Synthesis and characterization of N-(o-vanillinidene)-p-anisidine and N,N′-bis(o-vanillinidene)ethylenediamine and their metal complexes

Article abstract of DOI:10.1081/SIM-120021648

Two Schiff bases, N-(o-vanillinidene)-p-anisidine (o-VPAH) and N,N′-bis(o-vanillinidene)ethylenediamine (o-VEDH₂), and eleven complexes of the compositions [M(L)(OAc)(H₂O)] {where M = Cu(II) (1), Co(II) (2), Mn(II) (3) or Ni(II) (4) and OAcH = CH₃COOH}, [Zn(L)₂]·H₂O (5), [M(L′)(H₂O)₂] {where M = Cu(II) (6) or Ni(II) (7)}, [Zn(L′)]·2H₂O (8), [Sm(L′)(OAc)(H₂O)] (9), [Th(L′)(NO₃)₂] (10) and [UO₂(L′)(H₂O)]· H₂O (11) (where LH = o-VPAH, and L′H₂ = o-VEDH₂), were prepared. From the elemental analyses, IR, electronic and NMR spectra, magnetic susceptibility measurements and thermal studies, the mode of chelation of the ligands and geometry of the complex molecules were assigned. In all of the complexes, o-VPAH acts as a monobasic-bidentate ligand and o-VEDH₂ acts as a dibasic-tetradentate ligand. The presence of water is revealed by thermograms and supported by the presence of relevant bands in their IR spectra. Suitable structures have been proposed for these complexes.

Full text of DOI:10.1081/SIM-120021648

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Synthesis and Characterization of
N‐(o‐Vanillinidene)‐p‐anisidine and
N,N′‐bis(o‐Vanillinidene)ethylenediamine and Their
Metal Complexes
R. C. Maurya a , P. Patel a & S. Rajput a
a Coordination Chemistry Laboratory, Department of P. G. Studies and Research in Chemistry,
R. D. University, Jabalpur, ‐482 001, India
Version of record first published: 20 Aug 2006.
To cite this article: R. C. Maurya , P. Patel & S. Rajput (2003): Synthesis and Characterization of
N‐(o‐Vanillinidene)‐p‐anisidine and N,N′‐bis(o‐Vanillinidene)ethylenediamine and Their Metal Complexes, Synthesis and
Reactivity in Inorganic and Metal-Organic Chemistry, 33:5, 817-836
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 5, pp. 817–836, 2003
Synthesis and Characterization of
N-(o-Vanillinidene)-p-anisidine and
N,N’-bis(o-Vanillinidene)ethylenediamine
and Their Metal Complexes
*
R. C. Maurya, P. Patel, and S. Rajput
Coordination Chemistry Laboratory, Department of P. G. Studies and
Research in Chemistry, R. D. University, Jabalpur, India
ABSTRACT
Two Schiff bases, N-(o-vanillinidene)-p-anisidine (o-VPAH) and N,N’-
bis(o-vanillinidene)ethylenediamine (o-VEDH2), and eleven complexes
of the compositions [M(L)(OAc)(H2O)] {where M = Cu(II) (1), Co(II)
(2), Mn(II) (3) or Ni(II) (4) and OAcH = CH3COOH}, [Zn(L)2]ꢀH2O
(5), [M(L’)(H2O)2] {where M = Cu(II) (6) or Ni(II) (7)}, [Zn(L’)]ꢀ2H2O
(8), [Sm(L’)(OAc)(H2O)] (9), [Th(L’)(NO3)2] (10) and [UO2(L’)(H2O)]ꢀ
H2O (11) (where LH = o-VPAH, and L’H2 = o-VEDH2), were prepared.
*
Correspondence: R. C. Maurya, Coordination Chemistry Laboratory, Department of
P. G. Studies and Research in Chemistry, R. D. University, Jabalpur-482 001, India;
E-mail: rcmaurya@sancharnet.in.
817
DOI: 10.1081/SIM-120021648
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

818
Maurya, Patel, and Rajput
From the elemental analyses, IR, electronic and NMR spectra, magnetic
susceptibility measurements and thermal studies, the mode of chelation
of the ligands and geometry of the complex molecules were assigned.
In all of the complexes, o-VPAH acts as a monobasic-bidentate ligand
and o-VEDH2 acts as a dibasic-tetradentate ligand. The presence of
water is revealed by thermograms and supported by the presence of
relevant bands in their IR spectra. Suitable structures have been pro-
posed for these complexes.
Key Words: N-(o-vanillinidene)-p-anisidine; N,N’-bis(o-vanillinidene)-
ethylenediamine; Cu(II); Co(II); Mn(II); Ni(II); Zn(II); Sm(III); Th(IV);
UO2(VI) complexes.
INTRODUCTION
Chelating ligands containing O and N donor atoms show broad bio-
logical activity and are of special interest because of the variety of ways in
which they are bonded to metal ions.[1,2] Aromatic hydroxyaldehydes form
stable complexes and the presence of a phenolic hydroxyl group at their o-
position imparts an additional donor site in the molecule making it bi-
dentate. Such a molecule coordinates with the metal ion through the
carbonyl oxygen and deprotonated hydroxyl group. The chelating properties
of Schiff bases derived from o-hydroxyaldehydes and ketones are well
established.[3–5]
Chelate complexes of formylferrocene and acetylferrocene salicyloyl-
hydrazones with transition metals have been synthesized and characterized
by Xian[6] et al. The ligands are bidentate and their complexes in DMF
are non-electrolytes. Mononitrosyl derivatives of iron and cobalt com-
plexes of quadridentate ligands derived from 2-hydroxy-1-naphthalde-
hyde and ethylenediamine, o-phenylenediamine and 4-methyl-o-phe-
nylenediamine have been synthesized and characterized by Larkworthy[7]
and coworkers.
In view of the coordinating ability of Schiff bases derived from o-
hydroxyaromatic aldehydes along with their biological activity, we have
synthesized and characterized the two aroyl Schiff bases, 1) N-(o-
vanillinidene)-p-anisidine (o-VPAH), and 2) N,N-bis(o-vanillinidene)ethy-
lenediamine (o-VEDH2). Among the aromatic aldehydes, an isomer of
vanillin, i.e., o-vanillin is used. It is 3-methoxysalicylaldehyde. Vanillin is a
constituent of fruits of the widely occurring plant Vanilla Planifolia. It can
easily be obtained by the treatment of spent wood pulp with alkali.

N-(o-Vanillinidene) Complexes
819
In order to explore the ligational behaviour of theses two ligands, we
have prepared a series of their metal complexes with Cu(II), Co(II), Ni(II),
Mn(II), Zn(II), Sm(III), Th(IV) and UO2(VI), and characterized them by
various physico-chemical techniques. The results of our studies are included
in this paper.
EXPERIMENTAL
Materials
o-Vanillin, ethylenediamine, p-anisidine and dimethylformamide (Sisco
Chem. Industry, Bombay), Co(CH3COO)2ꢀ4H2O, Ni(CH3COO)2ꢀ4H2O,
Zn(CH3COO)2ꢀ2H2O, Cu(CH3COO)2ꢀH2O, Mn(CH3COO)2ꢀ4H2O and UO2-
(CH3COO)2ꢀ2H2O (E. Merck, Germany), Th(NO3)4ꢀ6H2O and Sm(CH3-
COO)3ꢀ3H2O (Indian Rare Earth Ltd.) were used as supplied. Ethanol and
other solvents employed were of A.R. grade.
Synthesis of Ligands
An ethanolic solution (30 mL) of o-vanillin (50 mmol, 7.60 g) was
added to the ethanolic solution (15–20 mL) of p-anisidine (50 mmol, 6.15
g)/ethylenediamine (25 mmol, 1.17 mL). The resulting mixture was then
refluxed on a water bath for 4–5 h. A coloured solid mass separated out on
cooling. It was then filtered by suction, washed with ethanol, diethyl ether
and subsequently dried over anhydrous CaCl2 in a desiccator. The purity of
the ligands was checked by TLC. Both Schiff base ligands are insoluble in
all common organic solvents, viz., acetone, alcohol, benzene, etc. but
soluble in polar solvents, viz., DMF, DMSO, etc.
Synthesis of Metal Complexes of o-VPAH
Metal complexes of o-VPAH were synthesized by mixing a solution
of o-VPAH (5 mmol, 1.28 g) in the minimum quantity of dimethylfor-
mamide (ꢁ 20 mL) and an ethanolic solution (ꢁ 30 mL) of the metal salt
[Cu(CH3COO)2ꢀH2O (5 mmol, 0.99 g), Co(CH3COO)2ꢀ4H2O (5 mmol, 1.24
g), Ni(CH3COO)2ꢀ4H2O (5 mmol, 1.24 g), Mn(CH3COO)2ꢀ4H2O (5 mmol,
1.22 g)] or Zn(CH3COO)2ꢀ2H2O (2.5 mmol, 0.55 g)]. The resulting mixture
was then refluxed on an electric heating mantle at 80 °C for ꢁ4 h. On
cooling a coloured complex precipitated, was filtered, washed with alcohol
and finally with diethyl ether and dried over anhydrous CaCl2.

820
Maurya, Patel, and Rajput
Synthesis of Metal Complexes of o-VEDH2
Metal complexes of N,N’-bis(o-vanillinidene)ethylenediamine (o-
VEDH2) were synthesized by mixing a hot solution of o-VEDH2 (5 mmol,
1.64 g) in a minimum quantity of dimethylformamide (ꢁ20 mL) and
an aqueous-ethanolic (1:1, 30 mL) solution of the metal salt [Ni(CH3-
COO)2ꢀ4H2O (5 mmol, 1.24 g), Zn(CH3COO)2ꢀ2H2O (5 mmol, 1.10 g),
Cu(CH3COO)2ꢀH2O (5 mmol, 0.99 g), Sm(CH3COO)3ꢀ3H2O (5 mmol, 1.90
g), of Th(NO3)4ꢀ6H2O (5 mmol, 2.94 g) or UO2(CH3COO)2ꢀ2H2O (5 mmol,
2.12 g)]. The resulting mixture was then refluxed on an electric heating
mantle at 80 °C for ꢁ4 h. On cooling, the coloured complexes precipitated
out which were filtered by suction, washed with ethanol and finally with
diethyl ether and dried in vacuo over anhydrous CaCl2.
Figure 1. Synthesis of Schiff base ligands.

N-(o-Vanillinidene) Complexes
821
Table 1. Physical characteristics and microanalytical data of the ligands.
Empirical
formula
(formula
weight)
Found (calc.), %
M.p. Yield
(°C) (%)
Ligand
Solubility Color
C
H
N
o-VPAH C15H15N1O3 230 65 Sol. in
(LH)
Brown 69.72 5.72 5.64
(70.04) (5.83) (5.44)
(257.00)
DMF and
DMSO
o-VEDH2 C18H20N2O4 260 75 Sol. in
(L’H2)
Yellow 65.49 5.76 8.23
(65.85) (6.09) (8.53)
(328.00)
DMF and
DMSO
RESULTS AND DISCUSSION
The Schiff base ligands o-VPAH and o-VEDH2 were prepared from
o-vanillin according to the equations in Figure 1.
The formation of the Schiff bases is consistent with the micro-
analytical data of the ligands. The microanalytical data, melting points,
colours, % yields and other details are given in Table 1. The 1H NMR
spectra of the Schiff base ligands are given in Figures 2 and 3 along with
the indexing of various protons. The formation of the Schiff base ligands
are confirmed by the appearance of the azomethine proton (–CH=N–)
signal at 8.95 ppm in o-VPAH and 8.2 ppm in o-VEDH2.[8] This is further
supported by the appearance of a band in the IR spectra of the ligands
Figure 2. 1H NMR spectrum of the ligand o-VPAH.

822
Maurya, Patel, and Rajput
Figure 3. 1H NMR spectrum of the ligand o-VEDH2.
for n(C=N) (azomethine) at 1610 and 1620 cm–1 in o-VPAH and o-
VEDH2, respectively. Both ligands exhibit signals for aromatic, OCH3,
and phenolic (OH) protons at 6.7–7.4 ppm, 3.18–3.86 ppm and 13.47
ppm, respectively[9] Unfortunately, a signal for the phenolic proton in o-
VEDH2 could not be observed due to recording of the spectrum up to only
10 ppm.
Compositions and Characterization of Metal Complexes
The metal complexes of o-VPAH and o-VEDH2 were prepared ac-
cording to the following equations:
EthanolÀDMF
Reflux
MðCH3COOÞ2ꢀnH2O þ LH
þ CH3COOH þ ðn À 1ÞH2O
½MðLÞðCH3COOÞðH2Oފ
ð1Þ
M ¼ CuðIIÞ ð1Þ; n ¼ 1; M ¼ CoðIIÞ ð2Þ=MnðIIÞ ð3Þ=NiðIIÞ ð4Þ;
n ¼ 4; LH ¼ o-VPAH

N-(o-Vanillinidene) Complexes
823
ð2Þ
ð3Þ
ZnðCH3COOÞ2ꢀ2H2O þ 2o-VPAH
Ethanol-DMF
½Znðo-VPAÞ2Šꢀ2H2Oð5Þ þ 2CH3COOH þ H2O
Reflux
Ethanol-DMF
MðCH3COOÞ2 ꢀnH2O þ L0H2
½MðL0ÞðH2OÞ2Š
Reflux
þ 2CH3COOH þ ðn À 1ÞH2O
M ¼ CuðIIÞð6Þ; n ¼ 1; M ¼ NiðIIÞð7Þ; n ¼ 4; L0H2 ¼ oÀVPAH2
Ethanol-DMF
ZnðCH3COOÞ2 ꢀ2H2O þ L0H2
½ZnðL0ފꢀ2H2O ð8Þ
Reflux
ð4Þ
ð5Þ
þ2CH3COOH
Ethanol-DMF
Reflux
SmðCH3COOÞ3 ꢀ3H2O þ L0H2
½SmðL0Þ-
ðCH3COOÞðH2Oފ ð9Þ þ 2CH3COOH þ 2H2O
Ethanol-DMF
ThðNO3Þ4 ꢀ6H2O þ L0H2
½ThðL0ÞðNO3Þ2Š ð10Þ
Reflux
þ 2HNO3 þ 6H2O
ð6Þ
Ethanol-DMF
Reflux
UO2ðCH3COOÞ2 ꢀ2H2O þ L0H2
ꢀ H2O ð11Þ þ 2CH3COOH
½UO2ðL0ÞðH2Oފ-
ð7Þ
The microanalytical data, some physical properties, such as, decom-
position temperatures and colours as well as % yields of the complexes are
given in Table 2. All the complexes are soluble in DMF and DMSO. They
were characterized by the following physical studies.
Infrared Spectra
The ligand o-VPAH contains two potential donor sites: 1) the
azomethine nitrogen and 2) the phenolic oxygen while the ligand o-VEDH2
has four potential donor sites: 1) two azomethine nitrogens and 2) two
phenolic oxygens.
Both of the ligands (Table 3) show a characteristic band at 1610 and
1620 cm–1, respectively, due to n(C=N) of the azomethine group.
Bonding of this nitrogen is indicated by the shifting of n(C=N) to lower

824
Maurya, Patel, and Rajput

N-(o-Vanillinidene) Complexes
825

826
Maurya, Patel, and Rajput

N-(o-Vanillinidene) Complexes
827
(10–25 cm–1) wave numbers in the complexes.[10] The characteristic
phenolic n(OH), due to the presence of an hydroxy group at the o-position,
was observed in o-VPAH and o-VEDH2 at 3400 and 3300 cm–1
,
respectively.[2] A band at 1450 cm–1 due to n(C–O) of the phenolic group
was also observed in both ligands. The sharp band due to the phenolic (O–
H) of the two ligands should be absent in all of the complexes under study
to indicates the coordination of the phenolic oxygen, after deprotonation, to
the metal ion. But due to the presence of a broad band (vide infra) for
lattice and coordinated water, it is difficult to confirm with certainty the
coordination of the phenolic oxygen after deprotonation. However, such
coordination is supported by the shifting of the phenolic n(C–O) band to
lower wave numbers (see Table 3) in the complexes.[2] The coordination of
the azomethine nitrogen and phenolic oxygen is further supported by the
appearance of two non-ligand bands at 510–540 and 400–460 cm–1, due to
n(M–O)[11] and n(M–N),[12] respectively.
The presence of coordinated water[13] in the complexes (1), (2), (3),
(4), (6), (7), (9) and (10) is indicated by the presence of either a broad band
at 3550–3200 cm–1 or two broad bands at 3490–3550, and 3350–3400
cm–1. The other characteristic bands for coordinated water could not be
definitively characterized. The presence of lattice/coordinated water[14] in
the complexes (5), (8) and (11) is revealed by the presence of a broad band
in the region 3600–3400 cm–1.
The unidentate coordination of acetate ion in the complexes (1), (2),
(3), (4) and (9) is supported by the presence of two bands at 1605–1640
cm–1 and 1300–1330 cm–1, due to nas(COO) and nsy(COO) modes, res-
pectively[15] (Dn = ꢁ300 cm–1).
In the spectrum of the complex [Th(o-VED)(NO3)2] three additional
bands which are not present in the spectrum of the free ligand o-VEDH2 are
observed. Of these, the band at 1015 cm–1 is assigned to the n2 mode of
the NO3 group. The bands at 1480 and 1380 cm–1 are the two split bands
n4 and n1, respectively, of the coordinated nitrate ion. The magnitude of
Dn = (n4 À n1) = 100 cm–1 shows the unidentate coordination of the
nitrate ion.[16]
The IR spectrum of the uranium complex (11) exhibits two bands at
920 and 840 cm–1 which are assignable to nas(O=U=O) and nsy(O=U=O)
modes, respectively. This observation indicates that the linearity of the
O=U=O group is maintained in the complex.[17]
The force constant (f) for the nas(O=U=O) mode was calculated for
complex (11) by following the method of McGlynn et al.[18] It was found to
˚
be 7.03 m dyne/A, and agrees well with the force constant values of similar
dioxouranium(VI) complexes.[19] From this value, the U–O bond distance
RU-O was calculated by using Jone’s equation,[20,21] RU
= 1.08f–1/3
+
O

828
Maurya, Patel, and Rajput
1.17, where f is the force constant for the nas(O=U=O). It was found to
˚
˚
be 1.73 A, and this is in the usual range (1.60–1.92 A) observed for
dioxouranium(VI) complexes.[17,19]
Conductance Measurements
The observed molar conductances of the complexes in 10–3 molar
solutions in DMSO lie in the range 6.9–11.2 ohm–1 cm2 mole–1 (Table 2).
This is consistent with the non-electrolytic nature of these complexes.[22]
Magnetic Susceptibility Measurements
In the present investigation, complexes (1) and (6) of Cu(II) exhibit
magnetic moments of 2.05 and 1.88 B.M., respectively. These data indicate
tetrahedral geometry for compound (1) and octahedral geometry for
compound (6). The Co(II)-o-VPA complex in the present study displays a
magnetic moment of 4.30 B.M. suggesting a tetrahedral geometry for this
complex.[23,24] Nickel(II) forms complexes of the coordination numbers 4,
5 and 6. The complexes (4) and (7) display magnetic moment values of
3.82 and 3.01 B.M., respectively. These results suggest a tetrahedral geo-
metry for complex (4) and an octahedral one for complex (7). The observed
room temperature magnetic moment value of the Mn-o-VPA complex is
5.94 B.M., which is consistent with high-spin manganese(II). Because of
the additional stability of the half filled d-shell, manganese(II) generally
forms high-spin complexes.
The observed room temperature magnetic moment value of the Sm-o-
VED complex (9) is found to be 1.62 B.M. This agrees well with the
theoretical value calculated from the Van Vleck equation,[25] which sug-
gests that the 4f electrons play a negligible role in bonding. In both the
cases, the Zn-o-VPA (5) and Zn-o-VED (8) complexes, a tetrahedral struc-
ture is proposed and the diamagnetic behaviour was confirmed. The Th-o-
VED (10) and UO2(VI)-o-VED (11) complexes were found to be diamag-
netic as expected.
Thermogravimetric Analysis
Two representative compounds of each ligand system, o-VPAH and o-
VEDH2, were subjected to thermogravimetric analyses. The compound (1)
shows a weight loss in the temperature range 195 °C to 228 °C to be 5.0%
(calcd. weight loss for 1 mole of H2O: 4.5%) corresponding to the elimi-
nation of one molecule of coordinated water.[13] Further decomposing oc-
curs at 315 °C and continues up to 360 °C. This weight loss is found to be

N-(o-Vanillinidene) Complexes
829
15.0% against a theoretical weight loss of 15.6% due to removal of one
coordinated acetate group from the complex (Figure 4). These weight loss
data thus agree with the IR results for this complex.
The thermogravimetric curve of compound (5) exhibits a weight loss of
3.0% (calcd. weight loss for H2O, 3.0%) in the temperature range 99 °C to
141 °C. As this weight loss starts at lower temperature (99 °C), it suggests
the presence of one lattice water[26] molecule in this compound. This cor-
roborates the IR results (vide supra). The thermogram shows a steep weight
loss of 63% in the temperature range 255 °C to 420 °C that could not be
correlated. Beyond 420 °C no significant weight loss could be observed.
The thermogram of compound (9) registers a weight loss of 3.0%
(calcd. weight loss for one mole H2O, 3.2 %) in the temperature range 95–
120 °C, suggesting the loss of one coordinated water[14] molecule. The fur-
ther weight loss shown by this compound could not be correlated. Finally,
the residue attains a constant composition corresponding to Sm2O3 at 890
°C (calcd. mass retained 62.9 %; observed = 60.0%).
The thermogravimetric curve of compound (11) shows a weight loss of
6.0 % (calcd. 5.9%, assuming a weight loss for two moles of H2O mole-
cules), which starts from 78 °C and is completed at 141 °C. This may be
100
90
80
70
60
50
Atmosphere : N2
Heating Rate : 15 °C/min.
Sample wt. : 3.00 mg
Chart Speed : 5 mm/min
40
30
20
10
100
110
210
310
410
510
610
710
810
910
T (°C)
Figure 4. TG curve of [Cu(o-VPA)(OAc)(H2O)] (1).

830
Maurya, Patel, and Rajput
due to the presence of one lattice and one coordinated water[14] molecule in
this complex, which is consistent with the IR spectral data (vide supra). A
second weight loss of 42% (calcd. 42.1%, assuming weight loss for one
o-VED molecule) was observed in the temperature range 213 to 261 °C.
This corresponds to the elimination of one coordinated o-VED group. The
decomposition continues with the gradual weight loss, and it ceases at
[27]
about 800 °C. The final residue (observed 35.2 %) corresponds to U3O8
(calcd. 35.6).
Electronic Spectra
The electronic spectra of four representative compounds, [Cu(o-VPA)-
(OAc)(H2O)] (1), [Ni(o-VPA)(OAc)(H2O)] (4), [Cu(o-VED)(H2O)2] (6) and
[UO2(o-VED)(H2O)]ꢀH2O (11) were recorded in the range 260–800 nm.
The diffuse reflectance spectrum of the compound [Cu(o-VPA)(OAc)-
(H2O)] (1) exhibits three absorption bands at 304 nm (32,894 cm–1), 403 nm
(24,813 cm–1) and 580 nm (17,241 cm–1). The appearance of the last two
broad bands is indicative of a modified (square-planar) stereochemistry due to
Jahn-Teller distortion, as reported elsewhere.[8] The first band of relatively
high intensity is assigned as ligand ! metal charge transfer transition.[28]
This result, coupled with the magnetic data of this complex (2.05 B.M.),
suggests a square-planar geometry.
The diffuse reflectance spectrum of [Ni(o-VPA)(OAc)H2O] (4)
(Figure 5) shows two absorption bands at 319 nm (31,347 cm–1
)
(e = 972 L mol–1 cm–1) and 416 nm (24,038 cm–1) (e = 370 L mol–1
cm–1). The first band, which is of relatively high intensity, is attributed to a
Figure 5. Diffuse reflectance spectrum of [Ni(o-VPA)(OAc)(H2O)] (4).

N-(o-Vanillinidene) Complexes
831
ligand ! metal charge transfer transition.[28] The second broad band cor-
3
responds to the transition T1 (P) 3T1(F) for a tetrahedral complex, which
is of much lower energy as compared with octahedral complexes.[29] The
magnetic moment value (3.82 B. M.) also ruled out the possibility of oc-
tahedral complexes.
The diffuse reflectance spectrum of [Cu(o-VED)(H2O)2] (6) shows
three spectral peaks at 280 nm (35,714 cm–1), 317 nm (26,954 cm–1) and
568 nm (17,605 cm–1). The third broad peak at 568 nm is most probably
2
due to the T2g 2E2g transition suggesting a distorted octahedral geometry
for this complex.[30] The first and second spectral peaks of relatively higher
intensities are due to ligand !metal charge transfer transitions.
The diffuse reflectance spectrum of complex [UO2(o-VED)(H2O)]ꢀH2O
(11) exhibits two spectral bands at 263 nm (38,022 cm–1) (e = 556 L mol–1
cm–1) and 333 nm (30,030 cm–1) (e = 412 L mol–1 cm–1) assignable to
p !p* and n !p* transition, respectively, of the azomethine linkage.
The third band appearing at 421 nm (23,752 cm–1) (e = 398 L mol–1 cm–1)
3
in this complex is assigned to the 1S+ g ! pu transition typical of the
O–U–O symmetric stretching frequency, ns(O=U=O), for the first ex-
cited state.[2]
Figure 6. 1H NMR spectrum of [Zn(o-VPA)2]ꢀH2O (5).

832
Maurya, Patel, and Rajput
.
Figure 7. 1H NMR spectrum of [Zn(o-VED)]ꢀ2H2O (8).
1H NMR Spectral Data
1H NMR spectra of the Zn-o-VPA (Figure 6) and Zn-o-VED (Figure 7)
complexes were recorded in DMSO-d6. Comparison of the chemical shifts
of the ligands (Figures 2 and 3) with those of the complexes shows that the
signal due to the phenolic proton (OH) is absent in the complexes,
suggesting the coordination of the phenolic oxygen to the metal ion after
deprotonation. The azomethine proton (–CH=N–) undergoes a significant
shift, indicating the coordination of the azomethine nitrogen to the metal
ion.[8] Thus, the 1H NMR data confirm the monobasic, bidentate (ON)
nature of o-VPAH and the dibasic, tetradentate (OONN) nature of (o-
VEDH2), which already have been suggested by the IR spectral data.
CONCLUSIONS
Satisfactory analytical data as well as all the studies presented above
suggest that the present complexes may be formulated as [M(L)(OAc)(H2O)]
{where M = Cu(II), Co(II), Mn(II) or Ni(II) and OAcH = CH3COOH}, [Zn-
(L)2]ꢀH2O, [M(L’)(H2O)2] {where M = Cu(II) or Ni(II)}, [Zn(L’)]ꢀ2H2O,
[Sm(L’)(OAc)(H2O)], [Th(L’)(NO3)2] and [UO2(L’)(H2O)]ꢀH2O (where
LH = o-VPAH, and L’H2 = o-VEDH2). From the analytical data and the

N-(o-Vanillinidene) Complexes
833
Figure 8. Proposed structures of complexes.

834
Maurya, Patel, and Rajput
physical studies discussed above, the ligand o-VPAH has been shown to act as
a bidentate, monobasic ligand which coordinates through the enolic oxygen
and azomethine nitrogen and forms complexes with copper(II), nickel(II),
cobalt(II) and manganese(II) in 1:1 stoichiometric ratio and with zinc(II) in
1:2 ratio. o-VEDH2 acts as a tetradentate, dibasic ligand coordinating through
two azomethine nitrogens and two enolic oxygens and forms complexes with
Cu(II), Ni(II), Zn(II), Sm(II), Th(IV) and U(VI)O2 in 1:1 stoichiometric ratio.
The proposed structures of these complexes are shown in Figure 8. The
coordination numbers of the complexes are given in Table 2.
ACKNOWLEDGMENTS
The authors are thankful to Professor S. D. Tripathi, Vice-Chancellor
of this University, for encouragement, and Professor K. K. Mishra, Head,
Department of Chemistry, for laboratory facilities and helpful discussions.
Analytical facilities provided by the Central Drug Research Institute, Luck-
now, India, and the Regional Sophisticated Instrumentation Centre, Indian
Institute of Technology, Chennai, India, are gratefully acknowledged.
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Received August 17, 1998
Accepted February 4, 2003
Referee I: M. H. Dickman
Referee II: R. H. Gayhart