined against all data by full matrix least-squares on F2 using aniso-
tropic displacement parameters for all non-hydrogen atoms. All
the hydrogen atoms were included in the refinement at geometri-
cally ideal positions and refined with a riding model [18]. The
MERCURY package, DIAMOND and ORTEP-3 programs were used
for generating molecular structures [19–21].
Zn, 9.03%. M.p. 250 °C; IR (KBr, cmꢁ1): 3607
m
(OH); 2963
m(NH);
1691
m(C@O), 1429 m(C@N); 663 (pyridine) and 825 (phenyl).
UV–Vis. [kmax, DMSO, nm]: 396, 354, 329 and 313. Scheme 1 gives
a general method of synthesis of the ligand and its complexes.
3. Results and discussion
2.4. Synthesis
A methanol solution of Co(II) and Zn(II) salts react with ppt and
yielded complexes 1 and 2, respectively. The single crystal X-ray
diffraction studies indicate that the ligand (ppt) adopts the mono-
dentate binding nature in both the complexes. All the complexes
are air stable, non-hygroscopic crystalline solids, which are par-
tially soluble in common organic solvents but soluble in DMF
and DMSO and can be kept in desiccators over a prolonged period
without any sign of decomposition.
2.4.1. Synthesis of phenyl-(5-pyridin-4-yl[1,3,4]thiadiazol-2-yl)-
amine (ppt)
A mixture of isonicotinic acid hydrazide (2.74 g, 20 mmol) and
phenyl isothiocyanate (2.4 mL, 20 mmol) in absolute ethanol was
refluxed for 8 h at 65 °C. The solid 1-isonicotinoyl-4-phenyl thio-
semicarbazide obtained upon cooling was filtered off, washed suc-
cessively with water and diethyl ether, dried and crystallized from
ethanol. 1-Isonicotinoyl-4-phenyl thiosemicarbazide (2.72 g,
10 mmol) was added portion wise in 10 ml conc. H2SO4 and stirred
for 2 h with cooling. The mixture was poured over crushed ice and
the precipitated solid was filtered off, washed twice with cold
water (50 ml) and dried. The yellow crystals of ppt suitable for
X-ray analysis were obtained by slow crystallization in methanol
for 15 days. Yield: 85%.
3.1. IR spectra
The bands at 3003 and 1484 cmꢁ1 in the free ligand may be as-
signed to the
moiety and
trum of compound 1 reveals the characteristic bands due to
m
(NH) of the imine group adjacent to the thiadiazole
m(C@N) of thiadiazole group, respectively. The spec-
Anal. Found: C, 61.35; H, 3.93; N, 21.95; S, 12.58%. Calc. for
m
(S@O) sulphate, m(C@N) thiadiazole and pyridine rings at 1564,
C
13H10N4S (254.31): C, 61.40; H, 3.96; N, 12.60; S, 20.60%. M.p.
1433 and 677cmꢁ1 respectively, suggesting bonding of sulphate
,
140 °C; IR (KBr, cmꢁ1): 3003
m
(NH), 1484 (C@N), 685 (pyridine)
m
and pyridine nitrogen to metal ion. The compound 2 shows a neg-
ative shift of 22 cmꢁ1 in the pyridine ring vibration on complexa-
tion in comparison to the free ligand suggesting bonding via
pyridine nitrogen with Zn(II). A band at 1691 cmꢁ1 corresponding
and 826 (phenyl). 1H NMR (DMSO-d6, d, ppm): [8.86 (2H), 8.19
(2H)] pyridine; [7.60 (2H), 7.37 (1H), 7.11 (2H)] phenyl; 4.84
(1H, NH). 13C NMR (DMSO-d6, d, ppm): [146.42 C(4,5), 140.01
C(2), 122.93 C(3,6)] pyridine; [141.58 C(8), 129.30 C(10,12),
122.93 C(11), 122.07 C(9,13)] phenyl and [166.60 C(7), 153.88
C(1)] thiadiazole carbons of ppt. The tentative structure of ppt is
depicted in Fig. 1.
to
in the complex. The persistence of a band due to
tra of both the complexes indicates the non-involvement of this
m
(C@O) of acetate indicates the presence of monodentate acetate
m
(NH) in the spec-
group in coordination.
A broad band in the region 3622–
3607 cmꢁ1 indicates the presence of coordinated/uncoordinated
2.4.2. Synthesis of complex 1
water molecule in the complexes 1 and 2.
A methanol solution (15 mL) of CoSO4ꢀ7H2O (0.281 g, 1 mmol)
was stirred with a methanol solution (15 mL) of ppt (0.250 g,
1 mmol). The resulting clear brown solution was filtered off, where
upon the single crystals of 1 suitable for X-ray analyses were ob-
tained by slow evaporation of the solution over a period of 15 days.
Yield: 55%.
3.2. Electronic spectra and magnetic moment
Complex 1 shows a magnetic moment of 5.2 BM and the pres-
4
ence of a broad d–d band around 867 nm assigned to the T1g
(F) ? 4T2g (F) transition, suggest its octahedral geometry. Other
high energy bands observed at 441, 388, 358 and 332 nm may be
due to charge transfer/intraligand transitions [22]. The higher en-
ergy bands at 396, 354, 329 and 313 nm in compound 2 arise be-
cause of the charge transfer/intraligand transitions from
coordinated and uncoordinated nitrogen atoms to the aromatic
ring and imine of the ppt.
Anal. Found: C, 31.75; H, 2.43; N, 11.38; S, 13.00; Co, 11.94%.
Calc. for C13H12CoN4O9S2 (491.32): C, 31.77; H, 2.46; N, 11.40; S,
13.05; Co, 11.99%. M.p. 235 °C,
3622 (OH); 2985 (NH); 1564 m(S@O) sulphate; 1433 m(C@N);
l
eff = 5.20 BM; IR (KBr, cmꢁ1):
m
m
677 (pyridine) and 818 (phenyl). UV–Vis. [kmax, DMSO, nm]: 867,
441, 388, 358 and 332.
3.3. Crystal structure description of complexes 1 and 2
9
H
N
5
4
S
1
10
11
Crystallographic data and structural refinement details related
to complexes 1 and 2 are given in Table 1 and selected bond
lengths and angles in Table 2. The X-ray analysis of 1 reveals the
presence of four water molecules, monodentate sulphate and a
ppt ligand coordinated to Co(II), resulting in a distorted octahedral
geometry (Fig. 2). There is one uncoordinated interstitial water
3
8
2
N
N
13
N
6
7
12
Fig. 1. Phenyl-(5-pyridin-4-yl-[1,3,4]thiadiazole-2-yl)-amine.