Manganese(II) and zinc(II) complexes of 4-phenyl(2-methoxybenzoyl)-3- thiosemicarbazide: Synthesis, spectral, structural characterization, thermal behavior and DFT study

Article abstract of DOI:10.1016/j.poly.2014.02.029

The ligand 4-phenyl(2-methoxybenzoyl)-3-thiosemicarbazide (Hpmt), forms isostructural [Mn(pmt)₂(o-phen)] (1) and [Zn(pmt)₂(o-phen) ] (2) complexes containing o-phen as coligand which have been characterized by analytical, spectroscop

Full text of DOI:10.1016/j.poly.2014.02.029

Polyhedron 73 (2014) 98–109
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Manganese(II) and zinc(II) complexes of 4-phenyl
(2-methoxybenzoyl)-3-thiosemicarbazide: Synthesis, spectral,
structural characterization, thermal behavior and DFT study
a
b
a
a,
A. Singh a, M.K. Bharty a, , R.K. Dani , Sanjay Singh , S.K. Kushawaha , N.K. Singh
⇑
⇑
a Department of Chemistry, Banaras Hindu University, Varanasi 221 005, India
b Department of Chemical Science IISER-Mohali, Knowledge City, Sector 81, S.A.S Nagar, Mohali 140306, Punjab, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The ligand 4-phenyl(2-methoxybenzoyl)-3-thiosemicarbazide (Hpmt), forms isostructural [Mn(pmt)2
(o-phen)] (1) and [Zn(pmt)2(o-phen)] (2) complexes containing o-phen as coligand which have been
characterized by analytical, spectroscopic (IR, UV–Vis, NMR), magnetic susceptibility, TGA and single
crystal X-ray data. Both complexes crystallize in monoclinic systems with the space group P2/n. The com-
plexes have distorted octahedral geometry around the metal center. The ligand in the complexes is coor-
dinated through the deprotonated hydrazinic nitrogen and carbonyl oxygen. The hydrazinic nitrogen
coordinates with a shorter M–N distance than the o-phen nitrogen and bond lengths in the chelate ring
systems are intermediate between single and double bond distances, suggesting considerable delocaliza-
tion of charge. There is a good agreement between the geometrical parameters obtained by X-ray crys-
tallography to those generated by DFT method. The thermal degradations of complexes 1 and 2 have
been investigated by thermogravimetric analyses which indicate that the final residues left are Mn(NCO)2
and Zn(NCSNH)2. The small HOMO–LUMO energy gap suggests low excitation energy for the complexes.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 23 October 2013
Accepted 13 February 2014
Available online 26 February 2014
Keywords:
Thiosemicarbazide
Mn(II) and Zn(II) complexes
Crystal structure
Supramolecular architecture
DFT
TGA
1. Introduction
analytical chemistry, catalysis, electrochemistry, ring-opening
metathesis polymerization and biochemistry [17–23]. However,
Thiosemicarbazide is the simplest representative of the ligands
having nitrogen and sulfur as donors. Thiosemicarbazide and
substituted thiosemicarbazides are an importantant class of inter-
mediate used for the synthesis of five membered nitrogen–sulfur
or nitrogen–oxygen heterocyclic compounds [1–3]. The chemistry
of thiosemicarbazide/ substituted thiosemicarbazide complexes
has received much attention owing to their significant biological
and medicinal properties which are dependent upon the chemical
nature of the moiety attached to the C@S carbon atom [4–7]. 1,4-
Disubstituted-thiosemicarbazide are biologically versatile com-
pounds displaying a variety of biological effects which include
anti-inflammatory [8], antimycobacterial [9,10], antimicrobial
[11–13], antifungal [14], antibacterial [15,16] and antiviral [10]
activities. Metal complexes containing 1,10-phenanthroline and
bipyridine have gained importance because of their versatile roles
as building blocks for the synthesis of metallo-dendrimers and as
molecular scaffolding for supramolecular assemblies, and in
most diimine complexes reported are homo ligand compounds of
the general formula [M(N–N)3]n+ or [M(N–N)2(NCS)2] which have
shown variable spin transition properties with temperature [24].
Mixed ligand complexes can be a synthetic challenge to tune the
various properties of the transition metal complexes. A few papers
are available on the transition metal complexes of 1,4-substituted
thiosemicarbazide [25,26] but there is no report on the synthesis
and structural characterization of the mixed ligand complexes con-
taining bidentate N,N donors and 1,-4-disubstituted thiosemicar-
bazide. In this paper, we report the synthesis and structural
characterization of Mn(II) and Zn(II) complexes of 4-phenyl(2-
methoxybenzoyl)-3-thiosemicarbazide and the DFT calculations
have been done to corroborate the structural data.
2. Experimental
2.1. Chemical and starting materials
Commercial reagents were used without further purification
and all experiments were carried out in open atmosphere. Phenyl
isothiocyanate, methyl-2-methoxy benzoate (Sigma Aldrich),
⇑
Corresponding authors. Tel.: +91 5426702452; fax: +91 5422368127.
E-mail addresses: manoj_vns2005@yahoo.co.in (M.K. Bharty), singhnk_bhu@
yahoo.com (N.K. Singh).
http://dx.doi.org/10.1016/j.poly.2014.02.029
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

A. Singh et al. / Polyhedron 73 (2014) 98–109
99
hydrazine hydrate (SD Fine) were used as received. 2-Methoxy
benzoic acid hydrazide was prepared by reported method [27].
All the synthetic manipulations were carried out in open atmo-
sphere and at room temperature. The solvents were dried and dis-
tilled before use following the standard procedure.
washed with ethanol and air dried. The precipitate was suspended
in methanol and stirred with a methanol solution of 1,10-phenan-
throline (0.200 g, 1 mmol) at the room temperature which resulted
in a clear yellow solution. This was filtered off and kept for crystal-
lization. Yellow needle shaped crystals of the complex suitable for
an X-ray analyses were obtained by slow evaporation of the above
solution over a period of 10 days. Yield: 70%. M.p: 508 K. Anal. Calc
for C42H36ZnN8O4S2 (711.61): C, 59.52; H, 4.25; N, 13.23; S, 7.56.
2.2. Physical measurements
Carbon, hydrogen and nitrogen contents were estimated on a
CHN Model CE-440 Analyser and on an Elementar Vario EL III Carlo
Erba 1108. Magnetic susceptibility measurements were performed
Found: C, 59.54; H, 4.24; N, 13.23; S, 7.25%. IR data (
KBr): 3259s (NH); 1566 thioamide I [b(NH)+ (CN)] s; 1351 thio-
amide II [ (CN)+b(NH)] s; 1018 (N–N) s; 1586 (C@O); 930
m ,
cmꢀ1
m
m
m
m
m
m
at room temperature on
a
Cahn Faraday balance using
(C@S).1H NMR (300 MHz, DMSO-d6; dppm): 9.00 (s, 1H, NH);
8.58 (s, 1H, NH); 6.87–8.05 (aromatic protons); 3.87 (m, 3H,
–OCH3). The 13C NMR (DMSO-d6; d ppm): 177.66 (C@S), 152.66
(C@O), 116.93–130.75 (aromatic ring carbons), 65.39 (–OCH3).
UV–Vis [kmax, Nujol mulls, nm]: 325, 350.
Hg[Co(NCS)4] as the calibrant and electronic spectra were recorded
on a SHIMADZU 1700 UV–Vis spectrophotometer. IR spectra were
recorded in the 4000–400 cmꢀ1 region as KBr pellets on a Varian
Excalibur 3100 FT-IR spectrophotometer. 1H and 13C NMR spectra
were recorded in DMSO-d6 on a JEOL AL300 FT NMR spectrometer
using TMS as an internal reference. Thermogravimetric analyses
(TG-DTA) of the compounds were performed on a Perkin Elmer-
STA 6000 thermal analyzer at a heating rate of 5 °C/min in N2
atmosphere.
3. Results and discussion
The ligand 4-phenyl(2-methoxybenzoyl)-3-thiosemicarbazide
react with Mn(OAC)2ꢁ4H2O and Zn(OAC)2ꢁ2H2O and then with o-
phen in methanol solution yielding [Mn(pmt)2(o-phen)] (1) and
[Zn(pmt)2(o-phen)] (2), respectively. In both the complexes, the
metal is bonded through deprotonated thiohydrazide nitrogen
and carbonyl oxygen of the ligand. The six coordination of Mn(II)
and Zn(II) is completed by coordination of one molecule of o-phen
and two molecules of the ligand. These complexes are stable to-
ward air and moisture. Scheme 1 depicts the formation of the li-
gand and complexes containing o-phen as co-ligand. The
complexes 1 and 2 are soluble in chloroform and melt at 498 and
508 K, respectively.
2.3. X-ray crystallography
Crystals suitable for X-ray analyses of complexes 1 and 2 were
grown at room temperature. X-ray diffraction data were obtained
at 293(2) K on an Oxford Diffraction Gemini diffractometer
equipped with CRYSALIS PRO., using a graphite mono-chromated Mo
Ka (k = 0.71073 Å) radiation source. A semi-empirical multi scan
absorption correction was applied to the X-ray data of both com-
pounds. The structure was solved by direct methods (SHELXL-13)
and refined by full matrix least-square on F2
(SHELXL) using aniso-
tropic displacement parameters for all non-hydrogen atoms. All
hydrogen atoms were included in calculated position and refined
with a riding model [28]. Figures were drawn using the programs
MERCURY and ORTEP-3 [29,30].
3.1. IR spectra
Complexes 1 and 2 show the absence of
m(N–H) band at
3201 cmꢀ1 indicating loss of hydrogen from the nitrogen of thiohy-
drazide group which is supported by a small positive shift of
2.4. Synthesis
13 cmꢀ1 in
m
(N–N). The IR spectra of complexes 1 and 2 show a
negative shift of 48–68 cmꢀ1 in
(C@O) indicating bonding of the
carbonyl oxygen to the metal ion. Furthermore, complexes 1 and
2 show a very small positive shift in (C@S) as compared to the free
m
2.4.1. Preparation of 4-phenyl(2-methoxybenzoyl)-3-
thiosemicarbazide (Hpmt)
The ligand 4-phenyl(2-methoxybenzoyl)-3-thiosemicarbazide
(Hpmt) was prepared as reported in literature [31].
m
ligand, showing that the thiohydrazide sulfur is not participating in
bonding but the small positive shift can be attributed to the
involvement of sulfur in hydrogen bonding with the hydrogen of
o-phen. Thus, it is clear from the IR data that the ligand acts as uni-
negative bidentate in complexes 1 and 2 bonding through deproto-
nated thiohydrazide nitrogen and carbonyl oxygen [32].
2.4.2. Preparation of [Mn(pmt)2(o-phen)] (1)
Methanolic solutions of Mn(OAc)2ꢁ4H2O (0.246 g, 1 mmol) and
Hpmt (0.6 g, 2 mmol) were mixed and continuously stirred for
30 min at room temperature. The resulting white precipitate was
filtered off, washed with ethanol and air dried. The precipitate
was suspended in methanol and stirred with a methanol solution
of 1,10-phenanthroline (0.2 g, 1 mmol). The resulting clear yellow
solution was filtered off and kept for crystallization, which resulted
after slow evaporation of the above solution over a period of
20 days, yellow rod shaped crystals of complex suitable for X-ray
analyses. Yield: 70%. M.p: 498 K. Anal. Calc. for C42H36MnN8O4S2
(835.87): C, 60.29; H, 4.30; N, 13.39; S, 7.65. Found: C, 60.25; H,
3.2. Electronic spectra and magnetic moments
The magnetic moment value of 5.85 B.M. for [Mn(pmt)2(o-
phen)] (1) suggests the presence of high spin Mn(II) with five un-
paired electrons. The electronic spectrum of 1 shows a band at
648 nm which may be assigned to the 6A1g?4T1g transition in an
octahedral geometry [33]. Other high energy bands in complex 1
cmꢀ1, KBr): 3272s
m
(NH); 1594s
occurring at 280 and 310 nm are due to
tions, respectively. [Zn(pmt)2(o-phen)] (2) is diamagnetic and
p?
p⁄ and n?p⁄ transi-
4.35; N, 13.28; S, 7.6%. IR data (
thioamide I [b(NH) + (CN)]; 1346 thioamide II [
1018 (N–N) s; 1604 (C@O); 928 (C@S). UV–Vis [kmax, Nujol
mulls, nm]: 280, 310, 648.
m
m
m(CN)+b(NH)];
shows two high intensity bands at 325 and 350 nm due to
p?
p⁄
m
m
m
and n?p⁄ transitions, respectively.
2.4.3. Preparation of [Zn(pmt)2(o-phen)] (2)
3.2.1. 1H and 13C NMR spectra
Methanolic solution of Zn(OAc)2ꢁ2H2O (0.218 g, 1 mmol) was
added to the methanolic solution of Hpmt (0.6 g, 2 mmol) and
the reaction mixture was stirred continuously at room tempera-
ture for 30 min. The resulting white precipitate was filtered off,
The 1H NMR spectrum of [Zn(pmt)2(o-phen)] (2) shows two sig-
nals at 9.00 (s, 1H) and 8.58 (s, 1H, NH) ppm due to the proton of
NH group attached to carbonyl and phenyl group, respectively. The
methoxy hydrogens appear at 3.87 ppm. Phenyl and o-phen ring

100
A. Singh et al. / Polyhedron 73 (2014) 98–109
O
S
O
NH2
N
H
NH
N
H
N
H
EtOH
+
SCN
70 0
C
OCH3
OCH3
MeOH
(i) M((OAc)2·nH2O
(ii) O-phen
H3CO
S
H
N
N
H
N
O
N
O
M
N
N
HN
OCH3
NH
S
M = Mn , Zn
Scheme 1. Syntheses of Mn(II) and Zn(II) complexes.
protons appear as multiplet between d 6.87–8.05 ppm. The 13C
spectrum of [Zn(pmt)2(o-phen)] (2) shows signals at d 177.66,
152.66 and 65.39 ppm for (C@S), (C@O) and –OCH3 carbons,
respectively. The aromatic carbons appear between d 116.93–
130.75 ppm. A negative shift of 2.02 ppm in C@O and disappear-
ance of one NH proton attached to C@S group suggests bonding
through carbonyl oxygen and one thiohydrazide nitrogen after
deprotonation.
decompositions between 320–360 °C show the weight loss
(24.31% for 1 and 24.52% for 2) of o-phen from both the complexes.
The third decomposition between 500 and 550 °C for complex 1,
corresponds to loss (52.28%) of two PhNHCSN moiety and the last
decompositions between 600 and 700 °C show the degradation of
the remaining organic moieties (17.24%) and finally Mn(NCO)2 is
left as a residue. Whereas, the third decomposition for complex
2, corresponds to loss (42.42%) of two PhCONH moiety between
410 and 450 °C and the last decompositions between 720 and
760 °C show the degradation of the remaining organic moieties
(26.03%) and finally Zn(NCSNH)2 is left behind. The corresponding
endo and exothermic peaks in DTA at 305, 360 and 470 and 810 °C
for complex 1 and at 340, 480 and 540 and 800 °C for complex 2
were obtained.
3.3. Thermal gravimetric analysis
The thermal properties of complexes [Mn(pmt)2(o-phen)] (1)
and [Zn(pmt)2(o-phen)] (2) were studied by TG and DTA in the
temperature range 30–900 °C under
a nitrogen atmosphere
(Fig. 1). Thermogravimetric analysis of complexes 1 and 2 showed
that the complexes start decomposing around 200 °C and thermo-
grams exhibit four distinct decompositions at 200, 360, 550 and
700 °C for Mn(II) complex and at 200, 320, 410 and 720 °C for Zn(II)
complex. The weight loss (6.162 for 1 and 7.02% for 2) around
220 °C could be ascribed to the loss of –OCH3 moiety and second
3.4. Crystal structure description of complexes 1 and 2
Figs. 5 and 7 show the ORTEP diagram of [Mn(pmt)2(o-phen)]
(1) and [Zn(pmt)2(o-phen)] (2), respectively, together with the
atomic numbering scheme. In both complexes, the metal ions,
Fig. 1. Thermograms of [Mn(pmt)2(o-phen)] (1) and [Zn(pmt)2(o-phen)] (2).

A. Singh et al. / Polyhedron 73 (2014) 98–109
101
Fig. 2. Optimized structure (a), MEP (b) and contour plot (c) of ligand Hpmt.
Fig. 3a. Charge distribution on atoms of Hpmt.
Zn(II) and Mn(II), posses distorted octahedral geometry. The crys-
tallographic asymmetric units in the complexes [Mn(pmt)2
(o-phen)] (1) and [Zn(pmt)2(o-phen)] (2), comprise of two complex
molecules. The details of data collection, structure solution and
refinement of complexes 1 and 2 are listed in Table 1. Some
selected bond distances and bond angles in these structures are
compiled in Tables 3 and 4. The metal center is coordinated in an
N4O2 manner by two uninegative ligand moieties using pairs of
hydrazine nitrogen, carbonyl oxygen and o-phen nitrogen; forming
three five membered chelate rings. The carbon–sulfur bond length
[1.680(2) Å] is purely a C@S double bond which remains uncoordi-
nated and takes part in N–Hꢁ ꢁ ꢁS hydrogen bonding providing a
supramolecular architecture. The hydrazine moiety, which
connects two functional groups viz. carbo and thiocarbo involves
the whole system in resonance. Consequently, N–N and C@O
distances are found to be intermediate between single and
double-bond lengths indicating a delocalization of -electrons.
The average bond lengths N2–N1 = 1.388, N1–C7 = 1.323,
N2–C8 = 1.342, C7–O1 = 1.266 Å for and N1–N2 = 1.385,
p
1
N1–C8 = 1.318, N2–C9 = 1.340, C8–O2 = 1.270 Å for 2, suggest
considerable delocalization of charge. The distances within the
chelate rings are intermediate between single and double bond
lengths as compared to the corresponding bond lengths in Hpmt.
The bite angles 160.83(7) [N(2)–Mn(1)–N(4)] and 109.82(11)°
[N(2)–Mn(1)–N(2)] for complex 1 and 164.28(4) [N(2)–Zn(1)–
N(4)] and 103.39(14)° [N(2)–Zn(1)–N(2)] for complex 2 suggest
substantial deviation from an octahedral geometry. In both the
complexes hydrazine nitrogen bonds with a shorter M–N distance
than the o-phen nitrogen which indicates that the hydrazinic
nitrogen bonds more strongly than the o-phen nitrogens. The bond

102
A. Singh et al. / Polyhedron 73 (2014) 98–109
Fig. 3b. Charge distribution on atoms of [Mn(pmt)2(o-phen)] (1).
Fig. 3c. Charge distribution on atoms of [Zn(pmt)2(o-phen)] (2).
distances and angles are very much similar to those reported
earlier for octahedral complexes of thiosemicarbazide [34,35]. In
both complexes the chelate rings formed by the ligand and the
2-methoxy phenyl ring lie nearly in the same plane and form an
extended coplanar system. The values of the dihedral angles for
complexes 1 and 2 are 57.89° and 57.84°, respectively which is
greater than that of the ligand (44.10°) suggesting that these two
rings adopt more open structure in the complexes as compared
to the ligand which are structurally identical except for a slight
variation in bond lengths and angles (Tables 3 and 4). The

A. Singh et al. / Polyhedron 73 (2014) 98–109
103
Fig. 4. Frontier molecular orbital diagrams of Hpmt.
Fig. 5. ORTEP diagram of [Mn(pmt)2(o-phen)] (1) at 30% ellipsoids probability level. Hydrogen atoms are omitted for clarity.
intramolecular N–Hꢁ ꢁ ꢁO hydrogen bonding occurring between
hydrazinic hydrogen and carbonyl oxygen which was present in
Hpmt is retained in complexes. The crystal structures of the
complexes 1 and 2 are stabilized through weak intramolecular
N–Hꢁ ꢁ ꢁO and N–Hꢁ ꢁ ꢁS interactions formed between hydrazinic
hydrogen and carbonyl oxygen/ thioamide sulfur producing

104
A. Singh et al. / Polyhedron 73 (2014) 98–109
Fig. 6. N–Hꢁ ꢁ ꢁO, C–Hꢁ ꢁ ꢁS and C–Hꢁ ꢁ ꢁO hydrogen bonds forming a sheet like structure in complex 2.
Fig. 7. ORTEP diagram of [Zn(pmt)2(o-phen)] (2) at 30% ellipsoids probability level. Hydrogen atoms are omitted for clarity.
supramolecular architecture [Figs. 6 and 8]. Complexes 1 and 2 are
further stabilized by intermolecular C–Hꢁ ꢁ ꢁS interactions occurring
between thioamide sulfur and hydrogens of o-phen ring (See
Fig. 10).
performed with GAUSSIAN 03 and GAUSS VIEW 4.1 [36] program
packages. The structure optimization of 4-phenyl(2-methoxyben-
zoyl)-3-thiosemicarbazide have been done using DFT method with
functional B3LYP and basis set 6-311G(d,p) whereas the geometry
optimization for the Mn(II) and Zn(II) complexes have been done
using basis sets Lanl2DZ [37,38] which is most popular and serves
the purpose of including the pseudopotential of the core electrons
of the metal ions. The input geometry of the complexes for the DFT
calculations was generated from single crystal X-ray data. The opti-
mized energy of Hpmt and its complexes 1 and 2 were ꢀ905.290
3.5. DFT calculations of ligand Hpmt and its Mn(II) and Zn(II)
complexes
All calculations for 4-phenyl(2-methoxybenzoyl)-3-thiosemi-
carbazide as well as its complexes with Mn(II) and Zn(II) have been

A. Singh et al. / Polyhedron 73 (2014) 98–109
105
Table 1
(Hpmt), ꢀ2484.971 (Mn) and ꢀ2446.640 (Zn) a.u respectively. The
deviation in the geometrical parameters are due to the fact that the
DFT calculations are done for an isolated molecule in gaseous
phase while the X-ray crystallographic data were obtained from
crystal lattice of complex molecules and shown in Tables 2–4.
The optimized geometries of Hpmt and the complexes along with
the atomic labeling scheme are shown in Fig. 2a and Fig. 9. From
Mullikan charge distribution on atoms of Hpmt and its complexes
(Figs. 3a–c), we observed that the charges on the ligand redistrib-
uted, as a result of complex formation. The charge on the carbonyl
oxygen which is bonded to metal has lower value {ꢀ0.379 [ligand],
ꢀ0.458 [Mn(II)] and ꢀ0.494 [Zn(II)]} whereas the charge on nitro-
gen which is bonded to metal has higher value{ꢀ0.278 [ligand],
ꢀ0.227 [Mn(II)] and ꢀ0.212 [Zn(II)]}. The magnitude of the charges
on carbon atoms was found to be either positive or negative.
Crystallographic data for complexes 1 and 2.
Parameters
1
2
Empirical formula
Formula weight
Crystal system
Space group
T (K)
C
42H36MnN8O4S2
C42H36ZnN8O4S2
846.32
monoclinic
P2/n
835.87
monoclinic
P2/n
293(2)
293(2)
k, Mo K
a (Å)
b (Å)
c (Å)
b (°)
a
(Å)
0.71073
20.5608(10)
10.3699(4)
21.1878(10)
116.993(6)
4025.4(3)
4
1.379
0.485
1732
0.71073
20.2813(18)
10.3655(7)
21.1656(17)
116.924(10)
3967.3(5)
4
1.417
0.778
2080
V (Å3)
Z
qcalc (g/cm3)
l
(mmꢀ1
)
F(000)
Crystal size (mm3)
0.29 ꢂ 0.27 ꢂ 0.25 0.28 ꢂ 0.27 ꢂ 0.25
3.6. Molecular electrostatic potential and contour maps
h Range for data collections (°)
Index ranges
3.32–28.99
ꢀ24 6 h 6 28,
ꢀ14 6 k 6 11,
ꢀ28 6 l 6 28
10762
3.03–29.21
ꢀ25 6 h 6 18,
ꢀ13 6 k 6 11,
ꢀ25 6 l 6 26
9117
To predict reactive sites for electrophilic and nucleophilic pro-
cesses for the Hpmt, electrostatic surface potentials were obtained
at the B3LYP/6-311G(d,p) optimized geometry. The MEP mapped
surface of the Hpmt and its complexes were calculated by DFT/
B3LYP/6-311G(d,p){C,H,N,O,S}/Lanl2DZ method at the 0.02 iso-
values and 0.004 density values . The red color scheme of MEP is
the negative electrostatic potentials. The red region show atoms
with lone pairs; the intensity of the color is proportional to the
absolute value of the potential energy. The positive electrostatic
potentials are shown in blue color region which characterize the
C–H bonds. The yellow/green areas cover parts of the molecule
where electrostatic potentials are close to zero (C–C, C–N and
C@S bonds). The MEP mapped surfaces are shown in Figs. 2b and
9. The different values of the electrostatic potential at the surface
are represented by different colors. Potential increases in the order
red < orange < yellow < green < blue. The color code of these maps
is in the range of ꢀ0.069 to +0.069 a.u. for Hpmt, ꢀ0.061 to
+0.061 a.u. for [Mn(pmt)2(o-phen)] and ꢀ0.104 to +0.104 a.u. for
[Zn(pmt)2(o-phen)], where blue and red colors indicate the stron-
gest attraction and repulsion, respectively. The negative red re-
gions of MEP are related to electrophilic reactivity and the
positive (blue) ones to nucleophilic reactivity. Negative (red) re-
gions in the Hpmt were found around the carbonyl oxygen and po-
sitive regions (blue) are around H of hydrazinic nitrogens. Thus, it
would be predicted that an electrophile would preferentially attack
No. of reflections collected
No. of independent reflections
(Rint
6191
6156
)
No. of data/restrains/parameters
10762/0/515
0.982
0.0469, 0.0941
0.0849, 0.1134
0.291, ꢀ0.414
9117/0/515
0.970
0.0453, 0.1056
0.0810, 0.1378
0.276, ꢀ0.386
Goodness-of-fit (GOF) on F2
R1a, wR2 [(I > 2
r
(I)]
b
R1a, wR2 (all data)
b
Largest difference in peak/hole
(e Åꢀ3
)
a
R1
R2 = [
=
R
||Fo| ꢀ |Fc||
R|Fo|.
b
R
w (|F2o| ꢀ |F2c|)2/
R .
w|F2o|2]1/2
Table 2
Interatomic distances (Å) and angles (°) for Hpmt.
Bond length (Å) Bond angles (°)
(Exp.)*
(Cal.)
(Exp.)*
(Cal.)
S(1)–C(7)
N(1)–C(8)
C(7)–N(3)
N(2)–C(7)
O(1)–C(8)
N(1)–N(2)
1.667(2)
1.329(3)
1.350(3)
1.344(3)
1.238()
1.738
1.371
1.383
1.371
1.275
1.391
C(8)–N(1)–N(2)
C(7)–N(2)–N(1)
O(1)–C(8)–N(1)
N(2)–C(7)–S(1)
C(9)–C(8)–O(1)
120.2(2)
120.8(2)
119.9(2)
121.5(2)
122.1(2)
116.81
122.64
119.27
120.74
122.66
1.365(3)
⁄
Experimental data on bond length and bond angle of Hpmt given in Table 2 have
been obtained from our own sample.
Table 3
Interatomic distances (Å) and angles (°) for [Mn(pmt)2(o-phen)] (1).
Mn1
Mn2
(Cal.)
Bond lengths (Exp.)
S(1)–C(8)
1.690(2)
1.393(2)
2.219(2)
1.263(3)
1.334(3)
1.323(3)
2.155(15)
2.288(2)
S(2)–C(28)
N(6)–N(5)
1.695(2)
1.388(2)
2.226(19)
1.266(3)
1.342(3)
1.314(3)
2.169(15)
2.272(2)
1.764
1.403
2.062
1.318
1.378
1.335
2.022
2.018
N(2)–N(1)
N(2)–Mn(1)
C(7)–O(1)
N(2)–C(8)
N(1)–C(7)
Mn(1)–O(1)
Mn(1)–N(4)
N(6)–Mn(2)
C(27)–O(3)
N(6)–C(28)
N(5)–C(29)
Mn(2)–O(3)
Mn(2)–N(8)
Bond angles (Exp.)
N(1)–N(2)–Mn(1)
O(1)–Mn(1)–O(1)
O(1)–Mn(1)–N(2)
O(1)–Mn(1)–N(2)
N(2)–Mn(1)–N(2)
O(1)–Mn(1)–N(4)
N(2)–Mn(1)–N(4)
N(4)–Mn(1)–N(4)
N(2)–Mn(1)–N(4)
109.25(13)
160.98(10)
74.12(6)
N(5)–N(6)–Mn(2)
O(3)–Mn(2)–O(3)
O(3)–Mn(2)–N(6)
O(3)–Mn(2)–N(6)
N(6)–Mn(2)–N(6)
O(3)–Mn(2)–N(8)
N(6)–Mn(2)–N(8)
N(8)–Mn(2)–N(8)
N(6)–Mn(2)–N(8)
109.35(13)
155.83(9)
74.27(6)
91.35(6)
107.46(10)
99.27(6)
90.41(7)
72.81(10)
160.91(7)
109.08
166.62
80.10
80.10
96.63
93.06
92.01
81.09
167.25
94.81(7)
109.82(11)
101.56(7)
89.02(7)
72.46(10)
160.83(7)

106
A. Singh et al. / Polyhedron 73 (2014) 98–109
Table 4
from carbonyl side no such crowd is observed (shown by arrow
Interatomic distances (Å) and angles (°) for [Zn(pmt)2(o-phen)] (2).
3). Hence, the positive metal ions preferably bind through the car-
bonyl oxygen and hydrazinic nitrogen sides so that the negative
potential shares with positive metal ion.
Zn1
Zn2
(Cal.)
Bond lengths (Exp.)
Zn(1)–O(2)
Zn(1)–N(2)
Zn(1)–N(4)
S(1)–C(9)
O(2)–C(8)
N(1)–C(8)
N(1)–N(2)
N(2)–C(9)
2.121(19)
2.143(2)
2.183(3)
1.695(3)
1.270(4)
1.318(4)
1.385(3)
1.340(4)
Zn(2)–O(4)
Zn(2)–N(6)
Zn(2)–N(8)
S(2)–C(30)
O(4)–C(29)
N(5)–C(29)
N(5)–N(6)
N(6)–C(30)
2.100(2)
2.130(3)
2.216(3)
1.699(3)
1.269(4)
1.318(4)
1.396(3)
1.329(4)
2.115
2.192
2.379
1.767
1.312
1.340
1.399
1.374
3.7. Frontier molecular orbital (FMO) analysis
The HOMO energy characterizes the ability of electron dona-
tion, the LUMO characterizes the ability of electron acceptance
and the gap between HOMO and LUMO characterizes the molecu-
lar chemical stability [39]. The HOMO–LUMO energy and the en-
Bond angles (Exp.)
O(2)–Zn(1)–O(2)
O(2)–Zn(1)–N(2) 77.18(8)
162.94(12) O(4)–Zn(2)–O(4)
O(4)–Zn(2)–N(6)
N(2)–Zn(1)–N(2) 103.39(14) N(6)–Zn(2)–N(6)
168.70(13) 168.76
77.38(9) 76.73
106.66(14) 105.34
97.22(9) 91.91
163.47(10) 157.37
ergy gap (DE) for Hpmt and complexes have been calculated at
DFT/B3LYP/6–311G(d,p) level. 3D plots of the HOMO and LUMO
for Hpmt and complexes 1 and 2 are shown in Fig. 4 and 11,
respectively. It can be seen that the HOMO orbital is located mainly
at the HNCS moiety and phenyl ring of the Hpmt as a result of their
electron withdrawing effect on the OCH3 group, which in turn
causes an increase in the LUMO electronic density as located on
methoxy phenyl ring. Methoxy phenyl ring makes very little con-
tribution to electronic density of HOMO, whereas in LUMO the
phenyl ring does not make contribution to form frontier molecular
orbitals. The values of the energy separation between the HOMO
and LUMO are 4.293, 2.426 and 2.205 eV for Hpmt and complexes
1 and 2, respectively. The small HOMO–LUMO energy gap means
low excitation energy for the complexes, a good stability and a
low chemical hardness for the complex. The electronic transition
from the ground state to the excited state due to a transfer of elec-
O(2)–Zn(1)–N(4) 96.18(8)
N(2)–Zn(1)–N(4) 90.97(10)
N(2)–Zn(1)–N(4) 164.28(10) N(6)–Zn(2)–N(8)
O(2)–Zn(1)–N(4) 97.28(9)
N(4)–Zn(1)–N(4) 75.60(13)
N(1)–N(2)–Zn(1) 108.32(17) N(5)–N(6)–Zn(2)
O(4)–Zn(2)–N(8)
N(6)–Zn(2)–N(8)
89.33(10)
91.75(9)
75.11(13)
88.14
91.91
73.70
O(4)–Zn(2)–N(8)
N(8)–Zn(2)–N(8)
108.41(18) 108.42
C(8)–O(2)–Zn(1) 112.83(18) C(29)–O(4)–Zn(2) 113.65(19) 114.24
to the ligand (Hpmt) at the O and N positions as indicated by arrow
1 (Fig. 2b). According to the calculated results, the MEP map shows
that the negative potential sites are on electronegative oxygen
atom as well as the positive potential sites are around the hydro-
gen atoms (more at hydrazinic moiety). These sites give informa-
tion about the region from where the compound can have
noncovalent interactions.
trons from the HOMO to LUMO level is mainly via
The chemical hardness of a molecule is defined by the formula [39]
p
ꢁ ꢁ ꢁ
p transition.
The contour maps are also calculated at same level of calcula-
tions of the MEP mapped surface of the Hpmt. The contour map
of electrostatic potential is shown in Fig. 2c also confirms the dif-
ferent negative and positive potential sides of the Hpmt is in accor-
dance with the molecular electrostatic potential. The red lines are
around carbonyl oxygen, thione sulfur and methoxy oxygen side.
But the attack of electrophile from thione sulfur and methoxy oxy-
gen side is restricted due to crowd (shown by arrow 2) whereas
g
¼ ꢀEHOMO þ ELUMO=2
where EHOMO and ELUMO are the energies of the HOMO and LUMO
molecular orbitals. The value of for Hpmt and complexes 1 and
2 are 2.146, 1.213 and 1.102 eV, respectively. The above result is
supported by the presence of UV–Vis bands at 280 and 310 nm
for complex 1 and at 325 and 350 nm for complex 2 which indicates
that complex 2 is softer than complex 1.
g
Fig. 8. N–Hꢁ ꢁ ꢁO, C–Hꢁ ꢁ ꢁO and C–Hꢁ ꢁ ꢁS interactions forming a linear structure in complex 1.

A. Singh et al. / Polyhedron 73 (2014) 98–109
107
Fig. 9. Optimized structures of complexes 1 and 2.
Fig. 10. MEP map of complexes 1 and 2.

108
A. Singh et al. / Polyhedron 73 (2014) 98–109
Fig. 11. FMO diagrams of complexes 1 and 2.
Cambridge CB2 IEZ, UK; fax: (+44)1223-336-033; or e-mail: depos-
4. Conclusion
it@ccdc. cam. ac. uk.
This paper reports the syntheses, spectral and crystal structure
investigations of two new isostructural octahedral complexes
[Mn(pmt)2(o-phen)] (1) and [Zn(pmt)2(o-phen)] (2) derived from
4-phenyl(2-methoxybenzoyl)-3-thiosemicarbazide (Hpmt) con-
taining o-phen as coligand. TGA show that the complexes are sta-
ble up to 200 °C, indicating the absence of lattice water as well as
coordinated water and finally Mn(NCO)2 and Zn(NCSNH)2 are ob-
tained as the residue. The optimized energy of Hpmt and com-
plexes are ꢀ905.290 (Hpmt), ꢀ2484.971 {[Mn(pmt)2(o-phen)]}
and ꢀ2446.640 {[Zn(pmt)2(o-phen)]} a.u, respectively. MEP map
and contour plot of Hpmt show that the metal ions preferably bind
through the carbonyl oxygen and hydrazine nitrogen forming a
stable five membered chelate ring. The small HOMO–LUMO energy
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