Hydrolysis of 4-(4-oxopentan-2-ylideneamino)benzoic acid and in-situ formation of nickel(II), zinc(II) and cadmium(II) complexes of 4-aminobenzoic acid

Article abstract of DOI:10.1016/j.ica.2012.09.005

Metal(II) acetates of nickel, zinc and cadmium facilitate hydrolysis of 4-(4-oxopentan-2-ylideneamino)benzoic acid (iminocarb). In the case of nickel a dinuclear iminocarb complex is proposed as intermediate species to form nickel complex of 4-aminobenzoic acid (Haben). The nickel complex formed from hydrolysis has a composition [Ni(O₂CCH₃) ₂(Haben)₂(H₂O)₂]·2H ₂O. In this complex, the nitrogen atoms of the 4-aminobenzoic acid ligands coordinate to nickel ion and the benzoic acid end of the ligands remain free. A five coordinate [Zn(aben)₂(py)(H₂O)] complex is obtained from a similar reaction of iminocarb with zinc(II) acetate followed by reaction with pyridine (py). On the other hand the reaction of iminocarb with cadmium(II) acetate forms a coordination polymer [{Cd(aben)₂(H ₂O)}·H₂O]_n.

Full text of DOI:10.1016/j.ica.2012.09.005

Inorganica Chimica Acta 394 (2013) 430–435
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Hydrolysis of 4-(4-oxopentan-2-ylideneamino)benzoic acid and in-situ formation
of nickel(II), zinc(II) and cadmium(II) complexes of 4-aminobenzoic acid
⇑
Nithi Phukan, Jubaraj B. Baruah
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2012
Received in revised form 6 September 2012
Accepted 8 September 2012
Available online 17 September 2012
Metal(II) acetates of nickel, zinc and cadmium facilitate hydrolysis of 4-(4-oxopentan-2-ylideneami-
no)benzoic acid (iminocarb). In the case of nickel a dinuclear iminocarb complex is proposed as interme-
diate species to form nickel complex of 4-aminobenzoic acid (Haben). The nickel complex formed from
hydrolysis has a composition [Ni(O2CCH3)2(Haben)2(H2O)2]Á2H2O. In this complex, the nitrogen atoms
of the 4-aminobenzoic acid ligands coordinate to nickel ion and the benzoic acid end of the ligands
remain free. A five coordinate [Zn(aben)2(py)(H2O)] complex is obtained from a similar reaction of imino-
carb with zinc(II) acetate followed by reaction with pyridine (py). On the other hand the reaction of
iminocarb with cadmium(II) acetate forms a coordination polymer [{Cd(aben)2(H2O)}ÁH2O]n.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Imine-hydrolysis
4-Aminobenzoic acid
Coordination effect
Five-coordinate complex
Coordination polymer
1. Introduction
reactions to establish the coordination effect during iminocarb
hydrolysis.
Imines are extensively used as ligands in coordination chemis-
try [1–3]. Many organic transformations of imines are catalysed by
various metal complexes [2,4–11]. The conversion of an imine to a
carbonyl compound is relatively easy and this transformation is
used in protecting carbonyl groups [12–14]. Several pathways are
possible for formation of a carbonyl compound from an imine.
The hydrolysis [15–24], oxidative cleavage of C@N bond [25–28]
and disproportionation reactions [29–31] are common paths for
such transformations. Taking b-ketoimine as an example these
paths are shown in Scheme 1. Ketoimines are well known for their
ability to form interesting metal complexes [2,23]. We are inter-
ested to study the role of metal ions in hydrolytic cleavage of
C@N bond of imines of 4-aminobenzoic acid, as they are formed
from hydrolytic cleavage of some medicines that are used to eval-
uate pancreatic function and measured in urine [32]. We selected a
model compound 4-(4-oxopentan-2-ylideneamino)benzoic acid
(abbreviated as iminocarb) for such a study, as this ligand has a car-
boxylic acid group at one end and a b-ketoimine group at other end
(Scheme 2). Both these groups efficiently bind to metal ions and
are capable of forming chelates. We also felt that the presence of
a binding site at a remote place from a hydrolysis site, would not
only bind a metal ion but also assist in hydrolysis. In this article
we report the hydrolysis of iminocarb leading to different metal
complexes with 4-aminobenzoic acid (Haben). We discuss such
2. Experimental
2.1. Preparation of 4-(4-oxopentan-2-ylideneamino)benzoic acid
(iminocarb)
The ligand iminocarb was prepared by modifying reported pro-
cedure [33]. To a well stirred solution of 4-aminobenzoic acid
(0.27 g, 2 mmol) in methanol (10 ml), acetylacetone (0.26 ml,
2 mmol) was added. The reaction mixture was refluxed for 6 h at
60 °C. A yellow precipitate was obtained upon cooling. The reaction
mixture was filtered and the precipitate was collected. The product
iminocarb was recrystallized from methanol. Isolated yield: 86%. IR
(KBr, cmÀ1): 3459 (b), 1697 (s), 1599 (s), 1557 (s), 1289 (s), 1253
(s), 1218 (s), 1179 (s). 1H NMR (DMSO-d6): 12.61 (s, 1H), 7.91 (d,
8.4 Hz, 2H), 7.28 (d, 8.4 Hz, 2H), 5.33 (s, 1H), 2.10 (s, 3H), 1.98 (s,
3H).
2.2. Complex [Ni(O2CCH3)2(Haben)2(H2O)2]Á2H2O (1)
To a methanol solution of iminocarb (0.04 g, 0.2 mmol), nicke-
l(II) acetate tetrahydrate (0.05 g, 0.2 mmol) was added, a dark
green precipitate was obtained. The precipitate was dissolved in
a minimum amount of dimethylformamide and filtered. The fitrate
was kept for crystallization for a week; dark green crystals were
obtained. Isolated yield: 62%, IR (KBr, cmÀ1): 3407 (b), 1600 (s),
1394 (s), 1310 (s), 1281 (s), 1188 (s), 1113 (s), 1024 (m), 924 (s).
⇑
Corresponding author. Tel.: +91 361 2582311; fax: +91 361 2690762.
E-mail address: juba@iitg.ernet.in (J.B. Baruah).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.09.005

N. Phukan, J.B. Baruah / Inorganica Chimica Acta 394 (2013) 430–435
431
R
R
R
O
OH
O
OH
N
OH
N
HN
H2O
+
RNH2
+
Hydrolysis
Disproportionation
Oxidative
O
OH
RNHOH
+
Scheme 1. Some possible paths of carbonyl group formation from an imine.
coordination site
NH2
OH
+
Mn+
O
H2N
coordination site
O
COOH
Mn+
N
Mn+
chelation site
O
O
I
Mn+
or
hydrolysis
O
Mn+
H2N
Mn+
N
O
O
H
O
O
COOH
II
coordination site
4-(4oxopentan-2-ylideneamino)benzoic acid
Scheme 2. One possible intermediate metal complex during hydrolysis of iminocarb and its products.
Molar conductance (methanol, RT) 27.2 S cm2 molÀ1. Visible (kmax
,
7.2 Hz, 2H), 6.51 (d, 8.8 Hz, 4H), 5.55 (s, 4H). Molar conductance
(methanol, RT) 5.9 S cm2 molÀ1
methanol) 673 nm
(
e
= 99 L molÀ1 cmÀ1); 725
(
e
= 86 L molÀ1
.
cmÀ1).
2.3. Complex [Zn(aben)2(py)(H2O)] (2)
2.4. Complex [{Cd(aben)2(H2O)}ÁH2O]n (3)
To a well stirred solution of iminocarb (0.04 g, 0.2 mmol) in
methanol (10 ml), zinc(II) acetate dihydrate (0.04 g, 0.2 mmol)
was added, after 1hr the resulting reaction mixture was filtered
and to the filtrate pyridine (1 ml) was added. The transparent li-
quid obtained was kept for crystallization. After 10 days colorless
crystals were obtained. Isolated yield: 60%. IR (KBr, cmÀ1): 3375
(w), 3304 (w), 2926 (w), 1605 (w), 1553 (m), 1511 (w), 1434 (w),
1398 (s), 1256 (w), 1182 (w), 1020 (w), 787 (m), 699 (m). 1H
NMR (DMSO-d6): 7.86 (t, 7.6 Hz, 3H), 7.62 (d, 8.4 Hz, 4H), 7.46 (t,
To a well stirred solution of iminocarb (0.04 g, 0.2 mmol) in
methanol (10 ml), cadmium(II) acetate dihydrate (0.05 g,
0.2 mmol) was added, a colorless precipitate was obtained. The
precipitate was dissolved in minimum amount of methanol. The
reaction mixture was filtered and the transparent liquid was kept
for crystallization. After 1 week colorless crystals were obtained.
Isolated yield: 67%. IR (KBr, cmÀ1): 3365 (s), 3291 (w), 3159 (w),
1607 (s), 1519 (s), 1409 (s), 1256 (w), 1176 (w), 1093 (w), 1012
(w), 943 (m). 1HNMR (DMSO-d6): 8.62 (bs, 2H), 7.86 (t, 7.6 Hz,

432
N. Phukan, J.B. Baruah / Inorganica Chimica Acta 394 (2013) 430–435
Table 1
plexes of these metal ions (Scheme 3). These complexes are
Crystallographic parameters of the complexes 1 and 2.
formed through hydrolysis of the iminocarb. Since all the com-
plexes obtained are from hydrolysis of iminocarb, we can alterna-
tively say that the hydrolysis of the iminocarb is facilitated by
these metal(II) acetates. Due to the strong binding ability of
b-ketoimine, the iminocarb is expected to form metal complexes
with these metal ions; we could not isolate any such stable com-
plex. However, solution study has led us to propose intermediacy
of such complex. At this juncture it is worth mentioning that
these metal acetates independently react with Haben to form
insoluble metal complexes. Similar situations were reported dur-
ing the preparation of metal-aromatic carboxylate complexes
[34–36] and in such cases ancillary ligands were used to over-
come the insolubility problem. The iminocarb forms a stable com-
plex with tin(IV) [33]. The tin(IV) complex has relatively more
covalent Sn–O and Sn–N bonds which resists hydrolysis of the
complex.
Compound No.
1
2
Formulae
Mol. wt.
Crystal system
Space group
T (K)
k (Å)
a (Å)
b (Å)
c (Å)
C
18H30N2NiO14
C19H19N3O5Zn
434.74
monoclinic
P21/n
557.15
monoclinic
P21/n
296(2)
296(2)
0.71073
6.7822(3)
18.1737(9)
10.6188(5)
90.00
97.332(2)
90.00
1298.15(11)
2
0.71073
6.8027(4)
27.7694(17)
10.3788(6)
90.00
96.079(3)
90.00
1949.6(2)
4
a
(°)
b (°)
c
(°)
V (Å3)
Z
D (Mg mÀ3
)
1.425
0.815
1.481
1.295
Absorption
Coefficient
(mmÀ1
)
The nickel(II) acetate tetrahydrate hydrolyses iminocarb leading
to the formation of di-(j-N-4-aminobenzoic acid)di-aqua nickel(II)
Absorption
correction
none
none
acetate dihydrate (1). It is an acetate complex (Fig 1a) having two
4-aminobenzoic acid ligands. The non-ionic nature of the com-
pound is reflected by its molar conductance (27.2 S cm2 molÀ1).
The complex has an octahedral geometry with two aqua-ligands,
two amino groups from the Haben and two acetate ligands. The
complex 1 has a highly symmetric structure. The structure has a
mirror plane of symmetry which is also apparent from its space
group (P21/n). The structure of the compound is shown in Fig. 1a
and selected bond parameters are shown in the caption of
Fig. 1a. The complex possesses intra-molecular hydrogen bond be-
tween a carbonyl oxygen of acetate with one coordinated aqua li-
gand through O5–HÁ Á ÁO4 interaction (dDÁ Á ÁA, 2.64 Å, \D–HÁ Á ÁA
143.1°). The lattice water molecules form hydrogen bonds with
acid group of the Haben through O7–HÁ Á ÁO2 and O7–HÁ Á ÁO2 inter-
actions (dDÁ Á ÁA, 2.81 Å and dO7Á Á ÁO1, 3.00 Å; \O7–HÁ Á ÁO2, 178.0°; and
\O7–HÁ Á ÁO1, 160.5°). The water molecules in the crystal lattice are
also linked to carboxylates of acetate groups through O6–HÁ Á ÁO4
interactions (dO6Á Á ÁO4, 2.78 Å \O7–HÁ Á ÁO2 154.3°). The N1–HÁ Á ÁO1
interactions (dN1Á Á ÁO1, 2.30 Å \N1–HÁ Á ÁO1 158.0°), as well as C2–
HÁ Á ÁO4 (dC2Á Á ÁO4, 3.30 Å \C2–HÁ Á ÁO4 135.7°) are pertinent hydrogen
bonds in the crystal lattice (Fig. 1b). Each molecule of the complex
in the lattice can be visualized to be surrounded by six other
molecules as shown in Fig. 1c. Thus a central molecule is held to
six-other through supramolecular interactions.
F(000)
584
896
Total reflections
Reflections, I > 2
Maximum h (°)
Ranges (h, k, l)
3221
2953
28.50
3378
2728
25.25
r(I)
À9 6 h 6 9, À24 6 k 6 24, À8 6 h 6 8,
À14 6 l 6 14
À30 6 k 6 30,
À12 6 l 6 9
95.7
Complete to 2h (%)
Data/restrain/
98.0
3221/7/183
3378/3/274
parameter
Goodness-of-fit (F2)
1.053
1.042
R1 [I > 2
wR2 [I P 2
R1 (all data)
wR2 (all data)
r
(I)]
0.0351
0.1008
0.0378
0.1031
0.0372
0.0947
0.0468
0.0988
r(I)]
1H), 7.62 (d, 8.0 Hz, 4H), 7.48 (t, 7.2 Hz, 2H), 6.48 (d, 8.0 Hz, 4H),
5.53 (s, 4H). Molar conductance (DMF, RT) 2.4 S cm2 molÀ1
The crystallographic parameters of the complexes 1 and 2 are
listed in Table 1.
.
3. Results and discussion
The reaction of iminocarb with metal(II) acetates of nickel,
zinc and cadmium led to formation of 4-aminobenzoic acid com-
[Zn(aben)2(py) (H2O)] + AcAcH + CH3CO2H
2
py
Zn(O2CCH3)2.2H2O
MeOH
MeOH
Ni(O2CCH3)2.2H2O
iminocarb
[{Cd(aben)2(H2O)}.H2O]n
[Ni(O2CCH3)2(Haben)2(H2O)2].2H2O
+
DMF
MeOH
Cd(O2CCH3)2.2H2O
1
3
+ AcAcH
+ AcAcH + CH3CO2H
COOH
O
NH2
Haben =
HOOC
N
Where iminocarb =
py = pyridine
Scheme 3. Formation of metal complexes of Haben from hydrolysis of iminocarb.

N. Phukan, J.B. Baruah / Inorganica Chimica Acta 394 (2013) 430–435
433
Fig. 1. (a) Structure of [Ni(O2CCH3)2(Haben)2(H2O)2]Á2H2O (1) (ORTEP drawn with 50% thermal ellipsoids, water of crystallisations are ommited) Selected bond-distances and
bond-angles are Ni1–O5, 2.0670(12) Å; Ni1–O3, 2.0583(11) Å; Ni1–N1, 2.1593(14) Å; \N1–Ni1–O5, 90.87(6)°; \N1–Ni–O3, 87.75(5)°; \O3–Ni1–O5 85.52(5)°. (b) Weak
interactions in the crystal lattice of 1 (30% thermal ellipsoids). (c) Packing diagram showing a molecule of 1 (CPK) surrounded by six other molecules. (d) UV–Vis spectra of (i)
the iminocarb in methanol (10À4 M, 2 ml); (ii) immediately after addition of nickel(II) acetate tetrahydrate (10À4 M) to (i). Same solution of iminocarb with nickel(II) acetate
after (iii) 1 day, (iv) 3 days and (v) 4 days.
The IR spectra of the Haben has sharp absorptions at 3461 (mN–H
cmÀ1, 3364 ( O–H) cmÀ1, 1666 ( C@O) cmÀ1, 1624 (mN–Hscissoring
cmÀ1 and 1601 (
)
)
solution of sodium salt of acetylacetone shows p–
p⁄ transition at
m
m
288 nm; whereas the nickel(II) acetylacetonate has similar absorp-
tion peak at 294 nm [41]. Based on the analogy of the structural
backbone of acetylacetone and iminocarb, the absorbances ob-
m
C@C) cmÀ1, whereas the IR of the nickel complex
1 has broad absorption at 3407 cmÀ1. The sharp absorption at
3407 cmÀ1 is attributed to N–H and O–H stretching frequencies
of the coordinated amino group and free carboxylic acid. The IR
served at 342 and 339 nm are attributed to the p–
p⁄ transition of
iminocarb in respective cases. The change in absorption is attrib-
uted to the formation of an intermediate complex A as depicted
in Scheme 4. From Fig. 1d it is clear that as time progresses peak
intensity of 339 nm reaches a maximum and then decreases. The
isolated complex 1 does not show absorption at this wavelength.
On the basis of these observations, we propose a mechanism for
hydrolysis of iminocarb as illustrated in Scheme 4. We propose a
binuclear aqua-bridged nickel(II) complex A as an intermediate
species for the hydrolysis. The intermediate has a highly symmet-
ric structure which can lead to the final product 1. It is an estab-
lished fact that the nickel(II) acetate forms aqua-bridged
binuclear complexes with nitrogen donor ancillary ligands [37].
Such complexes have structural similarity to biologically impor-
tant metal hydrolases [42,43]. Thus, in another sense we can sug-
gest this mechanism to be a bio-mimicking process [44]. Our
hydrolytic reaction is sensitive to pH and works at near neutral
conditions (pH of about 7.5–8.5). The reaction is also anion specific.
The use of halide or nitrate salt for similar reactions did not give
satisfactory result. Further, addition of sodium acetate in excess
from an external source also did not facilitate the hydrolysis of imi-
nocarb. Thus, it is presumed that the acetate ions remain bound to
the metal during the course of the reaction as shown in the reac-
tion mechanism. The hydrolysis of iminocarb by nickel(II) acetate
was also monitored by GC–mass. The reaction takes place under
catalytic condition (10 mol% of nickel(II) acetate) at room temper-
ature in methanol.
absorptions observed at 1697 (
for iminocarb are not present in 1 but it has a strong absorption
at 1600 (
C@O) cmÀ1. This shows that carboxylate group has highly
m m
C@O) cmÀ1 and 1599 ( C@N) cmÀ1
m
delocalized electrons. In fact the complex has free carboxylic acid
with equal C7–O1 and C7–O2 distances (1.259 Å each). This is
due to formation of hydrogen bond by the carboxylic acid with lat-
tice water molecules. The interesting feature of complex 1 is the
monodentate coordination mode of acetate group. Generally, nick-
el(II) acetate undergoes ligand replacement reactions with benzo-
ates [37]. The nickel-aben complex having dioxime ligands are
reported earlier [38]. N-functionalized nickel-aben complex shows
carboxylate binding [39]. There is an example of an ionic complex
having N-coordinated Haben with nickel(II) chloride [40]. The com-
plex 1 on the other hand is a neutral complex, having carboxylates
within the coordination sphere. The IR spectra of the insoluble
product from reaction of nickel(II) acetate with Haben has similar-
ity to the IR spectra of cadmium complex 3 and it suggests that
they have similar structure. Thus, direct mixing of nickel(II) acetate
with Haben leads to a coordination polymer with carboxylate and
amino groups as bridges.
The complex 1 absorbs at 673 and 725 nm due to d–d transi-
tions (assigned vide extinction coefficient). Formation of the com-
plex (1) from iminocarb was monitored by UV–Vis spectroscopy.
The iminocarb has absorption maximum at 342 nm. The absorption
at 342 nm of a solution of iminocarb increases on addition of nick-
el(II) acetate solution (Fig. 1d). The increase is accompanied by a
shift in the absorbance to 339 nm. It is reported that an alcoholic
The reaction of zinc(II) acetate with iminocarb followed by
treatment with pyridine (py) in methanol led to the formation of

434
N. Phukan, J.B. Baruah / Inorganica Chimica Acta 394 (2013) 430–435
OH
+ Ni(O2CCH3)2.4H2O
N
O
O
HO
O
O
HO
CH3
H
O
H2O
H2O
O
O
NH2
OH2
N
H2
O
O
O
Ni
H2O
O
O
H2O
O
Ni
Ni
O
N
H2N
H
O
O
O
O
H3C
O
O
O
intermediate (A)
OH
+
CO2H
O
Scheme 4. A plausible mechanism of nickel(II) mediated hydrolysis reaction of iminocarb.
Fig. 2. (a) The structure of [Zn(aben)2(py)(H2O)] (2) (drawn with 50% thermal ellipsoids). Selected bond distances and bond angles are Zn1–O1, 2.012(16) Å; Zn1–O2,
2.412(17) Å; Zn1–O4, 1.911(17) Å; Zn1–O5, 2.056(18) Å; Zn1–N3, 2.021(2) Å; \O1–Zn1–O2, 58.41(6)°; \O5–Zn1–O2, 154.47(7)°; \O1–Zn–N3, 109.04(7)°; \O4–Zn1–N3,
135.59(8)°. (b) The weak interactions among different molecules of 2 to form self-assembly.
[Zn(aben)2(py)(H2O)] (2). The complex has very interesting
structural features (Fig. 2a). It has five-coordinate geometry around
zinc ion, which is relatively less common in zinc chemistry. It has
an intermolecular hydrogen bonded structure. The coordinated
water molecule and amino groups of the aben form very interesting
cyclic hydrogen bond R44(8) motifs. The motifs are comprise
HÁ Á ÁO2, 148.9°). These cyclic motifs arise from interactions of four
molecules of the complex 2. The cyclic structure can be compared
to a rectangle having two oxygen atoms of carboxylate placed at
two corners and two nitrogen atoms of two amino groups at other
two corners. Further to this, there is O5–HÁ Á ÁO3 interactions
among aqua ligand and monodentate carboxylate of a neighboring
molecule (dDÁ Á ÁA, 2.72 Å, \D–HÁ Á ÁA 157.9°). The important weak
interactions responsible for making self-assemble structure are
shown in Fig. 2b. The complex 2 is presumably formed during
of N1–HÁ Á ÁO2–H–N2–HÁ Á ÁO1Á Á ÁH–N1 interactions (dN1Á Á ÁO2
,
2.95 Å; dN2Á Á ÁO1, 3.05 Å; dN1Á Á ÁO1, 2.93 Å and dN2Á Á ÁO2, 3.06 Å; \N1–
HÁ Á ÁO2, 163.0°; \N2–HÁ Á ÁO1, 176.8° \N1–HÁ Á ÁO1, 156.9°; \N2–

N. Phukan, J.B. Baruah / Inorganica Chimica Acta 394 (2013) 430–435
435
Acknowledgements
One of the author (N.P.) thanks Council of Scientific and Indus-
trial Research (New Delhi) for a Junior Research Fellowship.
Appendix A. Supplementary material
CCDC 868737 and 868738 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.09.005.
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just after addition of cadmium(II) acetate(10À4 M); (c) coordination polymer 3 in
methanol (10À4 M).
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crystallization. The pyridine possibly replaces the coordinated
nitrogen of aben during crystallization. In fact the IR spectrum of
the product before dissolving it in pyridine has similarities to the
IR spectra of the product 3 (whose structure is polymeric). Unfor-
tunately, we are unable to obtain crystalline product in this case
without pyridine. The zinc(II) acetate quenches the absorption of
a methanol solution of iminocarb. During the course of measure-
ment there is oscillation on changes in absorbance with time.
The trend in increase or decrease is not consistent, it may be due
to the equilibration between C@N and C@O bond formation along
with the crystallization of the product. Thus, a complete conclusion
is not reached. A polymeric aben-zinc complex is reported in liter-
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conductance.
The reaction of cadmium(II) acetate with iminocarb in methanol
gave the 4-aminobenzoate complex [{Cd(aben)2(H2O)}ÁH2O]n (3).
The compound 3 has a similar structure to the already reported
one [48]. The cadmium complex 3 is also non-ionic with very
low molar conductance. The hydrolysis of iminocarb by cadmium
is apparent from its UV–Vis spectra. It is observed that immedi-
ately after addition of cadmium(II) acetate to iminocarb forms 3
as shown in Fig. 3. The absorption of iminocarb at 342 nm gets
drastically quenched on addition of cadmium acetate and new
absorption peak at 282 nm appears. This new peak matches with
the peak of the coordination polymer 3. The complete conversion
of iminocarb to 3 in solution does not take place even after four
days. Thus, it is suggested that there is an equilibrium between
C@N cleavage and formation of C@O bond. The precipitation dur-
ing the equilibration process is the driving force for the formation
of 3. The bridging binding mode of the 3 suggests that it is formed
through a cadmium–iminocarb intermediate complex. Such inter-
mediate is possible as the size of cadmium is relatively bigger
and can expand its coordination number [34].
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ions facilitate the hydrolysis of iminocarb. The coordination modes
of ligands in the isolated metal complexes provide evidences to-
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resemblance to biological system is proposed to explain the nickel
mediated hydrolysis. The structure of cadmium-aben complex
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