Structural variations in self-assembled cadmium benzoate complexes

Article abstract of DOI:10.1016/j.poly.2007.01.005

A series of mixed ligand cadmium(II) complexes having 3,5-dimethylpyrazole and aromatic carboxylate are structurally characterized. The effect of substituent on aromatic ring and also the effect of composition on co-ordination behavior of these complexes are ascertained. Hydrogen bonded self-assembled mononuclear complexes are obtained from composition [Cd(L)₂(L_a)₂] where L_a = 3,5-dimethylpyrazole L = R-C₆H₄COO- [R = H (1), 2-Cl (2), 4-OH (3), 2-OH (4)]. The cadmium complex (5) having composition [Cd(L)₂(L_a)(H₂O)] (L = 2-NO₂-C₆H₄COO-) is tetra-nuclear. The complex has eight and six co-ordination around cadmium and self-assembles through hydrogen bonding leading to form extended chain structure. The four complexes (1-4) have six co-ordinated trigonal prismatic geometry around cadmium ions. Cadmium complexes having composition [Cd(L)₂(L_a)] such as R = 4-NO₂ (6), 4-Cl (7), and 1-naphthoate complex (8) are co-ordination polymers with seven co-ordination geometry around cadmium. In these co-ordination polymers different Cd-Cd distances are observed for alternate pair of cadmium ions. For example in the case of the co-ordination polymer of 4-nitro-benzoate complex the Cd-Cd distance between alternate pairs are 4.138 ?, and 3.748 ?. The 1-naphthoate complex having pyridine has composition [Cd(L)₂(L_b)₂](H₂O)] (9) where L_b = pyridine and L = 1-naphthoate has seven co-ordination with a distorted pentagonal bipyramid geometry.

Full text of DOI:10.1016/j.poly.2007.01.005

Polyhedron 26 (2007) 2612–2620
www.elsevier.com/locate/poly
Structural variations in self-assembled cadmium benzoate complexes
*
Kusum Bania, Nilotpal Barooah, Jubaraj B. Baruah
Department of Chemistry, Indian Institute of Technology, Guwahati 781 039, India
Received 8 December 2006; accepted 5 January 2007
Available online 14 January 2007
Abstract
A series of mixed ligand cadmium(II) complexes having 3,5-dimethylpyrazole and aromatic carboxylate are structurally characterized.
The effect of substituent on aromatic ring and also the effect of composition on co-ordination behavior of these complexes are ascer-
tained. Hydrogen bonded self-assembled mononuclear complexes are obtained from composition [Cd(L)2(La)2] where La = 3,5-dim-
ethylpyrazole L = R–C6H4COO– [R = H (1), 2-Cl (2), 4-OH (3), 2-OH (4)]. The cadmium complex (5) having composition
[Cd(L)2(La)(H2O)] (L = 2-NO2–C6H4COO–) is tetra-nuclear. The complex has eight and six co-ordination around cadmium and self-
assembles through hydrogen bonding leading to form extended chain structure. The four complexes (1–4) have six co-ordinated trigonal
prismatic geometry around cadmium ions. Cadmium complexes having composition [Cd(L)2(La)] such as R = 4-NO2 (6), 4-Cl (7), and 1-
naphthoate complex (8) are co-ordination polymers with seven co-ordination geometry around cadmium. In these co-ordination poly-
mers different Cd–Cd distances are observed for alternate pair of cadmium ions. For example in the case of the co-ordination polymer of
˚
˚
4-nitro-benzoate complex the Cd–Cd distance between alternate pairs are 4.138 A, and 3.748 A. The 1-naphthoate complex having pyr-
idine has composition [Cd(L)2(Lb)2](H2O)] (9) where Lb = pyridine and L = 1-naphthoate has seven co-ordination with a distorted pen-
tagonal bipyramid geometry.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Cadmium complexes; Self-assembly; Hydrogen-bonding; Co-ordination polymers
1. Introduction
Such synthesis would lead to thermodynamically stable
complex. It would also throw light on the co-ordination
chemistry and nucleation process. One of the criteria to
prepare complexes from multiple components, is that the
ligands should have comparable reactivity and competitive
enough to form complexes containing the components of
interest. Since many of the polymeric carboxylate com-
plexes have dinuclear frame in the backbone [1], synthesis
of carboxylate complexes under such competitive environ-
ment would enable one to establish the limiting condition
at which a dinuclear paddle wheel structure would deform
and finally lead to a mononuclear structure as shown in
Scheme 1. Our recent results suggest that the variation of
reaction condition leads to different co-ordination com-
plexes in the case of copper [6a], nickel [6b,6c], cobalt
[6d] and zinc [6e].
The metal carboxylate chemistry has been of great inter-
est for their co-ordination behavior as well as for making
metallo-organic frameworks [1]. Out of different metal
carboxylates, cadmium carboxylates are of special interest
for their interesting material properties [2] as well as for
their versatile co-ordination behavior [3]. Mixed carboxyl-
ate complexes of cadmium have interesting polymeric
structure [4] and cadmium carboxylates also form double
salts having interesting structures [5]. Since there are
several possible co-ordination numbers for cadmium com-
plexes [3]; it is important to understand how the co-ordina-
tion number as well as preferential co-ordination of a
ligand occurs. Multi components reactions under ambient
condition may be important to achieve such rationale.
Among competitive ligands aromatic carboxylic acid
along with 3,5-dimethylpyrazole or pyridine with acetate
metal salts have been envisaged [6]. With a similar objective
*
Corresponding author. Tel.: +91 361 2582311; fax: +91 361 2690762.
E-mail address: juba@iitg.ernet.in (J.B. Baruah).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.01.005

K. Bania et al. / Polyhedron 26 (2007) 2612–2620
2613
O
O
M
O
O
O
M
O
M
M
M
2
O
O
O
O
Scheme 1. Limiting condition of paddle-wheel structure going to mononuclear structure.
we pursued reactions of cadmium(II)acetate with aromatic
carboxylic acids followed by reaction with nitrogen donor
ligands such as 3,5-dimethylpyrazoles or pyridine and the
results are presented in this article.
stirred for 2 h. The solution was filtered and the filtrate on
standing led to crystallization of the product.
4. Crystalline yield and spectroscopic data of the compounds
2. Experimental
Complex 1: Crystalline yield 61%, 1H NMR (DMSO-d6)
7.98–7.96(m, 2H), 7.47–7.39(m, 3H), 5.76(s 1H), 2.13
(s, 6H). IR(KBr, cmꢀ1) 3434(bs), 1596(s), 1538(s), 1404(s),
1279(s), 1166(m), 1147(m), 1040(m), 1024(m), 855(m),
803(m), 723(s). Elemental Anal. Calc. for C24H26CdN4O4:
C, 52.66; H, 4.75. Found: C, 52.60; H, 4.74%. Complex
The X-ray diffraction data were collected at room tem-
perature [296(2) K] on a Bruker 3-circle diffractometer
(Bruker Nonius SMART APEX 2) equipped with CCD
area detectors, and using graphite-monochromated Mo
1
˚
Ka radiation (k = 0.71073 A) from 60W microfocus Sie-
2: Crystalline yield 30%, H NMR (DMSO-d6) 7.69(md,
mens Microsource with glass polycapillary optics. X-ray
diffraction data for all the crystals were collected using
Bruker SMART software. This software was also used
for indexing and determining unit cell parameters. The
structures were solved by direct methods and refined by
full-matrix least squares against F2 for all data using
SHELXTL software. All non-H atoms were refined by full-
matrix least squares in the anisotropic approximation
and the hydrogen atoms attached to these atoms the
hydrogen atoms have been located on the difference Fou-
rier maps. In all cases the hydrogen atoms attached to
polar atoms such as O and N were located on the differ-
ence Fourier maps and refined in the final structure in
isotropic approximation. Experimental absorption correc-
tion method is none in all cases. The crystal data are
given in Table 1. The proton NMR spectra were
recorded in a Varian 400 MHz spectrophotometer at
room temperature while the FT-IR spectra were recorded
in NICOLET IMPACT-410 spectrometer using OMNIC
software.
J = 8 Hz, 1H), 7.49–7.30(m, 3H), 5.74(s, 1H), 2.12(s, 6H).
IR(KBr, cmꢀ1
) 3445(bm), 3199(s), 3146(s), 1577(s),
1550(s), 1396(s), 1299(m), 1169(w), 1149(w), 1050(m),
860(m), 792(m), 755(s). Elemental Anal. Calc. for
C24H24CdN4O4Cl2: C, 46.77; H, 3.90. Found: C, 46.82;
H, 3.92%. Complex 3: Crystalline yield 15%, 1H NMR
(DMSO-d6) 12.00(s, 1H), 7.79–7.78(m, 1H), 7.31–7.27(m,
1H), 6.78–6.71(m, 2H), 5.73(s, 1H), 2.10(s, 6H). IR(KBr,
cmꢀ1) 3198(s), 3144(s), 3044(s), 2984(s), 1623(s), 1590(s),
1540(s), 1483(s), 1452(s), 1396(s), 1352(s), 1292(m),
1251(s), 1143(w), 1044(w), 875(w), 760(s). Complex 4:
1
Crystalline yield 34%, H NMR (DMSO-d6) 9.80(bs, 1H),
7.81(d, 8 Hz, 2H), 6.75(d, 8 Hz, 2H), 5.75(s,1H), 2.12(s,
6H). IR(KBr, cmꢀ1) 3420(bs), 3193(s), 3146(s), 1600(s),
1532(s), 1395(s), 1280(s), 1238(s), 1160(w), 1034(w),
825(m), 780(m). Complex 5: Crystalline yield 51%, 1H
NMR (DMSO-d6) 7.84(dd, 4, 8 Hz, 2H), 7.75(dd, J = 4,
8 Hz, 2H), 7.67–7.56(m, 4H), 5.75(m, 1H), 2.12(s, 6H).
IR(KBr, cmꢀ1) 3445(bs), 1592(s), 1573(s), 1393(s),1356(s),
1153(w), 783(w), 741(w). Complex 6: Crystalline yield
51%, 1H NMR (DMSO-d6) 8.27–8.25(m, 4H), 8.18–
3. Experimental procedure for preparation of the complexes
1–9
8.16(m, 4H), 5.74(s, 1H), 2.12(s, 6H). IR(KBr, cmꢀ1
)
3422(bs), 3199(s), 3136(s), 2931(s), 2875(s), 1572(s),
1388(s), 1339(s), 1031(m), 815(s), 727(m). Elemental Anal.
Calc. for C19H16CdN4O8: C, 42.16; H, 2.96. Found: C,
42.20; H, 2.99%. Complex 7: Crystalline yield 26%, 1H
NMR (DMSO-d6) 7.96–7.93(m, 4H), 7.47–7.45(4H),
5.74(s, 1H), 2.12(s, 6H). IR (KBr, cmꢀ1) 3269(bs), 1590(s),
1500(s), 1411(s), 1284(w), 1096(w), 858(m), 776(m). Com-
To a well-stirred solution of benzoic acid/substituted
benzoic acid (2 mmol) in methanol (10 ml) a solution of
cadmium acetate dihydrate (0.266 g, 1 mmol) in methanol
(5 ml) was added. The resulting homogeneous solution
was stirred at room temperature for 4 h. To this homoge-
neous solution 3,5-dimethylpyrazole (2 mmol) or pyridine
(2 mmol) was added and the colorless mixture was further
1
plex 8: Crystalline yield 24%, H NMR (DMSO-d6) 8.58
(s, 2H), 8.04(t, J = 8 Hz, 4H), 7.92(t, J = 8 Hz , 4H),

2614
K. Bania et al. / Polyhedron 26 (2007) 2612–2620
Table 1
Crystal data and refinement parameters for 1–9
1
2
3
4
5
Formulae
C24H26CdN4O4
546.89
C24H24CdN4O4Cl2
615.77
monoclinic
C2/c
23.7361(15)
11.2097(6)
10.6339(12)
90.00
115.578(5)
90.00
2552.1(4)
4
1.603
1.103
1240
C24H26CdN4O6
578.89
monoclinic
P21/n
13.1139(3)
13.0501(3)
14.7963(4)
90.00
94.2690(10)
90.00
2525.18(11)
4
1.523
0.910
1176
C24H26CdN4O6
578.89
monoclinic
P21/c
10.0548(5)
21.1953(12)
12.0152(7)
90.00
109.5650(10)
90.00
2412.8(11)
4
1.594
0.953
1176
C76H72CdN16O36
2235.10
triclinic
Molecular weight
Crystal system
Space group
monoclinic
P21/n
12.6043(5)
13.9558(6)
14.2804(6)
90.00
93.250(2)
90.00
2507.03(18)
4
ꢀ
P1
˚
a (A)
14.0437(8)
14.1965(9)
14.6448(10)
63.324(4)
62.683(3)
64.211(3)
2219.5(2)
1
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
Density (g cmꢀ3
)
1.448
0.906
1112
1.672
1.042
1120
Absorption coefficient (mmꢀ1
F(000)
)
Total number of reflections
Reflections I > 2r(I)
Maximum 2h (°)
9137
5097
28.40
ꢀ16 6 h 6 16,
ꢀ18 6 k 6 18,
ꢀ19 6 l 6 19
99.1
6235/0/310
1.019
16001
2703
28.21
ꢀ29 6 h 6 31,
ꢀ14 6 k 6 14,
ꢀ14 6 l 6 13
96.4
3044/0/161
1.050
25494
4609
28.37
ꢀ17 6 h 6 17,
ꢀ17 6 k 6 17,
ꢀ19 6 l 6 19
99.2
6270/0/336
1.012
12211
4351
28.38
ꢀ13 6 h 6 13,
ꢀ25 6 k 6 15,
ꢀ16 6 l 6 13
89.1
5394/0/336
0.995
24479
9028
28.38
ꢀ18 6 h 6 18,
ꢀ18 6 k 6 18,
ꢀ19 6 l 6 18
97.8
10849/0/623
1.017
Ranges (h,k, l)
Complete to 2h (%)
Data/restraints/parameters
Goodness of fit (F2)
R indices [I > 2r(I)]
R indices (all data)
0.0252
0.0689
0.0292
0.0785
0.0289
0.0683
0.0260
0.0628
0.0243
0.0615
6
7
8
9
Formulae
C
19H16CdN4O8
C19H16CdN2O4Cl2
519.64
triclinic
C27H22CdN2O4
550.87
monoclinic
P21/c
7.9424(9)
29.076(4)
10.5680(12)
90.00
97.118(7)
90.00
2421.3(5)
4
1.511
0.973
1112
C32H26CdN2O5
630.95
monoclinic
P21/n
15.7113(15)
6.0304(5)
29.197(3)
90.00
92.195(6)
90.00
2764.3(4)
4
1.516
0.834
1280
Molecular weight
Crystal system
Space group
540.76
triclinic
ꢀ
ꢀ
P1
P1
˚
a (A)
7.8825(6)
11.4426(10)
12.2286(10)
85.004(5)
72.214(5)
82.499(5)
1039.97(15)
2
7.8546(4)
10.8632(7)
13.3295(8)
111.717(3)
91.225(3)
97.744(2)
1043.85(11)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
Density (g cmꢀ3
)
1.727
1.105
540
1.653
1.328
516
Absorption coefficient (mmꢀ1
F(000)
)
Total number of reflections
Reflections (I > 2r(I))
Maximum 2h (°)
8297
3342
26.00
ꢀ9 6 h 6 9,
ꢀ13 6 k 6 13,
ꢀ15 6 l 6 15
88.3
3609/0/195
1.077
13329
4609
28.33
ꢀ10 6 h 6 10,
ꢀ14 6 k 6 14,
ꢀ17 6 l 6 17
97.5
5087/0/260
1.031
30720
3591
28.33
ꢀ10 6 h 6 10,
ꢀ38 6 k 6 38,
ꢀ13 6 l 6 14
99.3
5994/0/313
1.041
23494
5021
28.34
ꢀ20 6 h 6 20,
ꢀ7 6 k 6 8,
ꢀ37 6 l 6 39
98.3
6766/0/369
1.012
Ranges (h,k,l)
Complete to 2h (%)
Data/restraints/parameters
Goodness-of-fit (F2)
R indices [I > 2r(I)]
R indices (all data)
0.0202
0.0527
0.0243
0.0643
0.0531
0.1410
0.0325
0.0675
7.60–7.55(m, 4H), 5.73(s, 1H), 2.12(s,6H). IR(KBr, cmꢀ1
)
5. Results and discussion
3392(bs), 3056(w), 2923(w), 1547(s), 1396(s), 792(s). Com-
plex 9: Crystalline yield 23%, 1H NMR (DMSO-d6) 8.59(s,
1H), 8.09–8.04(m, 2H), 7.94(t, J = 8 Hz , 2H), 7.78(mt, J =
8 Hz, 2H), 7.61–7.54(m,2H), 7.41–7.38(m, 3H). IR(KBr,
The reaction of cadmium acetate with aromatic carbox-
ylic acid followed by treatment with 3,5-dimethylpyrazole
(La) led to mixed ligand cadmium complexes. The num-
ber of (La) ligand/s in cadmium carboxylate complexes
varies with the aromatic carboxylic acid from which it is
cmꢀ1
)
3444(bs), 2925(m), 1631(s), 1602(s), 1537(s),
1504(m), 1046(m), 1400(s), 1281(w), 1035(m), 790(s).

K. Bania et al. / Polyhedron 26 (2007) 2612–2620
2615
prepared. Either two nitrogen donor ligands or one nitrogen
donor ligand per cadmium ion are observed depending on
the substituents present in the aromatic carboxylate. For
example, the reaction of cadmium acetate dihydrate with
aromatic carboxylic acids such as benzoic acid, 2-chloro-
benzoic acid, 2-hydroxybenzoic acid or 4-hydroxybenzoic
acid in the presence of (La) led to the formation of corre-
sponding benzoate complexes having two benzoate groups
and two (La) ligands. The 2-nitro-, 4-nitro-, 4-chloro-ben-
zoic acids and 1-naphthoic acid led to complex having one
(La) and two carboxylate ligands per cadmium. However,
the 2-nitrobenzoate complex of cadmium contains an addi-
tional aqua ligand; which is absent in the case of 4-nitro-
benzoate complex. The results are depicted Scheme 2.
The crystal structure of each of these complexes is deter-
mined and the structures of the complexes 1–4 are shown in
Fig. 1. Trigonal prismatic geometry with six co-ordination
around cadmium ions are observed in the cases of the com-
plexes 1–4. The bond angles and bond distances of the
complexes are listed in Table 2 and structures of the com-
plexes are shown in Fig. 1. It may be mentioned that in the
case of 1 two types of cadmium ligand bonds in terms of
bond length are observed. There are four cadmium–ligand
bonds of similar length and two other are slightly longer. It
has been already reported [3a] that in cadmium complexes
outer and inner co-ordination spheres are possible and the
˚
outer Cd–N bond lengths are in the range of 2.5–2.7 A
˚
whereas inner ones are less by about 0.3 A from the outer
ones. In our system also the bond distances of the four
Cd–N and Cd–O bonds are comparable and makes a pseudo
tetrahedral inner structure comprising of Cd–O3, Cd–O4,
Cd–N1 and Cd–N4 bonds. The other two Cd–O1 and
[Cd(RC6H4COO)2(La)2]
Cd(OAc)2 2H2O + RC6H4COOH +La
La = 3,5-dimethylpyrazole
When R = H (1), 2-Cl (2) 4-OH (3), 2-OH (4)
[Cd (RC6H4COO)2(La)(H2O)n]
When R = 2-NO2, n = 1 (5); when R = 4-NO2, n = 0 (6) when R= 4-Cl, n =0 (7)
when RC6H4 = 1-naphthyl, n= 0 (8)
Scheme 2.
Fig. 1. Structures of cadmium benzoate complexes 1–4 and their hydrogen bonded assembly [ORTEP are drawn with 20% thermal ellipsoid, in cases of
(c) and (e) hydrogen atoms are omitted for clarity].

2616
K. Bania et al. / Polyhedron 26 (2007) 2612–2620
Table 2
Cadmium–ligand bond geometry (distances and angles) in complexes 1–4
˚
˚
Cd–L
Co–L (A)
L–Cdꢁ ꢁ ꢁL
\L–Cdꢁ ꢁ ꢁL (°)
Cd–L
Co–L (A)
L–Cdꢁ ꢁ ꢁL
\L–Cdꢁ ꢁ ꢁL (°)
For 1
For 2
Cd–O1
Cd–O2
Cd–O3
Cd–O4
Cd–N4
Cd–N1
2.561
2.234
2.276
2.480
2.254
2.278
O4–Cd–N4
O4–Cd–N1
O3–Cd–O1
O4–Cd–O2
O3–Cd–N1
O3–Cd–N4
80.96
125.52
95.16
107.04
93.87
Cd–O1
Cd–O2
Cd–O1
Cd–O2
Cd–N1
Cd–N1
2.371
2.358
2.371
2.358
2.272
2.272
O1–Cd–N1
N1–Cd–N2
O2–Cd–N1
O1–Cd–O2
O2–Cd–O2
O1–Cd–O1
114.56
87.34
92.27
92.77
89.89
136.88
132.13
For 3
For 4
Cd–O1
Cd–O2
Cd–O5
Cd–O4
Cd–N1
Cd–N3
2.288
2.400
2.779
2.222
2.259
2.779
N1–Cd–O4
O2–Cd–O5
O1–Cd–O4
O1–Cd–N1
O2–Cd–N3
N3–Cd–N1
95.64
90.98
96.84
105.56
90.74
94.27
Cd–O1
Cd–O2
Cd–O3
Cd–O4
Cd–N1
Cd–N4
2.365
2.379
2.422
2.302
2.251
2.276
O1–Cd–N4
O3–Cd–O2
O1–Cd–O4
O3–Cd–N1
O2–Cd–N4
O2–Cd–N1
85.03
97.98
100.11
85.20
139.05
100.64
˚
Cd–O4 bonds have bond length 2.561 and 2.480 A and
with bond angles O1–Cd–O4 137.62°, respectively. This
suggests that under suitable condition these two atoms
would serve as bridging group if another metal atom can
approach. However, in this case presence of two 3,5-dim-
ethylpyrazole ligands prevents further approach oxygen
to the cadmium ion to form co-ordination polymer. The
2-chlorobenzoate complex 2 has a more symmetric trigonal
prismatic structure. Both the compounds 1 and 2 have sim-
ilar hydrogen bonding interactions and they remain as
hydrogen bonded self-assemblies. In these two complexes
the N–H bond of 3,5-dimethylpyrazole interacts with the
carbonyl group of co-ordinated carboxylate ligand of
another molecule to form self-assemblies. Such assemblies
are further held by C23–Hꢁ ꢁ ꢁO2 interaction between C–H
of a methyl group with an oxygen atom of carboxylate
group of another molecule (Fig. 1a). The important bond
angles and distances for compound 1 are listed in Table
2. Cadmium complex of 4-amino-carboxylic acid adopts
two dimensional polymeric hydrogen bonded structure
[7]. The structure of the complexes 3 and 4 are shown in
Fig. 1c and e respectively. Both these complexes have six
co-ordinations with distorted trigonal prismatic geometry
and in the solid state they form H-bonded self-assembly.
The complex 3 has a one dimensional layer structure held
by N–Hꢁ ꢁ ꢁO interactions between the N–H of 3,5-dim-
ethylpyrazole un-coordinated nitrogen atoms with carbonyl
oxygen of 2-hydroxybenzoate. There is also intra-molecu-
lar hydrogen bonding (O6–Hꢁ ꢁ ꢁO2) between the hydroxy
groups with the carbonyl oxygen of the benzoate (Table
3). In the 4-hydroxybenzoate complex 4, hydrogen bonding
between hydroxy groups and the carbonyl oxygen of
another molecule adjacent to it takes place. In addition
to this, the opposite side of the molecule is associated with
N–Hꢁ ꢁ ꢁO interactions with another neighboring molecule
as illustrated in Fig. 3f. These interactions result in the for-
mation of three-dimensional hydrogen bonded network. It
is already reported that the picolinic acid forms six-coordi-
nated polymeric network. Our results also support that
N1O5 environment around cadmium [1n,2] can lead to
co-ordination polymer in one-dimension.
The nitro-substituent on the aromatic carboxylic acid
affects the structure as well as the co-ordination environ-
ment of cadmium complexes. The complex 5 has an
aqua-ligand and it is a tetra nuclear complex as shown in
Fig. 2a. The formation of such tetra nuclear complex is
attributed to the variation in composition due to the steric
effect of nitro-group at ortho-position leading to a thermo-
dynamically stable product. The complex 5 has eight co-
ordination around two central cadmium ion and the other
two cadmium ions at both the ends of the tetra nuclear
complex have six co-ordination geometry. Polymeric cad-
mium complexes having seven co-ordination is common
in co-ordination chemistry of cadmium [1a], however the
complex 5 is a rare example of tetra nuclear complex hav-
ing eight co-ordination. It is interesting to note that each of
the tetra nuclear complex possesses aqua-ligand at the end
cadmium atoms; each and these aqua ligands interacts with
Table 3
Hydrogen bonding geometry (distances and angles) in complexes 1–4
D–Hꢁ ꢁ ꢁA
dD–H
˚
dHꢁ ꢁ ꢁA
dDꢁ ꢁ ꢁA
\D–Hꢁ ꢁ ꢁA
(°)
˚
˚
(A)
(A)
(A)
For 1
C23–Hꢁ ꢁ ꢁO2
O4–Hꢁ ꢁ ꢁN2
N6–Hꢁ ꢁ ꢁO2
0.960
0.926
0.817
2.470
2.242
1.935
3.412
2.990
2.737
187.02
158.24
166.98
For 2
N2–Hꢁ ꢁ ꢁO1
For 3
0.880
1.961
2.821
165.57
O3–H. . .O2
O6–H. . .O4
N2–H. . . O5
0.730
0.803
0.854
1.963
1.933
2.062
2.683
2.729
2.864
168.42
171.25
156.08
For 4
O6–Hꢁ ꢁ ꢁO2
(intramolecular)
N2–Hꢁ ꢁ ꢁO1
N3–Hꢁ ꢁ ꢁO3
0.889
1.788
2.589
148.63
0.832
0.832
2.280
2.188
3.041
2.954
152.41
153.05

K. Bania et al. / Polyhedron 26 (2007) 2612–2620
2617
Fig. 2. (a) Structure of tetra nuclear complex 5 (hydrogen atoms are omitted for clarity). (b) The arrangement of ligands around the cadmium in the tetra
nuclear complex. (c) Hydrogen bonding interactions in the self assembled structure (drawn with 20% thermal ellipsoids).
the carbonyl group of another tetra-nuclear complex mak-
ing an one dimensional self-assembled polymeric structure.
Some of the important hydrogen bonding interactions
present in the hydrogen bonded assembly is listed in Table
4. This structure is also important from another point of
view is that it is an exception to the structure that is
observed as mononuclear complex from 2-chlorobenzoic
acid and 2-hydroxybenzoic acid which are ortho-substituted
aromatic carboxylates. However, it is observed that the
solid phases reaction of 2-nitrobenzoic acid with cadmium
acetate with (La) results in the formation of mononuclear
hexa-coordinated species namely tetra (3,5-dimethylpyra-
zole) cadmium(II) (2-nitrobenzoate). In the case of solid
phase reaction we did not observe tetra nuclear species
rather observed a mononuclear species; this suggests that
tetra nuclear species may be a kinetic control product. In
fact tetra-nuclear complex on heating transforms to mono-
nuclear hexa-coordinated complex.
The complex 6 has a polymeric structure with the car-
boxylate oxygen atoms as bridging atoms to the cadmium
ions. The structure of the complex 6 is shown in Fig. 3a.
The 4-nitrobenzoate complex 6 does not have aqua ligand
as compared to that of 5. Thus, it may be said that the posi-
tion of water molecule is occupied up by bridging oxygen
atom of a carboxylate group leading to co-ordination poly-
mer. In the one-dimensional polymer all the cadmium are
in seven co-ordination environment. The metal–ligand
bond geometries are listed in Table 5. Similar structures
are obtained in the case of 4-chlorobenzoate complex 7
as well as in the 1-naphthoate complex 8. Important bond
distances are listed in Table 5. In these two cases the metal–
ligand composition of the complex is identical to that of 6.
A similar reason may be put forward in these cases for
explaining polymer formation. The attack of one nitrogen
donor ligand is favored in these three complexes due to ste-
ric reasons and this makes approach of another molecule to
form bridging carboxylate bonds between two discrete
units. Careful analysis of the structure shows (Fig. 3b) that
every carboxylate can be a bridging as well as chelating in
the polymeric system. Such system can be constructed from
the dinuclear building blocks as depicted in Fig. 3f. Sup-
port to this fact arises from the fact that there are two dif-
ferent Cd–Cd distances in each of these complexes in
alternating manner. For example the Cd–Cd distances in
4-nitrobenzoate, 4-chlorobenzoate and 1-naphthoate com-
Table 4
Hydrogen bonding geometry (distances and angles) in complex 5
D–Hꢁ ꢁ ꢁA
dD–H
˚
dHꢁ ꢁ ꢁA
dDꢁ ꢁ ꢁA
\D–Hꢁ ꢁ ꢁA
(°)
˚
˚
(A)
(A)
(A)
N6–Hꢁ ꢁ ꢁO2
O1–Hꢁ ꢁ ꢁO17
0.817
0.748
1.935
2.092
1.998
2.737
2.831
2.766
166.98
169.24
167.41
˚
˚
˚
˚
˚
O6–Hꢁ ꢁ ꢁO17 (2ꢀx, 1ꢀy, 0.781
plexes are 4.138 A, 3.748 A; 4.119 A, 3.745 A and 4.152 A,
˚
z)
3.801 A respectively. The observation of long and short
O3–Hꢁ ꢁ ꢁO18
0.784
2.274
3.035
160.76
separation clearly indicates that there is a part of the poly-

2618
K. Bania et al. / Polyhedron 26 (2007) 2612–2620
Fig. 3. The structure of (a) 6 (b) ligand environment in the co-ordination polymer of 6, (c ) the structure of 7 (d) the repeated units in the co-ordination
polymer 8 (e) unit cell of 8 (f) representation showing a route for formation of co-ordination polymers in 6–8.
mer having paddlewheel type structure and another unit
has features of mononuclear structure and combination
of which is leading to the co-ordination polymers. Thus,
formation of mononuclear complexes may be imagined to
be from cleavage of such polymeric species. It may be pro-
posed that that the polymeric units are having mononu-
clear and dinuclear paddlewheel structure and each
paddlewheel can be squeezed to give mononuclear species
if the diagonal bridging atoms can be connected to the cad-
mium atom. Such distortion in paddlewheel would prefer-
entially take the system to a mononuclear species. This is
illustrated in Scheme 1, where arrows are indicating the
approach of an oxygen atom to cause distortion to a limit-
ing case and beyond which distortion would make two
mononuclear chelate from one parent bridged binuclear
system. We have observed in the case of copper [6a] and
cobalt [6e] and in nickel [6b,6c] that similar reactions are
highly sensitive to the reaction conditions. However, the
present study is designed such a way that all the reactions
are carried out under identical molar ratios and identical
condition. The driving force in the case of cadmium com-
plexes to have polymeric form thus arises from the compe-
tition between the steric factor and attack of a bridging
ligand to form co-ordination polymer. The (4-chloro-2-
methylphenoxy) acetate complex of cadmium(II) complex
has polymeric structures having six coordination number
of cadmium [8]. In this complex, two water molecules
and a carboxylate group serves as bridging ligand [8]. All
the complexes presented in this manuscript are also charac-
terized by recording their proton-NMR. The integration of
protons confirmed that they have the same composition in
solution and solid state. However, it is found that for com-
plex 5 and 9 in DMSO the water signals of the complexes
are merged with the water signal from dissolved water in
the solvent. Each of the complexes has characteristic N–
H stretching frequency from the 3,5-dimethylpyrazole ring
however, at a different position. For example, complex 1
has absorption at 3434 cmꢀ1 for N–H stretching whereas
the 3,5-dimethyl pyrazole has absorption at 3201 cmꢀ1
The compound has absorption frequencies that have
.

K. Bania et al. / Polyhedron 26 (2007) 2612–2620
2619
Table 5
Cadmium–ligand bonding geometry (distances and angles) in complex 6, 7, 8 and 9
˚
˚
Cd–L
Co–L (A)
L–Cdꢁ ꢁ ꢁL
\L–Cdꢁ ꢁ ꢁL (°)
Cd–L
Co–L (A)
L–Cdꢁ ꢁ ꢁL
\L– Cdꢁ ꢁ ꢁL (°)
For 6
For 7
Cd–O1
Cd–O2
Cd–O5
Cd–O6
Cd–N3
2.219
2.767
2.291
2.524
2.279
O6–Cd–O1
O5–Cd–N3
O5–Cd–O50
O2–Cd–N3
O6–Cd–N3
87.71
87.65
75.37
77.78
148.02
Cd–O1
Cd–O3
Cd–O2
Cd–O4
Cd–N1
2.293
2.479
2.383
2.209
2.271
O1–Cd–O2
O4–Cd–O3
O1–Cd–N1
O2–Cd–N1
O2–Cd–O3
101.99
97.75
104.08
78.11
77.78
For 9
Cd–O1
Cd–O2
Cd–O3
Cd–O4
Cd–N1
Cd–N2
Cd–O5(aq)
2.430
2.384
2.484
2.363
2.358
2.356
2.328
O4–Cd–N2
O4–Cd–N2
O4–Cd–N1
O3–Cd–O2
O4–Cd–O5(aq)
O5–Cd–N2(aq)
O5–Cd–N1(aq)
97.23
91.47
85.40
84.51
81.35
88.37
95.21
For 8
Cd–O2
Cd–O1
Cd–O3
Cd–O4
Cd–N1
2.302
2.461
2.402
2.212
2.253
O1–Cd–O3
O2–Cd–O20
O3–Cd–N1
O1–Cd–O4
O2–Cd–N1
77.52
75.44
77.85
89.25
104.59
characteristic features of bi-dentate carboxylate ligand [9].
For example the complex 1 has absorption at 1538(mas) and
1404(ms) cmꢀ1 due to the bidentate carboxylic acid group.
The parent benzoic acid has absorptions at 1682 and
1421 cmꢀ1. The other mono-nuclear complexes also have
similar trends in absorptions over the parent carboxylic acid,
confirming bi-dentate nature of the carboxylate groups. The
complexes 6, 7, 8 have both bidentate and bridging carboxy-
lates from crystallographic study. Although, in these cases
clear distinction could not be made between the two type
of binding mode from the IR-absorptions but some infer-
ence can be made; for example in the case of 7, the absorp-
tions from carboxylate groups occurs at 1590, 1500, 1411
and 1390 cmꢀ1 in contrast to the parent carboxylic acid
namely 4-chlorobenzoic acid, which has absorptions at
tion of cadmium acetate with 1-naphthoic acid and
pyridine
CdðOAcÞ22H2O þ 1-C10H7COOH þ Lb
! ½CdðC10H7COOÞ2ðLbÞ2ðH2OÞꢂ
ð1Þ
9
where Lb = pyridine
This reaction led to complex having composition [M(L)2-
(Lb)2(H2O)] (9) where L is 1-naphthoate and Lb is pyridine.
As expected from the trend from the composition that in this
class of compound there is no polymeric structure, we have
found it to be so for the complex. It is found that the complex
has a distorted pentagonal bipyramidal seven co-ordination
geometry as shown in Fig. 4a. Four oxygen atoms from
naphthoate groups and oxygen atom of the aqua ligand form
the basal plane. The axial positions are taken up by two pyr-
idine ligands. The complex in solid state has extensive hydro-
gen bonded structure through the interaction of the aqua
1683, 1592, 1424 cmꢀ1
.
Since we have obtained a polymeric structure for the 1-
naphthoate complex 8, we extended our study to the reac-
Fig. 4. (a) The structure of 9 (hydrogen atoms are omitted for clarity). (b) The hydrogen bond interactions between two molecules of 9 (drawn with 20%
thermal ellipsoid).

2620
K. Bania et al. / Polyhedron 26 (2007) 2612–2620
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ligand with the oxygen of carboxylate groups. The hydrogen
bonded chain like structures are formed from O5–Hꢁ ꢁ ꢁO3
with 0.901 (dD–H), 1.934 (dHꢁ ꢁ ꢁA), 2.766 (dDꢁ ꢁ ꢁA), 152.759
(\D–Hꢁ ꢁ ꢁA/°) and O5–Hꢁ ꢁ ꢁO2 with 0.809 (dD–H), 1.995
(dHꢁ ꢁ ꢁA), 2.727 (dDꢁ ꢁ ꢁA) 150.18 (\D–Hꢁ ꢁ ꢁA/°). The hydrogen
bonding between two molecules of 9 is shown in Fig. 4b.
In conclusion it has been possible to rationalize the rela-
tion between composition and structure in 3,5-dimethypy-
razole containing cadmium carboxylates. The cadmium
carboxylate complex having composition [Cd(L)2(La)2]
leads to mononuclear structure and the composition
[Cd(L)2(La)] leads to polynuclear co-ordination polymers,
whereas the complex having the composition [Cd(L)2(La)-
(H2O)] leads to tetranuclear complex. It is also observed
that the compositions are more important than the substi-
tuent at the ortho or para-position of the aromatic carbox-
ylate ligands, however, to a great extent the composition of
La containing cadmium carboxylates are decided by the
substituents; keeping a close correlation between the steric
factor with thermodynamic control of synthesis. The over-
all structure in solid state is stabilized by various weak
interactions. The cadmium complex having the composi-
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bipyramid structure.
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Appendix A. Supplementary material
CCDC 626304, 626305, 626306, 626307, 626308,
626309, 6263010, 6263011 and 626312 contain the supple-
mentary crystallographic data for this paper. These data
can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.poly.2007.01.005.
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