Synthesis, spectroscopic characterization, and 3D molecular modeling of lead(II) complexes of unsymmetrical tetradentate Schiff-base ligands

Article abstract of DOI:10.1007/s11164-011-0319-6

Solid complexes of Pb(II) with unsymmetrical Schiff-base ligands (H ₂L) derived from 2-aminobenzophenone, thiosemicarbazide, semicarbazide, salicylaldehyde, 2-hydroxynaphthaldehyde, and o-hydroxyacetophenone have been synthesized and characterized by elemental analysis, conductance measurements, molecular weight measurement, and UV-Vis, FTIR, ¹H NMR, and ¹³C NMR spectroscopy. The spectral studies suggest the ligands behave as dibasic tetradentate ligands with ONNO/ONNS donor atom sequences toward the central metal ion. From the microanalytical data, the stoichiometry of the complexes was found to be 1:1 (metal:ligand). The physicochemical data suggest a tetracoordinated environment around the metal ion. Three-dimensional molecular modeling and analysis of bond lengths and bond angles have also been conducted for a representative compound, [PbL¹], to substantiate the proposed structures.

Full text of DOI:10.1007/s11164-011-0319-6

Res Chem Intermed (2011) 37:1087–1101
DOI 10.1007/s11164-011-0319-6
Synthesis, spectroscopic characterization,
and 3D molecular modeling of lead(II) complexes
of unsymmetrical tetradentate Schiff-base ligands
Har Lal Singh
Received: 22 February 2011 / Accepted: 27 April 2011 / Published online: 15 May 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Solid complexes of Pb(II) with unsymmetrical Schiff-base ligands (H2L)
derived from 2-aminobenzophenone, thiosemicarbazide, semicarbazide, salicylal-
dehyde, 2-hydroxynaphthaldehyde, and o-hydroxyacetophenone have been synthe-
sized and characterized by elemental analysis, conductance measurements,
molecular weight measurement, and UV–Vis, FTIR, 1H NMR, and 13C NMR
spectroscopy. The spectral studies suggest the ligands behave as dibasic tetradentate
ligands with ONNO/ONNS donor atom sequences toward the central metal ion.
From the microanalytical data, the stoichiometry of the complexes was found to be
1:1 (metal:ligand). The physicochemical data suggest a tetracoordinated environ-
ment around the metal ion. Three-dimensional molecular modeling and analysis of
bond lengths and bond angles have also been conducted for a representative com-
pound, [PbL1], to substantiate the proposed structures.
Keywords Unsymmetrical tetradentate Schiff base Á Pb(II) complexes Á
2-Aminobenzophenone Á Thiosemicarbazide Á Semicarbazide Á Aldehyde/ketone Á
Spectral studies
Introduction
The coordination chemistry of Schiff bases has been widely explored, though its use
in supramolecular coordination chemistry remains largely unexplored. The Schiff
base moiety is potentially ambidenate and can coordinate through nitrogen with
either oxygen or sulfur atoms. The vast literature on structural studies of Schiff-base
complexes reveals some interesting features of their coordination behavior [1–8].
H. L. Singh (&)
Department of Chemistry, Faculty of Engineering & Technology,
Mody Institute of Technology and Science, Lakshmangarh, Sikar, Rajasthan, India
e-mail: hlsingh9@rediffmail.com
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H. L. Singh
Thiosemicarbazones and semicarbazones are now well established as important
classes of sulfur and oxygen donor ligands, particularly for transition metal ions
[9–12]. This is because of the remarkable biological activity observed for these
compounds, which has since been shown to be related to their metal-complexing
ability. These compounds have a great variety of biological activity ranging from
antimicrobial, antineoplastic, antimalarial, antiviral, and antitumor [13–17].
Schiff bases with N2O2 donor atoms are well known to co-ordinate with a variety of
metal ions and have attracted much interest in recent years because of their rich co-
ordination chemistry [18–20]. Tetradentate Schiff bases are reported to have a variety
of biological, clinical, and analytical applications [21–24]. Many symmetrical
tetradentate Schiff bases of diamines with aldehydes and ketones have been prepared
and studied intensively. However, less attention has been focused on unsymmetrical
tetradentate Schiff bases derived from diamines with different aldehydes and ketones
[25–27].
For this reason, this paper reports the results of an investigation of unsymmetrical
Schiff-base complexes. Schiff bases (L1H2–L6H2) were obtained by means of the
condensation reaction among 2-aminobenzophenone, thiosemicarbazide, semicarb-
azide, salicylaldehyde, 2-hydroxynaphthaldehyde, and o-hydroxyacetophenone in
the hope they might provide us with valuable theoretical information for exploring
metal-based bacteriostatic and carcinostatic pharmaceuticals with high efficacy and
low toxicity. In this effort, we also introduced the azomethine (–C=N–) linkage in
the hope it would result in notable variety in the chemistry and other behavior of
such compounds. The synthesized compounds (L1H2–L6H2) were used as
tetradentate ligands toward divalent metal atom solely through the azomethine
nitrogen and phenolic oxygen, forming a stable chelate ring.
Experimental
Chemicals used in this work, viz, 2-aminobenzophenone, thiosemicarbazide, semi-
carbazide, salicylaldehyde, 2-hydroxynaphthaldehyde, o-hydroxyacetophenone, and
lead(II) acetate were of analytical grade. Solvents used were dried and purified by
standard methods and moisture was excluded from the glass apparatus by use of CaCl2
drying tubes. Melting points are determined in open capillaries and are uncorrected.
General procedure for synthesis of the ligands
The ligands were prepared by a reported method [28]. A typical procedure for
synthesis of Schiff bases is as follows. A 50-mL solution of 0.001 mol (0.197 g)
2-aminobenzophenone, 0.001 mol thiosemicarbazide (0.0911 g)/semicarbazide
(0.0751 g), and 0.001 mol salicylaldehyde (0.122 g)/2-hydroxynaphthaldehyde
(0.172 g)/o-hydroxyacetophenone (0.137 g), in absolute ethanol was heated under
reflux for approximately 4 h. The precipitate thus formed was cooled to room
temperature and collected by filtration, followed by recrystallization from ethanol
(Scheme 1).
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Synthesis, spectroscopic characterization and 3D molecular modeling
1089
Scheme 1 Synthesis of ligands
L1H2 is prepared by reacting 2-aminobenzophenone with salicylaldehyde and
semicarbazone (H2L1); colour, yellow; yield, 72%; mp, 162 °C (dec.) and elemental
analysis (%), calcd. for C21H18N4O2: C, 70.40; H, 5.06; N, 15.63; found: C: 70.52;
H, 5.02; N, 15.56; molecular weight: found, 343.63, calcd. 358.39. Infrared (KBr,
cm-1): m(C=N), 1655 (1648); m(OH/NH), 3300–3070; m(C=O), 1705; m(C–O) 1220;
m(C–N) 1352; m(N–N) 1040. UV–Vis (kmax, nm): 390, 214, 265. 1H NMR (DMSO-
d6, d ppm): 12.97(s, 1H, Ph-OH), 9.12 (s, 1H, –CH=N–), 8.09 (s, 1H, NH),
6.96–7.69 (m, 13H, aromatic), 4.67 (s, 2H, NH2); 13C NMR (DMSO, d ppm): 172.5
(–C=O), 167.9 (C–OH), 162.2 (158.6) (C=N), 164.1, 137.2, 128.4, 128.1, 121.8,
119.9 (aromatic carbons).
L2H2 is prepared by reacting 2-aminobenzophenone with o-hydroxyacetophe-
none and semicarbazone; colour, brownish yellow; yield, 68%; mp, 180–182 °C
(d) and elemental analysis (%), calcd. for C22H20N4O2: C, 70.95; H, 5.41; N, 15.04;
found: C: 70.84; H, 5.47; N, 14.93; molecular weight: found, 381.58, calcd. 372.43.
Infrared (KBr, cm-1): m(C=N), 1660 (1658); m(OH/NH), 3300–3070; m(C=O),1710;
1
m(C–O) 1220; m(C–N) 1355; m(N–N) 1037. UV–Vis (kmax, nm): 390, 214, 265. H
NMR (DMSO-d6, d ppm): 12.94 (s, 1H, Ph-OH), 8.10 (s, 1H, NH), 6.90–7.65
(m, 13H, aromatic), 4.45 (s, 2H, NH2), 2.18 (s, 3H, –C(CH3)=N–); 13C NMR
(DMSO, d ppm): 172.5 (–C=O), 168.5 (C–OH), 162.2 (158.6) (C=N), 164.1, 137.2,
128.4, 121.8, 128.1, 119.9 (aromatic carbons).
123

1090
H. L. Singh
L3H2 is prepared by reacting 2-aminobenzophenone with salicylaldehyde and
thiosemicarbazone; colour, brownish yellow; yield, 75%; and elemental analysis
(%), calcd. for C21H18N4OS: C, 67.36; H, 4.85; N, 14.96; S, 8.56; found: C: 67.26;
H, 4.87; N, 14.90; S, 8.60; molecular weight: found, 382.88, calcd. 374.45. Infrared
(KBr, cm-1): m(C=N), 1650 (1648); m(OH/NH), 3300–3070; m(C=S), 1325; m(C–O)
1218; m(C–N) 1352; m(C–) 860; m(N–N) 1034. UV–Vis (kmax, nm): 390, 214, 265.
1H NMR (DMSO-d6, d ppm): 12.40 (s, 1H, Ph-OH), 9.09 (s, 1H, –CH=N–), 8.02
(s, 1H, NH), 6.95–7.55 (m, 13H, aromatic), 4.50 (s, 2H, NH2); 13C NMR (DMSO, d
ppm): 172.5 (–C=O), 169.8 (C–OH), 162.2 (158.6) (C=N), 164.1, 137.2, 128.4,
128.1, 121.8, 119.9 (aromatic carbons).
L4H2 is prepared by reacting 2-aminobenzophenone with o-hydroxyacetophe-
none and thiosemicarbazide; colour, brown; yield, 77%; and elemental analysis (%),
calcd. for C22H20N4OS: C, 68.02; H, 5.12; N, 14.42; S, 8.25; found: C: 67.84; H,
5.10; N, 14.35; S, 8.30; molecular weight: found, 397.65, calcd. 388.49. Infrared
(KBr, cm-1): m(C=N), 1660 (1656); m(OH/NH), 3300–3070; m(C=S), 1320; m(C–O)
1
1225; m(C–S) 840; m(N–N) 1032; UV–Vis (kmax, nm): 390, 214, 265. H NMR
(DMSO-d6, d ppm): 12.18 (s, 1H, Ph-OH), 8.15 (s, 1H, NH), 6.92–7.62 (m, 13H,
aromatic), 4.45 (s, 2H, NH2), 2.15 (s, 3H, –CH=N–); 13C NMR (DMSO, d ppm):
172.5 (–C=O), 167.8 (C–OH), 162.2 (158.6) (C=N), 164.1, 137.2, 128.4, 128.1,
121.8, 119.9 (aromatic carbons);
L5H2 is prepared by reacting 2-aminobenzophenone with 2-hydroxynaphthalde-
hyde and semicarbazone; colour, orange; yield, 78%; mp, 204 °C (d) and elemental
analysis (%), calcd. for C25H20N4O2: C, 73.51; H, 4.94; N, 13.72; found: C: 73.36;
H, 4.90; N, 13.76; molecular weight: found, 401.25, calcd. 408.46. Infrared (KBr,
cm-1): m(C=N), 1658 (1652); m(OH/NH), 3300–3070; m(C=O), 1702; m(C–O) 1222;
1
m(C–N) 1350; m(m–m) 1035. UV–Vis (kmax, nm): 390, 214, 265. H NMR (DMSO-
d6, d ppm): 13.12 (s, 1H, Ph-OH), 9.86 (s, 1H, –CH=N–), 8.12 (s, 1H, NH),
6.78–7.92 (m, 15H, aromatic), 4.38 (s, 2H, NH2); 13C NMR (DMSO, d ppm): 172.5
(–C=O), 170.1 (C–OH), 162.2 (158.6) (C=N), 164.1, 137.2, 128.4, 128.1, 121.8,
119.9 (aromatic carbons).
L6H2 is prepared by reacting 2-aminobenzophenone with 2-hydroxynaphthalde-
hyde and thiosemicarbazide; colour, dark brown; yield, 70%; and elemental analysis
(%), calcd. for C25H20N4OS: C, 70.73; H, 4.75; N, 13.20; S, 7.55; found: C: 70.65;
H, 4.83; N, 13.06; S, 7.60; molecular weight: found, 415.21, calcd. 424.52. Infrared
(KBr, cm-1): m(C=N), 1655 (1650); m(OH/NH), 3300–3070; m(C=S), 1322; m(C–O)
1220; m(C–N) 1350; m(C–S) 835; m(N–N) 1038; UV–Vis (kmax, nm): 390, 214, 265;
1H NMR (DMSO-d6, d ppm): 11.90 (s, 1H, Ph-OH), 9.95 (s, 1H, –CH=N–), 8.06
(s, 1H, NH), 7.02–7.92 (m, 15H, aromatic), 4.60 (s, 2H, NH2); 13C NMR (DMSO, d
ppm): 172.5 (–C=O), 168.4 (C–OH), 162.2 (158.6) (C=N), 164.1, 137.2, 128.4,
128.1, 121.8, 119.9 (aromatic carbons).
Synthesis of lead(II) complexes
The complexes were prepared under anhydrous conditions by slow addition of a dry,
hot methanol solution of lead(II) acetate in 1:1 molar ratio to a solution of the Schiff
base in hot absolute methanol. The mixture was heated under reflux with constant
123

Synthesis, spectroscopic characterization and 3D molecular modeling
1091
stirring for 30 min, giving a clear solution; heating under reflux was then continued
for 5–7 h. The acetic acid liberated in the reaction was removed azeotropically with
solvent. Excess solvent was removed under reduced pressure and the compound was
dried under vacuum at 45 5 °C after repeated washing with dry cyclohexane. The
compounds were purified by recrystallization from methanol. The purity of the
compounds was checked by TLC using silica gel G as adsorbent.
Analytical methods and spectral measurements
Lead was determined gravimetrically as lead sulfate. Nitrogen and sulfur were
determined by the Kjeldahl and Messenger methods, respectively. Molar conduc-
tance measurements were made in anhydrous dimethylformamide at 45 5 °C
using a Systronics model 305 conductivity bridge. Molecular weight determinations
were carried out by the Rast camphor method. Electronic spectra were recorded in
DMSO on a Thermo Scientific UV1 spectrophotometer. Infrared spectra in the
region 4,000–400 cm-1 were recorded on a Perkin–Elmer RX1 FTIR spectrometer.
1H NMR spectra were recorded on a Jeol (model FX 90Q) using DMSO-d6 as
solvent at 89.55 MHz. 13C NMR spectra were recorded on a 90 MHz Jeol (FX 90Q)
NMR spectrometer using dry DMSO as solvent at 84.25 MHz. TMS was used as
1
internal reference for H NMR and 13C NMR.
Three-dimensional molecular modeling studies
Three-dimensional molecular modeling was performed for a representative com-
pound by use of CS Chem 3D Ultra Molecular Modeling and Analysis software [29],
interactive graphics software that enables rapid structure building and geometry
optimization with minimum energy and molecular display.
Results and discussion
New lead–Schiff-base complexes were synthesized by reaction of lead(II) acetate
with the ligands in 1:1 molar ratios using anhydrous methanol as solvent. These
reactions proceed with the liberation of acetic acid, which was removed azeotrop-
ically, as indicated below (Scheme 2).
The reactions were found to be quite facile and were complete after heating under
reflux for 5–7 h. Physical characteristics, and micro analytical and molar conduc-
tance data for the metal–ligand complexes are given in Table 1. The analytical data
for the complexes are indicative of a 1:1 molar ratio (metal:ligand) and correspond
well with the general formula [Pb(ONNX)]. All the complexes are intensely coloured
Scheme 2 Representative equation illustrating the formation of Pb(II) complexes
123

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H. L. Singh
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Synthesis, spectroscopic characterization and 3D molecular modeling
1093
Table 2 Important IR spectral data (cm-1) of Schiff bases and their corresponding lead(II) complexes
Compound m(OH) m(C=N–) m(C–N) m(C=O/C=S) m(C–O/C–S) m(N–N) m(Pb / N) m(Pb–O)
L1H2
PbL1
L2H2
PbL2
L3H2
PbL3
L4H2
PbL4
L5H2
PbL5
L6H2
PbL6
3300–3070 1655
1625
3300–3070 1660
1635
3300–3070 1650
1622
3300–3070 1660
1632
3300–3070 1658
1630
3300–3070 1655
1626
1352
1385
1355
1386
1352
1380
1354
1385
1350
1380
1350
1382
1705
1685
1710
1696
1325
1290
1320
1292
1702
1688
1322
1285
1220
1040
1072
1037
1070
1034
1066
1032
1061
1035
1070
1038
1065
–
–
–
1252
535
–
466
–
1220
–
1254
538
–
470
–
1218/860
1248/780
1225/840
1252/790
1222
–
530
–
462
–
–
540
–
460
–
–
1256
540
–
460
–
1220/835
1245/790
–
542
455
solids. They are partly soluble in common organic solvents and only soluble in DMF
and DMSO. The chelates were dissolved in DMF and the molar conductance of
10-3 M solution at 45 °C was measured. The molar conductance valves of the
complexes fall in the range 18–25 X-1 cm2 mol-1 indicating that these chelates are
non-electrolytes. The elemental analysis results agree with the formulae proposed for
the ligands and also confirmed the Pb(ONNX) (Fig. 2) composition of the Pb(II)
chelates.
Infrared spectra
The IR spectra of the free ligands (Table 2) show characteristic bands at 3070–3300,
1703, 1657 (1650), 1354 and 1219 cm-1 assignable to intramolecular hydrogen
bonded hydroxyl m(OH), carbonyl m(C=O), azomethine m(C=N), aryl azomethine
m(C–N), and phenolic m(C–O) stretching modes [30, 31], respectively, (Table 2). The
absence of a weak broad band in the 3070–3300 cm-1 region, noted in the spectra of
the metal complexes, indicates deprotonation of the intramolecular hydrogen bonded
OH group on complexation and subsequent coordination of phenolic oxygen to the
metal ion. This is further supported by the upward shift in the phenolic m(C–O) [32]
to the extent of 25–40 cm-1. On complexation, the m(C=N) band is shifted to lower
wave number relative to the free ligand, indicating that the nitrogen of the azo-
methine group is coordinated to the metal ion, which may be attributed to lowering of
the m(C=N) bond order as a result of Pb / N bond formation [33]. This is supported
by upward shift in m(C–N) to the extent of 10–30 cm-1. The FTIR spectra of metal
chelates contained new bands in the 530–542 cm-1 range, assigned to (Pb / N),
and in the 455–470 cm-1 range, assigned to (Pb–O) [34, 35].
The disappearance of a band due to m(C=O) and appearance of new bands at
1550–1570 and 1365–1370 cm-1 assignable to m(NCO-) [36] are indicative of
deprotonation of the NH proton and bonding through the imidolate oxygen. The IR
123

1094
H. L. Singh
spectra of the thiosemicarbazones do not show any absorption band at
*2570 cm-1, indicating that in the solid state the thione form is present. Further,
for the ligands a strong band at *1322 cm-1 is indicative of m(C=S). The lowering
of this band in the form of m(C–S) can be attributed to coordination of the ligands
through the thiolo sulfur atom. For the ligands, the bands observed at 3450–
3370 cm-1 are because of the symmetric and asymmetric modes of the amino
(NH2) group. These bands are observed at almost the same position in the spectra of
the lead complexes suggesting the non-involvement of this amino group in
chelation.
Electronic spectra
In the electronic spectra of the ligands a band at 220 nm is observed which may be
assigned to the lB band of the phenyl ring. This shifts to longer wavelength on
complexation and is observed at 232 nm in the complexes. Also, the ligands’
chromophore[C=N, which is observed at 280 nm, shifts to higher wavelength and
is observed at 295 nm in the complexes. In the spectra of ligands, a band observed at
345 nm, because of the secondary band of benzene, which is red shifted because of
the presence of [C=N–. However, this appears at 372 nm in the complexes,
possibly because of polarization of the C=N bond by the metal–ligand electron
interaction. Three sharp bands are observed in the region 240–262 nm and are
assigned as charge-transfer bands, indicating the formation of r bond and (dp–pp)
bonds between the p-orbitals of sulfur and the vacant d orbitals of the metal atom.
Complexes are then expected to show long-wavelength metal to ligand charge
transfer (MLCT) bands if the ligands provide empty orbitals at low energies.
Accordingly, compounds are coloured owing to the presence of such MLCT bands
in the visible region.
1H NMR spectra
All the protons were found in their expected regions. The conclusions drawn from
these studies lend further support to the mode of bonding discussed in their IR
spectra. In the spectra of lead(II) complexes, coordination of the ligands via
azomethine nitrogen, phenolic and ketonic oxygen, and thiolic sulfur was
established by the downfield shifting of these signals in the lead(II) complexes,
because of the increased conjugation and coordination [37]. The number of protons
calculated from the integration curves and those obtained from the values of the
expected CHN analyses agree with each other. It was observed that DMSO had no
coordinating effect either on the spectra of the ligands or on its metal complexes. In
the proton magnetic resonance spectra of the ligands, sharp signals at d 2.18 ppm
and d 9.09–9.95 ppm are observed, because of –C(CH3)=N– and –CH=N–,
respectively. These move downfield (d 0.10 ppm) in the complexes in comparison
with the original position in the ligands, because of coordination of azomethine
nitrogen with the metal atom. This is probably because of the donation of a lone pair
of electrons by the nitrogen to the central metal atom resulting in the formation of a
coordinate linkage (Pb / N). The ligands also give OH proton signals at d
123

Synthesis, spectroscopic characterization and 3D molecular modeling
1095
12.50 0.50 ppm (s) which is absent from the spectra of the corresponding lead
complexes, showing, thereby, chelation of the ligand moiety through the deproto-
nated phenolic oxygen. The broad signal exhibited by the ligand because of the
NH proton at d 8.08 0.07 ppm disappears in the lead complexes, indicating
coordination of the nitrogen by covalent bond formation by the sulfur/oxygen with
the metal because of tautomerisation of the ligand in the enol–keto form. The
ligands give a complex multiplet signal in the region d 6.78–7.92 ppm (m) for the
aromatic protons and these remain at almost the same position in the spectra of
the metal complexes. The appearance of signals from NH2 protons at the same
positions in the ligand and its complexes show the non-involvement of this group in
coordination.
13C NMR spectra
13C NMR spectra of the ligands and their corresponding lead complexes were
recorded in dry DMSO. The signals from the carbon atoms attached to the ketonic/
thiolic and azomethine groups in the ligands appear at *d 167.6 ppm and *d 160.1
(158.9) ppm, respectively. However, in the spectra of the corresponding lead
complexes, these signals appear at d 161.5 ppm (because of the ketone/thiol group)
and d 152.4 (149.7) ppm (because of the azomethine groups), respectively. The
substantial shifts in the positions of these signals clearly indicate the involvement of
these functional groups in bond formation with the metal. Although it is also
possible that the shifting of the azomethine carbon signal is because of a change in
hybridization of the nitrogen attached to the ketone/thiol group, in the light of IR,
1
UV, and H NMR spectral studies it seems more plausible that the shifting of the
signals for these carbons is because of the involvement of ketonic oxygen/sulfur and
azomethine nitrogen in bonding.
Thus, on the basis of above discussion, it is evident that the ligands coordinate
through the phenolic/ketonic oxygen, thiolic sulfur, and azomethine nitrogen to the
lead atom and thus the ligand behaves as a bifunctional tetradentate species.
The Pb(II) complexes can possibly be represented by the structure in Fig. 1, with the
central lead atom being in the tetra-coordinate environment. The structures
proposed for all the Pb(II) complexes are shown in Fig. 1.
Fig. 1 Structures of the Pb(II) complexes
123

1096
H. L. Singh
Fig. 2 Three-dimensional
structure of the [PbL1]
complexes
3D molecular modeling and analysis
Because of the tetra-coordination of these complexes and taking into account of
the irregular tetrahedral geometry, 3D molecular modeling was performed for
compound [PbL1] (1), as representative compound, on the basis of the irregular
tetrahedral structure. Details of the bond lengths and bond angles as per the 3D
structure (Fig. 2) are given in Tables 3 and Table 4, respectively. For convenient
study of the different bond lengths and bond angles, the various atoms of the
compound in question are numbered in Arabic numerals. In all, 130 measurements
of the bond lengths (49 in numbers), plus the bond angles (81 in numbers) are
listed. Except for a few cases, optimum values of both the bond lengths and the
bond angles are given in the tables, with the actual values. The actual bond
lengths/bond angles given in Tables 3 and 4 are calculated values as a result of
energy optimization in CHEM 3D Ultra, and the optimum bond length/bond angle
values are the standard bond lengths/bond angles established by the builder unit of
CHEM 3D. Some values of standard bond lengths/bond angles are missing,
possibly because of limitations of the software; we have already noticed this when
modeling other systems. In most cases, the actual bond lengths and bond angles
are close to the optimum values, confirming the proposed structure of the
compound [Pb(II)L1].
Conclusion
Complexes L1–L6, derivatives of Schiff bases, have been successfully synthesized
and characterized. Elemental analysis C, H, N, and Pb results were in agreement
with predicted formulae. Results from infrared and NMR spectroscopy of the
ligands and complexes showed that coordination takes place via the oxygen atom
from the ketone group and the nitrogen atom from the azomethine groups. As a
result, in the solid and liquid states the lead(II) atoms are in a four coordinated
environment.
123

Synthesis, spectroscopic characterization and 3D molecular modeling
1097
Table 3 Bond lengths of the compound [PbL1]
˚
Actual (A)
˚
Optimum (A)
No.
Atoms
1
N(7)–Pb(27)
Pb(27)–O(28)
C(17)–O(28)
N(9)–Pb(27)
C(19)–H(40)
N(18)–H(39)
N(18)–H(38)
C(15)–H(37)
C(14)–H(36)
C(13)–H(35)
C(12)–H(34)
C(11)–H(33)
C(6)–H(32)
C(3)–H(31)
C(2)–H(30)
C(1)–H(29)
C(23)–H(42)
Pb(27)–O(26)
C(24)–C(25)
C(23)–C(24)
C(22)–C(23)
C(21)–O(26)
C(21)–C(22)
C(25)–C(20)
C(20)–C(21)
C(19)–C(20)
C(24)–H(43)
C(17)–N(18)
N(16)–C(17)
C(14)–C(15)
C(13)–C(14)
C(12)–C(13)
C(11)–C(12)
C(15)–C(10)
C(10)–C(11)
C(25)–H(44)
N(9)–N(16)
C(8)–C(10)
C(8)–N(9)
2.1460
2.1100
4.0620
2.1460
1.1000
1.0500
1.0500
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
2.1100
1.3370
1.5169
1.3370
2.7945
1.3370
1.3370
1.3370
1.3370
1.1000
1.2660
1.2600
1.3949
1.3948
1.3948
1.3949
1.3948
1.3948
1.1000
1.2480
1.3370
1.6579
1.1000
1.2600
1.2600
2
3
1.4210
4
5
1.1000
1.0500
1.0500
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
1.1000
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
1.4200
1.4200
1.4200
1.3550
1.4200
1.4200
1.4200
1.5030
1.1000
1.4620
1.2600
1.4200
1.4200
1.4200
1.4200
1.4200
1.4200
1.1000
1.4180
1.5030
1.2600
1.1000
1.2600
1.4560
C(22)–H(41)
N(7)–C(19)
C(5)–N(7)
123

1098
H. L. Singh
Table 3 continued
˚
Actual (A)
˚
Optimum (A)
No.
Atoms
43
44
45
46
47
48
49
C(5)–C(6)
C(4)–C(8)
C(4)–C(5)
C(3)–C(4)
C(2)–C(3)
C(6)–C(1)
C(1)–C(2)
1.3370
1.3370
1.3370
1.3370
1.3370
1.3370
1.5259
1.4200
1.5030
1.4200
1.4200
1.4200
1.4200
1.4200
Table 4 Bond angles of the compound [Pb(II)L1]
No.
Atoms
Actual (8)
Optimum (8)
1
Pb(27)–O(28)–C(17)
O(28)–Pb(27)–O(26)
O(28)–Pb(27)–N(9)
O(28)–Pb(27)–N(7)
O(26)–Pb(27)–N(9)
O(26)–Pb(27)–N(7)
N(9)–Pb(27)–N(7)
Pb(27)–O(26)–C(21)
H(44)–C(25)–C(24)
H(44)–C(25)–C(20)
C(24)–C(25)–C(20)
H(43)–C(24)–C(25)
H(43)–C(24)–C(23)
C(25)–C(24)–C(23)
H(42)–C(23)–C(24)
H(42)–C(23)–C(22)
C(24)–C(23)–C(22)
H(41)–C(22)–C(23)
H(41)–C(22)–C(21)
C(23)–C(22)–C(21)
O(26)–C(21)–C(22)
O(26)–C(21)–C(20)
C(22)–C(21)–C(20)
C(25)–C(20)–C(21)
C(25)–C(20)–C(19)
C(21)–C(20)–C(19)
H(40)–C(19)–C(20)
H(40)–C(19)–N(7)
C(20)–C(19)–N(7)
53.1730
114.6507
104.0000
109.5000
109.5000
109.5000
109.5000
60.5255
2
3
4
5
6
7
8
9
120.0000
120.0000
120.0000
122.9658
122.9658
114.0685
123.6612
123.6612
112.6776
120.0000
120.0000
120.0000
104.4290
135.5707
119.9992
119.9988
119.9988
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
124.3000
124.3000
120.0000
120.0000
120.0000
120.0000
120.0000
116.5000
123.5000
123

Synthesis, spectroscopic characterization and 3D molecular modeling
1099
Table 4 continued
No.
Atoms
Actual (8)
Optimum (8)
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
H(39)–N(18)–H(38)
H(39)–N(18)–C(17)
H(38)–N(18)–C(17)
O(28)–C(17)–N(18)
O(28)–C(17)–N(16)
N(18)–C(17)–N(16)
C(17)–N(16)–N(9)
H(37)–C(15)–C(14)
H(37)–C(15)-C(10)
C(14)–C(15)–C(10)
H(36)–C(14)–C(15)
H(36)–C(14)–C(13)
C(15)–C(14)–C(13)
H(35)–C(13)–C(14)
H(35)–C(13)–C(12)
C(14)–C(13)–C(12)
H(34)–C(12)–C(13)
H(34)–C(12)–C(11)
C(13)–C(12)–C(11)
H(33)–C(11)–C(12)
H(33)–C(11)–C(10)
C(12)–C(11)–C(10)
C(15)–C(10)–C(11)
C(15)–C(10)–C(8)
C(11)–C(10)–C(8)
Pb(27)–N(9)–N(16)
Pb(27)–N(9)–C(8)
N(16)–N(9)–C(8)
C(10)–C(8)–N(9)
C(10)–C(8)–C(4)
N(9)–C(8)–C(4)
120.0000
120.0000
120.0000
138.4324
83.1352
118.8000
122.0000
126.0000
107.5000
120.0000
120.0000
138.4324
104.0000
120.0002
120.0002
119.9996
120.0012
120.0012
119.9976
119.9991
119.9991
120.0018
119.9994
119.9994
120.0013
120.0015
120.0015
119.9969
120.0029
119.9986
119.9986
104.0000
80.0151
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
107.5000
108.9436
108.9436
142.1128
120.0000
120.0000
115.0000
120.0000
120.0000
120.0000
119.9988
120.0000
119.9988
119.9988
120.0000
120.0000
120.0000
Pb(27)–N(7)–C(19)
Pb(27)–N(7)–C(5)
C(19)–N(7)–C(5)
H(32)–C(6)–C(5)
H(32)–C(6)–C(1)
C(5)–C(6)–C(1)
120.0000
120.0000
N(7)–C(5)–C(6)
120.0000
120.0000
120.0000
120.0000
N(7)–C(5)–C(4)
C(6)–C(5)–C(4)
C(8)–C(4)–C(5)
123

1100
H. L. Singh
Table 4 continued
No.
Atoms
Actual (8)
Optimum (8)
71
72
73
74
75
76
77
78
79
80
81
C(8)–C(4)–C(3)
C(5)–C(4)–C(3)
H(31)–C(3)–C(4)
H(31)–C(3)–C(2)
C(4)–C(3)–C(2)
H(30)–C(2)–C(3)
H(30)–C(2)–C(1)
C(3)–C(2)–C(1)
H(29)–C(1)–C(6)
H(29)–C(1)–C(2)
C(6)–C(1)–C(2)
119.9988
120.0000
120.0000
120.0000
120.0000
124.0860
124.0860
111.8279
124.0855
124.0855
111.8290
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
120.0000
Acknowledgments The author is thankful to Professor P.K. Das, Dean, Faculty of Engineering and
Technology, Mody Institute of Technology and Science, Deemed University, Lakshmangarh, Sikar for
providing necessary facilities.
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