Zinc(II) and mercury(II) complexes with Schiff bases: Syntheses, spectral, and structural characterization

Article abstract of DOI:10.1080/00958972.2012.699634

Schiff bases o-vanilidene-1-aminobenzene (HL¹) and o-vanilidene-2-methyl-1-aminobenzene (HL²) lead to the formation of mono-and bis-[(Cl)Zn(L¹)] (1), [(Cl)Zn(L²)] (2), [(Cl)Hg(L¹)] (3), [(Cl)Hg(L

Full text of DOI:10.1080/00958972.2012.699634

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Zinc(II) and mercury(II) complexes with
Schiff bases: syntheses, spectral, and
structural characterization
R.K. Dubey a , P. Baranwal a & A.K. Jha b
a Synthetic Inorganic and Metallo-organic Research Laboratory,
Department of Chemistry, University of Allahabad, Allahabad –
211 002, Uttar Pradesh, India
b Department of Chemistry, G.B. College Naugachia, T.M.
Bhagalpur University, Bhagalpur – 853204, Bihar, India
Available online: 06 Jun 2012
To cite this article: R.K. Dubey, P. Baranwal & A.K. Jha (2012): Zinc(II) and mercury(II) complexes
with Schiff bases: syntheses, spectral, and structural characterization, Journal of Coordination
Chemistry, 65:15, 2645-2656
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Journal of Coordination Chemistry
Vol. 65, No. 15, 10 August 2012, 2645–2656
Zinc(II) and mercury(II) complexes with Schiff bases: syntheses,
spectral, and structural characterization
R.K. DUBEY*y, P. BARANWALy and A.K. JHAz
ySynthetic Inorganic and Metallo-organic Research Laboratory, Department of Chemistry,
University of Allahabad, Allahabad – 211 002, Uttar Pradesh, India
zDepartment of Chemistry, G.B. College Naugachia, T.M. Bhagalpur University,
Bhagalpur – 853204, Bihar, India
(Received 9 August 2012; in final form 26 April 2012)
Schiff bases o-vanilidene-1-aminobenzene (HL1) and o-vanilidene-2-methyl-1-aminobenzene
(HL2) lead to the formation of mono- and bis-[(Cl)Zn(L1)] (1), [(Cl)Zn(L2)] (2), [(Cl)Hg(L1)] (3),
[(Cl)Hg(L2)] (4), [Zn(L1)2] (5), [Zn(L2)2] (6), [Hg(L1)2] (7), and [Hg(L2)2] (8) complexes by
reactions of zinc(II) and mercury(II) chlorides in different mole ratio(s). Complexes 1–8 have
been characterized by elemental analyses (Zn, Hg, C, H, Cl, and N), melting point and spectral
(IR, 1H-NMR), PXRD, molar conductivity measurement, and TGA. Conductivity measure-
ments suggest non-electrolytes. Structural compositions have been assigned by mass spectral
studies. Four-coordinate geometry may be assigned to these complexes tentatively. Structural
study reveals that in 1–4 two metal centers are held together by two bridged (ꢀ2-Cl)
chlorides, whereas 5–8 contain two bidentate Schiff-base ligands around one metal-producing
monomers.
Keywords: Synthesis; Schiff bases; Zn(II) and Hg(II) complexes; IR; NMR; FAB-MS;
TOF-MS; PXRD; TGA; Conductivity measurement
1. Introduction
Group 12 metal complexes of Schiff bases have interest [1] for the ease of synthesis,
versatility, and wide range of complexing ability [2]. They can be used as corrosion
inhibitors for metals and alloys and for potential antibacterial, antiviral, and antitumor
effects [3–5]. Metal complexes of biologically important ligands are sometimes more
effective than free ligand [3]. Schiff bases are potential anticancer drugs [6] and when
administered as their metal complexes, anticancer activity is enhanced in comparison to
free ligand [7]. Two new series of complexes of zinc(II) and mercury(II) with new Schiff
*Corresponding author. Email: rajalkoxy@yahoo.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.699634

2646
R.K. Dubey et al.
bases, HL1 and HL2, are of interest.
H3CO
OH
CH=N
X
HL1 : X =
HL2 : X =
H3C
Zinc is involved in a number of enzymatic functions, fulfilling both structural and
catalytic roles [8]. Mercury has been used as a constituent in bactericides, antiseptics,
skin ointment, and laxatives [9, 10]; toxicity of mercury and its compounds are well
known [11]. As part of our [12–14] interest in the synthesis and coordination chemistry
of group 12 metal complexes containing Schiff bases, we describe the synthesis and
characterization of new [(Cl)M(L)] and [M(L)2] complexes with HL1 (o-vanilidene-1-
aminobenzene) and HL2 (o-vanilidene-2-methyl-1-aminobenzene), where M ¼ Zn(II)
and Hg(II).
2. Experimental
All materials and solvents were purified by standard procedures [15]. Zinc and mercury
chloride were purchased from Merck and used without purification. Elemental analyses
for C, H, and N were performed on a Heraceous Carlo Erba 1108 elemental analyzer.
Zinc(II) and mercury(II) were estimated by reported methods [16]. Infrared spectra of
ligands and complexes, 4000–200 cmꢀ1, were recorded in KBr pellets on a Perkin-Elmer
1000 FT-IR spectrophotometer. NMR spectra of the ligands and the complexes were
recorded in CDCl3 and DMSO-d6, respectively, on a Bruker DRX-300 spectrometer at
a sweep width of 300 MHz and a sweep time of 300 s. Molar conductances of the
complexes were measured in DMSO (10ꢀ3 mol Lꢀ1) using a Coronation Digital
Conductivity Meter. FAB-MS spectra were recorded on a JEOLSX 102/DA-6000 mass
spectrometer/data system using argon/xenon (6 kV, 10 mA) as the FAB gas and TOF-
MS spectra were recorded on a Q-TOF MS instrument. The thermogravimetric (TG)
analysis of the solid complex was performed using a TGAꢀ510H thermogravimetric
analyzer (Shimadzu) from ambient to 800ꢁC with a 20ꢁC min heating rate using N2.
X-ray powder diffraction of the complexes was recorded on a Rigaku Model D/Max-
˚
2200 PC using Cu-Ka1 radiation (ꢁ ¼ 1.5406 A).
2.1. Syntheses
2.1.1. Preparation of ligands
2.1.1.1. o-Vanilidene-1-aminobenzene (HL1). Equimolar amounts of o-vanillin (5 g,
33.0 mmol) and aniline (3.060 g, 33.0 mmol) in methanol (ꢂ30 cm3) were refluxed on a

Vanilidene Schiff bases
2647
water bath for ꢂ5 h. The analytically pure light yellow ligand was obtained. The yield of
HL1 was 5.42 g (72.6%); m.p. ¼ 250ꢁC. For C14H13NO2 Anal. Calcd (%): C, 73.92; H,
5.72; N, 6.16. Found (%): C, 73.88; H, 5.65; N, 6.11.
1
The H-NMR spectrum, ꢂ (ppm): 7.69–6.94 (m, 8H, CHar), 3.92 (t, 3H, OCH3),
8.3 (s, 1H, HC¼N), 13.26 (s, 1H, OH). IR spectrum, ꢃ (cmꢀ1): 1615 (C¼N),
1274 ((C–O)phenolic), 3445 (ꢃ(OHstretching)), 1352 (ꢂ(OHdeformation)).
2.1.1.2. o-Vanilidene-2-methyl-1-aminobenzene (HL2). Equimolar amounts of o-van-
illin (5 g, 33.0 mmol) and o-toluidine (3.54 g, 33.0 mmol) in methanol (ꢂ30 cm3) were
refluxed on a water bath for ꢂ5 h. The analytically pure light yellow ligand was
obtained as 5.98 g (75.4%); m.p. ¼ 231ꢁC. For C15H15NO2 Anal. Calcd (%): C, 74.59;
H, 6.23; N, 5.80. Found (%): C, 74.50; H, 6.17; N, 5.73.
1
The H-NMR spectrum, ꢂ (ppm): 7.9–6.8 (m, 7H, CHar), 3.9 (t, 3H, OCH3), 2.60
(t, 3H, CH3), 8.3 (s, 1H, HC¼N), 13.16 (s, 1H, OH). IR spectrum, ꢃ (cmꢀ1): 1617
(C¼N), 1272 ((C–O)phenolic), 3464 (ꢃ(OHstretching)), 1355 (ꢂ(OHdeformation)).
2.1.2. Synthesis of complexes
2.1.2.1. [(ꢀ-Cl)2Zn2(L1)2] (1). To
a suspension/solution of ZnCl2 (0.640 g,
4.69 m mol) in THF (ꢂ30 mL), a methanolic solution of the sodium salt of Schiff
base (1.170 g, 4.69 mmol) was added with constant stirring. The reaction mixture was
refluxed for ꢂ4 h, filtered to remove NaCl, and filtrate was concentrated by distillation
under reduced pressure. The product so obtained was purified by recrystallization from
THF (purity was further checked by TLC) to afford brown crystalline solid. The yield
of the complex was 1.109 g (72.2%); decomposition point ¼ 280ꢁC. For C28H24N2O4
Cl2Zn2 Anal. Calcd (%): C, 51.40; H, 3.70; N, 4.28; Cl, 10.84; Zn, 20. Found (%): C,
51.33; H, 3.65; N, 4.26; Cl, 10.82; Zn, 19.96.
The 1H-NMR spectrum, ꢂ (ppm): 7.83–6.56 (m, 8H, CHar), 4.59 (t, 3H, OCH3), 8.74
(s, 1H, HC¼N). IR spectrum, ꢃ (cmꢀ1): 1592 (C¼N), 1292 ((C–O)phenolic), 1031
(OCH3), 460 (Zn–N), 348 (Zn–O), 244 ((Zn–Cl)bridging), TOF-MS: 652.18 m/z;
calculated mass (649.97), molar conductivity: 10.34 ꢀꢀ1 molꢀ1 cm2.
2.1.2.2. [(ꢀ-Cl)2Zn2(L2)2] (2). To a hot suspension/solution of ZnCl2 (0.729 g,
5.35 mmol) in THF (ꢂ30 mL), a methanolic solution of the sodium salt of Schiff base
(1.408 g, 5.35 mmol) was added with constant stirring. The product was obtained by the
similar procedure used for 1. The product was formed as a yellow powder, 1.289 g
(70.6%); decomposition point ¼ 295ꢁC. For C30H28N2O4Cl2Zn2 Anal. Calcd (%): C,
52.81; H, 4.14; N, 4.11; Cl, 10.39; Zn, 19.17. Found (%): C, 52.75; H, 4.07; N, 4.05; Cl,
10.39; Zn, 19.13.
1
The H-NMR spectrum, ꢂ (ppm): 8.11–7.06 (m, 7H, CHar), 4.51 (t, 3H, OCH3),
2.77 (t, 3H, CH3), 8.69 (s, 1H, HC¼N). IR spectrum, ꢃ (cmꢀ1): 1591 (C¼N), 1295
((C–O)phenolic), 1029 (OCH3), 462 (Zn–N), 352 (Zn–O), 249 ((Zn–Cl)bridging), FAB-MS:
681 m/z; calculated mass (678), molar conductivity: 8.97 ꢀꢀ1 molꢀ1 cm2.
2.1.2.3. [(ꢀ-Cl)2Hg2(L1)2] (3). To a solution of HgCl2 (1.45 g, 5.35 mmol) in THF
(ꢂ30 mL), a methanolic solution of the sodium salt of Schiff base (1.33 g, 5.35 mmol)
was added with constant stirring. The product was obtained by the above process as a

2648
R.K. Dubey et al.
reddish brown crystalline solid. The yield was 1.812 g (73.3%); decomposition
point ¼ 285ꢁC. For C28H24N2O4Cl2Hg2 Anal. Calcd (%): C, 36.37; H, 2.62; N, 3.03;
Cl, 7.67; Hg, 43.39. Found (%): C, 36.32; H, 2.62; N, 3.01; Cl, 7.63; Hg, 43.38.
The 1H-NMR spectrum, ꢂ (ppm): 8.71–6.66 (m, 8H, CHar), 4.46 (t, 3H, OCH3), 8.61
(s, 1H, HC¼N). IR spectrum, ꢃ (cmꢀ1): 1588 (C¼N), 1282 ((C–O)phenolic), 1031
(OCH3), 413 (Hg-N), 320 (Hg–O), 5200 ((Hg–Cl)bridging), FAB-MS: 928 m/z; calcu-
lated mass (926.05), molar conductivity: 11.64 ꢀꢀ1 molꢀ1 cm2.
2.1.2.4. [(ꢀ-Cl)2Hg2(L2)2] (4). To a solution of HgCl2 (1.23 g, 4.48 mmol) in THF
(ꢂ30 mL), a methanolic solution of the sodium salt of Schiff base (1.18 g, 4.48 mmol)
was added with constant stirring. The product was obtained as above as a blackish
brown crystalline solid, 1.611 g (75%); decomposition point ¼ 292ꢁC. For
C30H28N2O4Cl2Hg2 Anal. Calcd (%): C, 37.82; H, 2.96; N, 2.94; Cl, 7.44; Hg, 42.11.
Found (%): C, 37.69; H, 2.91; N, 2.90; Cl, 7.45; Hg, 42.07.
The 1H-NMR spectrum, ꢂ (ppm): 7.79–6.83 (m, 7H, CHar), 4.39 (t, 3H, OCH3), 2.69
(t, 3H, CH3), 8.57 (s, 1H, HC¼N). IR spectrum, ꢃ (cmꢀ1): 1590 (C¼N), 1278 ((C–
O)phenolic), 1029 (OCH3), 411 (Hg–N), 318 (Hg–O), 5200 ((Hg–Cl)bridging), FAB-MS:
952 m/z; calculated mass (954.08), molar conductivity: 12.86 ꢀꢀ1 molꢀ1cm2.
2.1.2.5. [Zn(L1)2] (5). To a solution of ZnCl2 (0.290 g, 2.13 mmol) in THF
(ꢂ30 mL), a methanolic solution of the sodium salt of Schiff base (1.061 g,
4.26 mmol) in 1 : 2 molar ratio was added with constant stirring; separated NaCl was
removed by filtration. The product was recrystallized from THF (purity further checked
by TLC). A brown crystalline solid complex was obtained, 0.803 g (72.9%); decom-
position point ¼ 303ꢁC. For C28H24N2O4Zn Anal. Calcd (%): C, 64.93; H, 4.67; N,
5.41; Zn, 12.63. Found (%): C, 64.86; H, 4.66; N, 5.40; Zn, 12.62.
The 1H-NMR spectrum, ꢂ (ppm): 7.91–6.54 (m, 8H, CHar), 4.43 (t, 3H, OCH3), 8.68
(s, 1H, HC¼N). IR spectrum, ꢃ (cmꢀ1): 1588 (C¼N), 1289 ((C–O)phenolic), 1030
(OCH3), 463 (Zn–N), 359 (Zn–O), FAB-MS: 517 m/z; calculated mass (516.10), molar
conductivity: 9.14 ꢀꢀ1 molꢀ1 cm2.
2.1.2.6. [Zn(L2)2] (6). To a solution of ZnCl2 (0.246 g, 1.81 mmol) in THF
(ꢂ30 mL), a methanolic solution of the sodium salt of Schiff base (0.950 g,
3.61 mmol) in 1 : 2 molar ratio was added with constant stirring. The product was
obtained by analogous procedure to that used for 5. The product formed as a dark
brown crystalline solid, 0.743 g (73%); decomposition point ¼ 317ꢁC. For
C30H28N2O4Zn Anal. Calcd (%): C, 66.00; H, 5.17; N, 5.13; Zn, 11.98. Found (%):
C, 65.72; H, 5.08; N, 5.06; Zn, 11.94.
The 1H-NMR spectrum, ꢂ (ppm): 8.13–7.09 (m, 7H, CHar), 4.39 (t, 3H, OCH3), 2.82
(t, 3H, CH3), 8.64 (s, 1H, HC¼N). IR spectrum, ꢃ(cmꢀ1): 1593 (C¼N), 1290 ((C–
O)phenolic), 1029 (OCH3), 464 (Zn–N), 366 (Zn–O), FAB-MS: 545 m/z; calculated mass
(544.13), molar conductivity: 14.26 ꢀꢀ1 molꢀ1 cm2.
2.1.2.7. [Hg(L1)2] (7). To a solution of HgCl2 (0.673 g, 2.48 mmol) in THF
(ꢂ30 mL), a methanolic solution of the sodium salt of Schiff base (1.236 g,
4.96 mmol) in 1 : 2 molar ratio was added with constant stirring. The product was
obtained by analogous procedure as for 5. The product formed as a brownish black

Vanilidene Schiff bases
2649
crystalline solid, 1.192 g (73.6%); decomposition point ¼ 305ꢁC. For C28H24N2O4Hg
Anal. Calcd (%): C, 51.49; H, 3.70; N, 4.29; Hg, 30.71. Found (%): C, 51.40; H, 3.65;
N, 4.31; Hg, 30.67.
The 1H-NMR spectrum, ꢂ (ppm): 8.04–6.98 (m, 8H, CHar), 4.33 (t, 3H, OCH3), 8.49
(s, 1H, HC¼N). IR spectrum, ꢃ (cmꢀ1): 1584 (C¼N), 1288 ((C–O)phenolic), 1031
(OCH3), 407 (Hg–N), 315 (Hg–O), TOF-MS: 650.42 m/z; calculated mass (654.14),
molar conductivity: 17.17 ꢀꢀ1 molꢀ1 cm2.
2.1.2.8. [Hg(L2)2] (8). To a solution of HgCl2 (0.703 g, 2.59 mmol) in THF
(ꢂ30 mL), a methanolic solution of the sodium salt of Schiff base (1.363 g,
5.17 mmol) in 1 : 2 molar ratio was added with constant stirring. The product was
obtained as above as a brownish black crystalline solid, 1.248 g (70.8%); decomposition
point ¼ 314ꢁC. For C30H28N2O4Hg Anal. Calcd (%): C, 52.90; H, 4.14; N, 4.11; Hg,
29.45. Found (%): C, 52.82; H, 4.13; N, 4.31; Hg, 29.41.
The 1H-NMR spectrum, ꢂ (ppm): 7.53–6.55 (m, 7H, CHar), 4.28 (t, 3H, OCH3), 2.75
(t, 3H, CH3), 8.44 (s, 1H, HC¼N). IR spectrum, ꢃ (cmꢀ1): 1589 (C¼N), 1289 ((C–
O)phenolic), 1029 (OCH3), 410 (Hg–N), 321 (Hg–O), FAB-MS: 681 m/z; calculated mass
(682.18), molar conductivity: 15.54 ꢀꢀ1 molꢀ1 cm2.
3. Results and discussion
Zinc(II) and mercury(II) complexes have been synthesized by interactions of ZnCl2 and
HgCl2 with sodium salt of the o-vanilidene-1-aminobenzene (HL1) and o-vanilidene-2-
methyl-1-aminobenzene (HL2) in different molar ratio to yield mono (chloro) (1–4) and
bis complexes 5–8. The detailed synthetic procedures of both ligands and all complexes
are given in schemes 1 and 2.
These complexes are colored, non-hygroscopic solids, soluble in polar solvents such
as DMF, DMSO, and pyridine. The complexes have been characterized by elemental
analyses, spectral studies, and molar conductivity measurements with some studied by
PXRD and thermogravimetric analysis. Conductivity measurements indicate the
characteristics of nonelectrolytes, 8.97–17.17 ꢀꢀ1 molꢀ1 cm2, for all the studied
complexes [17].
3.1. IR spectra
The tentative assignments of IR spectral bands for HL1, HL2, monochloro-, and
bis-complexes are given in section 2. The ligands possess two potential donor sites, the
phenolic oxygen and the azomethine nitrogen.
The ligands exhibit characteristic bands for ꢃ(C¼N) at 1615 and 1617 cmꢀ1
,
respectively. Bonding of the azomethine [18, 19] is indicated by the shift of ꢃ(C¼N) to
lower frequency 1595–1584 cmꢀ1 in the complexes. Bonding through phenolic oxygen
after deprotonation is revealed by the disappearance of ꢃ(OH) phenolic bands at 3445
and 3464 cmꢀ1 for HL1 and HL2, respectively, and the appearance of bands [20, 21] due
to ꢃ(C–O) at much lower frequencies (1295–1278 cmꢀ1) in the complexes. Coordination
of azomethine nitrogen and phenolic oxygen is further supported by two bands [22, 23]

2650
R.K. Dubey et al.
O
C
H3C
NH2
o-toluidine
H
OH
O
CH3
o-vanillin
dry-MeOH
Δ ∼5h
H3C
N
CH
OH
O
CH3
L2H= o-vanilidene-2-methyl-1-aminobenzene
dry-THF
MCl2
Δ ∼
4h
1:2
1:1
H3C
O
CH3
CH
O
N
H3C
O
CH3
Cl
Cl
N
CH
O
CH
N
M
M
M
N
O
O
O
CH3
CH3
CH
CH3
O
CH3
[M(L2)2]
[(μ-Cl)2M(L2)2]
[M= Zn(II) {2 & 6}; Hg(II) {4 & 8}]
Scheme 1. Synthesis of L1H and complexes.
at 366–315 cmꢀ1 and 464–407 cmꢀ1 due to ꢃ(M–O) and ꢃ(M–N), respectively. HL1 and
HL2 exhibit bands for ꢃ(OCH3) at 1031 and 1029 cmꢀ1, respectively, which remain
unchanged in the complexes [24], indicating that this group does not participate in
coordination.
In zinc(II) chloro complexes for bridging zinc chloride ꢃ(Zn–Cl) occurred at 249–
244 cmꢀ1 due to delocalization of electrons in the chelate ring. This band suggests
bridging chloride between two zinc(II) centers; in the mercury(II) chloro complexes
bridging ꢃ(Hg–Cl) occur much lower [25], 5200 cmꢀ1, as expected [26].

Vanilidene Schiff bases
2651
O
C
H3C
H
NH2
OH
o-toluidine
O
CH3
o-vanillin
dry-MeOH
Δ ∼5h
H3C
N
CH
OH
O
CH3
L2H= o-vanilidene-2-methyl-1-aminobenzene
dry-THF
MCl2
Δ ∼ 4h
1:2
1:1
H3C
O
CH3
CH
O
N
H3C
O
CH3
Cl
Cl
N
O
CH
M
M
CH
M
N
O
N
O
CH3
O
O
CH3
CH
CH3
CH3
[M(L2)2]
[(μ-Cl)2M(L2)2]
[M= Zn(II) {2 & 6}; Hg(II) {4 & 8}]
Scheme 2. Synthesis of L2H and complexes.
3.2. 1H-NMR spectra
For further evidence regarding the coordination of HL1 and HL2, 1H-NMR spectra of
the ligand and complexes (1–8) were recorded in DMSO-d6. Comparison of the
chemical shifts shows that the signal due to the phenolic proton (OH) is absent in the
complex, suggesting coordination of the phenolic oxygen to the metal

2652
R.K. Dubey et al.
Figure 1. TOF-MS spectrum of [(ꢀ-Cl)2Zn2(L1)2] (1).
Figure 2. FAB-MS spectrum of [(ꢀ-Cl)2Zn2(L2)2] (2).
after deprotonation. The azomethine proton at 8.38–8.31 ppm in the ligand appeared at
8.74–8.44 ppm in the complexes [27, 28], this supports the coordination of azomethine
nitrogen to metal. These conclusions are also supported by IR spectral data. A strong
signal at ꢂ13.26, ꢂ13.16 ppm may be attributed to phenolic proton of HL1 and HL2,
respectively, whereas 1H-NMR spectra of the corresponding metal complexes of Zn(II)
and Hg(II) are devoid of signals due to OH.

Vanilidene Schiff bases
2653
Figure 3. FAB-MS spectrum of [(ꢀ-Cl)2Hg2(L1)2] (3).
Figure 4. TOF-MS spectrum of [Hg(L1)2] (7).
3.3. Mass spectrum
The mass spectra of zinc(II) and mercury(II) complexes exhibit molecular ion peaks
(m/z) corresponding to their molecular association, representing monomeric and
dimeric complexes. The m/z values for the eight complexes are given in section 2,
whereas mass spectra for 1, 2, 3, and 7 are given as figures 1–4. Spectra 1 and 4 are
obtained by TOF-MS whereas 2 and 3 were recorded by FAB-MS spectrometry. In 1
and 7, most fragment ions were observed as a group of peaks due to the presence of

2654
R.K. Dubey et al.
Figure 5. TGA curve of [(Cl)Hg(L2)] (4).
various isotopes of these metals and chlorides. The mass fragmentation pattern
(Supplementary material) of [(ꢀ-Cl)2Zn2(L1)2], [(ꢀ-Cl)2Hg2(L1)2], and [Hg(L1)2] con-
firm the composition and structure of these complexes. FAB-MS spectrum [29, 30] of 3
showed characteristic molecular ion peak for dimer [(C28H24N2O4Cl2Hg2) Calcd mass
926.05] at 928 m/z due to various isotopes including mercury and chloride [12]. Various
peaks represent successive degradation of the complex by formation of a monomer, for
which a molecular ion peak was observed at 464 m/z. The TOF-MS spectra of 1 and 7
show molecular ion peaks at 652.18 (Calcd 649.97) and 650.42 (Calcd 654.14),
respectively. Other important peaks were also observed at m/z 572.93, 546.93, 516.92,
346.84, 423.88, 362.84, 290.83, 247.95, 221.94, 213.79, 191.93, and 114.89 due to the
.
.
formation of various radicals C14H12ClNHO2Zn. , C6H5 , HCN, ZnCl. , OCH3 ,
C6H5O. , O. , in 1, whereas 7 showed some prominent peaks at m/z 623.07, 593.04,
577.00, 549.97, 515.94, 472.87, 446, 438.83, 416.82, 412.81, 386.80, and 293.69 due to
.
.
the formation of various radicals C6H5 , CH3 , HCN, Hg. .

Vanilidene Schiff bases
2655
Figure 6. The powdered X-ray diffraction spectrum of [(Cl)Hg(L2)] (4).
3.4. Thermogravimetric analysis
The thermal analysis [13] of [(ꢀ-Cl)2Hg2(L2)2] (4) (C30H28N2O4Cl2Hg2) was performed
from 50ꢁC to 800ꢁC in dynamic nitrogen. Figure 5 exhibits weight loss between 170.5ꢁC
and 380ꢁC. The molecular mass of 4 is 954.62 and the % weight loss of the complex is
52.679%, which is equal to the approximate weight of the complex 511.31 (53.56%). It
is clear that elimination of one coordinated ligand, one mercury along with two
chlorines from the complex takes place. Thereafter the weight of residue 443.31
[HgC15H14O2N] was obtained. Thermogram of 7 from ambient to 900ꢁC shows that
total % weight loss of the complex is 66.7688%, equal to approximate weight of the
complex 441 (67.5345 %) leaving HgO as residue at 217 m/z after elimination of ligands.
3.5. PXRD studies
X-ray diffraction [13] spectrum of solid powder of 4 clearly showed the crystalline
material (figure 6). Diffraction pattern comprises a number of sharp Bragg’s reflections
corresponding to different orientation of crystallites. Broadening of the diffraction
pattern beyond that expected from instrumental factors is generally attributed to
crystallite size [31]. Non-uniform broadening of lines is attributed to anisotropic
crystallites [32, 33]. Line broadening is used here to calculate the crystallite size using
˚
the Debye Scherrer formula [34]. The crystallite size is 328.14 A.
4. Conclusion
Eight Schiff-base complexes of Zn(II) and Hg(II) have been synthesized containing
bidentate ligands. The structural composition has been tentatively proposed by mass
spectral studies, showing isotopic molecular ion peaks. The position of the molecular
ion peak in the mass spectrum is consistent with the empirical molecular formula as
indicated from the elemental analysis. Thermal analysis of [(ꢀ-Cl)2Hg2(L2)2] (4) and

2656
R.K. Dubey et al.
[Hg(L1)2] (7) confirm the dimeric and monomeric molecular association. Molar
conductivity measurement indicates that the complexes are non-electrolytes.
Acknowledgments
The authors are grateful to Director, C.D.R.I., Lucknow, for providing spectral and
analytical data and also IIT, Delhi, for thermal analysis. Nanophosphor Application
Center, University of Allahabad, is also acknowledged for PXRD studies of one of the
compounds.
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