Anion-directed structural diversity in the complexes of Cd(II)-arylazoimidazole: Synthesis, spectral characterization and crystal structure

Article abstract of DOI:10.1016/j.poly.2003.07.006

Cadmium(II) complexes of 1-alkyl-2-(arylazo)imidazoles [RaaiR′ (where R = H (a), Me (b); R′ = Me (1/3/5/7), Et (2/4/6/8)] are described in this work. Three representative complexes of the series, [Cd(HaaiMe) ₂Cl₂] (3a), [Cd(HaaiEt)₄](ClO₄) ₂ (6a) and [Cd(HaaiMe)₄](NO₃) ₂·2H₂O (7a), have been characterized by single crystal X-ray diffraction measurements. In these complexes, cadmium is seated at the center of a tetrahedron. In [Cd(HaaiMe)₂Cl₂] (3a), the neutral metallo-organic compound consists of a central cadmium atom surrounded by two HaaiMe ligands and two chlorides. In [Cd(HaaiEt)₄] (ClO₄)₂ (6a), the cation consists of a central cadmium atom surrounded by four HaaiEt ligands. [Cd(HaaiMe)₄] (NO ₃)₂·2H₂O (7a) is a tetragonal channel structure. Nitrate and interstitial water molecules assemble into a square-grid supramolecule (ca. 7 × 7 A?) and each grid is interlocked by chains parallel to the Z-axis passing through the middle of the square arms to form a layer in the ac- (or bc-) plane with a brick-wall topology (dimension 11.2 × 7 A?).

Full text of DOI:10.1016/j.poly.2003.07.006

Polyhedron 22 (2003) 3161–3169
www.elsevier.com/locate/poly
Anion-directed structural diversity in the complexes of
Cd(II)-arylazoimidazole: synthesis, spectral characterization
and crystal structure
a
B.G. Chand , U.S. Ray , G. Mostafa , Tian-Huey Lu , Lawrence R. Falvello ,
a
b
b
c
c
Tatiana Soler , Milagres Tomas , C. Sinha
c
a,
*
ꢀ
a
Department of Chemistry, University of Burdwan, Burdwan 713104, India
b
Department of Physics, National Tsing-Hua University, Hisnchu 300, Taiwan, ROC
Department of Inorganic Chemistry and Aragoꢀn Materials Science Institute, University of Zaragoza,
Plaza San Francisco s/n, E- 50009 Zaragoza, Spain
c
Received 6 May 2003; accepted 2 July 2003
Abstract
Cadmium(II) complexes of 1-alkyl-2-(arylazo)imidazoles [RaaiR0 (where R ¼ H (a), Me (b); R0 ¼ Me (1/3/5/7), Et (2/4/6/8)] are
described in this work. Three representative complexes of the series, [Cd(HaaiMe)2Cl2] (3a), [Cd(HaaiEt)4](ClO4)2 (6a) and
[Cd(HaaiMe)4](NO3)2 ꢀ 2H2O (7a), have been characterized by single crystal X-ray diffraction measurements. In these complexes,
cadmium is seated at the center of a tetrahedron. In [Cd(HaaiMe)2Cl2] (3a), the neutral metallo-organic compound consists of a
central cadmium atom surrounded by two HaaiMe ligands and two chlorides. In [Cd(HaaiEt)4] (ClO4)2 (6a), the cation consists of a
central cadmium atom surrounded by four HaaiEt ligands. [Cd(HaaiMe)4] (NO3)2 ꢀ 2H2O (7a) is a tetragonal channel structure.
ꢁ
Nitrate and interstitial water molecules assemble into a square-grid supramolecule (ca. 7 ꢁ 7 A) and each grid is interlocked by
chains parallel to the Z-axis passing through the middle of the square arms to form a layer in the ac- (or bc-) plane with a brick-wall
ꢁ
topology (dimension 11.2 ꢁ 7 A).
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Arylazoimidazoles; Cadmium (II) complexes; Square grid; X-ray structure
1. Introduction
stronger affinity towards imidazole-N (N) in the
M(N,N0)-chelated structures. These have been con-
cluded on the basis of M–N(N0) bond length data of the
complexes. Non-transition metal complexes of arylazo-
heterocycles have been studied recently [13–16]. We have
reported Zn(II) [13,14] and Hg(II) [15,16] complexes of
some of the members of the arylazoheterocycles. It is
observed that the non-transition metals prefer hetero-
cyclic-N during their interaction with N,N0 donor li-
gands. 2-(Arylazo)pyridines and 2-(arylazo)pyrimidines
form distorted chelate complexes of Zn(II) [13] and
Hg(II) [16]. 1-Alkyl-2-(arylazo)imidazoles (RaaiR0) act
as monodentate imidazole-N donor ligands during their
reaction with Zn(II) and Hg(II) metal ions [14,16].
In this paper we present an account on cadmium(II)
complexes of RaaiR0, a member of the zinc triad. In
The work stems from our interest in the exploration
of coordination chemistry of arylazoimidazoles [1–16].
The ligands act, in general, as a N,N0-bidentate chelator
where N and N0 refer to imidazole-N (N) and azo-N (N0)
donor centers, respectively. Major progress has been
made in the area of transition metals [1–10]. Metal ions
have preferential binding affinity towards N or N0. For
example, Ru(II) [2–5] and Os(II) [6] prefer to coordinate
with azo-N while Pd(II) [8] and Pt(II) [9,10] have a
* Corresponding author. Tel.: +91-342-57683/2530452; fax: +91-342-
64452/2557683.
E-mail addresses: bdnuvlib@giasclol.vsnl.net.in, c_r_sinha@yahoo.
com (C. Sinha).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.07.006

3162
B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
the cationic complexes of cadmiuꢂm(II)-arylazoimidaz-
oles the counterions are Clꢂ, ClO4 and NO3ꢂ. The X-
ray structure studies reveal the structural differences of
the complexes which have originated from the nature
of the anions. The anions do not only function as
counterions to the molecule but are also a part of the
structural integrity. Sometimes they play a key role to
form bridge, helical structures and 1D, 2D, 3D net-
works. Anions are classified based on their charges,
nature, denticity, periodic position, structures, etc.
[17,18]. For example, Clꢂ sometimes acts as a bridginꢂg
ligand and can form 1D chains [19,20], CO32ꢂ, NO3
are planar anions (D3h) that coꢂntribute to 2D ar-
rangements [21–24]; BF4ꢂ, ClO4 being tetrahedral
(Td) symmetric are reasonable agents to generate 3ꢂD
Warning: Cadmium and its compounds are toxic
[39–41], and perchlorate salts are potential explosives.
Only small amounts should be prepared.
2.2. Physical measurements
Microanalytical (C, H, N) data were obtained from a
Perkin–Elmer 2400 CHNS/O elemental analyzer. Con-
ductivity was measured with a Systronics model 304
conductivity meter. Spectroscopic data were obtained
using the following instruments: UV–Vis, JASCO UV/
Vis/NIR model V-570; IR (KBr, cmꢂ1 disk, 4000–200
cmꢂ1), JASCO FT-IR model 420 spectrophotometers and
1H NMR, Bruker 300 MHz FT-NMR spectrometer.
networks [25–29]; anions like M(CN)6nꢂ, PF6ꢂ, SbF6
,
2.3. Synthesis of [Cd(HaaiMe)2Cl2] (3a)
etc. are used to generate superstructures [30]. Oxo-
anions are able to synthesize aꢂpolymeric geometry via
hydrogen bonding [30–34], N3 and SCNꢂ are special
anions to construct varieties of networks and also
participate in spin exchange processes in transition
metal complexes [35–38]. In this paper we find out how
the anions control the structure of cadmium(II) com-
plexes of 1-alkyl-2-(arylazo)imidazoles (RaaiR0). Both
spectral and X-ray crystallographic studies are detailed
in each case.
1-Methyl-2-(phenylazo)imidazole (0.08 g, 0.4 mmol) in
MeOH (10 ml) was added in dropwise to a stirred meth-
anolic solution (10 ml) of CdCl2 (0.18 g, 0.1 mmol) at
room temperature (298 K). The orange–yellow solution
was left undisturbed for 2 weeks. Bright orange crystals
were obtained. These were then washed with water and
finally, dried in vacuo. The yield was 0.04 g (65%). Mi-
croanalytical data of the complex is given below:
[Cd(HaaiMe)2Cl2] (3a): Found: C, 43.28; H, 3.5; N, 20.11.
[C20H20N8Cl2Cd] requires C, 43.22; H, 3.6; N, 20.16%; IR
(KBr, cmꢂ1) 1558m, 1508m, 1438m, 323w, 302w.
All other complexes in this series were prepared by
the same procedure. The yield varied from 60% to 65%
and microanalytical data of the complexes are as fol-
lows. [Cd(HaaiEt)2Cl2] (4a): Found: C, 45.18; H, 4.09;
N, 19.10. [C22H24N8Cl2Cd] requires C, 45.26; H, 4.14;
N, 19.19%; IR (KBr, cmꢂ1) 1559m, 1508m, 1443m,
324w, 294w. [Cd(MeaaiMe)2Cl2] (3b): Found: C, 45.12;
H, 4.03; N, 19.26. [C22H24N8Cl2Cd] requires C, 45.26;
H, 4.14; N, 19.19%; IR (KBr, cmꢂ1) 1559m, 1509m,
1425m, 326w, 296w. [Cd(MeaaiEt)2Cl2] (4b): Found: C,
47.05; H, 4.55; N, 18.22. [C24H28N8Cl2Cd] requires C,
47.11; H, 4.61; N, 18.31%; IR (KBr, cmꢂ1) 1558m,
1504m, 1428m, 324w, 294w.
2.4. Synthesis of [Cd(HaaiMe)4](ClO4)2 (5a)
2. Experimental
1-Methyl-2-(phenylazo)imidazole (0.09 g, 0.45 mmol)
in MeOH (10 ml) was added in dropwise to a stirred
methanolic solution (10 ml) of Cd(ClO4)2 ꢀ 6H2O (0.03 g,
0.1 mmol) at room temperature (298 K). The orange
solution was left undisturbed for 2 weeks. Bright or-
ange–red crystals were obtained. These were then
washed with water and finally, dried in vacuo. The yield
was 0.08 g (75%). Microanalytical data of the complex is
given below: [Cd(HaaiMe)4](ClO4)2 (5a): Found: C,
45.42; H, 3.76; N, 21.15. [C40H40N16Cl2O8Cd] requires
C, 45.48; H, 3.81; N, 21.21%; IR (KBr, cmꢂ1) 1581m,
1505s, 1440m, 1085vs, 625w.
2.1. Materials
Imidazole was purchased from Sisco Research Lab,
India. CdCl2 and Cd(NO3)2 ꢀ 6H2O were obtained from
Loba Chemicals, Bombay, India. Cd(ClO4)2 ꢀ 6H2O was
prepared by adding CdCO3 to HClO4 and crystallizing
the product from warm water. All other chemicals and
solvents were reagent grade and used as received. 1-Al-
kyl-2-(arylazo)imidazole (RaaiR0) was prepared by the
reported procedure [1].

B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
3163
All other complexes in this series were prepared by
the same procedure. The yield varied from 70% to 75%
and microanalytical data of the complexes are as
follows. [Cd(HaaiEt)4](ClO4)2 (6a): Found: C, 47.44; H,
4.27; N, 20.10. [C44H48N16Cl2O8Cd] requires C, 47.51;
H, 4.34; N, 20.1%; IR (KBr, cmꢂ1) 1558m, 1502s,
1444m, 1091vs, 627w. [Cd(MeaaiMe)4](ClO4)2 (5b):
Found: C, 47.42; H, 4.24; N, 20.09. [C44H44N16Cl2
O8Cd] requires C, 47.51; H, 4.34; N, 20.14%; IR (KBr,
cmꢂ1) 1559m, 1508s, 1456m, 1089vs, 623w. [Cd(Meaa-
iEt)4](ClO4)2 (6b): Found: C, 49.26; H, 4.78; N, 19.07.
[C48H56N16Cl2O8Cd] requires C, 49.34; H, 4.83; N,
19.18%; IR (KBr, cmꢂ1) 1558m, 1503s, 1447m, 1089vs,
623w.
and microanalytical data of the complexes are as fol-
lows. [Cd(HaaiEt)4](NO3)2 ꢀ 2H2O (8a): Found: C,
49.54; H, 4.99; N, 23.66. [C44H52N18O8Cd] requires C,
49.24; H, 4.85; N, 23.50%; IR (KBr, cmꢂ1) 3438mb,
1558m, 1504m, 1439m, 1384s. [Cd(MeaaiMe)4](NO3)2 ꢀ
2H2O (7b): Found: C, 49.48; H, 5.01; N, 23.60. [C44H56
N18O10Cd] requires C, 49.24; H, 4.85; N, 23.50%; IR
(KBr, cmꢂ1) 3436mb, 1559m, 1508m, 1431m, 1383s.
[Cd(MeaaiEt)4](NO3)2 ꢀ 2H2O (8b): Found: C, 50.91; H,
5.40; N, 22.56. [C48H60N18O8Cd] requires C, 51.04; H,
5.32; N, 22.33%; IR (KBr, cmꢂ1) 3428mb, 1559m,
1502m, 1436m, 1383s.
2.6. X-ray diffraction study
2.5. Synthesis of [Cd(HaaiMe)4](NO3)2. 2H2O (7a)
Suitable single crystals of complexes 3a (orange,
0.2 ꢁ 0.15 ꢁ 0.15 mm), 6a (red, 0.50 ꢁ 0.40 ꢁ 0.38 mm)
and 7a (red, 0.36 ꢁ 0.29 ꢁ 0.16 mm) were mounted on a
Siemens CCD diffractometer equipped with graphite
The complex was synthesized by a similar procedure
to 6a with the use of 1-methyl-2-(phenylazo)imidazole
(0.07 g, 0.4 mmol) in MeOH (10 ml) and a methanolic
solution (10 ml) of Cd(NO3)2 ꢀ 6H2O (0.03 g, 0.1 mmol)
at room temperature (298 K). The orange solution was
left undisturbed for 2 weeks. Bright orange–red crystals
were obtained. They were then washed with water and
finally, dried in vacuo. The yield was 0.07 g (70%).
Microanalytical data of the complex is given below:
[Cd(HaaiMe)4](NO3)2 ꢀ 2H2O (7a): Found: C, 47.04; H,
4.18; N, 24.95. [C40H44N18O8Cd] requires C, 47.22; H,
4.33; N, 24.79%; IR (KBr, cmꢂ1) 3448mb, 1559m,
1504m, 1436m, 1384s.
ꢁ
monochromated Mo Ka (k ¼ 0:711073 A) radiation.
The crystallographic data, conditions for the intensity
data collection and some features of the structure re-
finements of all the complexes are listed in Table 1. The
unit cell parameters and crystal-orientation matrices
were determined for the three complexes by least squares
refinements of all reflections. The intensity data were
corrected for Lorentz and polarization effects and an
empirical absorption correction was also employed us-
ing the SAINT program for complexes 3a, 6a [42] and the
SADABS program for complex 7a [43]. A total of 13 450,
14 593 and 14 716 reflections were measured and 4002,
4325 and 2716 reflections were assumed applying the
All other complexes in this series were prepared by
the same procedure. The yield varied from 65% to 70%
Table 1
Summarized crystallographic data for [Cd(HaaiMe)2Cl2] (3a), [Cd(HaaiEt)2](ClO4)2 (6a) and [Cd(HaaiMe)2](NO3)2 ꢀ 2H2O (7a)
[Cd(HaaiMe)2Cl2] (3a)
[Cd(HaaiEt)2](ClO4)2 (6a)
[Cd(HaaiMe)2](NO3)2 ꢀ 2H2O (7a)
C40H48CdN18O10
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C20H20CdCl2N8
555.74
C44H48CdCl2N16O8
1112.28
293(2)
1053.36
100(2)
293(2)
monoclinic
P21=c
monoclinic
C2=c
tetragonal
I41=a
Unit cell dimensions
ꢁ
a (A)
13.8422(10)
13.5039(10)
12.2983(9)
96.0530(10)
2286.0(3)
4
19.4733(15)
13.1084(10)
19.5613(15)
93.079(2)
4986.1(7)
4
14.051(3)
14.051(3)
22.814(5)
90.00
ꢁ
b (A)
ꢁ
c (A)
b (°)
V (A )
3
ꢁ
4504.2(17)
4
Z
ꢁ
k (A)
0.71073
1.214
0.71073
0.613
0.71073
0.564
l(Mo Ka) (mmꢂ1
2h range (°)
)
3.0–56.4
1.615
280
3.8–56.6
1.482
321
3.4–57.36
1.553
178
Dcalc (Mg mꢂ3
)
Refine parameters
Reflection total
Unique reflections
R1½I > 2rðIÞꢃ
wR2
13450
5138
14593
5523
14716
2716
0.0300
0.0752
1.027
0.0467
0.1323
1.019
0.0549
0.1374
1.135
Goodness of fit

3164
B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
condition I > 2rðIÞ for complexes 3a, 6a and 7a, re-
spectively. All these structures were solved by direct
methods and followed by successive Fourier and differ-
ence Fourier syntheses. During refinement of 7a the
NO3 anion was found to have symmetry imposed dis-
order. Full matrix least squares refinements on F02 were
carried out using SHELXL 97 with anisotropic displace-
ment parameters for all non-hydrogen atoms. Hydrogen
atoms were constrained to ride on the respective carbon
or nitrogen atoms with isotropic displacement parame-
ters equal to 1.2 times the equivalent isotropic dis-
placement of their parent atom in all cases. All
calculations were carried out using SHELXS 97 [44],
SHELXL 97 [44], PLATON 99 [45] and ORTEP-3 [46]
programs.
Fig. 1. X-ray structure of Cd(HaaiMe)2Cl2 (3a).
Table 2
ꢁ
3. Result and discussion
Selected bond distances (A) and angles (°) for [Cd(HaaiMe)2Cl2] (3a)
Bond distances
Bond angles
3.1. Synthesis and formulation
Cd–Cl(1)
Cd–Cl(2)
Cd–N(1)
Cd–N(5)
Cd–N(4)
Cd–N(8)
2.488238)
Cl(1)–Cd–Cl(2)
Cl(1)–Cd–N(1)
Cl(1)–Cd–N(4)
Cl(1)–Cd–N(5)
Cl(2)–Cd–N(1)
Cl(2)–Cd–N(4)
Cl(2)–Cd–N(5)
N(1)–Cd–N(4)
N(1)–Cd–N(5)
N(4)–Cd–(N5)
N(5)–Cd–N(8)
Cd–N(1)–C(3)
Cd–N(5)–C(13)
115.61(3)
107.91(6)
84.6(5)
2.4376(8)
2.266(2)
2.282(2)
2.470(2)
3.006(2)
Ligands used are 1-alkyl-2-(arylazo)imidazole
[RaaiR0, where R ¼ H (a), Me (b); R0 ¼ Me (1), Et (2)],
they are unsymmetrical N,N0-bidentate chelator, where N
and N0 refer to N(imidazole) and N(azo) donor centers,
respectively. Methanolic solutions of CdCl2 and RaaiR0
in 1:4.5 or higher mole proportion have isolated orange–
yellow to orange crystalline products of composition
Cd(RaaiR0)2Cl2 (3, 4). [Cd(RaaiR0)4](ClO4)2 (5, 6) and
[Cd(RaaiR0)4](NO3)2 ꢀ 2H2O (7, 8) complexes were syn-
thesized on a reacting methanolic solution of the respec-
tive cadmium salts and RaaiR0 withꢂthe mole ratꢂio 1:4.5.
[Cd(Meaaie)2(H2O)2]X2 (X ¼ ClO4 (9b), NO3 (10b))
are also isolated immediately after mixing a methanolic
solution of the cadmium(II) salts and RaaiR0 in the
metal:ligand mole ratio of 1:2.5. However, on keeping
the solution for a week to crystallize the complexes, only
the tetrakis, cadmium(II) complexes, [Cd(MeaaiMe)4]X2
(5b–8b) were obtained. Microanalytical data support the
composition of the complexes. Each class of complex has
been structurally confirmed by the single crystal X-ray
diffraction study. Cd(RaaiR0)2Cl2 (3, 4) are non-con-
ducting (K ¼ 22–30 Xꢂ1 cmꢂ1 molꢂ1) and complexes 5–8
show the usual 1:2 molar conductivity (K ¼ 180–210 Xꢂ1
cmꢂ1 molꢂ1).
92.18(6)
123.76(6)
85.89(5)
N(3)–N(4) 1.261(3)
N(7)–N(8) 1.257(3)
105.85(6)
64.12(7)
106.27(8)
168.03(7)
60.01(4)
121.04(18)
126.49(18)
64.12(7); N(5)–Cd–N(8), 60.01(4)°] in a forced chelated
CdN4Cl2 coordination sphere. The Cd–N(azo) distances
are closer to the sum of the van der Waals radii of Cd(II)
and N(azo) [47]. Hence, chelation is excluded and Ha-
aiMe acts as a monodentate-N(imidazole) donor ligand.
The ligand is planar. The two ligands make a dihedral
angle of 71.87 (7)°. The azo group (–N @ N–) binds to
phenyl and imidazolyl groups. Bond length C(3)–N(3),
ꢁ
1.389(4) and C(4)–N(4), 1.416(4) A suggest the azo group
favors the imidazole ring more than the phenyl ring. The
N @ N bond lengths, N(3)–N(4), 1.261(3) and N(7)–N(8),
ꢁ
1.257(3) A are closer to the free ligand value, 1.250(1) A
ꢁ
[48,49]. The Cd–N(imidazole) distance [Cd–N(1),
ꢁ
2.266(2); Cd–N(5), 2.282(2) A] is comparable with re-
ported data [50]. The Cd–Cl bond distances are 2.4883(8)
ꢁ
and 2.4376(8) A. The angles extended in tetrahedral
3.2. Molecular structures
3.2.1. [Cd(HaaiMe)2Cl2] (3a)
CdN2Cl2 geometry are Cl(1)–Cd–Cl(2) 115.61(3), N(1)–
Cd–N(5), 106.27(8)° and suggest a small distortion. All
other angles are within the limits of distorted Td-geome-
try (Table 2).
An ORTEP view of Cd(HaaiMe)2Cl2 is shown in
Fig. 1. The Cd center is tetrahedrally surrounded showing
a CdN2Cl2 coordination sphere. Each HaaiMe acts as a
monodentate-N(imidazole) donor ligand. Bond length
data in Table 2 suggest unusually long Cd–N(azo)
3.2.2. [Cd(HaaiEt)4](ClO4)2 (6a)
The cationic complex [Cd(HaaiEt)4]2þ (Fig. 2) con-
sists of a central cadmium atom surrounded by four
ꢁ
[Cd–N(4), 2.470(2); Cd–N(8), 3.006(2) A] and very small
chelate angle N(imidazole)–Cd–N(azo) [N(1)–Cd–N(4),

B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
3165
Table 3
ꢁ
Selected bond distances (A) and angles (°) for [Cd(HaaiEt)4](ClO4)2
(6a)
Bond distances
Bond angles
Cd–N(1)
Cd–N(5)
Cl–O(1)
2.261(3)
2.260(3)
1.412(4)
1.360(4)
1.378(5)
1.400(5)
1.254(4)
1.385(5)
1.412(4)
1.328(4)
1.256(4)
1.378(5)
1.419
N(1)–Cd–N(1)*
N(1)–Cd–N(5)*
N(1)*–Cd–N(5)
N(5)–Cd–N(5)*
130.85(13)
97.86(11)
97.86(11)
131.15(14)
Cl–O(4)
Cl–O(2)
Cl–O(3)
N(1)*–Cd–N(5)* 101.96(11)
N(1)–Cd–N(5)
O(3)–Cl–O(4)
O(2)–Cl–O(1)
O(1)–Cl–O(3)
O(1)–Cl–O(4)
O(2)–Cl–O(3)
O(2)–Cl–O(4)
Cd–(N1)–C(1)
N(4)–N(3)–C(3)
N(3)–N(4)–C(4)
Cd–N(5)–C(12)
Cd–N(5)–C(14)
101.96(11)
111.0(4)
111.8(4)
109.8(3)
111.9(3)
102.4(4)
109.7(4)
129.8(2)
112.8(3)
114.2(3)
130.2(3)
124.4(2)
N(3)–N(4)
N(3)–C(3)
N(4)–C(4)
N(5)–C(14)
N(7)–N(8)
N(7)–C(14)
N(8)–C(15)
Fig. 2. X-Ray structure of [Cd(HaaiEt)4](ClO4)2 (6a).
N(8)–N(7)–C(14) 112.8(3)
N(7)–N(8)–C(15) 114.4(3)
Cd–N(1)–C(3)
124.1(1)
HaaiEt ligands. The Cd is sitting at the center of a tetra-
hedron. The four Cd–N bond lengths are almost equal
ꢁ
and the length is 2.260(3) A. HaaiEt acts as a monod-
HaaiMe ligand, the N @ N distance of the azo moiety,
entate ligand and binds via the N(imidazole) donor
center. The coordination environment about Cd is
compressed along the crystallographic c-axis in such a
way that two of the N–Cd–N angles are higher than the
ꢁ
1.263(5) A, is near the upper limit of the average of all
ꢁ
values found for this unit (1.240 A) and is quite similar
to the average value found for Car–N @ N– motifs (1.255
ꢁ
A) [51] (cf. Table 4).
tetrahedral angle with
a value of N1–Cd–N1*,
It is interesting to note thatꢂthe solvent water mole-
cules interact with anion NO3 through –NO3–water–
NO3–water–hydrogen bonding interactions to form a
chain along the a-direction and these chains interact
with a chain along the b-direction via the sequence –
NO3–water–water–NO3–water–water–NO3–running
along the c-direction (Table 5, Fig. 4). The 1D chains
line up in the ab-plane and by virtue of 4-fold symmetry,
assemble into a square-grid supramolecule with grid
130.85(13)° and N5–Cd–N5*, 131.15(14)°. Two other
N–Cd–N angles show a lower value, each of them,
N1–Cd–N5* and N1*–Cd–N5, being 97.86(11)°.
The remaining N–Cd–N angles (N1*–Cd–N5* or N5*–
Cd–N1*) are 101.96(11)° (Table 3). The angular dis-
tortion from a regular tetrahedron may be due to steric
crowding among the pendant azophenyl groups. The 1-
ethyl-imidazole and phenyl group at the two sides of the
azo (N @ N) group are planar. The N @ N bond length is
ꢁ
av. 1.255(4) A and is near to the free ligand value
ꢁ
(1.250(1) A) [48,49].
3.2.3. [Cd(HaaiMe)4](NO3)2 ꢀ 2H2O (7a)
The cationic complex (Fig. 3) consists of a central
cadmium atom surrounded by four HaaiMe ligands
with the cadmium center sitting on a site of crystallo-
ꢂ
graphic symmetry (4). The coordination environment
about the cadmium is compressed like 6a along the
crystallographic c-axis, in such a way that two of the N–
Cd–N angles are splayed open, with a value 139.49(16)°,
while the other angles about the cadmium atom have a
common value of 96.89(5)°. The Cd–N distance of
ꢁ
2.283(3) A differs only slightly from the average value of
ꢁ
2.30 A reported for Cd–N (imidazolate) distances in a
compilation of average structural parameters [50], in
which it is also reported that the range of these Cd–N
values is quite broad (the lower and upper quartile
ꢁ
values are 2.26 and 2.35 A). Along the backbone of the
Fig. 3. X-Ray structure of [Cd(HaaiMe)4](NO3)2 (7a).

3166
B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
Table 4
ꢁ
Selected bond distances (A) and angles (°) for [Cd(HaaiMe)4](NO3)2 ꢀ
2H2O (7a)
Bond distances
Bond angles
Cd–N(1)A
N(1)–C(3)
N(1)–C(1)
N(3)–N(4)
N(3)–C(3)
N(4)–C(5)
N(5)–O(2)
N(5)–O(3)
N(5)–O(1)
2.283(3)
1.326(5)
1.356(5)
1.263(5)
1.374(5)
1.412(5)
1.195(15)
1.228(18)
1.275(18)
N(1)a–Cd(1)–N(1)b
N(1)a–Cd(1)–N(1)
N(1)b–Cd(1)–N(1)
N(1)a–Cd(1)–N(1)c
N(1)b–Cd(1)–N(1)c
N(1)–Cd(1)–N(1)c
C(1)–N(1)–Cd(1)
N(4)–N(3)–C(3)
N(1)–C(3)–N(3)
N(3)–N(4)–C(5)
Cd–(N1)–C(3)
96.89(5)
139.49(16)
96.88(5)
96.88(5)
139.49(16)
96.88(5)
130.4(3)
112.3 (3)
128.1(4)
115.7(3)
120.9(3)
126.0(19)
107.9(17)
126(2)
O(2)–N(5)–O(3)
O(2)–N(5)–O(1)
O(3)–N(5)–O(1)
A Cd–N(1)/N(1)a=b=c distances are the same.
Table 5
Contact distances in the anion framework of [Cd(HaaiMe)4](NO3)2 ꢀ
2H2O (7a)
Fig. 5. Interlocked anion framework of the square-grid supramolecule
ꢁ
in the ab-plane (grid dimension ca. 7 ꢁ 7 A).
Contact
Distance
ꢁ
(A)
Contact
Distance
ꢁ
(A)
O(1) ꢀ ꢀ ꢀ O(1)Wi
O(2) ꢀ ꢀ ꢀ O(1)Wi
O(3) ꢀ ꢀ ꢀ O(1)W
2.97(3)
2.81(4)
2.74(4)
O(1) ꢀ ꢀ ꢀ O(2)W
O(3) ꢀ ꢀ ꢀ O(2)W
O(3) ꢀ ꢀ ꢀ O(2)Wii
3.03(2)
1.97(3)
2.82(4)
ꢁ
(dimension 11.2 ꢁ 7 A) (Fig. 6). These interactions fa-
cilitate the generation of an infinite 3D supramolecular
anion network. The channels parallel to the Y -axis are
filled with cationic species, Cd(HaaiEt)42þ, of whose the
pendant arm, coordinated HaaiEt, penetrates into the
square grid voids (looking like two antenna of a cock-
roach). It should be mentioned that though the anion
network formation is evident from figures, Figs. 4–6,
due to the symmetry-imposed disorder of NO3 (vide
supra) it is really impossible to segregate the two-dis-
order parts of the network.
O(1)W ꢀ ꢀ ꢀ O(2)Wii 2.72(3)
O(1)W ꢀ ꢀ ꢀ O(2)W 2.97(3)
O(2)W ꢀ ꢀ ꢀ O(2)W
2.60(3)iii
Symmetry code: (i) x; 1=2 þ y; ꢂz; (ii) ꢂ1 ꢂ x; 1=2 ꢂ y; z;
(iii) 1=4 ꢂ y; 3=4 þ x; ꢂ1=4 ꢂ z.
ꢁ
dimension ca. 7 ꢁ 7 A as shown in Fig. 5. Every square
ꢂ
grid is interlocked by chains parallel to the Z-axis
passing through the middle of the square arms to form a
layer in the ac- (or bc-) plane with brick-wall topology
Fig. 4. A perspective view of a part of the anion framework showing the –NOꢂ3 –O(water)– interactions (doted line) in the structure of 7a.

B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
3167
correspond to intra-ligand n ! pꢄ and p ! pꢄ transi-
tions [52].
The 1H NMR spectra of Cd(RaaiR0)2Cl2 and
Cd(RaaiR0)4X2 (X ¼ NO3, ClO4) are recorded in
CDCl3. The spectral data are set out in Table 6. Data
reveal that the signal in the spectra of Cd(RaaiR0)4X2
are shifted to higher
d
values compared to
Cd(RaaiR0)2Cl2. Imidazole protons 4- and 5-H appear
at lower d values, in general, relative to aryl protons 7-H
to 11-H. On comparison with free ligand data the im-
idazole protons (4- and 5-H) suffer significant shifting to
higher d values by ꢅ0.5 and 0.4 ppm, respectively. The
aryl protons are also shifted by 0.1–0.4 ppm. This is in
support with the bonding of imidazole-N ! Cd(II) in
the complexes and overall charge drifting from the li-
gand. Aryl signals shift to the lower field side on Me-
substitution to the aryl ring. This may be due to the
electron donating effect of the Me-group.
ꢁ
Fig. 6. A view of the brick-walled channel (dimension 11.2 ꢁ 7 A) filled
3.3.1. Thermal studies
Effect of temperature on the complexes has been
carried out on representative compounds. Because of the
with cations in the ac-/bc-plane.
ꢂ
ꢂ
3.3. Spectral studies
explosive nature of ClO4 and NO3 salts, the thermal
program of 5b and 7b are restricted to the temperature
range 300–450 K while the thermogram of 3b has been
observed up to 800 K. In the case of Cd(MeaaiMe)2Cl2
(3b) mass loss has been observed in the temperature
range 480–540 K and corresponds to loss of coordinated
MeaaiMe groups. The final residue is observed at 750 K
which corresponds to CdO. Cd(MeaaiMe)4(ClO4)2 does
not show any thermal loss up to 480 K. We did not
proceed further to prevent any damage to equipment
due to a possible explosion. This observation supports
that there is no coordinated or crystallized water or
methanol (since preparation has been done from water–
methanol, see Section 2) to the molecule. Cd(Mea-
aiMe)4(NO3)2 (5b) shows two overlapped thermal loss
The IR stretching frequencies of the complexes are
assigned by comparing with the free ligand values [52].
Not all the bands have been assigned and some signifi-
cant stretching frequencies are set out. The m(N @ N) is
shifted to a lower frequency by 20–30 cmꢂ1 compared to
the free ligand value. Cd(RaaiR0)2Cl2 show two m(Cd–
Cl) at ca.0 324 and ca. 298 cmꢂ1. The m(ClO4) of
[Cd(RaaiR )4](ClO4)2 appears at 1082–1091cmꢂ1 with a
weak stretch at 624–627 cmꢂ1
[Cd(RaaiR0)4](NO3)2 appear at ca. 1382–1384 cmꢂ1
. The m(NO3) of
.
The reflectance spectra of the complexes show intense
bands at 470–490 and 360–380 nm along with a weak
transition at 500–510 nm. These intense transitions
Table 6
1H NMR spectral data in CDCl3
Compounds
4-Ha
5-Ha
7-Hb
11-Hb
8,10-H
9-H
1-CH3/–CH2–CH3
Me
Cd(HaaiMe)2Cl2 (3a)
Cd(MeaaiMe)2Cl2 (3b)
7.44
7.40
7.45
7.42
7.48
7.55
7.60
7.55
7.50
7.56
7.43
7.62
7.22
7.20
7.25
7.20
7.34
7.39
7.44
7.40
7.36
7.38
7.35
7.36
8.05 (8.0)
7.91 (8.5)
8.08 (9.0)
7.94 (8.0)
7.90 (10.0)
7.94 (10.0)
8.05 (9.0)
7.92 (9.0)
7.85 (9.0)
7.94 (8.0)
7.86 (8.0)
7.91 (10.0)
8.05 (8.0)
7.91b (8.5)
8.08 (9.0)
7.44 (8.0)
7.90 (10.0)
7.94 (10.0)
8.05 (9.0)
7.92 (9.0)
7.85 (9.0)
7.94 (8.0)
7.86 (8.00
7.91 (10.0)
7.52c
7.31b (8.5)
7.55c
7.34b (8.0)
7.52c
7.58b (8.0)
7.68c
7.24b (8.0)
7.45c
7.29b (8.0)
7.50c
7.23 (8.0)
7.52c
4.13
4.13
4.84e (15.0)
4.80e
3.99
2.42
2.44
2.46
2.44
2.45
2.44
d
Cd(HaaiEt)2Cl2 (4a)
d
Cd(MeaaiEt)2Cl2 (4b)
[Cd(HaaiMe)4](ClO4)2 (5a)
[Cd(MeaaiMe)4](ClO4)2 (5b)
4.04
[Cd(HaaiEt)4](ClO4)2 (6a)
d
4.94e (20.0)
4.55e (20.0)
4.11
d
[Cd(MeaaiEt)4](ClO4)2 (6b)
[Cd(HaaiMe)4](NO3)2 (7a)
[Cd(MeaaiMe)4](NO3)2 (7b)
4.18
4.45e (20.0)
4.52e (22.0)
d
[Cd(HaaiEt)4](NO3)2 (8a)
d
[Cd(MeaaiEt)4](NO3)2 (8b)
a Broad singlet.
b Doublet.
c Multiplet.
d d[(1-CH2)–CH3], 1.52 (7.5) (4a), 1.49 (7.5) (4b), 1.52 (6a), 1.55 (6b), 1.57 (8a), 1.55 (8b).
e Quintet.

3168
B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
[5] P. Byabartta, J. Dinda, P.K. Santra, C. Sinha, K. Panneerselvam,
F.-L. Liao, T.-H. Lu, J. Chem. Soc., Dalton Trans (2001) 2825.
[6] P. Byabartta, S. Pal, C. Sinha, F.-L. Liao, K. Paneerselvam, T.-H.
Lu, J. Coord. Chem. 55 (2002) 479.
steps within the temperature range 350–380 and 415–440
K and the overall loss corresponds to two moles of H2O.
This is revealed from the X-ray crystal structure study of
the complex.
[7] D. Das, T.K. Misra, C. Sinha, Transition Met. Chem. 23 (1998)
233.
[8] J. Dinda, P.K. Santra, C. Sinha, L.R. Falvello, J. Organomet.
Chem. 629 (2001) 28.
4. Conclusion
[9] S. Pal, D. Das, P. Chattopadhyay, C. Sinha, K. Panneerselvam,
T.-H. Lu, Polyhedron 19 (2000) 1263.
In this paper we have accounted for the effect of the
anion on the structure of molecules being formed from
cadmium(II) and 1-alkyl-2-(arylazo)imidazoles (RaaiR0).
Chloride (Clꢂ) has a stronger affinity to Cd(II) and thus
forms Cd(RaaiR0)2Cl2. The oxo anions, perchlorate
(ClO4ꢂ) and nitrate (NO3ꢂ), prefer to synthesize tetrakis
derivatives Cd(RaaiR0)42þ. In solution at lower M:L ratio
(1:2.5) precipitated compounds are [Cd(RaaiR0)2
(H2O)2]22þ; however, in an equilibriated solution on
crystallization Cd(RaaiR0)24þ are precipitated. Single
crystal structure determination helps us to identify the
[10] S. Pal, D. Das, C. Sinha, C.H.L. Kennard, Inorg. Chim. Acta 313
(2001) 21.
[11] P.K. Santra, T.K. Misra, C. Sinha, Indian J. Chem. A 38 (1999)
82.
[12] D. Das, A.K. Das, C. Sinha, Talanta 48 (1999) 1013.
[13] J.K. Nag, P.K. Santra, C. Sinha, F.-L. Liao, T.H. Lu, Polyhedron
20 (2001) 2253.
[14] B.G. Chand, U.S. Ray, J. Cheng, T.-H. Lu, C. Sinha, Polyhedron
22 (2003) 1213.
[15] K. Bag, T.K. Misra, C. Sinha, J. Indian Chem. Soc. 75 (1998) 421.
[16] B. Chand, U. Ray, P.K. Santra, G. Mostafa, T.-H. Lu, C. Sinha,
Polyhedron 22 (2003) 1205.
[17] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th
ed., Wiley, New York, 1988.
compounds. Cd(HaaiMe)4(NO3)2 ꢀ 2H2O provides a
ꢂ
[18] J.E. Huheey, Inorganic Chemistry, 3rd ed., Harper International
SI ed., New York, 1983.
square-grid supramolecule interacting through a NO3
–
HOH hydrogen bonded network and cation is grooved
into the channel.
[19] Y.-C. Liang, M.-C. Hong, R. Cao, W.-P. Su, Y.-J. Zhao, J.B.
Weng, Polyhedron 20 (2001) 2477.
[20] L.C. Tabares, J.A.R. Navarro, J.M. Salas, J. Am. Chem. Soc. 123
(2001) 383.
[21] Y.-J. Zhao, M.-C. Hong, Y.-C. Liang, W.-P. Su, R. Cao, Z.-Y.
Zhou, A.S.C. Chan, Polyhedron 20 (2001) 2619.
[22] R.S. Rarig, J. Zubieta, Inorg. Chim. Acta 319 (2001) 235.
[23] M. Fujita, Y.J. Kwon, S. Washizu, K. Ogura, J. Am. Chem. Soc.
116 (1994) 1151.
5. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 209310 for [Cd(HaaiEt)4]
(ClO4)2; CCDC No. 209311 for [Cd(HaaiMe)4]
(NO3)2 ꢀ 2H2O and CCDC No. 209312 for [Cd(Ha-
aiMe)2Cl2]. Copies of this information may be obtained
free of charge from the Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336-
033, e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
[24] B. Sui, J. Fan, T.A. Okamura, W.Y. Sun, N. Ueyama, New J.
Chem. 25 (2001) 1379.
[25] P.S. Mukherjee, T.K. Maji, G. Mostafa, W. Hibbs, N.R.
Chaudhuri, New J. Chem. 25 (2001) 760.
[26] A.J. Blake, N.R. Champness, S.S.M. Chung, W.-S. Li, M.
€
Schroder, Chem. Commun. (1997) 1675.
[27] C.-Y. Su, Y.-P. Cai, C.-L. Chen, F. Lissner, B.-S. Kang, W. Kaim,
Angew. Chem., Int. Ed. 41 (2002) 3371.
[28] K. Jin, X. Huang, L. Pang, J. Li, A. Appel, S. Wherland, Chem.
Commun. (2002) 2872.
[29] M. Rivas, J.C. Brammer, Coord. Chem. Rev. 183 (1999) 43.
[30] A. Datta, G.M. Golzar Hossain, N.K. Karan, K.M. Abdul Malik,
S. Mitra, Inorg. Chem. Commun. 6 (2003) 658.
[31] D. Braga, F. Grepioni, J.J. Novoa, Chem. Commun. (1998) 1959.
[32] J.J. Novoa, I. Nobeli, F. Grepioni, D. Braga, New J. Chem. 24
(2000) 5.
Acknowledgements
Financial support from the University Grants Com-
mission, New Delhi and the Ministry of Science and
Technology (Spain) under Grant PB98-1593 are grate-
fully acknowledged.
[33] D. Braga, F. Grepioni, E. Tangliavini, J.J. Novoa, F. Mota,
Chem. Eur. J. 6 (2000) 4536.
[34] P. Mukhopadhyay, P.K. Bharadwaj, G. Savitha, A. Krishnan,
P.K. Das, Chem. Commun. (2000) 1815.
[35] H. Zhang, X. Wang, K. Zhang, B.K. Teo, Coord. Chem. Rev. 183
(1999) 157.
References
[36] A.M. Golub, H. Kohler, V.V. Skepenko, Chemistry of Pseudo-
halides, Elsevier, Amsterdam, 1986.
[1] J. Dinda, U.S. Ray, G. Mostafa, T.-H. Lu, A. Usman, I.A. Razak,
S. Chantrapromma, H.K. Fun, C. Sinha, Polyhedron 22 (2003)
247.
[37] J. Ribas, M. Monfort, B.K. Ghosh, X. Solans, M. Font-Bardia,
J. Chem. Soc., Chem. Commun. 1986 (1995) 2375.
[38] E. Ruiz, J. Cano, S. Alvarez, P. Alemany, J. Am. Chem. Soc. 120
(1998) 11122.
[2] T.K. Misra, D. Das, C. Sinha, P.K. Ghosh, C.K. Pal, Inorg.
Chem. 37 (1998) 1672.
[39] Cadmium in the environment and its significance to man, Pollution
paper No. 17, Her MajestyÕs Stationery Office, London, 1980.
[40] SaxÕs Dangerous Properties of Industrial Materials, ninth ed., 617
pp.
[3] S. Pal, D. Das, P. Chattopadhyay, C. Sinha, K. Panneerselvam,
T.H. Lu, Polyhedron 19 (2000) 1263.
[4] P. Byabartta, Sk. Jasimuddin, B.K. Ghosh, C. Sinha, A.M.Z.
Slawin, J.D. Woollins, New J. Chem. 26 (2002) 1415.

B.G. Chand et al. / Polyhedron 22 (2003) 3161–3169
3169
[41] R.M. Izatt, J.J. Christensen, J.H. Rytting, Chem. Rev. 71 (1971)
439.
[49] A. Saha, C. Das, S. Goswami, S.-M. Peng, Indian J. Chem. A 40
(2001) 198.
[42] Bruker (1998). SMART and SAINT. Bruker AXS Inc., Madison,
WI, USA.
[50] A.G. Orpen, L. Brammer, F.H. Allen, O. Kennard, D.G. Watson,
R. Taylor, in: A.J.C. Wilson (Ed.), International Tables for
Crystallography, Vol. C: Mathematical, Physical and Chemical
Tables, Kluwer Academic Publishers, Dordrecht, 1995, Table
9.6.3.3.
[43] SADABS: Area-Detector Absorption Correction, Siemens Indus-
trial Automation Inc., Madison, WI, 1996.
[44] G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal
Structure, University of Gottingen, Germany, 1997.
[45] A.L. Spek, PLATON, Molecular Geometry Program, University of
Utrecht, The Netherlands, 1999.
[51] A.G. Orpen, L. Brammer, F.H. Allen, O. Kennard, D.G. Watson,
R. Taylor, in: A.J.C. Wilson (Ed.), International Tables for
Crystallography, Vol. C: Mathematical, Physical and Chemical
Tables, Kluwer Academic Publishers, Dordrecht, 1995, Table
9.5.1.1.
[46] L.J. Farrugia, ORTEP-3 for Windows, J. Appl. Cryst. 30 (1997) 565.
[47] A.G. Orpen, L. Brammer, F.H. Allen, O. Kennard, D.G. Watson,
R. Taylor, J. Chem. Soc., Dalton Trans. (1989) SI.
[48] D. Das, Ph.D. Thesis, Burdwan University, Burdwan, India, 1998.
[52] T.K. Misra, Ph.D. Thesis, Burdwan University, Burdwan, India,
1999.