Iodo bridged lead(II) compounds of azoimidazoles: Single crystal X-ray structures of [di-iodo-{1-methyl-2-(p-tolylazo)imidazole}lead(II)]n and {1-methyl-3-benzyl-2-(p-tolylazo)imidazolium}m-{tri-iodoplumbate(II)}m

Article abstract of DOI:10.1016/j.ica.2006.05.037

PbI₂ forms iodo-bridged neutral polymer upon reaction with 1-alkyl-2-(arylazo)imidazoles (RaaiR′). The reaction of PbI₂ and dialkyl imidazolium iodides [RaaiR′R″]⁺I^- has synthesized {1,3-dialkyl-2-(arylazo)imida

Full text of DOI:10.1016/j.ica.2006.05.037

Inorganica Chimica Acta 359 (2006) 4377–4385
www.elsevier.com/locate/ica
Iodo bridged lead(II) compounds of azoimidazoles:
Single crystal X-ray structures of
[di-iodo-{1-methyl-2-(p-tolylazo)imidazole}lead(II)]n and
{1-methyl-3-benzyl-2-(p-tolylazo)imidazolium}m-
{tri-iodoplumbate(II)}m
a
b
b
c
c
a,
*
K.K. Sarker , A.D. Jana , G. Mostafa , J.-S. Wu , T.-H. Lu , C. Sinha
a
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Raja Suboth Mullick Road, Kolkata 700 032, West Bengal, India
b
Department of Physics, Jadavpur University, Kolkata 700 032, West Bengal, India
Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan, ROC
c
Received 17 March 2006; received in revised form 19 May 2006; accepted 28 May 2006
Available online 9 June 2006
Abstract
PbI2 forms iodo-bridged neutral polymer upon reaction with 1-alkyl-2-(arylazo)imidazoles (RaaiR0). The reaction of PbI2 and dialkyl
imidazolium iodides [RaaiR0R00]+Iꢀ has synthesized {1,3-dialkyl-2-(arylazo)imidazolium}m-{tri-iodoplumbate(II)}m. The complexes are
characterized by different spectroscopic studies. Iodobridged chelated polymer, [Pb(RaaiR0)I2]n, has been established by single crystal
X-ray diffraction measurements in one case. Tri-iodoplumbates form iodo bridged anion polymer, which connects [RaaiR0R00]+ by
hydrogen bonding and are placed in between the pillars of [Pb(l-I)6]n motif.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Pb(II)-iodo complexes; Arylazoimidazole; Azoimidazolium; X-ray structures
1. Introduction
terms of the structure, chemical, photophysical and redox
properties. It has been suggested that the tendency of
iodine to reduce coordination number of the metal atom
is due to an increase in electron density at the metal center
caused by softer character and larger size of iodine relative
to lighter halogen [11,12]. Although Iꢀ is reluctant, in gen-
eral, to generate polymeric network with most of the metal
ions but Cu(I), Ag(I) form myriad of iodine bridged
dimers, cubanes, chains, strands, etc. [10,13]. Major disad-
vantage of the M–I bonding is the very high electronic flex-
ibility that is being influenced significantly by the coligands
compared to the M–Cl/Br bonds [14,15]. This has reasoned
to undertake the iodo complexes of lead (reasonable heavy
toxic metal) with chelating ligands. PbI2 and iodoplum-
bates are efficient photosensitizers and the thin films of
these compounds are studied for long time [16]. The lead
(II) complexes are interesting and are frequently discussed
In the recent years, inorganic–organic hybrid com-
pounds have attracted attention as an effective way to gen-
erate useful material of high mechanical and dimensional
stability. Metal ions display a range of coordination geom-
etries allowing for greater flexibility in constructing materi-
als with specific dimensions and topologies [1–9]. Halo
compounds of metals with d10 configuration show various
coordination numbers and configuration [10]. It is
observed that chloro compounds are commonly bridged
polymeric but the bromo and iodo derivatives are usually
monomeric. Iodo compounds often behave differently in
*
Corresponding author. Tel.: +91 94 3330 9907; fax: +91 33 2414 6584,
91 33 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.05.037

4378
K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 4377–4385
to consider the coordination and stereoactivity of heavy
metals, in particular, to the ‘stereochemical activity’ of
valence shell electron lone pairs [17–19]. The lead(II) com-
plexes of polypyridine systems have been studied only
recently [20,21].
crystals were collected and were suitable for single crystal
X-ray study. The yield was 0.11 g (67%).
All other complexes were prepared by the same
procedure. In all cases, crystalline products were obtained.
The yield varied from 60% to 75%. The microanalytical
data of the complexes are as follows, [Pb(HaaiMe)(I)2]n
(8a): Anal. Calc. for C10H10N4I2Pb: C, 18.54; H, 1.55; N,
8.65. Found: C, 18.60; H, 1.50; N, 8.70%. FT-IR (KBr disc,
cmꢀ1), m(N@N), 1430; m(C@N), 1588 cmꢀ1. UV–Vis spec-
tral data in DMF [kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]:
260 (14.10), 370 (13.10), 390 (12.90), 460 (0.45). [Pb(Mea-
aiMe)(I)2]n (8b): Anal. Calc. for C11H12I2N4Pb: C, 19.96;
H, 1.81; N, 8.47. Found: C, 19.90; H, 1.86; N, 8.40%.
FT-IR (KBr disc, cmꢀ1), m(N@N), 1436; m(C@N),
1597 cmꢀ1. UV–Vis spectral data in DMF [kmax(nm)
(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 262 (1.50), 368 (4.12), 384
(3.84), 412 (1.42), 464 (0.54). [Pb(HaaiEt)(I)2]n (9a): Anal.
Calc for C11H12I2N4Pb: C, 19.96; H, 1.81; N, 8.47. Found:
C, 20.02; H, 1.76, N, 8.40%. FT-IR (KBr disc, cmꢀ1),
m(N@N), 1437; m(C@N), 1588 cmꢀ1. UV–Vis spectral data
in DMF [kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 268 (7.40),
294 (3.60), 364 (13.00), 390 (8.98), 467 (0.25). [Pb(Meaa-
iEt)(I)2] (9b): Anal. Calc. for C12H14I2N4Pb: C, 21.33; H,
2.07; N, 8.29. Found: C, 21.40; H, 2.02; N, 8.20%. FT-IR
Our present programme is to explore the transition and
non-transition metal-iodo complexes of 1-alkyl-2-(aryl-
azo)imidazoles. Studies on the pseudohalide complexes of
transition [22–25] and non-transition [26–29] metals with
1-alkyl-2-(arylazo)imidazole have been discussed recently
by us. The end capping role of the chelating ligand in com-
bination with the pꢁ ꢁ ꢁp and C–Hꢁ ꢁ ꢁp interaction has led to
synthesize coordination polymers of different dimensional-
ity [30–33]. Arylazoimidazolium ions have selectively
bonded with anions like ReOꢀ4 [34,35]. This has encouraged
us to synthesise iodoplumbates of arylazoimidazolium sys-
tem. The compounds are characterized by spectroscopic
techniques and the structural confirmation has been carried
out by single crystal X-ray diffraction studies.
2. Experimental
2.1. Materials
Imidazole, different aromatic amines, and Pb(NO3)2
were purchased from E. Merck India. PbI2 was prepared
freshly from the mixture of Pb(NO3)2 and KI, and washed
with water just before use. All other chemicals and solvents
were of reagent grade and used as received. 1-Alkyl-2-(aryl-
azo)imidazole (RaaiR0) were prepared by the reported pro-
cedure [22–25].
(KBr disc, cmꢀ1), m(N@N), 1439; m(C@N), 1597 cmꢀ1
.
UV–Vis spectral data in DMF [kmax(nm)(10ꢀ3e(dm3
molꢀ1 cmꢀ1))]: 271 (7.10), 364 (7.08), 380 (10.60), 392
(10.90), 470 (0.44). [Pb(HaaiBz)(I)2]n (10a): Anal. Calc.
for C16H14I2N4Pb: C, 26.55; H, 1.94; N, 7.74. Found: C,
26.50; H, 1.90; N, 7.70%. FT-IR (KBr disc, cmꢀ1),
m(N@N), 1435; m(C@N), 1599 cmꢀ1. UV–Vis spectral data
in DMF [kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 293 (13.80),
300 (13.40), 362 (5.30), 385 (11.55), 465 (0.30). [Pb(Mea-
aiBz)(I)2] (10b): Anal. Calc. for C17H16I2N4Pb: C, 27.67;
H, 2.17; N, 7.60. Found: C, 27.60; H, 2.13; N, 7.67%.
FT-IR (KBr disc, cmꢀ1), m(N@N), 1438; m(C@N),
1602 cmꢀ1. UV–Vis spectral data in DMF [kmax(nm)
(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 267 (10.70), 382 (13.40), 468
(0.40).
2.2. Physical measurements
Microanalytical (C, H, N) data were obtained from a
Perkin–Elmer 2400 CHNS/O elemental analyzer. Spectro-
scopic data were obtained using the following instruments:
UV–Vis, Perkin–Elmer Lambda-25; IR (KBr disk, 4000–
200 cmꢀ1), Perkin–Elmer RX-1 spectrophotometer, and
1H NMR, Bruker 300 MHz FT-NMR spectrometer.
2.3.2. Synthesis of [Pb(MeaaiMeBz)+(I3)ꢀ] (14b)
To a methanolic solution (25 ml) of [MeaaiMeBz]+Iꢀ (1-
methyl-3-benzyl-2-(p-tolylazo)imidazolium iodide) (7b)
(0.2 g, 0.48 mmol), PbI2 (0.22 g, 0.48 mmol) was added
pinchwise and stirred and refluxed for 10 h. The solution
was filtered hot through G4 crucible and slowly evaporated
in air. Block shaped orange-red crystals were deposited on
the wall of the beaker and collected by filtration. These
crystals were ground and 2-methoxy-ethanol solution was
prepared. Methanol (2 volume) was added into this solu-
tion. After a week bright orange-red colored block shaped
crystals were separated and dried over CaCl2 in a desicca-
tor. The yield was 0.3 g (71%).
2.3. Preparation of compounds
2.3.1. Synthesis of [Pb(MeaaiMe)(I)2]n (8b)
1-Methyl-2-(p-tolylazo)imidazole (0.05 g, 0.25 mmol) in
MeOH (15 ml) was added dropwise to a stirred ethylene
glycol monomethyl ether solution (15 ml) of PbI2
(0.057 g, 0.12 mmol) at room temperature. The color was
changed to red-orange. The solution was then refluxed
for 2 h and red-orange crystalline compound was found
deposited on the glass surface. The solution was filtered
hot and allowed to evaporate slowly. Bright red-orange
crystals were obtained after a week. The crystals were col-
lected by filtration and washed with methanol. The crystals
were dissolved in a minimum volume of 2-methoxy-ethanol
and two volumes of methanol was added into it. The result-
ing mixture was then allowed to evaporate slowly. The
All other complexes were prepared by the same proce-
dure. In all cases, crystalline products were obtained. The
yield varied from 70% to 80% and microanalytical data
of the complexes are as follows. [HaaiMe2][PbI3] (11a):

K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 4377–4385
4379
Table 1
Anal. Calc. for C11H13I3N4Pb: C, 16.73; H, 1.65; N, 7.10.
Found: C, 16.66; H, 1.60; N, 7.05%. FT-IR (KBr disc,
cmꢀ1), m(N@N), 1432; m(C@N), 1588 cmꢀ1. UV–Vis spec-
tral data in DMF [kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]:
268 (1.07), 287 (8.90), 364 (23.00), 386 (10.28), 420 (4.35).
[MeaaiMe2][PbI3] (11b): Anal. Calc. for C12H15I3N4Pb: C,
17.93; H, 1.87; N, 6.97. Found: C, 18.00; H, 1.90; N,
7.05%. FT-IR (KBr disc, cmꢀ1), m(N@N), 1445; m(C@N),
Summarised crystallographic data for [Pb(MeaaiMe)I2] (8b) and [Mea-
aiMe(CH2Ph)+Pb(l-I3)ꢀ] (14)
[Pb(MeaaiMe)I2] (8b)
[MeaaiMe(CH2Ph)+-
Pb(l-I3)ꢀ] (14)
Empirical formula
Formula weight
Temperature (K)
Crystal system
C
11H12N4I2Pb
C18H19N4I3Pb
879.26
295
649.14
294
triclinic
triclinic
1591 cmꢀ1
.
UV–Vis
spectral
data
in
DMF
ꢀ
ꢀ
Space group
P1
P1
Crystal size (mm3)
Unit cell dimensions
0.20 · 0.15 · 0.10
0.20 · 0.10 · 0.10
[kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 270 (5.76), 353
(11.10), 381 (9.80), 397 (10.70), 400 (8.38). [HaaiEt2][PbI3]
(12a): Anal. Calc. for C13H17I3N4Pb: C, 19.09; H, 2.08;
N, 6.85. Found: C, 19.13; H, 2.12; N, 6.91%. FT-IR
˚
a (A)
8.3189(19)
9.672(2)
10.780(2)
71.522(4)
82.222(4)
78.459(4)
803.6(3)
2
0.71073
12.562
2.733
163
8646
8.109(11)
11.322(16)
13.618(19)
97.10(2)
94.45(3)
103.92(2)
1197(3)
2
0.71073
10.929
2.440
238
12763
˚
b (A)
˚
c (A)
(KBr disc, cmꢀ1), m(N@N), 1441; m(C@N), 1596 cmꢀ1
.
a (ꢁ)
b (ꢁ)
c (ꢁ)
UV–Vis spectral data in DMF [kmax(nm)(10ꢀ3e(dm3
molꢀ1 cmꢀ1))]: 274 (4.62), 365 (10.00), 387 (8.75), 410
(5.80). [MeaaiEt2][PbI3] (12b): Anal. Calc. for
C14H19I3N4Pb: C, 20.21; H, 2.29; N, 6.74. Found: C,
20.25; H, 2.24; N, 6.80%. FT-IR (KBr disc, cmꢀ1),
m(N@N), 1438; m(C@N), 1594 cmꢀ1. UV–Vis spectral data
in DMF [kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 310 (3.55),
370 (8.20), 390 (8.00), 414 (7.55). [HaaiBz2][PbI3] (13a):
Anal. Calc. for C23H21I3N4Pb: C, 29.32; H, 2.23; N, 5.95.
Found: C, 29.40; H, 2.27; N, 6.05%. FT-IR (KBr disc,
cmꢀ1), m(N@N), 1440; m(C@N), 1596 cmꢀ1. UV–Vis spec-
tral data in DMF [kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]:
270 (4.45), 350 (9.10), 388 (9.65), 397 (10.40), 428 (1.67).
[MeaaiBz2][PbI3] (13b): Anal. Calc. for C24H21I3N4Pb: C,
30.15; H, 2.41; N, 5.86. Found: C, 30.10; H, 2.45; N,
5.80. FT-IR (KBr disc, cmꢀ1), m(N@N), 1437; m(C@N),
3
˚
V (A )
Z
˚
k (A)
l (Mo Ka) (mmꢀ1
)
Dcalc (mg mꢀ3
)
Refined parameters
Total reflections
Unique data [I > 2r(I)]
2779
3343
a
R1 [I > 2r(I)]
wR2
0.0310
0.0640
0.96
1.18
ꢀ1.03
0.0320
0.0854
0.846
0.554
ꢀ1.078
b
Goodnessꢀ-o3f-fit
˚
˚
Dmax (e Aꢀ3
)
)
Dmin (e A
P
P
a
R = |Fo ꢀ Fc|/ Fo.
P
P
1=2
b
wR ¼ ½ wðF 2o ꢀ F c2Þ= wF 4oꢂ
are general but w are different,
2
w ¼ 1=½r2ðF o2Þ þ ð0:0695PÞ þ 0:0000Pꢂ for HaaiCH2PhH+Clꢀ Æ 2H2O;
w = 1/[r2(F2) + (0.0250P)2 + (0.0000P)] for 8b and w ¼ 1=½r2ðF 2oÞþ
1594 cmꢀ1
.
UV–Vis spectral data in DMF [kmax
2
ð0:0100PÞ þ ð0:0000PÞꢂ for 14 where P ¼ ðF 2o þ 2F c2Þ=3.
(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 280 (5.45), 370 (10.50),
380 (9.90), 405 (5.85). [HaaiMe(Bz)][PbI3] (14a): Anal.
Calc. for C17H17I3N4Pb: C, 23.58; H, 1.96; N, 6.47. Found:
C, 23.65; H, 2.00; N, 6.40%. FT-IR (KBr disc, cmꢀ1),
m(N@N), 1441; m(C@N), 1597 cmꢀ1. UV–Vis spectral data
in DMF [kmax(nm)(10ꢀ3e(dm3 molꢀ1 cmꢀ1))]: 260 (4.75),
366 (8.80), 390 (10.80), 410 (7.67). [MeaaiMe(Bz)][PbI3]
(14b): Anal. Calc. for C18H19I3N4Pb: C, 24.57; H, 2.16;
N, 6.37. Found: C, 24.55; H, 2.10; N, 6.40%. FT-IR
h 6 10, ꢀ12 6 k 6 12, ꢀ14 6 l 6 14 and angle varies
4.0ꢁ < 2h < 56.6ꢁ for (8b); ꢀ10 6 h 6 10, ꢀ15 6 k 6 14,
ꢀ17 6 l 6 18 and angle varies 3.04ꢁ < 2h < 56.62ꢁ for
(14b). A summary of the crystallographic data and struc-
ture refinement parameters is given in Table 1. Data were
corrected for Lorentz and polarization effects. Data reduc-
tion was carried out by using SAINT program. The structure
was solved by direct methods using SHELXS-97 [36] and
successive difference Fourier syntheses. All non-hydrogen
atoms were refined anisotropically. Full matrix least-
squares refinements on F 2o were carried out using SHELXL-
97 [37] with anisotropic displacement parameters for all
non-hydrogen atoms. Hydrogen atoms were constrained
to ride on the respective carbon or nitrogen atoms with
an isotropic displacement parameter equal to 1.2 times
the equivalent isotropic displacement of their parent atom
in all cases. All calculations were carried out using SHELXS-
97 [36], PLATON 99 [38], and ORTEP-3 [39] programs.
(KBr disc, cmꢀ1), m(N@N), 1445; m(C@N), 1592 cmꢀ1
.
UV–Vis spectral data in DMF [kmax(nm)(10ꢀ3e(dm3
molꢀ1 cmꢀ1))]: 310 (3.55), 365 (8.50), 378 (10.70), 440
(6.65).
2.4. X-ray crystal structure analyses
Crystals suitable for X-ray diffraction study of Pb(Mea-
aiMe)I2 (8b) and [1-Me-3-CH2Ph-2-(p-tolylazo)imidazo-
lium]+[PbI3]ꢀ (14b) were prepared by slow evaporation of
N,N-dimethylformamide solution of compound along with
few drops of methanol at ambient condition. Diffraction
data were collected with the Bruker SMART 1K CCD
area-detector diffractometer using fine focused sealed tube
graphite-monochromatized Mo Ka radiation (k =
3. Results and discussion
3.1. Synthesis and formulation
˚
The ligands used are 1-alkyl-2-(arylazo)imidazole
[RaaiR0, where R = H (a), Me (b); R0 = Me (1), Et (2),
0.71073 A). Unit cell parameters were determined from
least-squares method with the data in the range of ꢀ10 6

4380
K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 4377–4385
CH2Ph (3)], they are unsymmetrical N,N0-bidentate
chelator where N and N0 refer to N(imidazole) and
N(azo) donor centers, respectively. 1,3-Di-alkyl-2-(arylazo)-
imidazolium iodides (symmetrical: RaaiR02þIꢀ, R0 = Me,
Me (4); Et, Et (5); CH2Ph, CH2Ph (6). Unsymmetrical:
RaaiMe(CH2Ph)+Iꢀ (7)). The reaction between RaaiR0
and PbI2 in a 1:1 mole ratio in methanol and 2-methoxy-
ethanol mixture has isolated polymeric [Pb(RaaiR0)I2]n
(R0 = Me (8), Et (9), CH2Ph (10)) compounds. The
reaction between RaaiR02þIꢀ and PbI2 under identical
reaction conditions has synthesized tri-iodoplumbate,
[RaaiR02þPbI3ꢀ (R0 = Me (11), Et (12), CH2Ph (13) and
The þ1H NMR spectra of [Pb(RaaiR0)I2] (8–10),
½RaaiR0 ꢂ ½PbI3ꢂꢀ (11–14) are recorded in CDCl3. The atoms
2
numbering patterns are shown in Scheme 1. Data (Table 2)
reveal that the signals in the spectra of the complexes are
shifted downfield relative to free ligand values. This sup-
ports the coordination of ligand to Pb(II). An important
feature of the spectra is the shifting of imidazole protons
4-H and 5-H to lower d-values, in general, relative to aryl
protons (7-H–11-H). Imidazole protons suffer downfield
shifting by 0.3–0.4 ppm compared to the free ligand posi-
tion. This supports the strong preference of binding of imid-
azole-N to Pb(II). This property has been used to remove
lead(II) from polluted water passing through azoimidazole
MeaaiMeðCH2PhÞþPbIꢀ (14))].
3
3.2. Spectral studies
nPbI2 + nRaaiR/
+
⎯⎯⎯⎯→
[Pb(RaaiR/)I2]n
8-10
IR bands were assigned on comparing with free ligand
data [40]. Moderately intense stretching at 1595–1600 and
1435–1445 cmꢀ1 is due to m(C@N) and m(N@N), respec-
tively, for both types of complexes.
PbI2 + RaaiR/ R// + I- ⎯⎯⎯⎯→
[RaaiR/R//]+ [PbI3]-
11-14
Very low solubility of [Pb(RaaiR0)I2]n (8–10) in methanol
and acetonitrile has ruled out to carry out the solution spec-
tral studies. The complexes are soluble in DMF and the
spectra are recordꢀed in DMF solution. The ionic solids,
[RaaiR0R00]+[PbI3] (11–14), are soluble in acetonitrile
and the solution electronic spectra were recorded in the
wavelength range 250–900 nm. There are three bands and
+
N
N
N
N
N
N
R
R
R
N
N
out of them two are high intense (e ꢃ 104 molꢀ1 dm3 cmꢀ1
)
bands at 350–360 and 370–380 nm. On comparing with free
ligand spectra [26–29,40], we may conclude that these bands
are due to intramolecular charge transfer transitions. A
weak band (e ꢃ 103 molꢀ1 dm3 cmꢀ1) appears at 460–
475 nm. This may be due to MLCT transition from
Pb(II) ! p*(azoimine).
R
R
R = H (a), Me (b); R/ = Me (1), Et (2), CH2Ph (3)
R/ = R// = Me (4), Et (5), CH2Ph (6); R/ = Me, R// = CH2Ph (7)
Scheme 1.
Table 2
1H NMR spectral data in CDCl3 at room temperature
Compound
d, ppm (J, Hz)
4-Ha
5-Ha
7,11-Hb
8-10-H
9-Me
1-(3-)-Mee
4.01
1-(3-)-CH2
(1-(3-)-CH2)CH3
1.55 (7.0)
f
[Pb(HaaiMe)(I2)] (8a)
7.55
7.54
7.56
7.54
7.52
7.53
7.40
7.40
7.45
7.42
7.51
7.50
7.49
7.22
7.20
7.22
7.20
7.20
7.20
7.40
7.40
7.45
7.42
7.51
7.50
7.49
7.88 (7.00)
7.85
7.90 (7.0)
7.79 (7.00)
7.75
7.80 (7.0)
7.88 (7.0)
7.84 (7.0)
7.90 (7.0)
7.85 (7.0)
7.92 (7.0)
7.90 (7.0)
7.96 (7.0)
7.60c
[Pb(HaaiEt)(I2)] (9a)
7.62c
4.47 (9.0)d
5.62e
[Pb(HaaiBz)(I2)] (10a)g
[Pb(MeaaiMe)(I2)] (8b)
[Pb(MeaaiEt)(I2)] (9b)
7.63c
7.37 (7.00)b
7.35 (7.00)b
7.40c
2.48
2.45
2.45
3.97
4.48 (9.0)d
5.60e
1.55 (7.0)
[Pb(MeaaiBz)(I2)] (10b)g
½HaaiMeþ2 ꢂ½Pbðl-I3Þꢀꢂ ð11aÞ
½MeaaiMeþ2 ꢂ½Pbðl-I3Þꢀꢂ ð11bÞ
½HaaiEtþ2 ꢂ½Pbðl-I3Þꢀꢂ ð12aÞ
½MeaaiEtþ2 ꢂ½Pbðl-I3Þꢀꢂ ð12bÞ
7.52c
4.11
4.14
7.38 (7.0)b
7.55c
2.44
2.42
4.68 (10.0)d
4.70 (10.0)
5.75e
5.73e
5.75e
1.52 (7.0)
1.55 (7.0)
7.40 (7.00)b
7.55c
þ
ꢀ
g
½HaaiðCH2PhÞ2 ꢂ½Pbðl-I3Þ ꢂ ð13aÞ
þ
ꢀ
g
½MeaaiðCH2PhÞ2 ꢂ½Pbðl-I3Þ ꢂ ð13bÞ
7.42 (7.00)b
7.36 (7.00)b
2.48
2.48
[MeaaiMe(CH2Ph)+][Pb(l-I3)ꢀ] (14)g
a
Broad singlet.
Doublet.
Multiplet.
Quartet.
Singlet.
Triplet.
b
c
d
e
f
g
d (Ph): 7.40–7.55 ppm, multiplet.

K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 4377–4385
4381
resin [41–43]. Aryl signals shift to the lower field side on Me-
substitution to the aryl ring. This is due to electron donating
effect of the Me-group. There is no noteworthy difference in
the chemical shift data of [RaaiR0R00]+Iꢀ [44] and tri-iodo
plumbate compounds (11–14).
lazo)imidazole) and iodine atoms. The monomeric unit of
1D chain is shown in Fig. 1 and the bond parameters are
listed in Table 3. The structure shows non-planar asymmet-
rically bridged –Pb(l-I)2Pb– units. Lead is located in a dis-
torted octahedral environment with PbN2I4 coordination;
two N donor centers, N(imidazole) and N(azo), are coming
from chelated MeaaiMe ligand. The ligand lies on alternate
side of each chain, which runs parallel to c-axis. The pack-
ing of molecular chains is illustrated in Fig. 2. The unsym-
metrical nature of the ligand is reflected from the Pb–N
bond distance data in the chelated structure: the Pb–
3.3. Molecular structure
3.3.1. [Pb(MeaaiMe)I2]n (8b)
The structure of 8b consists of 1D chain of alternating
chelated lead(II) with MeaaiMe (1-methyl-2-(p-toly-
˚
N(imidazole), 2.477(5) A is shorter than Pb–N(azo),
˚
2.765(5) A length. The distortion may be originated from
small chelate angle \N(1)–Pb–N(4), 61.92(16)ꢁ and long
Table 3
Selected bond lengths and bond angles of [Pb(MeaaiMe)I2]n (8b)
˚
Bond lengths (A)
Bond angles (ꢁ)
Pb(1)–I(1)
Pb(1)–I(2)
Pb(1)–I(1)*
Pb(1)–I(2)**
Pb(1)–N(1)
Pb(1)–N(4)
N(3)–N(4)
N(3)–C(3)
N(4)–C(5)
3.0747 (5)
3.1378(8)
3.4762(8)
3.3336(7)
2.477(5)
2.765(5)
1.258(7)
1.399(8)
1.413(8)
N(1)–Pb(1)–N(4)
N(1)–Pb(1)–I(1)
N(4)–Pb(1)–I(1)
N(1)–Pb(1)–I(2)
N(4)–Pb(1)–I(2)
I(1)–Pb(1)–I(2)
N(1)–Pb(1)–I(2)*
N(4)–Pb(1)–I(2)*
I(1)–Pb(1)–I(2)*
I(2)–Pb(1)–I(2)*
N(1)–Pb(1)–I(1)**
N(4)–Pb(1)–I(1)**
I(1)–Pb(1)–I(1)**
I(2)–Pb(1)–I(1)**
Pb(1)–I(1)**–Pb(2)
Pb(1)–I(2)*–Pb(2)
61.92(16)
87.53(12)
84.00(11)
86.73(12)
148.63(11)
96.458(17)
84.46(12)
79.72(11)
163.716(15)
97.213(18)
169.44(12)
107.64(11)
89.78(2)
95.52(2)
90.22(2)
82.787(18)
Symmetry: * 1 ꢀ X, 1 ꢀ Y, 1 ꢀ Z; ꢀX, 1 ꢀ Y, 1 ꢀ Z.
**
Fig. 1. ORTEP view of a fragment of [Pb(MeaaiMe)I2]n.
Fig. 2. p-Sheet of [Pb(MeaaiMe)I2]n showing both C–Hꢁ ꢁ ꢁp and pꢁ ꢁ ꢁp interactions amongst inter-chain components.

4382
K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 4377–4385
Pb–N(azo) distance. The elongation of the Pb–N(azo) dis-
tance may have several reasons. First, the N(azo) belongs
to exocyclic N@N along with a pendant aryl group; thus
the van der Waals repulsion will be greater than N(imidaz-
ole). Second, the N(azo) has larger s-character compared to
N(imidazole) and thus it is more space demanding. Besides,
the presence of the lone pair results in a non-spherical
charge distribution around Pb(II) in solids to lower the
symmetry of the coordination of the negative ions around
proteins [50,51]. It inhibits heme synthesis and causes ane-
mia. Imidazole is present in most of the biomolecular
nucleic acids, proteins, DNA, and the preferential binding
of Pb(II) to imidazole–N may be the reason for very high
toxic efficiency of lead(II). The pendant phenyl ring of each
chelated MeaaiMe in the 1D chain of alternate molecular
fragment, Pb(MeaaiMe), penetrates into the groove of
neighbouring 1D chain. This ascertains a pꢁ ꢁ ꢁp interaction
˚
them [45,46]. Although Pb–N(azo) (2.765(5) A) is longer
˚
than Pb–N(imidazole) (2.477(5) A) but it is shorter than
˚
the sum of van der Waals radii of Pb (2.02 A) and
˚
N(azo) (1.55 A). This implies covalent interaction between
Pb(II) and N(azo).
In {PbI4} unit Is are bridged in pairs with adjacent
Pb(II) centers at either side of the central unit (Fig. 2).
Each chelating ligand, MeaaiMe, about Pb in the bridged
dimer is oriented in such a fashion that two N(azo) centers
are either coming closer or moving away from each other.
˚
The Pb–I distances (3.0747–3.4762 A) lie in the range of the
reported data [47,48]. The azo N@N bond length in che-
˚
lated MeaaiMe is 1.258(8) A. This is slightly elongated
˚
than that of free ligand value (1.251(7) A) [49]. The short
Pb–N(imidazole) bond length compared to Pb–N(azo) dis-
tance is in support of preferential stronger interaction of
Pb(II) with N(imidazole). Lead(II) is one of the heavy
metals exhibiting very high biochemical toxicity and carcin-
ogenicity due to its binding to –SH group to a class of thiol
Fig. 4. Anion polymer of [PbI6]4ꢀ penetrated into p-pillars constituted
nþ
by ½MeaaiMeðCH2PhÞꢂn through hydrogen bonding interaction.
Fig. 3. ORTEP view of ionic solid [MeaaiMe(CH2Ph)]+[PbI3]ꢀ.
Table 4
Selected bond lengths and bond angles of ½MeaaiMeðCH2PhÞþꢂ½PbIꢀꢂ
3
(14b)
˚
Bond lengths (A)
Bond angles (ꢁ)
Pb(1)–I(2)
3.230(3)
3.244(3)
3.251(3)
3.232(3)
3.235(3)
3.219(3)
1.26(1)
I(2)–Pb(1)–I(2)#2
I(2)–Pb(1)#2–I(1)#1
I(2)–Pb(1)–I(3)#1
I(1)–Pb(1)#1–I(3)#1
I(2)–Pb(1)–I(3)#2
I(2)–Pb(1)–I(1)#1
I(1)–Pb(1)#2–I(3)#1
I(3)–Pb(2)–I(1)
I(3)–Pb(2)–I(1)#2
Pb(2)–I(1)–Pb(1)#1
I(3)–Pb(2)#2–I(1)#2
Pb(1)–I(2)–Pb(2)
180.00
Pb(1)–I(1)#1
Pb(1)–I(3)#1
Pb(2)–I(2)
85.8(1)
95.6(1)
83.86(6)
84.4(1)
94.3(1)
96.14(6)
84.52(8)
95.48(8)
77.5(1)
84.52(8)
77.7(1)
Pb(2)–I(1)
Pb(2)–I(3)#2
N(1)–N(2)
N(2)–C(1)
1.41(1)
1.45(1)
N(1)–C(11)
Fig. 5. [MeaaiMe(CH2Ph)]+s are flanked between [PbI6]n pillars by
bifurcated C–Hꢁ ꢁ ꢁIꢁ ꢁ ꢁH–C interactions. Organic units also show intermo-
lecular C–Hꢁ ꢁ ꢁp interaction to stabilize the layer.
#2
Symmetry operators: #1 x, y, z; ꢀx, ꢀy, ꢀz.

K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 4377–4385
4383
nþ
Fig. 6. View of p-sheet through C–Hꢁ ꢁ ꢁp, face-to-face pꢁ ꢁ ꢁp interaction in ½MeaaiMeðCH2PhÞꢂ (for clarity (PbI3)ꢀ is omitted).
n
with pendant p-tolyl rings and imidazole groups. The
interaction is weak (Centroid (Cg)ꢁ ꢁ ꢁCentroid (Cg) dis-
(Fig. 6) and edge-to-face (Fig. 7) pꢁ ꢁ ꢁp stacking interac-
tions are observed between aromatic rings belonging to
adjacent chains in the network. Azoimidazolium unit con-
tains three different aromatic rings: p-tolyl (p-Tol), phenyl
(Ph) and imidazole (Imz). The pꢁ ꢁ ꢁp interactions are appro-
priate to Centroid (Cg)ꢁ ꢁ ꢁCentroid (Cg) distance of
˚
tance of p-tolylꢁ ꢁ ꢁp-tolyl, 4.012(4) A; imidazoleꢁ ꢁ ꢁp-tolyl,
˚
4.32(4) A), but the disposition of rings warrants to consider
that the arrangement is a 2D network (Fig. 2). The exis-
tence of inter-chain C–Hꢁ ꢁ ꢁp interaction (considering H
or Cꢁ ꢁ ꢁCentroid (Cg) of p-Tol ring (Imz-N-CH3) C(4)–
H(4)–p-Tol(2) (symmetry: 1 ꢀ X, 1 ꢀ Y, ꢀZ): H–p-Tol,
˚
˚
Imz(2)ꢁ ꢁ ꢁp-Tol(1) (3.602(8) A and dihedral, 4.53ꢁ) and
Imz(1)ꢁ ꢁ ꢁp-Tol(2) (3.872(8) A and dihedral, 4.53ꢁ) (1 and
˚
˚
2.78 A; Cꢁ ꢁ ꢁp-Tol, 3.556(9) A; \C–Hꢁ ꢁ ꢁp-Tol, 138ꢁ) consti-
tutes formal p-sheet as it is shown in Fig. 2.
2 in braces refer to two different molecules at adjacent).
These two interactions lead to form 1-D p-chain. The p-
chains exhibit C–Hꢁ ꢁ ꢁp interactions (H or Cꢁ ꢁ ꢁCentroid
3.3.2. [MeaaiMe(CH2Ph)]+ [PbI3]ꢀ (14)
(Cg) of Ph): C(12)–H(12)ꢁ ꢁ ꢁPh(2): H(12)ꢁ ꢁ ꢁPh(2), 2.83 A;
˚
˚
The molecular unit is shown in Fig. 3 and bond param-
eters are listed in Table 4. The structure is constituted from
iodo-bridged [PbI6]n anion polymer and [MeaaiMe-
(CH2Ph)]+ (Fig. 4). The polymer is constituted by six Pb–
I–Pb bridging and generates distorted octahedral PbI6
coordination arrangement. There are three different Pb–I
bond distances in between two Pb centers (Pb1 and Pb2).
C(12)ꢁ ꢁ ꢁPh(2), 3.687(11) A; \C–Hꢁ ꢁ ꢁPh, 154ꢁ where Ph(2)
is coming from N-CH2Ph in the molecule of adjacent chain
(symmetry: ꢀ1 ꢀ X, 1 ꢀ Y, ꢀZ). Inter-chain face-to-face
pꢁ ꢁ ꢁp interaction between (N-CH2)Phꢁ ꢁ ꢁPh(CH2-N) (Cen-
˚
troidꢁ ꢁ ꢁCentroid distance is 3.711(9) A; parallel) enables
˚
The Pb–I distances lie in the reported range, 3.2–3.4 A.
The anion chains are hydrogen bonded to 1-methyl-3-ben-
zyl-2-(p-tolylazo)imidazolium (MeaaiCH2PhMe+) ions
forming neutral sheets perpendicular to b. The organic
cations are placed in between the parallel pillars of {PbI6}n
and are held by hydrogen bonds with bridged-I (C(15)–
H(15)ꢁ ꢁ ꢁI(2e): C–H, 0.930; Hꢁ ꢁ ꢁI, 3.030(1); Cꢁ ꢁ ꢁI,
˚
3.884(11) A and \C–Hꢁ ꢁ ꢁI, 152.77ꢁ (symmetry: x, 1 + y,
z); C(18)–H(18B)ꢁ ꢁ ꢁI(2f): C–H, 0.960; Hꢁ ꢁ ꢁI, 2.990(1);
˚
Cꢁ ꢁ ꢁI, 3.830(12) A; \C–Hꢁ ꢁ ꢁI, 147.20ꢁ (symmetry: ꢀx,
ꢀy, ꢀz)) (Fig. 5). In C(18)ꢁ ꢁ ꢁH(18A)ꢁ ꢁ ꢁN(1): C–H, 0.960;
˚
Hꢁ ꢁ ꢁN, 2.220(1); Cꢁ ꢁ ꢁN, 2.906(12) A and \C–Hꢁ ꢁ ꢁN,
128.00ꢁ (symmetry: x, 1 + y, z). The hydrogen bondings
in C–Hꢁ ꢁ ꢁI pattern are scarce [52,53]. Both face-to-face
Fig. 7. Edge-to-face C–Hꢁ ꢁ ꢁp (Cg) interaction. The least distance (C12 to
˚
the center of Ring1) is 3.627 A.

4384
K.K. Sarker et al. / Inorganica Chimica Acta 359 (2006) 4377–4385
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to form a p-sheet. Parallel arrays of the planes of the aro-
matic moieties (Fig. 6) indicate that these interactions are
of the face-to-face ‘‘p-stacking’’ type [54,55]. There is also
edge-to-face
p-stacking
interaction
between
p-
˚
Tol(1)ꢁ ꢁ ꢁPh(2) and the distance is 3.627 A (Fig. 7) [56,57].
4. Conclusion
The work describes structural differences of di-iodo-
Pb(II)-arylazoimidazoles and arylazoimidazolium tri-iodo-
plumbate. The former gives iodo bridged 1-D neutral chain
where arylazoimidazole acts as an end capper. In the latter
compound, anion polymer is generated by iodo bridging in
tri-iodoplumbate where arylazoimidazolium cation is inter-
calated by hydrogen bonding and pꢁ ꢁ ꢁp forces. The NMR,
UV–Vis and IR spectral data also characterize the
compounds.
[24] D. Banerjee, U.S. Ray, J.-C. Liou, C.-N. Lin, T.-H. Lu, C. Sinha,
Inorg. Chim. Acta 358 (2005) 1019.
[25] U.S. Ray, D. Banerjee, B.G. Chand, J. Cheng, T.-H. Lu, C. Sinha, J.
Coord. Chem. 58 (2005) 1105.
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(2003) 1213.
5. Supplementary material
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23 (2004) 1669.
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[32] M. Nishio, M. Hirota, Y. Umezawa, The CH/p Interaction
(Evidence, Nature and Consequences), Wiley-VCH, New York,
1998.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre; the CCDC Nos. for 8b and 14 are 298934 and
298933, respectively. Copies of the information may be
obtained free of charge from the Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44 1223
336033; e-mail: deposit@ccdc.com.ac.uk or www.
ccdc.cam.ac.uk).
[33] C. Janiak, S. Temizdemir, S. Dechert, W. Deck, F. Girgsdies, J.
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Acknowledgements
[34] U.S. Ray, G. Mostafa, T.H. Lu, C. Sinha, Cryst. Eng. 5 (2002) 95.
[35] U.S. Ray, B.G. Chand, A.K. Dasmahapatra, G. Mostafa, T.-H. Lu,
C. Sinha, Inorg. Chem. Commun. 6 (2003) 634.
[36] G.M. Sheldrick, SHELXS-97 Program for the Solution of Crystal
Structure, University of Gottingen, Germany, 1997.
[37] G.M. Sheldrick, SHELXL-97 Program for the Refinement of Crystal
Structure, University of Gottingen, Germany, 1997.
[38] A.L. Spek, PLATON, Molecular Geometry Program, University of
Utrecht, The Netherlands, 1999.
Financial supports (CS) from the DST and CSIR, New
Delhi, are gratefully acknowledged. K.K.S. acknowledges
CSIR for a fellowship.
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