Synthesis, X-ray crystal structures and multinuclear NMR characterization of Hg(II) complexes of 2-[(E)-2-(aryl)-1-diazenyl]pyridine

Article abstract of DOI:10.1016/j.poly.2004.08.003

Two Hg(II) complexes, viz., dichloro-{2-[(E)-2-(4-methylphenyl)-1-diazenyl] pyridine}Hg(II) (1) and dichloro-{2-[(E)-2-(3-methylphenyl)-1-diazenyl]pyridine} Hg(II) (2) were characterized by ¹H, ¹³C and ¹⁹⁹Hg (NMR) and X-ray crystallographic techniques. Complex 2 is polymeric where the ligand coordinate via the pyridyl nitrogen, and all the chlorine atoms serving to bridge mercury atoms. In contrast, complex 1 has a dimeric structure with bidentate ligand chelation via the pyridyl nitrogen and one of the azyl nitrogens, with a terminal chlorine on each Hg and a μ,μ′-dichloro bridge between the mercury atoms.

Full text of DOI:10.1016/j.poly.2004.08.003

Polyhedron 23 (2004) 2323–2329
www.elsevier.com/locate/poly
Synthesis, X-ray crystal structures and multinuclear
NMR characterization of Hg(II) complexes of
2-[(E)-2-(aryl)-1-diazenyl]pyridine
a,
b
c
d,
**
Tushar S. Basu Baul *, Antonin Lycka , Ray Butcher , Frank E. Smith
a
Department of Chemistry, North-Eastern Hill University, NEHU Permanent Campus, Umshing, Shillong 793 022, India
b
Research Institute for Organic Syntheses, CZ-532 18 Pardubice-Rybitvi, Czech Republic
c
Department of Chemistry, Howard University, Washington, DC 20059, USA
d
Weill Cornell Medical College in Qatar, P.O. Box 24144, Doha, Qatar
Received 2 April 2004; accepted 2 August 2004
Available online 28 August 2004
Abstract
Syntheses and structural studies for the two complexes dichloro-{2-[(E)-2-(4-methylphenyl)-1-diazenyl]pyridine}Hg(II) (1) and
dichloro-{2-[(E)-2-(3-methylphenyl)-1-diazenyl]pyridine}Hg(II) (2) are reported. The solid-state structures of the complexes were
1
determined by X-ray diffraction methods and in addition, the complexes were characterized in solution using H, 13C and 199Hg
NMR spectroscopy. The X-ray structures reveal that the complexes adopt surprisingly different structures. Complex 2 has an
extended polymeric structure with 2-[(E)-2-(3-methylphenyl)-1-diazenyl]pyridine behaving as a monodentate ligand via the pyridyl
nitrogen, and all the chlorine atoms serving to bridge mercury atoms, whereas complex 1 has a dimeric structure with 2-[(E)-2-(4-
methylphenyl)-1-diazenyl]pyridine behaving as a bidentate ligand via the pyridyl nitrogen and one of the azo nitrogens, with a ter-
minal chlorine on each Hg and a l,l0-dichloro bridge between the mercury atoms. But the coordination geometry around the mer-
cury atom is similar in both complexes, each showing a distorted trigonal bipyramidal arrangement of the donor atoms. These
1
complexes were characterized in solution by H, 13C, 199Hg NMR spectroscopy.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: 2-[(E)-2-(aryl)-1-diazenyl]pyridine; Hg(II) complexes; NMR; Crystal structures
1. Introduction
for this reason that extensive studies with the 2-(aryl-
azo)pyridine (hereafter named as 2-[(E)-2-(aryl)-1-diaze-
nyl]pyridine, Fig. 1) system have been undertaken and a
number of studies of metal complexes containing this
type of ligand have been reported. These include inves-
tigations of complexes of Fe(II) [1,2], Ni(II) [2], Hg(II)
[3,4], Os(II) [5,6], Ru(II) [7–19], Cr(0), Mo(0), W(0)
[20,21], Cr(II) [22], Cu(I) [23], Rh(III) [24,25], Rh(I)
[26], Ag(I) [27], Re(III) [28], Co(II) [29], Mo(IV) [15],
Ru(III) [30], Sn(IV) [31] and organometallic complexes
of Re(I) [32] and Sn(IV) [33–37]. In spite of such a
wide-ranging series of studies on a variety of metal com-
plexes involving these ligands, the structures of the mer-
The metal complexes of heterocyclic a-diimine lig-
ands such as 2,20-bipyridine and 1,10-phenanthroline
have proven to be useful for studying such phenomena
as luminescence and photo reduction/oxidation. It is
*
Corresponding authors. Tel.: +91 364 2722627; fax: +91 364
2721000.
**
Tel.: 974 492 8206.
E-mail addresses: basubaul@nehu.ac.in (T.S. Basu Baul),
frs2003@med.cornell.edu (F.E. Smith).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.08.003

2324
T.S. Basu Baul et al. / Polyhedron 23 (2004) 2323–2329
3
the instrument used was a Bruker Avance 500 NMR
spectrometer equipped with a triple (1H/13C/broadband)
N
1
2'
3'
1
5 mm inverse probe. The H and 13C chemical shifts
4
N
R
4'
1'
were referred to internal TMS (d = 0.00). Samples were
dissolved either in acetone-d6 or DMSO-d6. Two-dimen-
sional experiments (gradient-selected (gs)-COSY, gs-
HSQC and gs-HMBC) were performed using the manu-
facturerÕs software (XWINNMR version 3.1). The
199Hg (64.50 MHz) NMR spectra were recorded on a
Bruker AMX 360 NMR spectrometer equipped with a
5 mm tunable broadband probe. The 199Hg chemical
shifts were referred to Hg(CH3)2 (d = 0.0) by a calcula-
tion procedure using N(199Hg ) = 17910841 Hz and
N(1H) = 100000000 Hz for proton resonance in tetra-
methylsilane [40]. Positive values of chemical shifts de-
note shifts to higher frequencies.
N
6
5
5'
(L1: R = 4-CH3 and L2: R = 3-CH3)
6'
Fig. 1. Generic structure of the ligand.
cury complexes have remained uncertain [3,4]. A mercu-
ration reaction was attempted with 2-[(E)-2-(phenyl)-1-
diazenyl]pyridine but gave no detectable mercuration
products, instead an addition product was isolated [3].
The same product (which was characterized by m.p.
and microanalytical data) was again prepared by react-
ing mercuric chloride and 2-[(E)-2-(phenyl)-1-diaze-
nyl]pyridine. Structures for the Hg(II) complexes of
analogous ligands have been proposed on the basis of
electronic, infrared and 1H NMR spectra. However
these studies cannot provide definitive conclusions con-
cerning the co-ordination geometry of the complexes [4].
In this paper, X-ray diffraction results are reported for
two mercury complexes in combination with their de-
2.3. Preparation of dichloro-{2-[(E)-2-(4-methylphe-
nyl)-1-diazenyl]pyridine}Hg(II) (1)
HgCl2 (0.345 g, 1.27 mmol) in 25 ml of acetone was
added drop-wise to a stirred acetone solution (15 ml)
containing L1 (0.25 g, 1.26 mmol). The reaction mixture
was stirred for 6 h at ambient temperature, and the sol-
vent was removed using a rotary evaporator. The result-
ing dry mass was washed thoroughly with petroleum
ether to remove any unreacted ligand, extracted into
acetone (20 ml) and filtered. The red solution was al-
lowed to evaporate slowly at ambient temperature until
crystallization occurred. This yielded red crystals of 1 in
90 % yield; m.p.: 192–194 ꢁC (180–181 ꢁC) [4]. Anal.
Calc. for C12H11N3HgCl2: C, 30.73; H, 2.35; N, 8.96.
Found: C, 30.71; H, 2.38; N, 8.92%. IR (cmꢀ1):
tailed H, 13C, 199Hg NMR spectroscopic data. Conse-
quently, we are able to be quite confident of our
descriptions of the structures of these complexes at least
in the solid state.
1
2. Experimental
2.1. Materials
1
m(C@N)py: 1599 vs. H NMR (acetone-d6) d: 8.83 (dd,
HgCl2 (Merck) was used without further purification.
All the solvents used in the reactions were of AR grade
and dried using standard literature procedures. The
ligands, viz., 2-[(E)-2-(4-methylphenyl)-1-diazenyl]pyri-
dine and 2-[(E)-2-(3-methylphenyl)-1-diazenyl]pyridine
(abbreviated as L1 and L2, respectively) were prepared
according to the literature methods [38,39]. The
complexes, dichloro-{2-[(E)-2-(4-methylphenyl)-1-diaze-
nyl]pyridine}Hg(II); L1HgCl2 (1) and dichloro-{2-[(E)-
1H, 3-H), 8.20 (ddd, 1H, 5-H), 8.00 (a part of AA0MM0
system, 2H, 20 and 60-H), 7.96 (dd, 1H, 6-H), 7.70 (ddd,
1H, 4-H), 7.47 (a part of AA0MM0 system, 2H, 30 and
50-H), 2.47 (s, 3H, CH3), ppm. (DMSO-d6) d: 8.80 (dd,
1H, 3-H), 7.96 (a part of AA0MM0 system, 2H, 20 and
60-H), 7.90 (dd, 1H, 6-H), 7.70 (ddd, 1H, 4-H), 7.49 (a
part of AA0MM0 system, 2H, 30 and 50-H), 7.17 (ddd,
1H, 5-H), 2.46 (s, 3H, CH3), ppm. 13C NMR (acetone-
d6) d: (C-1; not observed due to very low solubility),
151.09 (C-10), 150.31 (C-3), 144.87 (C-40), 140.69 (C-5),
131.12 (C-30 and 50), 127.24 (C-4), 124.56 (C-20 and
60), 117.85 (C-6), 21.34 (CH3), ppm. (DMSO-d6) d:
161.40 (C-1), 149.93 (C-10), 149.65 (C-3), 144.08 (C-40),
140.37 (C-5), 130.58 (C-30 and 50), 126.73 (C-4), 123.68
(C-20 and 60), 116.11 (C-6), 21.51 (CH3), ppm. 199Hg
NMR (DMSO-d6) d: = ꢀ1460.2 ppm.
2-(3-methylphenyl)-1-diazenyl]pyridine}Hg(II);
L2
HgCl2 (2) were prepared by a method similar to that re-
ported earlier with slight modifications [4]. A typical
procedure is described below (see Section 2.3).
2.2. Physical measurements
Carbon, hydrogen and nitrogen analyses were per-
formed with a Perkin–Elmer 2400 series II instrument.
IR spectra in the range 4000–400 cmꢀ1 were obtained
on a Perkin Elmer 983 spectrophotometer with samples
as KBr discs. For the 1H (500.13 MHz) and 13C (125.76
MHz) NMR spectra and two-dimensional experiments,
2.4. Preparation of dichloro-{2-[(E)-2-(3-methylphe-
nyl)-1-diazenyl]pyridine}Hg(II) (2)
An identical method to that used to prepare 1 was
employed. This led to the formation of red crystals of

T.S. Basu Baul et al. / Polyhedron 23 (2004) 2323–2329
2325
2 which were dried in vacuo. Yield, 82%; m.p.: 178–179
ꢁC (158 ꢁC) [4]. Anal. Calc. for C12H11N3HgCl2: C,
30.73; H, 2.35; N, 8.96. Found: C, 30.70; H, 2.36; N,
3.2. NMR data
1
The H and 13C NMR spectra of the complexes dis-
play distinct signals for the ligand skeletons. The num-
bering scheme employed for the assignments of
1
8.95%. IR (cmꢀ1): m(C@N)py: 1593 vs. H NMR (ace-
tone-d6) d: 8.88 (dd,1H, 3-H), 8.26 (ddd, 1H, 5-H),
8.07 (dd, 1H, 6-H), 7.93 (m, 1H, 20-H), 7.92 (m, 1H,
60-H), 7.76 (ddd, 1H, 4-H), 7.55 (m, 1H, 50-H), 7.50
(m, 1H, 40-H), 2.48 (s, 3H, CH3), ppm. (DMSO-d6) d:
8.83 (dd, 1H, 3-H), 8.22 (ddd, 1H, 5-H), 7.93 (dd, 1H,
6-H), 7.66 (m, 2H, 20 and 60-H), 7.74 (ddd, 1H, 4-H),
7.56 (m, 2H, 50-H), 7.51 (m, 1H, 40-H), 2.46 (s, 3H,
CH3), ppm. 13C NMR (acetone-d6) d: 161.68 (C-1),
152.79 (C-10), 150.33 (C-3), 141.35 (C-5), 140.66 (C-30),
134.80 (C-40), 130.41 (C-50), 127.94 (C-4), 124.60 (C-
20), 122.38 (C-60), 119.77 (C-6), 21.33 (CH3), ppm.
(DMSO-d6) d: 160.89 (C-1), 151.72 (C-10), 149.61
(C-3), 140.56 (C-5), 139.57 (C-30), 133.99 (C-40),
129.76 (C-50), 126.89 (C-4), 123.42 (C-20), 121.34 (C-
60), 116.44 (C-6), 20.08 (CH3) ppm. 199Hg NMR
1
individual H and 13C signals are shown in Fig. 1. The
efforts to use the NMR data in the elucidation of the
coordination mode of the ligand and the geometries of
the complexes were not successful since the solvents used
for the spectra (DMSO-d6 and acetone-d6) could influ-
ence the nature of the coordination sphere.
3.3. X-ray diffraction analysis for complexes 1 and 2
Pertinent crystallographic parameters are summa-
rised in Table 1. The atomic numbering scheme and
the coordination around the mercury atom for the com-
plexes 1 and 2 are illustrated in Figs. 2 and 3, respec-
tively. Selected bond lengths and bond angles are
listed in Table 2 (for 1) and 3 (for 2). Considering the
similarity of the ligands, the two complexes adopt sur-
prisingly different structures. Complex 2 has an extended
polymeric structure with 2-[(E)-2-(3-methylphenyl)-1-
diazenyl]pyridine behaving as a monodentate ligand
via the pyridyl nitrogen, and all the chlorine atoms serv-
ing to bridge mercury atoms, whereas complex 1 has a
dimeric structure with 2-[(E)-2-(4-methylphenyl)-1-dia-
zenyl]pyridine behaving as a bidentate ligand via the
pyridyl nitrogen and one of the azo nitrogens, with a ter-
minal chlorine on each Hg and a l,l0-dichloro bridge
between the mercury atoms. But the coordination geom-
etry around the mercury atom is similar in both com-
plexes, each showing a distorted trigonal bipyramidal
arrangement of the donor atoms.
(acetone-d6) d: = ꢀ1349.8
d: = ꢀ1433.2 ppm.
and
(DMSO-d6)
2.5. X-ray crystallography
The intensity data for dark red block-shaped crystals
of complexes 1 and 2 were measured on a Bruker P4S
˚
using Cu Ka radiation (k = 1.54178 A) and on a Bruker
˚
SMART 1K using Mo Ka radiation (k = 0.71073 A),
respectively. Empirical corrections were made from
psi-scan curves [41]. The structures were solved by direct
methods. All hydrogen atoms were given calculated
positions. Neutral atom scattering factors were taken
from the literature [42]. All computations were per-
formed using the SHELXTL programmes [43]. All refine-
ments were performed by full-matrix least-squares on
F2. The data were corrected for Lorentz and polariza-
tion effects.
3.3.1. Dichloro-{2-[(E)-2-(4-methylphenyl)-1- diaze-
nyl]pyridine}Hg(II) (1)
This complex occurs as centro-symmetric dimers in
the solid state with the ligand 2-[(E)-2-(4-methylphe-
nyl)-1-diazenyl]pyridine behaving as a bidentate via the
pyridyl nitrogen and one of the azo nitrogens, with
one bridging and one terminal chlorine atom. The geom-
etry around each mercury atom is probably best de-
scribed as being that of a distorted trigonal bipyramid,
with the terminal chlorine, one bridging chlorine and
the pyridyl nitrogen forming the trigonal plane and the
other bridging chlorine and one of the azo-nitrogen
atoms taking the axial positions. The structure is very
similar in many regards to that recently reported for di-
chloro-mercury(II)-2-(phenylazo)-pyrimidine [44]. The
bond angles making up the trigonal plane in 1 are
N(1)–Hg–Cl(2), 105.3(2)ꢁ; Cl(1)–Hg–Cl(2), 137.5(9)ꢁ
and N(1)–Hg–Cl(1), 117.0(2)ꢁ, giving a total of 359.8ꢁ.
The corresponding bond angles found for dichloro-
mercury(II)-2-(phenylazo)-pyrimidine are 105.3(2)ꢁ,
137.53(9)ꢁ and 117.0(2)ꢁ, giving a total of 359.8ꢁ. The
3. Results and discussion
3.1. Syntheses
The complexes dichloro-{2-[(E)-2-(4-methylphenyl)-
1-diazenyl]pyridine}Hg(II) (1) and dichloro-{2-[(E)-2-
(3-methylphenyl)-1-diazenyl]pyridine}Hg(II) (2) were
prepared in good yield by stirring stoichiometric
amounts of HgCl2 and L1 or L2 in acetone. The com-
plexes are stable and can be stored in the solid state at
room temperature for months. Selected characterization
data for the complexes are presented in the experimental
section. The microanalytical data are in agreement with
the calculated values and thus confirm the composition.
They are highly soluble in acetone and DMSO but
poorly soluble in common organic solvents.

2326
T.S. Basu Baul et al. / Polyhedron 23 (2004) 2323–2329
Table 1
Crystallographic data and structure refinement for L1HgCl2 (1) and L2HgCl2 (2)
Parameters
L1HgCl2 (1)
L2HgCl2 (2)
Empirical formula
Formula weight
Temperature (K)
Crystal size (mm)
Crystal system
Space group
C
937.46
24H22Cl4Hg2N6
C24H22Cl4Hg2N6
937.46
103 (2)
293 (2)
0.06 · 0.25 · 0.04
triclinic
0.12 · 0.40 · 0.48
triclinic
ꢀ
ꢀ
P1
P1
˚
Radiation (k, A)
Cu Ka (1.54178)
7.4967 (13)
9.416 (2)
Mo Ka (0.71073)
7.5149 (6)
9.2126 (6)
˚
a (A)
˚
b (A)
˚
c (A)
10.224 (3)
87.363 (16)
10.6784 (8)
a (ꢁ)
b (ꢁ)
c (ꢁ)
111.1840 (10)
97.7140 (10)
91.3030 (10)
78.346 (15)
80.456 (15)
696.9 (3)
3
˚
V (A )
681.06 (9)
1
2.286
Z
1
2.234
Dcalc (Mg/m3)
l (mmꢀ1), F (000)
h Range (ꢁ)
23.211, 436
4.42–68.05
2657
11.676, 436
2.38–28.28
5226
Reflections collected
Independent reflections (Rint
Absorption correction
)
2447 (0.0540)
empirical
3194 (0.0399)
semi-empirical from equivalents
0.89 and 0.62
full-matrix least-squares on F2
3194/0/165
Maximum and minimum transmission
Refinement method
0.94 and 0.11
full-matrix least-squares on F2
2447/0/165
Data/restraints/parameters
Goodness-of-fit on F2
1.040
1.080
Final R indices [I>2r(I)]
R indices (all data)
R1 = 0.0540, wR2 = 0.1448
R1 = 0.0588, wR2 = 0.1514
0.0008 (3)
R1 = 0.0433, wR2 = 0.1177
R1 = 0.0433, wR2 = 0.1186
0.0018 (11)
Extinction coefficient
˚
3
Largest differential peak and hole (e/A )
1.566 and ꢀ2.092
4.345 and ꢀ4.800
Fig. 2. Molecular structure and crystallographic numbering scheme for 1.
˚
Cl bond lengths of 2.428(2) and 2.909(2) A for 1
˚
compared to 2.42 and 2.92 A, for dichloro-
mercury(II)-2-(phenylazo)-pyrimidine. The equivalent
terminal Hg–Cl distances are found to be 2.368(3) and
˚
2.369(2) A, respectively, in 1 and 2, which is similar to
terminal Hg–Cl distances reported elsewhere [45]. A fea-
angle between the two ‘‘axial’’ bonds in 1, [N(2)–Hg–
Cl(2)] is 153.5(2)ꢁ whereas the corresponding angle for
dichloro-mercury(II)-2-(phenylazo)-pyrimidine
is
161.3ꢁ, indicating considerable distortions from linearity
in both complexes. Both of these complexes exhibit both
bridging and terminal Hg–Cl bonds, with bridging Hg–

T.S. Basu Baul et al. / Polyhedron 23 (2004) 2323–2329
2327
Fig. 3. Molecular structure and crystallographic numbering scheme for 2.
Table 2
Table 3
1
2
˚
˚
Selected bond lengths (A) and angles (ꢁ) for L HgCl2 (1)
Selected bond lengths (A) and angles (ꢁ) for L HgCl2 (2)
Bond length
Bond angle
Bond length
Bond angle
Hg–N(1)
2.368 (7)
2.368 (3)
2.428 (2)
2.541 (8)
2.909 (2)
2.909 (2)
1.265 (11)
1.413 (12)
1.444 (13)
N(1)–Hg–Cl(2)
N(1)–Hg–Cl(1)
N(1)–Hg–N(2)
Cl(1)–Hg–Cl(2)
Cl(2)–Hg–N(2)
Cl(1)–Hg–N(2)
Cl(1)–Hg–Cl(2)#1
N(1)–Hg–Cl(2)#1
N(2)–Hg–Cl(2)#1
Cl(2)–Hg–Cl(2)#1
C(1)–N(1)–Hg
Hg–Cl(2)–Hg#1
N(3)–N(2)–Hg
C(5)–N(1)–Hg
N(2)–N(3)–C(5)
N(3)–N(2)–C(6)
N(1)–C(5)–N(3)
C(6)–N(2)–Hg
C(12)–C(6)–N(2)
C(4)–C(5)–N(3)
C(7)–C(6)–N(2)
105.26 (19)
117.03 (19)
65.1 (3)
Hg–N(1)
Hg–Cl(1)
Hg–Cl(2)
2.223 (6)
N(1)–Hg–Cl(1)
N(1)–Hg–Cl(2)
N(1)–Hg–Cl(1)#1
Cl(2)–Hg–Cl(1)
Cl(1)–Hg–Cl(1)#1
Cl(2)–Hg–Cl(1)#1
C(5)–N(1)–Hg
92.51 (16)
156.27 (16)
88.08 (15)
109.49 (6)
91.30 (4)
99.82 (5)
113.4 (4)
88.70 (4)
114.4 (6)
126.7 (5)
113.7 (6)
114.5 (6)
Hg–Cl(1)
Hg–Cl(2)
Hg–N(2)
2.6071(16)
2.3691 (17)
2.7857 (15)
2.7857(15)
1.249 (8)
137.53 (9)
95.71 (17)
98.38 (17)
96.67 (9)
88.6 (2)
Hg–Cl(1)#1
Cl(1)–Hg#1
N(2)–N(3)
N(2)–C(5)
N(3)–C(6)
Hg–Cl(2)#1
Cl(2)–Hg#1
N(2)–N(3)
N(2)–C(6)
N(3)–C(5)
1.423 (9)
1.417 (9)
Hg–Cl(1)–Hg#1
N(2)–N(3)–C(6)
C(1)–N(1)–Hg
153.47 (17)
87.68 (8)
123.1 (6)
92.32 (8)
119.8 (6)
119.2 (6)
113.5 (8)
114.4 (8)
121.6 (7)
125.8 (5)
114.7 (8)
114.8 (9)
125.4 (8)
N(3)–N(2)–C(5)
C(11)–C(6)–N(3)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx,
ꢀy + 4, ꢀz + 1.
overall structures of 1 and 2, the two complexes still
share several common structural features. The geometry
around the Hg atoms in both is essentially that of a dis-
torted trigonal bipyramid, but in 2, the axial atoms are
the pyridyl nitrogen and one of the bridging chlorines
whilst the trigonal plane comprises the remaining three
bridging chlorine atoms. Another similar compound, di-
chloro-mercury(II)-1-ethyl-2-(phenylazo)-imidazole [44]
has the same dimeric structure reported here for 1 and
dichloro-mercury(II)-2-(phenylazo)-pyrimidine. How-
ever, the presence of the five-membered imidazole ring
in the ligand of this complex rather than the six-mem-
bered pyridine or pyrimidine rings in the other ligands
results in some differences in individual bond distances.
But the overall structural features are the same in all
three complexes.
Symmetry transformations used to generate equivalent atoms: #1 ꢀx,
ꢀy + 1, ꢀz.
ture of the structures of these two complexes is the
occurrence of a dinuclear l,l-chloro bridged Hg2Cl2
fragment, of almost identical dimensions in both. The
Hg–N distances in the two complexes are also compara-
˚
˚
ble, being 2.541(8) A (Hg–N(azo)) and 2.368(7) A (Hg–
˚
˚
N(pyridyl)) in 1 and 2.55 A (Hg–N(azo)) and 2.41 A
(Hg–N(pyrimidyl)) in dichloro-mercury(II)-2-(phenyl-
azo)-pyrimidine. The N–N distance for the azo groups
of the respective coordinated ligand molecules are 1.26
˚
A in both instances. Despite the great difference in the

2328
T.S. Basu Baul et al. / Polyhedron 23 (2004) 2323–2329
Fig. 4. Illustration of chlorine-bridging and polymeric structure of 2.
3.3.2. Dichloro-{2-[(E)-2-(3-methylphenyl)-1- diaze-
nyl]pyridine}Hg(II) (2)
Modifying the structure of the ligand by shifting the
methyl group on the phenyl ring from the para- (in 1)
to the meta- (in 2) position has a profound effect on
the structure of the resulting complex. In contradistinc-
tion to 1 (as described above), compound 2 has an
extended polymeric structure with 2-[(E)-2-(3-methyl-
phenyl)-1-diazenyl]pyridine behaving as a monodentate
ligand via the pyridyl nitrogen, and all the chlorine
atoms serving to bridge mercury atoms. In this case, nei-
ther of the azo nitrogens is coordinated to mercury. A
skewed repeating chain of Hg2Cl2 rhombohedra links
the molecular units together, as shown in Fig. 4. Adja-
cent Hg2Cl2 units are staggered, whereas alternate ones
lie in planes aligned parallel to one another. The coordi-
nated ligand molecules are all aligned along planes par-
allel to each other, but in a third direction, roughly at
right angles to the planes of each of the Hg2Cl2 rhombo-
hedra. In addition to the chlorine bridges, which hold
the units together in the polymeric structure, there are
hydrogen-bonding interactions which provide some
end-to-end cohesion between the monomeric units.
These hydrogen bonds link the hydrogen atom on the
carbon para- to the nitrogen in the pyridyl ring of each
ligand with one of the bridging chlorines on an adjacent
unit. The relevant bond distances are C(3)–H(3A) = 0.95
Fig. 5. Unit cell, chlorine bridging, and hydrogen bonding for 2.
[Cl(1A)–Hg–Cl(2B)] is 161.3ꢁ. These values are compa-
rable to those in 1.
4. Supplementary material
˚
˚
˚
A, H(3A). . .Cl(1) = 2.80 A and C(3)–Cl(1) = 3.49 A and
the angle C(3)–H(3A). . .Cl(1) is 130.3ꢁ. These hydrogen-
bonding interactions as well as the packing arrange-
ments in the crystal and the chlorine bridges are shown
in Fig. 5. The bond angles making up the trigonal plane
in 2 are N(1)–Hg–Cl(1), 92.5(2)ꢁ; N(1)–Hg–Cl(2),
156.3(2)ꢁ; and Cl(1)–Hg–Cl(1A), 109.5(6)ꢁ giving a total
of 358.3ꢁ. The angle between the two axial bonds in 2,
Full tables of bond lengths and angles, tables of non-
hydrogen and hydrogen atomic coordinates, anisotropic
thermal parameters for non-hydrogen atoms have been
deposited with Cambridge Crystallographic data center,
CCDC No. 230005 and 230006 for L1HgCl2 (1) and
L2HgCl2 (2), respectively. Copies of this information
may be obtained free of charge from the Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK

T.S. Basu Baul et al. / Polyhedron 23 (2004) 2323–2329
2329
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The financial support of the Department of Science &
Technology, New Delhi, India (Grant No. SP/S1/F26/
99, TSBB) and the support of the Grant Agency of the
Czech Republic (Grant No. 104/03/0393, AL) are grate-
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