Synthesis, spectral characterization and X-ray crystal structures of mercury(II)-azoimine compounds

Article abstract of DOI:10.1016/S0277-5387(03)00109-8

1-Ethyl-2-(phenylazo)imidazole (PaiEt, 2) and 2-(arylazo)pyrimidines (Raapm) (R=H (3a), p-Me (3b), p-Cl (3c)) are used to synthesize mercury(II) compounds. The complexes are characterized by elemental analysis, IR, UV-Vis, ¹H NMR spectral data and single crystal X-ray structures of di[chloro-{1-ethyl-2-(phenylazo)imidazole}(μ-chloro)-mercury(II)] (4) and di[chloro-{2-(phenylazo)pyrimidine} (μ-chloro)-mercury(II)] (5a). The first complex is a centro-symmetric dimer with two highly asymmetric chlorobridges which make the rhombohedral plane. The second complex forms an unsymmetric trapezohedral geometrical structure.

Full text of DOI:10.1016/S0277-5387(03)00109-8

Polyhedron 22 (2003) 1205ꢀ1212
/
www.elsevier.com/locate/poly
Synthesis, spectral characterization and X-ray crystal structures of
mercury(II)-azoimine compounds
Brojogopal Chand a, Umasankar Ray a, Prasanta Kumar Santra a, Golam Mostafa b,
Tian-Huey Lu b, Chittaranjan Sinha a,*
a Department of Chemistry, The University of Burdwan, Burdwan-713104, India
b Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan, ROC
Received 1 November 2002; accepted 17 January 2003
Abstract
1-Ethyl-2-(phenylazo)imidazole (PaiEt, 2) and 2-(arylazo)pyrimidines (Raapm) (Rꢀ
/
H (3a), p-Me (3b), p-Cl (3c)) are used to
Vis, 1H NMR spectral data and
synthesize mercury(II) compounds. The complexes are characterized by elemental analysis, IR, UVꢀ
/
single crystal X-ray structures of di[chloro-{1-ethyl-2-(phenylazo)imidazole}(m-chloro)-mercury(II)] (4) and di[chloro-{2-(phenyla-
zo)pyrimidine} (m-chloro)-mercury(II)] (5a). The first complex is a centro-symmetric dimer with two highly asymmetric chloro-
bridges which make the rhombohedral plane. The second complex forms an unsymmetric trapezohedral geometrical structure.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Arylazoimidazole; Azopyrimidine; Hg(II) complexes; Crystal structures
1. Introduction
aromatic unit [6]. They have been used successfully to
stabilize low valent metal redox states [17] and exhibit
Major development in heterocyclic-N donor ligands
has been started from transition metal complexes of
versatile reactivity to the organic part of the ligands [21ꢀ
23].
/
2,2?-bipyridine (bpy) and related ligands [1ꢀ7]. This has
/
lead to modification of M-bpy systems by choice of
substituent(s) and metal. Non-transition metal com-
plexes are a developing field in the area of polypyridine
ligands [8ꢀ15] and have been used as transition metal
/
supplements. Ligands may be modified substituting
pyridine by other heterocycle(s), incorporating steric
and electronic factors in the heterocyclic backbone
appending an extra donor center [6] etc. One group of
conjugated N-heterocycles is constructed by combining
with an arylazo (Arꢁ
known as arylazoheterocycles [16]. These are p-acidic
molecules and the active function is the azoimine group
/
N
ꢁ ꢂ
/
N) molecular unit. They are
The chemistry of non-transition metals of arylazohe-
terocycles has been started from the synthesis and
spectral characterization of mercury(II) complexes of
2-(arylazo)pyridines [24,25]. We have been able to
isolate organomercurials of 2-(arylazo)pyridines and
the site of mercuration [26] has been established by
charge density calculation. In an earlier report [27] of
chloromercuri complexes of 1-alkyl-2-(arylazo)imida-
zole we have established the structure of the complexes
(ꢁ
/
Nꢀ
/
Nꢁ
/
Cꢀ
/
Nꢁ
/
) (1) [16ꢀ20]. The p-acidity is dependent
/
on the nature of the heterocycle, number of hetero-
atoms, heterocyclic ring size and substituent(s) on the
* Corresponding author. Tel.: ꢁ
452.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
/
91-342-557-683; fax: ꢁ91-342-530-
/
1
by solution H NMR spectral data and they have been
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00109-8

1206
B. Chand et al. / Polyhedron 22 (2003) 1205ꢀ1212
/
Fig. 1. X-ray crystal structure of 4.
defined as mononuclear complexes, Hg(RaaiR?)Cl2. We
have now been able to crystallize mercury(II) complexes
of 1-ethyl-2-(phenylazo)imidazole and the X-ray struc-
ture shows a chloro bridged dinuclear system (Fig. 1). 2-
(Arylazo)pyrimidine (Raapm, 3) is a new class of
arylazoheterocycle [28,29] and mercury(II) complexes
are also described in this article. The single crystal X-ray
structure of one of the complexes 2-(phenylazo)pyrimi-
dine-chloro mercuri shows a chloro-bridged dimeric
type (Fig. 2). The structures and spectral properties
are described hereunder.
instruments: UVꢀ
570; IR (KBr disk, 4000ꢀ
model 420 spectrophotometer, and H NMR, Bruker
300 MHz FT-NMR spectrometer.
/
Vis, JASCO UV/Vis/NIR model V-
200 cmꢂ1), JASCO FT-IR
/
1
2.3. Synthesis of [Hg(PaiEt)Cl2]2 (4)
1-Ethyl 2-(phenylazo)imidazole (0.02 g, 0.1 mmol) in
MeOH (10 ml) was added dropwise to a stirred
methanolic solution (10 ml) of HgCl2 (0.0271 g, 0.1
mmol) at room temperature. The brownishꢀorange
/
solution was filtered and left undisturbed for 2 weeks.
The bright brownish-orange crystals were obtained by
the slow evaporation process. The crystals were col-
2. Experimental
lected by filtration, washed with cold waterꢀmethanol
/
(1:1, v/v) and dried over CaCl2 in vacuo. The yield was
0.033 g (70%). Detailed analyses and spectral character-
ization are reported elsewhere [27].
2.1. Materials
2-Aminopyrimidine and imidazole were purchased
from Aldrich. HgCl2 was obtained from Loba Chemi-
cals, Bombay, India. All other chemicals and solvents
were reagent grade and used as received. 2-(Aryla-
zo)pyrimidine (Raapm) [28] and 1-ethyl-2-(arylazo)imi-
dazole (PaiEt) [16] were prepared by reported
procedure.
2.4. Synthesis of [Hg(Raapm)Cl2]2 (5a)
[Hg(Raapm)Cl2]2 complexes were synthesized by the
same procedure described above with the use of the
respective 2-(arylazo)pyrimidine. The yield varied in the
range 45ꢀ60%.
/
2.2. Physical measurements
The microanalytical data of the complexes are:
[Hg(Haapm)Cl2]2 (5a): Anal. Found: C, 26.31; H, 1.73;
N, 12.27. Calc. for C20H16N8Cl4Hg2: C, 26.35; H, 1.76;
N, 12.29%. [Hg(p-Meaapm)Cl2]2 (5b): Anal. Found: C,
28.09; H, 2.10; N, 11.88. Calc. for: C22H20N8Cl4Hg2: C,
Microanalytical (C, H, N) data were obtained from a
Perkinꢀ/Elmer 2400 CHNS/O elemental analyzer. Spec-
troscopic data were obtained using the following

B. Chand et al. / Polyhedron 22 (2003) 1205ꢀ
/1212
1207
Fig. 2. X-ray crystal structure of 5a.
28.12; H, 2.14; N, 11.92%. [Hg(p-Claapm)Cl2]2 (5c):
Anal. Found: C, 24.47; H, 1.41; N, 11.40. Calc. for:
C20H14N8Cl6Hg2: C, 24.50; H, 1.43; N, 11.43%.
with 0.55/0.44 occupancy. Complex neutral atom scat-
tering factors were used throughout for all cases. All
calculations were carried out using SHELXS-97, [31],
SHELXL-97 [32], PLATON-99 [33] and ORTEP-3 [34]
programs.
2.5. X-Ray diffraction study
Suitable single crystals of complexes 4 and 5a were
3. Result and discussion
mounted on a Siemens CCD diffractometer equipped
˚
0.711073 A)
with graphite monochromated Mo Ka (lꢃ
/
3.1. Synthesis
radiation. The crystallographic data, conditions for the
intensity data collection and some features of the
structure refinements of all the complexes are listed in
Table 1. The unit cell parameters and crystal-orientation
matrices were determined for two complexes by least
squares refinements of all reflections. The intensity data
were corrected for Lorentz and polarisation effects and
an empirical absorption correction was also employed
using the SAINT program [30]. Data were collected
1-Ethyl-2-(phenylazo)imidazoles (PaiEt, 2) and 2-
(arylazo)pyrimidines (Raapm, 3) are unsymmetric bi-
dentate N,N?-donor ligands. On stirring a methanolic
solution of HgCl2 and the ligand 2/3 in a 1:1 mole
proportions the brownish-orange title compounds (4/5)
have been isolated. The molar conductivity measure-
ments in MeCN exhibit non-conducting (Lmꢁ
/
15ꢀ20
/
Vꢂ1 cmꢂ1) behaviour of the complexes. Microanalyti-
cal data (C, H, N) support the general composition of
the complexes and in both cases the structures have been
established by single-crystal X-ray diffraction study.
applying the condition I ꢀ2s(I). All these structures
/
were solved by direct methods and followed by succes-
sive Fourier and difference Fourier syntheses. Full
matrix least squares refinements on F2 were carried
out using SHELXL-97 with anisotropic displacement
parameters for all non-hydrogen atoms. Hydrogen
atoms were constrained to ride on the respective carbon
or nitrogen atoms with isotropic displacement para-
meters equal to 1.2 times the equivalent isotropic
displacement of their parent atom in all cases. During
refinements of complex 4, the ethyl group was found to
occupy two orientations (C10a, C11a and C10b, C11b)
3.2. Molecular structures
The crystals of dichloro-mercury(II)-1-ethyl-2-(phe-
nylazo)imidazole (4) and dichloro-mercury(II)-2-(phe-
nylazo)-pyrimidine (5a) were grown by slow
evaporation of the reaction mixture in methanol at
ambient condition for a week.

1208
B. Chand et al. / Polyhedron 22 (2003) 1205ꢀ1212
/
Table 1
Summarised crystallographic data for [Hg(PaiEt)Cl2]2 (4) and
[Hg(Haapm)Cl2]2 (5a)
Table 2
Selected bond distances (A) and angles (8) for [Hg(PaiEt)Cl2]2 (4)
˚
Bond distances
Bond angles
[Hg(PaiEt)Cl2]2 (4) [Hg(Haapm)Cl2]2 (5a)
Hgꢁ
Hgꢁ
/
Cl(1)
2.579(2)
2.344(2)
Cl(1)ꢁ
Cl(1)ꢁ
Cl(1)*
Cl(1)ꢁ
Cl(1)ꢁ
Cl(1)*ꢁ
Cl(1)*ꢁ
Cl(1)*ꢁ
Cl(2)
Cl(2)ꢁ
Cl(2)ꢁ
N(1)ꢁHgꢁ
HgꢁCl(1)ꢁ
/
Hgꢁ
Hgꢁ
/
Cl(2) 112.22(7)
87.28(6)
Empirical formula
Formula weight
Temperature (K)
Crystal system
C22H24Cl4Hg2N8
943.47
293(2)
C20H16Cl4Hg2N8
911.39
297(2)
/Cl(2)
/
/
Hgꢁ
Hgꢁ
Hgꢁ
N3ꢁ
Hgꢁ
/
Cl(1)*
N(1)
N(4)
N(4)
Hg*
2.7971(12)
2.204(5)
2.757(5)
1.252(7)
4.822(7)
/
Hgꢁ
Hgꢁ
Hgꢁ
Hgꢁ
Hgꢁ
/
N(1) 109.59(16)
monoclinic
C2/c
monoclinic
P21/n
/
/
/
N(4)
85.25(11)
N(1) 88.78(15)
N(4) 148.77(12)
108.36(6)
Space group
/
/
/
Crystal size (mm)
Unit cell dimensions
0.40ꢄ
/
0.30ꢄ
/
0.20 0.22ꢄ
/0.16ꢄ/0.07
/
/
/
/
/
/
˚
a (A)
16.2363(12)
11.1765(8)
15.9223(12)
98.7030(10)
2856.1(4)
4
7.5548(9)
26.801(3)
12.8035(15)
97.235(2)
2571.8(5)
4
˚
b (A)
/
Hgꢁ
/
N(1) 135.20(17)
N(4) 102.53(12)
˚
c (A)
/
Hgꢁ
/
b (8)
V (A)
/
/
N(4)
65.53(18)
92.72(6)
3
˚
/
/
Hg*
Z
l (A)
Cꢁ
Cꢁ
/
H
/
ꢀ ꢀ ꢀ
/
p bonds
pa
˚
0.71073
11.139
0.71073
12.366
˚
˚
/
H
/
ꢀ ꢀ ꢀ
/
d(H/
ꢀ ꢀ ꢀ
/
p) (A) d(C
/
ꢀ ꢀ ꢀ
/
p) (A)
B(CHp) (8)
/
m (Mo Ka) (mmꢂ1
U range
h k l range
)
2.2ꢀ
210
90k 0
200l 0
/
28.3
1.5ꢀ
100
350
160
/
28.3
h 0
k 0
l 016
C(10a)ꢁ
Cg(1)
/H(10a)
/
ꢀ ꢀ ꢀ
/
3.079
3.059
2.728
2.714
3.370
3.402
3.402
3.443
3.553
3.903
101.21
102.50
131.41
145.11
117.18
ꢂ
/
/
h 0
/
20
ꢂ
/
/
/
10
ꢂ
/
/
/
14
ꢂ
/
/
/
23
C(10a)ꢁ
Cg(1)
/H(10b)/
ꢀ ꢀ ꢀ
/
ꢂ/
/
/
18
ꢂ/
/
/
Dcalc (Mg mꢂ3
Refine parameters
Reflection number total 9011
)
2.194
2.354
305
C(11a)ꢁ
Cg(1)
/
H(11c)
H(10c)
H(11f)
ꢀ ꢀ ꢀ
/
ꢀ ꢀ ꢀ
/
181
16140
6056
C(10b)ꢁ
Cg(1)
/
/
ꢀ ꢀ ꢀ
/
Unique reflections
R1a [I ꢀ
2s(I)]
wR2b
Goodness of fit
3446
/
0.0424
0.1022
1.050
0.0476
0.0719
1.08
C(11b)ꢁ
Cg(1)
/
/
/
a
Cg(1) denotes ring: C4ꢁ
/
C5ꢁ
/
C6ꢁ
/
C7ꢁ
/
C8ꢁC9.
/
2 2
2 2 12
//
aRꢃ
wꢃ
1/[s2(F0)2ꢁ
[s2(F0)2ꢁ
(F0 2ꢁ2Fc 2)/3 Goodness of fit is defined as [a[w(Fo 2ꢂ
/
ajjFojꢂ
/
jFcjj/ajFoj. bwR2ꢃ
/
[aw(Fo2ꢂ
Fc ) / aw(Fo ) ], where;
/
/
/
(0.0346P)2ꢁ
/
11.5057P] for [Hg(PaiEt)Cl2]2 and wꢃ1/
/
plane makes a dihedral angle of 73.2(8)8 with the
rhombohedral plane. The pendant phenyl ring in
chelated PaiEt is no longer planar with the chelate
/
(0.0178P)2ꢁ
/
5.9766P] for [Hg(Haapm)Cl2]2 where Pꢃ
/
/
/
Fc 2)2]/(noꢂ
/
1
//
2
nv)], where n0 and nv denote the numbers of data and variables,
respectively.
plane and is inclined at an angle of 20.85(5)8. The Nꢀ
/N
˚
bond length is 1.252(7) A which is close to the free
3.2.1. [Hg(PaiEt)Cl2]2 (4)
ligand value [36,37]. The HgꢁN(1) bond distance of
/
˚
˚
N(4), 2.757(5) A. The
N(4)] bond length is less than that of
The crystal structure of the complex is shown in Fig. 1
and the bond parameters are listed in Table 2. The
structure shows a chloro bridged dinuclear Hg2Cl2 unit.
PaiEt acts as a N,N?-donor organic capping agent and a
non-bridged-Cl atom lies in a semi-axial position. The
complex exists as a centro-symmetric dimer with two
2.204(5) A is shorter than Hgꢁ
/
Hgꢁ
/
N(azo) [Hgꢁ
/
the sum of the van der Waals radii [35] of Hg(II) and
N(sp2). This supports some sort of interaction of N(azo)
with Hg(II). The bond length data of Hgꢁ
/
N(imidazole),
[HgꢁN(1)] accounts the preferential bonding of Hg(II)
/
highly asymmetric chloro bridges [Hgꢁ
/
Cl(1), 2.579(2)
Cl(1)*, 2.797(18) A] and two terminal Cl with
˚
2.344(2) A distance. The atomic arrangements N(1),
to imidazole-N [38,39]. This selectivity has been em-
ployed during purification of polluted water or separa-
tion of mercury from mixtures/ores [39,40]. In addition
to van der Waals forces, the crystal structure is mainly
˚
and Hgꢁ
/
C(3), N(3), N(4), Hg constitute a chelate plane with a
˚
mean atomic deviation B0.07 A. The atoms N(1), N(4),
/
stabilized by Cꢁ
/
Hꢀp interactions (Table 2).
/
Hg, Cl(1), Cl(1)* constitute a highly distorted square
˚
plane and Hg lies 0.81(8) A above the mean plane. The
HgꢁCl(2) bond lies in a semi-axial manner above the
HgꢁN(2)ꢁCl(2) plane in which the chelate plane is
twisted so that HgꢁN(4) bond moves towards Cl(2) and
HgꢁN(1) is away from the HgꢁCl(2) bond. This is
reflected from the bond angle data; N(4)ꢁHgꢁCl(2),
102.53(12)8; N(1)ꢁHgꢁCl(2), 135.20(17)8. The dimeric
bridging unit Hg2Cl2 describes a rhombohedral plane.
The rhombohedral angles are Cl(1)ꢁHgꢁCl(1)*,
87.28(6)8 and Hg*ꢁCl(1)ꢁHg, 92.72(6)8. The chelate
/
3.2.2. [Hg(Haapm)Cl2]2 (5a)
/
/
The molecular structure of the complex is shown in
Fig. 2 and the bond parameters are listed in Table 3.
Each discrete molecular unit consists of a dinuclear
chloro bridged Hg2Cl2 fragment. Haapm acts as N,N?-
donor end capping agent and a non-bridged-Cl atom lies
/
/
/
/
/
/
/
in a semi-axial position. The bridged Hg2Cl2 constitutes
˚
/
/
a good plane with maximum deviation (B0.01 A) and is
/
/
/
unsymmetric unlike the preceding example. This is

B. Chand et al. / Polyhedron 22 (2003) 1205ꢀ
/1212
1209
Table 3
Selected bond distances (A) and angles (8) for [Hg(Haapm)Cl2]2 (5a) and some non-covalent bond parameters
˚
Bond distances
Bond angles
Hg(1)ꢁ
Hg(1)ꢁ
Hg(1)ꢁ
Hg(2)ꢁ
Hg(2)ꢁ
Hg(2)ꢁ
Hg(1)ꢁ
Hg(1)ꢁ
Hg(2)ꢁ
Hg(2)ꢁ
/
Cl(1)
Cl(3)
Cl(4)
Cl(2)
Cl(3)
Cl(4)
N(1)
N(4)
N(5)
N(8)
2.373(2)
2.419(2)
2.924(2)
2.349(2)
2.964(2)
2.386(2)
2.411(5)
2.548(5)
2.409(5)
2.615(5)
1.210(7)
1.265(7)
3.929(1)
Cl(1)ꢁ
Cl(1)ꢁ
Cl(1)ꢁ
Cl(1)ꢁ
N(1)ꢁHg(1)ꢁ
N(1)ꢁHg(1)ꢁ
N(1)ꢁHg(1)ꢁ
N(4)ꢁHg(1)ꢁ
N(4)ꢁHg(1)ꢁ
Cl(3)ꢁHg(1)ꢁ
Cl(3)ꢁHg(2)ꢁ
Cl(3)ꢁHg(2)ꢁ
Cl(3)ꢁHg(2)ꢁ
Cl(3)ꢁHg(2)ꢁ
Cl(4)ꢁHg(2)ꢁ
Cl(4)ꢁHg(2)ꢁ
Cl(4)ꢁHg(2)ꢁ
N(5)ꢁHg(2)ꢁ
N(5)ꢁHg(2)ꢁ
N(8)ꢁHg(2)ꢁ
Hg(1)ꢁCl(3)ꢁ
Hg(1)ꢁCl(4)ꢁ
/
Hg(1)ꢁ
Hg(1)ꢁ
Hg(1)ꢁ
Hg(1)ꢁ
/
N(1)
N(4)
Cl(3)
Cl(4)
116.97(13)
93.33(12)
137.35(6)
97.86(5)
/
/
/
/
/
/
/
/
/
/
/
/
N(4)
Cl(3)
Cl(4)
Cl(4)
Cl(3)
64.85(17)
105.67(13)
85.70(12)
150.41(12)
103.88(12)
86.09(5)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
Cl(4)
Cl(4)
Cl(2)
N(5)
N(8)
Cl(2)
N(8)
N(5)
N(7)ꢁ
/
N(8)
N(4)
/
/
85.78(5)
95.2(6)
N(3)ꢁ
/
/
/
Hg(1)ꢁ
/
Hg(2)
/
/
84.45(13)
147.83(12)
144.79(6)
99.88(12)
100.99(13)
63.38(17)
114.18(13)
97.08(12)
93.20(6)
/
/
/
/
/
/
/
/
/
/
N(8)
Cl(2)
Cl(2)
/
/
/
/
/
/
Hg(2)
Hg(2)
/
/
94.92(5)
Hydrogen-bonds
Dꢁ ꢀ ꢀ ꢀ
˚
H)(A)
˚
A) (A)
˚
A) (A)
/
H
/
/A
d(Dꢁ
/
d(H/
ꢀ ꢀ ꢀ
/
d(D/
ꢀ ꢀ ꢀ
/
ꢃ(DHA) (8)
/
C(1)ꢁ
/
H(1)
/
ꢀ ꢀ ꢀ
/
Cl(4)
Cl(3)I
0.93
0.93
0.93
2.805
2.783
2.720
3.502(6)
3.567(8)
3.447(6)
132.58
142.50
135.65
C(9)ꢁH(9)ꢀ ꢀ ꢀ
/
/
/
C(11)ꢁH(11) Cl(3)
/
/
ꢀ ꢀ ꢀ
/
p
/
ꢀ ꢀ ꢀp Interactions
ꢀ ꢀ ꢀp Interactions
Ring(i)0Ring(j)
/
p
/
/
Cgꢁ
/Cg distance
Dihedral angle (8)
Perpendicular distance to J ring
˚
(A)
Perpendicular distance to J ring
˚
(A)
˚
(A)
/
Cg(1)0
Cg(1)0
Cg(2)0
Cg(2)0
Cg(4)0
/
Cg(3)ii
Cg(3)iii
Cg(2)iv
Cg(4)i
Cg(4)v
3.596(4)
3.834(4)
4.112(3)
3.578(4)
3.718(4)
1.54
7.55
0.03
3.53
0.00
3.492
3.360
3.456
3.537
3.444
3.507
3.554
3.456
3.502
3.444
/
/
/
/
Cg(I) denotes rings: Cg(1)ꢀ
C16ꢁC17ꢁC18ꢁC19ꢁC20. Symmetry code: (i)1ꢁ
/
N1ꢁ
/
C1ꢁ
/
C2ꢁ
/
C3ꢁ
/
N2ꢁ
/
C4; Cg(2)ꢀ
/
N5ꢁ
/
C11ꢁ
/
C12ꢁ
/
C13ꢁ
/
N6ꢁ
/
C14; Cg(3)ꢀ
/
C5ꢁ
/
C6ꢁ
/
C7ꢁ
/
C8ꢁ
/
C9ꢁ
/
C10; Cg(4)ꢀ
/
C15ꢁ
/
/
/
/
/
/
x,y,z; (ii) ꢂ
/
1ꢁx,y,z; (iii) ꢂ
/
/
1/2ꢁ
/
x, 3/2ꢂ
/
y,1/2ꢁz; (iv) 1ꢂ
/
/
x,1ꢂ
/
y,ꢂ
/
z; (v) ꢂ
/
x,1ꢂy,1ꢂz.
/
/
˚
(maximum deviation B0.08 A). The pendent phenyl
ring lies in a plane of the chelate ring (av. deviation,
trapezohedral in geometry [41]. The atomic arrange-
ments Hg(1), N(1), C(4), N(3), N(4) and Hg(2), N(5),
/
C(14), N(7), N(8) constitute the chelate plane(s) with a
˚
1.98).
maximum deviation B
/
0.09 A. The atoms Hg(1), N(1),
N(4), Cl(3), Cl(4) and Hg(2), N(5), N(8), Cl(3), Cl(4)
Two
[Hg(PaiEt)Cl2]2. The Hg(1)ꢁ
higher distortion than the Hg(2)ꢁ
Hg
centers
are
Haapm chelate ring suffers
Haapm unit. In
C(4) and C(4)ꢁ
inequivalent
unlike
/
constitute two square planes (maximum deviation B
/
/
˚
0.06 A) and their dihedral angle is 4.60(0)8. Hg(1) and
Hg(1)ꢁ
/
Haapm the N(3)ꢁ
/
N(4), N(3)ꢁ
/
/
˚
˚
Hg(2) lie 0.13 A and*
square planes. The bond angle values Cl(3)ꢁ
Hg(2), 94.92(5)8 pro-
/
0.09 A above their respective
N(1) bond distances are elongated by 0.055, 0.030 and
˚
0.008 A, respectively than that of the respective bond
/
Hg(1)ꢁ
/
Cl(4), 86.09(5)8 and Hg(1)ꢁ
vide support for the distorted geometry. The acute
/
Cl(4)ꢁ
/
distances of the Hg(2)ꢁ
N(1) and Hg(2)ꢁN(5) have similar bond distances,
Hg(1)ꢁN(4) is shortened by 0.067 A compared to that
of Hg(2)ꢁ N bond distance is
/
Haapm unit. Although Hg(1)ꢁ
/
/
˚
chelate bite angles extended by 2-(phenylazo)pyrimidine
/
on coordination to Hg(II), N(1)ꢁ
/
Hg(1)ꢁ
/
N(4),
/
N(8). The free ligand Nꢀ
/
64.85(17)8 and N(5)ꢁHg(2)ꢁN(8), 63.38(17)8 may be
/
/
not available with this particular molecules, but data
the reasons for geometrical distortion. The chelate
plane(s) makes dihedral of av. 1058 with the respective
square plane. The ligand (Haapm) is almost planar
from 2-(phenylazo)pyridine [37] and 1-methyl-2-(pheny-
N bond lengths 1.258(1)
lazo)imidazole [36] show the Nꢀ
/
˚
and 1.250(1) A, respectively. The NꢀN bond distances
/

1210
B. Chand et al. / Polyhedron 22 (2003) 1205ꢀ1212
/
in this complex are shorter N(3)ꢁ
/
N(4), 1.265(7) and
N(8), 1.210(7) A compared to the reported values.
The average NꢀN distance is also less than that of the
preceding example, [Hg(HaaiEt)Cl2]. The NꢀN dis-
tances are unusually different; the N(7)ꢁN(8) bond
0.6 A. It is unclear at present
bonds, the structure is stabilized by aromatic pꢀp
stacking interactions (Table 3). The rings in adjacent
dimers are almost parallel to each other, the dihedral
/
˚
N(7)ꢁ
/
/
/
angles between these planes being in the range of 0.0ꢀ
/
/
3.58. The perpendicular distance between these planes is
˚
˚
3.537(2) A. Hence, there is a series of
essentially parallel units whose relative disposition is
length is shortened by ꢁ
/
in range 3.360(2)ꢀ
/
why this is so and it may be due to distortion in the
Hg2Cl2 bridging geometry. This perturbation is also
ideal for aromatic pꢀp stacking interactions, forming a
/
propagated to the Hgꢁ
/
N(azo) bond distance value;
3D supramolecular continuum.
˚
Hg(2)ꢁ
/
N(8), 2.615(5) A is greater than Hg(1)ꢁN(4),
2.548(5) A. In the bridged trapezium Hg2Cl2 unit the
/
˚
˚
Cl(3) distance (2.419(2) A) is longer than that of
Hg(1)ꢁ
Hg(2)ꢁ
Hg(2)ꢁ
/
3.3. Spectral studies
˚
˚
Cl(4) is 2.924(2) A and
/
Cl(4) (2.386(2)A); Hg(1)ꢁ
/
˚
Cl(3) is 2.964(2) A.
/
The spectral characterization (IR, UVꢀ
NMR) of [Hg(RaaiR?)Cl2]2 (4) are reported elsewhere
[27]. [Hg(Raapm)Cl2]2 (5) exhibits n(CꢀN) and n(NꢀN)
at 1600ꢀ1625 and 1385ꢀ
1390 cmꢂ1, respectively. The
HgꢁCl stretchings appear at 325ꢀ330 and 300ꢀ305
cmꢂ1. These support two types of Hgꢁ
Cl bonds. This
/
Vis, 1H
Hg(1)ꢁ
tions on their respective square planes. The chelate ring
around Hg(1) is twisted in a manner so that Hg(2)ꢁN(4)
approaches closer to Cl(1) (N(4)ꢁHg(1)ꢁCl(1),
93.33(12)8) and HgꢁN(1) is away from Cl(1) (N(1)ꢁ
Hg(1)ꢁCl(1), 116.97(13)8). A similar situation is also
observed around Hg(2) where Cl(2)ꢁHg2ꢁN(8) is
97.08(12)8 and Cl(2)ꢁHg2ꢁN(5) is 114.18(13)8. The
bond length data show that the Hg(2)ꢁ
/
Cl(1) and Hg(2)ꢁ
/
Cl(2) are in semi-axial posi-
/
/
/
/
/
/
/
/
/
/
/
/
/
/
is also supported from the X-ray crystal structure study
/
/
(vide infra).
The solution electronic spectra of these complexes
were recorded in DMSO between 200 and 900 nm
/
/
/Cl(4) distance
˚
(2.386(2) A) is less than that of Hg(1)ꢁ
/Cl(4) (2.924(2)
(Table 4). There are four bands in the UVꢀ
and three of them are high intensity ( ꢂ
104) bands at
255ꢀ260, 315ꢀ320 and 340ꢀ345 nm. On comparing with
/
Vis region
˚
A). Thus the bridging Cl binds one Hg center more
covalently than the second one. The axial HgꢁCl
/
ꢁ
/
/
/
/
/
˚
˚
Cl(2), 2.349(2) A) is
(Hg(1)ꢁ
shorter than bridged Hgꢁ
The bond length data (Hgꢁ
N(azo), NꢁN, CꢁN) reveal that the interaction of
Hg(1) with Haapm is stronger than Hg(2). The Hgꢁ
N(azo) (Hg(1)ꢁN(4), 2.548(5), Hg(2)ꢁN(8), 2.615(5)
/
Cl(1), 2.373(2) A; Hg(2)ꢁ
Cl bonds.
N(pyrimidine), Hgꢁ
/
the free ligands spectra [27,29], we may conclude that
they come from intramolecular charge transfer transi-
/
/
/
tions. The fourth band appears at 435ꢀ445 nm and is
/
/
/
/
/
/
˚
A) bond lengths are less than the sum of the van der
Waals radii [35]. This supports the bonding interaction
between Hg(II) and N(azo).
The comparison of the Hgꢁ
/
N(heterocycle) bond
N(imidazole),
2.204(13) A and [Hg(Haapm)Cl2]2 (5a) HgꢁN(pyrimi-
length between [Hg(PaiEt)Cl2]2 (4), Hgꢁ
/
˚
/
˚
dine), 2.452(6) A exhibit overwhelming affinity of Hg(II)
to N(imidazole). It is known that imidazole is less p-
acidic than pyrimidine [6] and hence N(imidazole) is
softer than N-(pyrimidine). Mercury(II) is a soft border-
line acid. That is why Hg(II) binds strongly with
imidazole-N [38].
Intermolecular hydrogen bonding generates a mole-
cular stair in which the chelated Hgꢁ
/
[Nꢀ
/
Nꢁ
/
Cꢀ
/
Nꢁ]fragment functions as a footboard and the perpen-
/
dicular bridging unit Hg2Cl2 acts as a wall connector to
the stairs (Fig. 3). Each dimer alternately generate
polymer stairs. One of the two non-bridged Cl atoms
in the bridging Hg2Cl4 unit makes a H-bonding contact
with the o-H of a pendant phenyl ring of papm of a
neighboring dimer. While opposite bridged Cl atoms in
this dimer unit hydrogen bond with the m-H of a papm
of a second neighboring dimer. The process continues to
make the molecular stair. In addition to hydrogen
Fig. 3. H-bonding structure of 5a.

B. Chand et al. / Polyhedron 22 (2003) 1205ꢀ
/1212
1211
Table 4
UVꢀ
Vis a and 1H NMRb spectral data for [Hg(Raapm)Cl2]2 (5)
/
Compound
UVꢀ
/
Vis lmax/nm (10ꢂ3 e/Mꢂ1 cmꢂ1
)
1H NMR d, ppmꢀ
/(J, Hz)
4,6-H c
5-H
8,12-H
9,11-H
10-H
Me
(5a)
(5b)
(5c)
422 (975), 344 (12637)
316 (9680), 258 (11886)
440 (1545), 342 (41072)
318 (44259), 230 (35181)
435 (569), 345 (9462)
320 (7609), 240 (9778)
9.03 (5.4)
7.68 d
7.9 9
(8.8)
7.90 c
(8.2)
8.07 c
(8.5)
7.68 d
7.68d
2.44
9.01
(6.3)
9.07
(6.5)
7.65 c
(7.2)
7.73 c
(7.5)
7.47 c
(8.2)
7.85 c
(8.5)
ꢀ/
ꢀ/
ꢀ/
a
Solvent DMSO.
Solvent DMSO-d6.
b
c
Doublet.
Multiplet.
d
weak in intensity ( ꢂ
/
ꢁ
/
103). This may refer to Hg(II)0
/
References
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The H NMR spectra of 5 are recorded in DMSO-d6
and the signals are assigned (Table 4) unambiguously by
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/
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/
/
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