S. Chandrasekar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 136–146
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the range 2825–2870 cmꢁ1, lower in magnitude compared with
the value in CH3 compounds (2860–2935 cmꢁ1) whereas the asym-
metric stretching modes for the complex 2a lie in the same region
2924 and 2985 cmꢁ1. The asymmetric and symmetric stretching
vibrations of CH3 group have been identified in 3112, 3093, 3021,
3015 cmꢁ1. Methyl groups are generally referred as electron-do-
nating substituent in the aromatic ring systems. The observed
asymmetric and symmetric CH3 deformations vibrations for the
complex 2a are listed in the Table 3.
complexes, respectively. Similarly the Sn–Cl stretching vibrations
for the complexes 2a and 2b are observed at 378, 307 cmꢁ1 and
399, 366 cmꢁ1 in FT-Raman spectra, respectively.
CC vibrations
The ring C@C and C–C stretching vibrations, known as semicir-
cle stretching usually occur in the region 1625–1400 cmꢁ1. Hence
in the present study, the FT-IR bands identified at 1666, 1621,
1613 cmꢁ1 and the FT-Raman band at 1612 cmꢁ1 are assigned to
C–C stretching vibrations of the complex 2a. The bands ascribed
at 1679, 1653, 1639, 1623, 1592, 1542, 1518, 1508, 1482,
1346 cmꢁ1 in FT-IR spectrum and 1624, 1591, 1518, 1483,
1346 cmꢁ1 in FT-Raman have been designated to C-C stretching
modes for the complex 2b. The theoretically calculated C-C stretch-
ing modes for the complexes 2a and 2b are found at 1665, 1620,
1613, 1465 cmꢁ1 and 1680, 1652, 1640, 1625, 1592, 1540, 1519,
1483, 1345 cmꢁ1, respectively.
CH2 vibrations
For the assignments of CH2 group frequencies, basically six fun-
damentals can be associated with each CH2 group namely, CH2
symmetric stretch; CH2 asymmetric stretch; CH2 scissoring and
CH2 rocking, which belong to in-plane vibrations and two out-of-
plane vibrations, viz., CH2 wagging and CH2 twisting modes, which
are expected to be depolarized. The asymmetric CH2 stretching
vibrations are generally observed above 3000 cmꢁ1, while the sym-
metric stretch will appear between 3000 and 2900 cmꢁ1 [44,45]. In
the title complexes, the band at 2912, 2906 and 2936, 2928 cmꢁ1
in FT-IR spectra is assigned to CH2 asymmetric stretching modes
for the complexes 2a and 2b, respectively. The medium strong
band at 2790, 2735 cmꢁ1 and 2858, 2844 cmꢁ1 in FT-Raman are
attributed to CH2 symmetric stretching. Theoretically value at
2911, 2906, 2936, 2631 and 2793, 2735, 2856 and 2840 cmꢁ1 by
B3LYP/LanL2DZ method exactly correlate with the experimental
observations.
Aromatic CH2 compounds have a band of weak-to-medium
intensity of 1500–200 cmꢁ1 belong to CH2 bending vibrations
[42]. The CH2 group of the complex is capable of different bending
vibrations such as scissoring, wagging, rocking and twisting. These
vibrations give rise to variable intensity bands at lower wavenum-
ber region. In the present study, the prominent bands at 1584,
1573, 1578, 1555 cmꢁ1 in FT-IR spectrum 1583 cmꢁ1 in FT-Raman
spectrum are assigned to CH2 scissoring mode. In aromatic com-
plexes, the wagging modes are expected in the region 1200 –
1000 cmꢁ1 with a moderate to strong intensity. For the complexes
2a and 2b, the weak bands at 1253, 1218 cmꢁ1 in IR and 1254 cmꢁ1
in Raman and 1266, 1225 cmꢁ1 IR and 1267, 1221 cmꢁ1 in Raman
are assigned to CH2
CN vibrations
The identification of C-N vibration is a difficult task, since the
mixing of vibrations is possible in their region. In the present work,
the bands observed at 1466, 1378, 1347 cmꢁ1 in FT-IR spectrum
and 1417, 1379, 1346 cmꢁ1 in FT-Raman spectrum are assigned
to C-N stretching vibrations for the complex 2a. The C–N stretching
vibrations of the complex 2b are found at 1450, 1428, 1413,
1373 cmꢁ1 in FT-IR and 1449, 1419 cmꢁ1 in FT-Raman spectrum.
The theoretically calculated values of C–N stretching vibrations
also fall in the region 1468–1348 cmꢁ1 for 2a and 1451–
1374 cmꢁ1 for the complex 2b by B3LYP/LanL2DZ level of theory.
Conclusions
We have reported the synthesis of
a bis(p-methylben-
zyl)(dichloro)(1,10-phenanthroline)Sn(IV) and bis(p-chloroben-
zyl)(dichloro)(1,10-phenanthroline)Sn(IV) complexes. The tin
complexes having cis platin type structures are of importance in
designing the anti-cancer drugs. In our complexes, the similar type
of structures is confirmed as a result of the reaction. The spectral
and structural studies revealed the formation of complexes in
which the tin atom is hexa coordinated. Optimized geometry and
vibrational wavenumbers of 2a and 2b complexes were studied
with aid of density functional theory method with B3LYP/LanL2DZ
level basis set. The various modes of vibrations are assigned unam-
biguously using the results of PED output obtained from the nor-
mal coordinate analysis. The calculated wavenumbers are well
agreement with the experimental results. The HOMO–LUMO ener-
gy gap value suggests the possibility of intermolecular charge
transfer within the complexes.
C–Cl vibrations
The C–Cl stretching mode appears as mixed mode. In the lower
region, C–Cl stretching vibrations appear in the region 760–
505 cmꢁ1 and C–Cl deformation vibrations appear in the region
420–250 cmꢁ1. For simple chlorine compounds, C–Cl absorption
is in the region 750–700 cmꢁ1 [42]. From the above literature the
band observed at 753, 724 cmꢁ1 in FT-IR spectrum are assigned
to C–Cl stretching vibrations. The shift of lower frequency of 2b
is due to much greater electronegativity of Cl as compared to car-
bon atoms. Thus Cl atom acquires small positive charge and the
carbon atom acquires small negative charge. The inductive effect
of chlorine attracts electrons from C–Cl bond, which increases
the force constants and leads to an increase in the absorption
frequency.
Acknowledgements
The Authors are thankful to the IISc., Bangalore and IIT Chennai,
India for providing library and NMR instruments facilities usage in
time. The Institute of Physics, University of Neuchatel, Switzerland
is gratefully acknowledged for its service in solving structure solu-
tion of crystals.
Sn–C and Sn–Cl vibrations
Infrared-spectroscopy has provided valuable information on the
molecular geometry of organotin compounds. Particularly impor-
tant is the criterion established for determining the configuration
of SnC3 and SnC2 moieties in chlorotrimethyltin and
dichlorodimethyltin derivatives. Characteristic infrared absorp-
Appendix A. Supplementary data
Crystallographic data (excluding structure factors) for the struc-
tures 2a and 2b have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication nos. CCDC
752146 (2a) & CCDC 752147 (2b). Copies of the data can be
obtained free of charge on application to CCDS, 12 Union Road,
tions of some tin-ligand stretching vibrations are
m(Sn–C), 600–
470 cmꢁ1 and (Sn–Cl), 390–310 cmꢁ1 [46]. Hence, in the present
m
study, the Sn–C stretching vibrations are observed at 562,
488 cmꢁ1 and 562, 464 cmꢁ1 in FT-Raman spectra for 2a and 2b