Synthesis, crystal structures and optical properties of mercury(II) halide compounds with (E)-N-(pyridin-2-ylmethylidene)arylamines: Effect of ligand R-group upon structure

Article abstract of DOI:10.1016/j.poly.2013.03.025

A systematic series of seven mercury compounds of (E)-N-(pyridin-2- ylmethylidene)arylamine (L), where L is a variously R substituted ligand, with the formulations [HgX₂L]₂: X = Cl; R = 4-CH ₂CH₃ (4), 4-OCH₂CH₃ (5), 4-Cl (6), 2-CO₂CH₃ (7), or 4-CO₂CH₃ (8); X = Br; R = 4-CO₂CH₃ (9a) and [HgX₂L]: X = Br; R = 4-CO₂CH₃ (9b) and X = I; R = 4-CO₂CH ₃ (10), were synthesized. All compounds have been structurally characterized by single-crystal X-ray diffraction studies and their spectroscopic (IR, NMR, UV-Vis and fluorescence) properties are described. The structural analyses reveal that compounds 4-9a are centrosymmetric binuclear compounds while compounds 9b (a polymorph of the binuclear compound 9a) and 10 are mononuclear compounds. The HgCl₂ compounds are more likely to dimerize via Hga[?Cl bridges complexed with (E)-N-(pyridin-2- ylmethylidene)arylamine ligands compared with their HgBr₂ and HgI₂ analogs. This feature of the structural chemistry is correlated with the enhanced Lewis acidity of the mercury in the HgCl₂ compounds. Moderating the electronegativity of the substituents in L is shown to influence the strength of the Hg-N(imino) bond in HgCl₂L compounds.

Full text of DOI:10.1016/j.poly.2013.03.025

Polyhedron 55 (2013) 270–282
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Polyhedron
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Synthesis, crystal structures and optical properties of mercury(II) halide
compounds with (E)-N-(pyridin-2-ylmethylidene)arylamines: Effect of ligand
R-group upon structure
a
b
c,
d
Tushar S. Basu Baul a, , Sajal Kundu , Herbert Höpfl , Edward R.T. Tiekink , Anthony Linden
⇑
⇑
a Department of Chemistry, North-Eastern Hill University, NEHU Permanent Campus, Umshing, Shillong 793 022, India
b Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, 62209 Cuernavaca, Mexico
c Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
d Institute of Organic Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
A systematic series of seven mercury compounds of (E)-N-(pyridin-2-ylmethylidene)arylamine (L), where
L is a variously R substituted ligand, with the formulations [HgX2L]2: X = Cl; R = 4-CH2CH3 (4), 4-OCH2CH3
(5), 4-Cl (6), 2-CO2CH3 (7), or 4-CO2CH3 (8); X = Br; R = 4-CO2CH3 (9a) and [HgX2L]: X = Br; R = 4-CO2CH3
(9b) and X = I; R = 4-CO2CH3 (10), were synthesized. All compounds have been structurally characterized
by single-crystal X-ray diffraction studies and their spectroscopic (IR, NMR, UV–Vis and fluorescence)
properties are described. The structural analyses reveal that compounds 4–9a are centrosymmetric binu-
clear compounds while compounds 9b (a polymorph of the binuclear compound 9a) and 10 are mono-
nuclear compounds. The HgCl2 compounds are more likely to dimerize via Hgꢀ ꢀ ꢀCl bridges complexed
with (E)-N-(pyridin-2-ylmethylidene)arylamine ligands compared with their HgBr2 and HgI2 analogs.
This feature of the structural chemistry is correlated with the enhanced Lewis acidity of the mercury
in the HgCl2 compounds. Moderating the electronegativity of the substituents in L is shown to influence
the strength of the Hg–N(imino) bond in HgCl2L compounds.
Received 7 February 2013
Accepted 13 March 2013
Available online 21 March 2013
Keywords:
Mercury
(E)-N-(Pyridin-2-ylmethylidene)arylamine
N,N-donor ligands
Spectroscopy
Structure elucidation
Crystal structure
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
analytical results, at the synthesis of new structures with desired
properties [4,5]. In line with the above, we recently reported on
The main group elements are typically defined as the set of s
and p block elements, plus zinc, cadmium, and mercury [1]. Group
12 compounds are particularly challenging to separate into main
group versus transition metal-type complexes, as zinc tends to be-
have more as a transition metal in terms of reactivity and coordi-
nation preferences. However, the Hg(II) ion typically adopts
either two-coordinate, linear geometries or distorted tetrahedral,
nearly disphenoidal-type of geometries, and therefore, tends to
have much more in common with main group elements owing to
this propensity. Main group elements have unique coordination
preferences and electronic properties, and thereby present oppor-
tunities for the preparation of novel structures with new and inter-
esting characteristics [1–3]. Moreover, crystal engineering
represents a fascinating and constantly growing field which aims
at understanding intermolecular interactions and, exploiting these
the syntheses and the self-assembly of some Hg(II) compounds
of composition [HgX2L], [HgX2L]2, [HgX2L]n and {[HgX2L]2}n where
X = chloride, bromide, iodide, nitrate, and azide, and L is a (E)-N-
(pyridin-2-ylmethylidene)arylamine [6]. The interplay between
the three components Hg, X, and L greatly influences the observed
structure type and patterns of self-assembly as monomeric tetra-
hedral, dimeric and polymeric trigonal bipyramidal, and polymeric
octahedral geometries were encountered. The results indicated
that dimeric structures with a trigonal bipyramidal geometry
(Scheme 1a) is prevalent among the reaction products of HgX2 with
L. Literature surveys have shown that different coordination num-
bers and geometries of the mercury center have been found when a
remote ligand substituent is altered. This phenomenon is not re-
stricted to mercury alone, but may be found in many other main
group element systems as well [7–9]. As a part of an on-going
investigation into the factor(s) that influence molecular geometry
in chemically similar compounds, the synthesis and structures of
eight new mercury(II) compounds are presented in which X and
the substituents (R) on the phenyl ring of L have been varied sys-
tematically (Scheme 1b). Six dimers and two mononuclear
⇑
Corresponding authors. Tel.: +91 3642722626; fax: +91 3642721000 (T.S. Basu
Baul), tel.: +60 3 7967 6775; fax: +60 3 7967 4193 (E.R.T. Tiekink).
E-mail addresses: basubaul@nenu.ac.in, basubaulchem@gmail.com (T.S. Basu
Baul), Edward.Tiekink@gmail.com (E.R.T. Tiekink).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.03.025

T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
271
Scheme 1a. Various structural motifs (i–iv) observed in mercury(II) compounds with (E)-N-(pyridin-2-ylmethylidene)arylamines, L (taken from Ref. [6]).
Scheme 1b. The L ligands used and the investigated compounds 4–10.

272
T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
Table 1
2. Results and discussion
Photophysical data for compounds 1–10 in acetonitrile solution.a
Compounds Electronic spectroscopic data kmax (nm); Photoluminescence
2.1. Syntheses
e
([Mꢁ1 cmꢁ1])
data
kem(nm)c
/
F
A systematic series of seven mercury compounds with the gen-
eral stoichiometry HgX2L has been prepared, where X is a chloride,
bromide or iodide, and L is a 4-R substituted Schiff base ligand, (E)-
N-(pyridin-2-ylmethylidene)arylamine where R = CH2CH3, OCH2-
CH3, Cl or CO2CH3 (4–6, 8–10) while compound 7 incorporates a
2-R substituted variant of L with R = CO2CH3, i.e. (E)-methyl-2-
((pyridin-2-ylmethylidene)amino)benzoate, in order to observe
the influence of ortho-substitution on the mercury coordination
geometry preferences. In alcohol, one equivalent of HgX2 reacts
rapidly with one equivalent of L (generated in situ from pyridine-
2-carboxaldehyde and a substituted aniline) to give a yellow pre-
cipitate from which mercury compounds of the formula [HgX2L]2
(4–8 and 9a) and [HgX2L] (9b and 10) were isolated and all the
complexes have been characterized crystallographically. Some re-
sults for mercury compounds 1–3 (see Scheme 1a; L = 4-CH3, i.e.
(E)-4-methyl-N-(pyridin-2-ylmethylidene)aniline and X = Cl (1),
Br (2) and I (3)) are also included herein for comparison; their
syntheses and crystal structures having been reported previously
1
2
3
4
5
6
7
8
348 (10781)
341 (13367)
340 (32679)
344 (32273)
352 (50678)
348 (22206)
338 (49032)
332 (28931)
323 (28506)
340 (20780)
413, 429
410, 432
411, 433
414, 427
416, 428
414, 428
395
414, 430
418, 429
412, 429
0.16
0.20
0.02
0.13
0.19
0.18
0.24
0.14
0.16
0.18
9ab
10
a
b
c
Data for the compounds 1–3 (Scheme 1a) were taken from Ref. [6].
Identical photophysical results were obtained for 9b.
The long wavelength emission appears as a shoulder in all cases except for 7.
compounds, one of which is a polymorph of a dimer, have been
structurally characterized by single-crystal X-ray diffraction and
spectroscopic (IR, NMR, UV–Vis and fluorescence) methods.
7
8
1.2
0.8
0.4
0.0
1.6
1.2
0.8
0.4
0.0
1
2
3
4
5
6
8
9a
10
320
360
400
440
320
360
400
440
Wavelength (nm)
Wavelength (nm)
Fig. 1. UV–Vis spectra of compounds 1–10 in acetonitrile (concentration 10ꢁ5 M). Spectra of compounds 7 and 8, with CO2CH3 substituents, are shown separately for
convenience.
7
8
1
2
3
4
5
6
8
9a
10
400
450
500
550
600
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
Fig. 2. Fluorescence spectra of compounds 1–10 in acetonitrile (concentration ꢂ10ꢁ5 M) obtained by excitation at the respective absorption maxima (refer to Table 1).
Spectra of compounds 7 and 8, with CO2CH3 substituents, are shown separately for convenience.

Table 2
Crystal data, data collection and refinement parameters for compounds 4–10.
4
5
6
7
8
9a
9b
10
Empirical formula
Formula weight
Crystal size (mm)
Crystal morphology
T (K)
C
28H28Cl4Hg2N4
C28H28Cl4Hg2N4O2
995.37
C24H18Cl6Hg2N4
976.30
C28H24Cl4Hg2N4O4
1023.33
0.15 ꢃ 0.23 ꢃ 0.35
tablet
C28H24Cl4Hg2N4O4
1023.33
0.10 ꢃ 0.20 ꢃ 0.38
prism
C28H24Br4Hg2N4O4
1201.14
C14H12Br2HgN2O2
600.57
C14H12HgI2N2O2
694.57
963.52
0.16 ꢃ 0.19 ꢃ 0.24
0.10 ꢃ 0.15 ꢃ 0.23
0.08 ꢃ 0.16 ꢃ 0.20
0.10 ꢃ 0.20 ꢃ 0.30
0.18 ꢃ 0.20 ꢃ 0.40
0.08 ꢃ 0.10 ꢃ 0.22
block
tablet
block
prism
prism
prism
293(2)
160(1)
100(2)
160(1)
160(1)
160(1)
160(1)
160(1)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/n
7.9022(10)
15.1805(19)
12.8797(16)
90
95.907(2)
90
1536.8(3)
2
triclinic
P1
monoclinic
P21/n
7.5555(7)
15.1188(14)
12.1988(12)
90
95.323(2)
90
1387.5(2)
2
monoclinic
P21/c
7.8632(1)
21.4478(5)
9.2592(1)
90
98.5421(11)
90
1544.23(4)
2
monoclinic
P21/n
10.31062(19)
12.9030(3)
11.14250(18)
90
93.2024(16)
90
1480.06(5)
2
triclinic
P1
triclinic
P1
triclinic
P1
ꢀ
ꢀ
ꢀ
ꢀ
8.0668(2)
9.0951(2)
10.5354(2)
80.9248(13)
84.2979(11)
79.8835(14)
749.38(3)
1
9.1931(3)
9.3905(2)
9.6450(3)
75.504(2)
82.229(2)
86.996(2)
798.57(4)
1
8.2963(2)
9.1120(3)
10.5952(3)
85.548(2)
88.100(2)
84.163(2)
794.14(4)
2
8.1462(2)
9.7827 (2)
10.9351(2)
82.3929(14)
86.3120(12)
81.9878(11)
854.40(3)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dx (g cmꢁ3
)
2.082
10.350
2.205
10.643
2.337
11.652
2.201
10.338
2.296
10.786
2.497
14.680
2.511
14.762
2.700
12.646
l
(mmꢁ1
)
Transmission factors (min, max)
h (°)
0.19, 0.29
2–25
0.17, 0.39
2–30
0.20, 0.46
2–25
0.10, 0.24
2–30
0.33, 1.00
3–29
0.065, 0.28
3–29
0.035, 0.17
3–29
0.13, 0.46
2–30
Reflections measured
Independent reflections; Rint
14471
2707; 0.045
2291
173
0.037
0.084
1.060
1.50, ꢁ0.51
22765
4348; 0.073
3884
183
0.033
0.087
1.045
1.98, ꢁ2.85
13015
2436; 0.051
2246
163
0.036
0.068
1.211
1.26, ꢁ1.54
36430
4494; 0.089
3979
191
0.046
0.138
1.099
4.54, ꢁ3.41
11742
3242; 0.026
2729
192
0.020
0.044
1.005
1.78, ꢁ0.78
12326
3511; 0.049
3140
192
0.029
0.057
1.033
0.99, ꢁ1.30
12018
3504; 0.056
3215
192
0.036
0.078
1.081
1.92, ꢁ2.37
20855
4962; 0.065
4456
192
0.029
0.070
1.090
1.37, ꢁ2.18
Reflections with [I > 2
Number of parameters
R(F) [I > 2 (I) reflections]
wR(F2) [all data]
Goodness-of-fit (GOF) on F2
(e Åꢁ3
r(I)]
r
D
qmax,
)
min

274
T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
Table 3
Selected bond lengths (Å) and angles (°) for 1–10.a
1b
2b
3b
4
5
6
7
8
9a
9b
10
Hg(1)–N(1)
2.354(6)
2.288(6)
2.295(6)
2.471(5)
2.467(5)
2.5010(7)
2.4994(7)
3.4749(8)
3.6344(8)
2.5779(7)
2.5831(7)
71.13(18)
71.30(18)
2.404(5)
2.343(5)
2.300(3)
2.329(5)
2.342(5)
2.262(3)
2.391(4)
2.344(4)
2.375(3)
Hg(1)–N(2)
2.490(6)
2.423(2)
3.011(2)
2.355(3)
70.3(2)
2.438(5)
2.6698(5)
–
2.473(5)
2.513(3)
2.488(5)
2.554(5)
2.535(3)
2.531(3)
2.401(4)
2.4996(6)
–
2.458(3)
2.6721(3)
–
Hg(1)–X(1)
2.4572(19) 2.4987(10) 2.4762(17) 2.4106(16) 2.5490(8) 2.5128(5)
2.9254(17) 3.0172(10) 2.9343(16) 3.2330(15) 2.8929(7) 3.3759(5)
Hg(1)–X(10)
Hg(1)–X(2)
2.6363(5)
69.73(18)
2.371(2)
2.3651(11) 2.3774(18) 2.3990(15) 2.3876(9) 2.4740(6)
71.00(11) 70.05(18) 69.05(16) 70.42(9) 68.40(11)
102.06(14) 121.87(12) 102.46(7) 107.82(9)
2.5168(6)
71.24(13)
2.6559(3)
69.75(10)
N(1)-Hg(1)–N(2)
N(1)–Hg(1)–X(1)
N(1)–Hg(1)–X(2)
N(2)–Hg(1)–X(1)
N(2)–Hg(1)–X(2)
N(1)–Hg(1)–X(1’)
N(2)–Hg(1)–X(10)
X(1)–Hg(1)–X(2)
X(1)–Hg(1)–X(1’)
X(2)–Hg(1)–X(1’)
70.28(18)
107.73(16) 144.52(13) 104.46(13)
141.55(14)
113.76(17) 96.39(13)
100.57(14)
104.54(14) 104.08(9)
122.60(15) 133.29(9)
115.77(10) 105.10(7)
106.52(10) 112.21(7)
114.29(14)
126.51(14) 97.36(12)
91.84(13) 86.24(11)
148.09(7) 106.50(9)
101.21(6) 95.60(8)
94.10(15)
107.83(12) 101.71(12)
108.38(12)
92.88(13)
103.86(13) 105.95(8)
88.23(14) 86.63(8)
157.94(13) 156.85(8)
95.20(8)
111.44(9)
114.94(7)
104.98(15) 111.26(12) 114.55(12)
113.72(12)
87.45(16)
107.44(13) 128.18(11) 104.19(7) 106.34(8)
87.90(14) 81.82(12) 89.20(7) 87.17(8)
157.51(13) 134.99(12) 157.83(7) 154.48(8)
121.52(9)
112.52(7)
74.98(13)
74.97(13)
–
–
–
–
156.50(16) 130.20(13)
129.66(12)
138.07(11) 115.66(3)
113.36(3)
–
–
133.685(17) 132.82(9)
122.44(4)
84.28(3)
93.59(3)
95.72(3)
131.21(7)
88.42(5)
88.96(5)
91.58(5)
136.59(6)
80.82(5)
87.86(5)
99.18(5)
109.41(3) 144.169(18) 120.02(2)
127.047(10)
85.66(7)
80.75(2)
77.54(2)
107.78(2)
108.31(2)
98.70(2)
102.94(2)
–
–
–
87.62(5)
91.72(6)
92.38(5)
91.41(2)
88.37(2)
88.59(2)
84.638(13)
87.056(15)
95.362(13)
–
–
–
–
–
–
90.34(7)
Hg(1)–X(1)–Hg(10) 94.34(7)
a
All compounds except 3, 9b and 10 are binuclear compounds in which the two halves are related by a crystallographic center of inversion. Primed atoms indicate the
longer Hgꢀ ꢀ ꢀX bridging distance to the second half of the dimer.
b
Data taken from the previously published crystal structures shown in Scheme 1a (compounds 1–3), see Ref. [6].
[6]. The mercury compounds are insoluble in the reaction medium
and can be re-crystallized using a large volume of acetonitrile (re-
fer to work-up procedure) to provide crystals suitable for X-ray
crystallography. Two polymorphs of 9 (9a and 9b) were character-
ized from two different batches of crystals, each obtained from
acetonitrile solution. The results of the crystal structure determi-
nations of 4–10 (see below) are consistent with the chemical and
spectroscopic analyses, giving clear evidence of the formation of
the 1:1 adducts between the bidentate N-donors and HgX2. Com-
pounds 4–10 are all air-stable and behave as non-electrolytes in
acetonitrile solution.
2.2. IR, NMR, UV–Vis and fluorescence spectroscopy
The infrared spectra of compounds 4–10 are very similar and
the IR assignments of selected diagnostic bands are included in
the Experimental section. The compounds display a moderately in-
tense IR band in the region 1620–1650 cmꢁ1 which is assigned to
the masym(C(H)@N) stretch of the coordinated Schiff base ligands
[6]. In addition, well resolved-sharp bands of variable intensity ob-
served in the regions 1600–1550, 1490–1480 and 1400–1430 cmꢁ1
are assigned to the coordinated pyridine ring [6,10–11]. These data
are in agreement with the coordination of imino- and pyridine-N
atoms to the mercury atom [6]. On the other hand, a very strong
band in the range 1700–1712 cmꢁ1 is detected in compounds 7–
10 which has been assigned to masym(OCO). The lowering of masym(-
OCO) band in 7 (1700 cmꢁ1) compared to its p-analogs 8–10 is sug-
gestive of (C@O ? Hg) coordination. The 1H NMR spectra were
recorded in DMSO-d6 solution and displayed the expected signals
which were generally broad. Coupling constants of some signals
for compounds 5, 6 and 10 could not be derived with certainty ow-
ing to the complicated splitting yet the multiplicity patterns could
be delineated.
Table 1 summarizes the UV–Vis and fluorescent properties of
compounds 4–10 along with the previously reported data for 1–3
[6]. The electronic spectra in acetonitrile solutions exhibit a coa-
lesced absorption band in the range of 320–350 nm (Fig. 1) which
is possibly the result of overlap of intramolecular charge transfer
transitions with a weak band due to MLCT transition from
Hg(II) ? p⁄ ligand, as noted earlier for the cognate systems [6].
Fig. 3. Perspective view of binuclear [HgCl2L1]2 4. Displacement ellipsoids are
drawn at the 30% probability level and unlabelled atoms are related by the
symmetry operation 1 ꢁ x, 1 ꢁ y, 1 ꢁ z.

T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
275
Fig. 4. Perspective view of binuclear [HgCl2L2]2 5. Displacement ellipsoids are drawn at the 50% probability level and unlabelled atoms are related by the symmetry operation
ꢁx, ꢁy, ꢁz.
The steady-state fluorescence studies have been employed as inde-
pendent evidence of complexation between the ligand and the
mercury ions. In acetonitrile solution, the compounds all display
broad emission bands at around kmax = 410 nm along with a shoul-
der at ꢂ430 nm, except for 7, which displayed a distinct absorption
at 395 nm, when they are excited at their respective absorption
maxima (Fig. 2), indicating the charge transfer nature of the tran-
sitions [6]. In general, all compounds show very low fluorescent
quantum yield (/F) [6]. No change in /F was perceived when the
substituents in the compounds were varied from 4-CH3 (1–3) to
4-CH2CH3 (4), 4-OCH2CH3 (5), 4-Cl (6), or 4-CO2CH3 (8–10). How-
ever, an appreciable change was noticed in the case of compound
7, which was shown to feature a close Hgꢀ ꢀ ꢀO interaction.
2.3. Molecular structures
The crystal and molecular structures of solvent-free 4–10 have
been determined with crystal data and selected geometric param-
eters for these collated in Tables 2 and 3, respectively. The HgCl2
structures with 4-substituted rings are discussed first and related
to their HgBr2 and HgI2 counterparts where applicable. The sole
example of a characterized HgX2 structure with a 2-substituted
aryl ring is discussed last. The molecular structures are uniformly
zero-dimensional, being mono- or, usually, bi-nuclear.
The binuclear molecule of [HgCl2L1]2 (4, Fig. 3) is the archetype
for most of the molecules described herein and, as such, is de-
scribed in more detail. The immediate environment for the mer-
cury atom is defined by the pyridyl-N1 and imino-N2 atoms
derived from the chelating (E)-4-ethyl-N-(pyridin-2-ylmethylid-
ene)aniline ligand and two chlorido ligands. The Hg–N(pyridyl)
bond length is significantly shorter than the Hg–N(imino) bond
length, a trend that is maintained in all molecules in the present
study. The resulting five-membered HgN2C2 chelate ring is planar
with the root-mean-square (r.m.s.) deviation of the fitted atoms
being 0.015 Å; the maximum deviation is 0.015(7) Å for the C6
atom. Overall, the chelating ligand exhibits a small twist from pla-
narity with the dihedral angle between the planes of the terminal
rings being 10.8(4)°. Molecules self-associate over a center of
Fig. 5. Perspective view of binuclear [HgCl2L3]2 6. Displacement ellipsoids are
drawn at the 30% probability level and unlabelled atoms are related by the
symmetry operation ꢁx, 1 ꢁ y, ꢁz.
inversion via unsymmetric
l2-chlorido bridges, the difference in
Hg–Cl1 and Hg–Cl1i bond lengths,
D
(Hg–Cl1), being 0.47 Å; sym-

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T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
Fig. 6. Perspective view of binuclear [HgCl2L5]2 8. Displacement ellipsoids are drawn at the 30% probability level and unlabelled atoms are related by the symmetry operation
ꢁx, 1 ꢁ y, ꢁz.
metry operation i: 1 ꢁ x, 1 ꢁ y, 1 ꢁ z. As anticipated, the terminally
coordinated chlorido atom forms a significantly shorter Hg–Cl
bond compared with those formed by the bridging chlorido atoms.
The coordination geometry is highly distorted owing in part to the
restricted bite angle of the chelating ligand (70.28(18)°) and the
disparate Hg–Cl bond lengths. The Cl3N2 donor set defines a coor-
dination geometry intermediate between square pyramidal and
trigonal bipyramidal as quantified by the value of the trigonality
Fig. 8. Perspective view of mononuclear [HgBr2L5] 9b. Displacement ellipsoids are
drawn at the 50% probability level.
Fig. 7. Perspective view of binuclear [HgBr2L5]2 9a. Displacement ellipsoids are
drawn at the 50% probability level and unlabelled atoms are related by the
Fig. 9. Perspective view of mononuclear [HgI2L5] 10. Displacement ellipsoids are
symmetry operation 1 ꢁ x, 1 ꢁ y, 1 ꢁ z.
drawn at the 50% probability level.

T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
277
Fig. 10. Perspective view of binuclear [HgCl2L4]2 7. Displacement ellipsoids are
drawn at the 30% probability level and unlabelled atoms are related by the
symmetry operation ꢁx, ꢁy, ꢁz.
Fig. 12. View in projection down the b-axis of the unit cell contents of [HgCl2L2]2 5.
The C–Hꢀ ꢀ ꢀ
p
(chelate) [C14–H143ꢀ ꢀ ꢀCg(HgN2C2)i = 2.81 Å, C14ꢀ ꢀ ꢀCg(HgN2C2)-
i = 3.652(5) Å, angle at H143 = 144° for symmetry operation i: ꢁx, 1 ꢁ y, 1 ꢁ z],
p
ꢀ ꢀ ꢀ
p
[Cg(N1,C1–C5)ꢀ ꢀ ꢀCg(C7–C12)ii = 3.636(2) Å, angle of inclination = 1.3(2)° for
ii: ꢁx, 1 ꢁ y, ꢁz; Cg(C7–C12)ꢀ ꢀ ꢀCg(C7–C12)iii = 3.599(2) Å, for iii: ꢁx, 1 ꢁ y, 1ꢁz], C–
Hꢀ ꢀ ꢀO [C3–H3ꢀ ꢀ ꢀO1iv = 2.53 Å, C3ꢀ ꢀ ꢀO1iv = 3.457(5) Å, angle at H3 = 167° for iv: 1 + x,
y, ꢁ1 + z] and C–Hꢀ ꢀ ꢀCl [C4–H4ꢀ ꢀ ꢀCl2v = 2.77 Å, C4ꢀ ꢀ ꢀCl2v = 3.616(5) Å, angle at
H4 = 169° for v: 1ꢁx, ꢁy, ꢁz; C6–H6ꢀ ꢀ ꢀCl1ii = 2.75 Å, C4ꢀ ꢀ ꢀCl2v = 3.639(4) Å, angle at
H6 = 155°] interactions are shown as purple, orange, blue and brown dashed lines,
respectively. (Colour online.)
index, s, = 0.42 which compares to the s values of 0.0 and 1.0 for
ideal square pyramidal and trigonal bipyramidal geometries,
respectively [12].
To a first approximation, the binuclear molecules of [HgCl2L2]2
(5, Fig. 4), [HgCl2L3]2 (6, Fig. 5) and [HgCl2L5]2 (8, Fig. 6) resemble
that just described for 4. The dimeric structures are centrosymmet-
ric and feature distorted penta-coordinate geometries with
s being
0.39, 0.44 and 0.16, respectively. The chelating ligands in 5, 6 and 8
range from planar in 5 to significantly twisted in 6 and 8 as seen in
the dihedral angles between the planes of the six-membered rings
of 1.3(2)°, 18.8(3)° and 24.41(14)°, respectively. Systematic varia-
tions in the geometric parameters are observed and these are cor-
related with the enhanced electronegativities of the substituents in
the 4-position of the aryl rings, i.e. OCH2CH3 (5), Cl (6) and CO2CH3
(8), compared with CH2CH3 in 4. As a general trend, as the electro-
negativity of the substituent increases, the Hg–N(imino) bond
lengths elongate with a concomitant reduction in the Hg–N(pyri-
dyl) distances, reflecting a reduction in the basicity of the imino-
N2 atom and a reduced tendency for coordination. This is echoed
Fig. 11. View in projection down the a-axis of the unit cell contents of [HgCl2L1]2 4.
The C–Hꢀ ꢀ ꢀ
p
(chelate) [C14–H14cꢀ ꢀ ꢀCg(HgN2C2)i = 2.82 Å, C14ꢀ ꢀ ꢀCg(HgN2C2)i = 3.743
(14) Å, angle at H14c = 162° for symmetry operation i: ½ + x, ½ ꢁ y, ꢁ½ + z] and pꢀ ꢀ ꢀp
[Cg(N1, C1–C5)ꢀ ꢀ ꢀCg(C7–C12)ii = 3.834(5) Å, angle of inclination = 10.8(4)° for ii: -
1 + x, y, z] interactions are shown as purple and orange dashed lines, respectively.
(Colour online.)
in the
D(Hg–N) values which vary from a small 0.13 Å for 4 to a

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T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
Fig. 13. View in projection down the c-axis of the unit cell contents of [HgBr2L5]2 9a. The
pꢀ ꢀ ꢀ
p
[Cg(N1, C1–C5)ꢀ ꢀ ꢀCg(C7–C12)i = 3.705(3) Å, angle of inclination = 9.0(2)° for i:
1 ꢁ x, 1 ꢁ y, ꢁz; Cg(C7–C12)ꢀ ꢀ ꢀCg(C7–C12)ii = 3.706(3) Å, for ii: ꢁx, 1 ꢁ y, ꢁz], C–Hꢀ ꢀ ꢀO [C3–H3ꢀ ꢀ ꢀO1iii = 2.32 Å, C3ꢀ ꢀ ꢀO1iii = 3.119(6) Å, angle at H3 = 142° for iii: 1 + x, ꢁ1 + y, z]
and C–Hꢀ ꢀ ꢀBr interactions [C4–H4ꢀ ꢀ ꢀBr2iv = 3.04 Å, C4ꢀ ꢀ ꢀBr2iv = 3.936(5) Å, angle at H4 = 157° for iv: 1 ꢁ x, ꢁy, 1 ꢁ z; C6–H6ꢀ ꢀ ꢀBr1i = 3.05 Å, C6ꢀ ꢀ ꢀBr1i = 3.903(4) Å, angle at
H6 = 150°] interactions are shown as orange, blue and brown dashed lines, respectively. (Colour online.)
maximum of 0.28 Å for 8. There are also variations in the Hg–Cl
bond lengths so that a general trend towards elongation of both
Hg–Cl1 and Hg–Cl2 bonds correlates with an increase in asymme-
try in the mode of coordination of the chelate. It is noted for 8 that
71.24(13)°, for the chelate angle, to 121.52(9)° for N2–Hg–Br2
(9b), and 69.75(10)° to 127.047(10)° for I1–Hg–I2 (10).
Finally, a comment on the relative orientations of the ester sub-
stituents in 8, 9a, 9b and 10 is apposite. Each ester group is twisted
out of the of the pyridyl ring to which it is connected, as quantified
by the values of the C9–C10–C13–O1 torsion angles of ꢁ13.9(5)°,
157.6(5)°, 12.6(7)° and ꢁ8.8(6)°, respectively. A difference in poly-
morphic 9a and 9b is noted in that the carbonyl–O1 atom is syn to
the chelate ring in 9a but anti in 9b; anti orientations are noted in 8
and 10. No correlation between the orientation of the ester group
and crystal packing was found.
the
l2-chlorido bridges are the most symmetric, i.e. D(Hg–
Cl1) = 0.34 Å.
It also proved possible to grow crystals of the 1:1 compounds of
each of HgBr2 and HgI2 with L5. Curiously, two polymorphic forms
of the 1:1 compound with HgBr2, namely [HgBr2L5]2 (9a) and
[HgBr2L5] (9b) were isolated, both from slow evaporation of an ace-
tonitrile solution. Polymorphs 9a and 9b each crystallize in the tri-
ꢀ
clinic space group P1 and have very similar unit cell characteristics
One other full set of HgX2, X = Cl, Br and I, structures, with an
identical (E)-N-(pyridin-2-ylmethylidene)arylamine ligand has
been reported, namely the 4-methyl derivatives, 1–3 (Scheme 1a;
Table 3) [6]. The trend towards mononuclear structures observed
for 8–10 is repeated in this series and was correlated with the in-
creased electronegativity of the chlorido ligands which enhanced
the capacity of the mercury atoms to expand their coordination
spheres and thereby dimerize.
(Table 2). The key difference between them is the formation of
intermolecular Hgꢀ ꢀ ꢀBr interactions only in the case of 9a.
In binuclear 9a (Fig. 7), molecules aggregate about a center of
inversion via asymmetric
l2-bromido bridges. In the unit cell of
9b (Fig. 8), the molecules are orientated differently with the closest
intermolecular Hgꢀ ꢀ ꢀBr contact being 4.3894(6) Å; further details
are given below. The distance of the longer Hg–Br bond of the
bridge in 9a, i.e. 3.3759(5) Å, is marginally within the sum of the
respective van der Waals radii, i.e. 3.40 Å, and this must be consid-
The final structure to be described is that of [HgCl2L4]2 (7,
Fig. 10). The L4 ligand features a CO2CH3 ester residue in the 2-po-
sition of the aryl ring and while a binuclear structure arises owing
ered a weak interaction only [13]. However, the presence of the l2
-
bromido bridge in 9a, even if weak, does have an impact upon the
geometric parameters about the mercury atom. Thus, compared
with the Hg–N bond lengths in 8, there has been a significant
reduction in asymmetry in 9a and this asymmetry is reduced even
further when intermolecular Hgꢀ ꢀ ꢀBr interactions are absent as in
9b. The differences in the shorter Hg–X bond lengths is also im-
to l2-chlorido bridges, as seen for the other HgCl2 derivatives, a
variation is observed in that the carbonyl–O1 forms a weak inter-
action, Hg–O1 = 2.764(4) Å, to the mercury atom. The presence of
the coordinating O1 atom in 7 results in an increase in the Hg–N
bond distances compared with those in the 4-substituted analog,
8 (Table 3). The Hgꢀ ꢀ ꢀCl1i bridging distance is significantly longer
in 7 than 8, i.e. 3.2330(15) cf. 2.8929(7) Å, with the result that
the Hg–Cl1 bond length is significantly reduced in 7; symmetry
operation i: ꢁx, ꢁy, ꢁz. The Cl3N2O donor set approximates a dis-
torted trigonal prism with the trigonal faces occupied by the (N1,
Cl2, Cl1i) and (N2, Cl1, O1) atoms.
pacted upon by bridging. In 8,
D(Hg–Cl) is 0.15 Å. When weak
bridging is present (9a), (Hg–Br) is 0.04 Å, and when absent
D
D
(Hg–Br) is 0.02 Å. The observed trends also apply to the isomor-
phous mononuclear HgI2 analog, [HgI2L5] (10, Fig. 9). Marked dif-
ferences are also noted in coordination geometries. In penta-
coordinated 9a, the value of
s is 0.17, indicating that in both 8
and 9a, the coordination geometry approaches square pyramidal
more so than in the other binuclear compounds reported herein.
By contrast, the coordination geometries of 9b and 10 are distorted
tetrahedral with ranges of angles subtended at mercury being
2.4. Supramolecular architectures
The crystal packing patterns in 4–10 are discussed in terms of
common types. While no classical hydrogen bonding is observed,

T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
279
Fig. 14. (a) View of the supramolecular chain aligned along the a-axis in [HgBr2L5] 9b. (b) View in projection down the a-axis of the unit cell contents, highlighting the
stacking of layers along the b-axis. The
pꢀ ꢀ ꢀp
[Cg(N1, C1–C5)ꢀ ꢀ ꢀCg(C7–C12)i = 3.687(3) Å, angle of inclination = 9.7(2)° for i: 1 ꢁ x, 1 ꢁ y, 1 ꢁ z; Cg(HgN2C2)ꢀ ꢀ ꢀCg(C7–
C12)ii = 3.880(3) Å, angle = 9.2(2)° for ii: ꢁx, 1 ꢁ y, ꢁz], C–Hꢀ ꢀ ꢀO [C5–H5ꢀ ꢀ ꢀO1iii = 2.28 Å, C5ꢀ ꢀ ꢀO1iii = 3.083(7) Å, angle at H5 = 142° for iii: 1 + x, y, ꢁ1 + z] and C–Hꢀ ꢀ ꢀBr
interactions [C6–H6ꢀ ꢀ ꢀBr2i = 2.91 Å, C6ꢀ ꢀ ꢀBr2i = 3.632(5) Å, angle at H6 = 134°] interactions are shown as orange (pink for chelate ring), blue and brown dashed lines,
respectively. (Colour online.)
p
ꢀ ꢀ ꢀ
on a chelate ring, which is known to have aromatic character
[14,15]. These sorts of interactions are increasingly being rec-
p
interactions predominate. Sometimes the
p
-system is based
a-axis are connected by
4, but in this case the columns are connected by additional
ne)ꢀ ꢀ ꢀ (arene) interactions as well as C–Hꢀ ꢀ ꢀCl contacts; the Cl2
atom is bifurcated.
p
(pyridyl)ꢀ ꢀ ꢀ
p
(arene) interactions as for
p(are-
p
ꢀ ꢀ ꢀ
p
p
ognized as being important in the supramolecular chemistry of
metal complexes [16–18]. Other interactions are often of the type,
In 5, a different pattern is observed, based on supramolecular
layers of molecules parallel to (ꢁ410). These form as a result of
C–Hꢀ ꢀ ꢀX and C–Hꢀ ꢀ ꢀ
p, again, sometimes the chelate ring defines the
-system [18–20]. Analysis of the crystal packing is based on the
p
C–Hꢀ ꢀ ꢀO, C–Hꢀ ꢀ ꢀCl (Hꢀ ꢀ ꢀCl = 2.75 Å) and
p(pyridyl)ꢀ ꢀ ꢀ
p
(arene)
standard geometric parameters embodied in PLATON [21]. Diagrams
were drawn with DIAMOND [22] and geometric parameters describ-
ing the intermolecular interactions are given in the respective fig-
ure captions.
interactions. The stacked layers are connected by p(are-
ne)ꢀ ꢀ ꢀ
p
(arene), C–Hꢀ ꢀ ꢀ (chelate) and C–Hꢀ ꢀ ꢀCl interactions
p
(Fig. 12). Analogous layers of molecules stack along the b-axis in
the crystal structure of 8 (Fig. S2) with the primary connections be-
The crystal packing of 4 is dominated by interactions occurring
tween them being of the type
In polymorph 9a, the layers are parallel to (110) and are stabi-
lized as a result of C–Hꢀ ꢀ ꢀO, C–Hꢀ ꢀ ꢀBr (Hꢀ ꢀ ꢀBr = 3.05 Å) and (pyri-
dyl)ꢀ ꢀ ꢀ (arene) interactions. The stacked layers are connected by
(arene)ꢀ ꢀ ꢀ (arene), C–Hꢀ ꢀ ꢀ (chelate) and additional C–Hꢀ ꢀ ꢀBr
interactions (Fig. 13).
p
(pyridyl)ꢀ ꢀ ꢀ
p(arene).
between
are stabilized by
p
-systems. Columns of molecules parallel to the a-axis
(pyridyl)ꢀ ꢀ ꢀ (arene) interactions, and these are
(che-
p
p
p
connected into a three-dimensional architecture by C–Hꢀ ꢀ ꢀ
p
p
late) interactions (Fig. 11). A similar pattern was observed in the
p
p
p
crystal structure of 6 (Fig. S1). Here, molecules aligned along the

280
T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
In 9b, supramolecular chains along the a-axis are formed as a
result of (arene) as well as (chelate)ꢀ ꢀ ꢀ (arene)
(pyridyl)ꢀ ꢀ ꢀ
p
p
p
p
interactions along with C–Hꢀ ꢀ ꢀBr contacts (Fig. 14a). These are con-
nected into layers by rather strong C–Hꢀ ꢀ ꢀO contacts. The layers
stack along the b-axis without specific interactions between them
(Fig. 14b). The crystal structure of 10 is isomorphous with 9b and
full details are given in the Supplementary materials (Fig. S3).
The polymorphic structures of 9a and 9b have clearly distin-
guishable patterns of packing with the stark difference relating
to the relative orientations of the HgBr2 fragments. In 9a, where
these approach each other via Hgꢀ ꢀ ꢀBr interactions, the packing in-
dex computes to 74.0%. A significantly less efficient packing index
of 68.5% is found for 9b, suggesting that 9a is thermodynamically
more stable.
Finally, the molecules in the crystal structure of [HgCl2L4]2 7 are
linked into layers in the bc-plane by
p
(chelate)ꢀ ꢀ ꢀ
p(arene) and C–
Hꢀ ꢀ ꢀO contacts (Fig. 15a) and consolidated into a three-dimen-
sional architecture by C–Hꢀ ꢀ ꢀBr contacts (Fig. 15b).
3. Conclusion
On the basis of the newly described structures and those of lit-
erature precedents, the preponderance of binuclear structures ob-
served when HgCl2 is complexed with (E)-N-(pyridin-2-
ylmethylidene)arylamine ligands is not repeated in the HgBr2
and HgI2 analogs, an observation correlated with the enhanced Le-
wis acidity of the mercury centers when X = Cl. Within the series of
HgCl2 compounds with (E)-N-(pyridin-2-ylmethylidene)-4-substi-
tuted-phenylamines, asymmetry in the mode of coordination of
the chelate could be moderated by increasing the electronegativity
of the substituent, owing to the weakening of the Hg–N(imino)
bond.
4. Experimental
4.1. General considerations
Caution! Compounds of mercury are highly toxic [23]. Care
must be taken when handling samples, and appropriate disposal
procedures are necessary. All chemicals were used as purchased
without purification: HgCl2, pyridine-2-carboxaldehyde (Merck),
HgBr2, HgI2 (Fine Chemicals), p-ethylaniline (Aldrich), p-ethoxylan-
iline (Across), p-chloroaniline, methylanthranilate, p-aminoben-
zoic acid (Hi-Media). Methyl p-aminobenzoate was prepared by
reacting p-aminobenzoic acid and SOCl2 in methanol by literature
method [24]. The (E)-N-(pyridin-2-ylmethylidene)arylamine deriv-
atives L1–L5 were prepared in situ from pyridine-2-carboxaldehyde
and the corresponding aniline. Solvents were purified by standard
procedures and were freshly distilled prior to use. Elemental anal-
yses, solution electrical conductivity measurements, IR, 1H NMR
and UV–Vis spectra were recorded on instruments and under con-
ditions as described elsewhere [6]. Fluorescence spectra were ob-
tained on a Hitachi model FL4500 spectrofluorimeter (with the
excitation and emission slits fixed at 10 and 20 nm, respectively)
and all spectra were corrected for the instrument response func-
tion and conditions as described earlier [6].
Fig. 15. (a) View of the supramolecular layer in [HgCl2L4]2 7. (b) View in projection
down the a-axis of the unit cell contents, highlighting the stacking of layers along
the a-axis and the C–Hꢀ ꢀ ꢀCl connections between them. The
pꢀ ꢀ ꢀp [Cg(HgN2C2)-
ꢀ ꢀ ꢀCg(C7–C12)i = 3.821(3) Å, angle of inclination = 3.2(2)° for i: 1 ꢁ x, ꢁy, 1 ꢁ z], C–
Hꢀ ꢀ ꢀO [C3–H3ꢀ ꢀ ꢀO1i = 2.60 Å, C3ꢀ ꢀ ꢀO1i = 3.418(7) Å, angle at H3 = 146°; C11–
H11ꢀ ꢀ ꢀO1ii = 2.54 Å, C11ꢀ ꢀ ꢀO1ii = 3.291(8) Å, angle at H3 = 136° for ii: x, ½ ꢁ y,
ꢁ½ + z] and C–Hꢀ ꢀ ꢀCl [C6–H6ꢀ ꢀ ꢀCl2iii = 2.73 Å, C6ꢀ ꢀ ꢀCl2iii = 3.559(6) Å, angle at
H5 = 146° for iii: 1 + x, y, z; C9–H9ꢀ ꢀ ꢀCl1iii = 2.81 Å, C9ꢀ ꢀ ꢀCl1iii = 3.558(7) Å, angle
at H5 = 136°] interactions are shown as orange, blue and brown dashed lines,
respectively. (Colour online.)
4.2. Synthesis of mercury compounds (4–10)
The preparations of the dihalomercury(II) compounds 4–10 are
very similar, so that the preparation of the dichloride derivative 4
is given here as a representative case.

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281
4.2.1. [HgCl2L1]2 (4)
5.47. Found: C, 33.05; H, 2.52; N, 5.86%. dm (CH3CN): 6
X
ꢁ1 cm2 -
To a solution of pyridine-2-carboxaldehyde (0.13 g, 1.23 mmol)
in ethanol (3 ml) was added a solution of p-ethylaniline (0.15 g,
1.23 mmol) in ethanol (2 ml). The mixture was stirred at ambient
temperature for 30 min. To this reaction mixture, a solution of
HgCl2 (0.33 g, 1.22 mmol) in methanol (20 ml) was added drop-
wise under stirring conditions which resulted in the immediate
formation of a yellow precipitate. The stirring was continued for
3 h and then the mixture was filtered. The residue was washed
with methanol (3 ꢃ 5 ml) and dried in vacuo. The dried solid was
dissolved by boiling in 40 ml of acetonitrile and filtered while
hot. The filtrate, upon cooling to r.t., afforded a yellow crystalline
material. Yield 0.29 g (47%). M.p. 213–215 °C. Anal. Calc. for C28H28-
Cl4Hg2N4: C, 34.88; H, 2.93; N, 5.82. Found: C, 34.80; H, 3.12; N,
molꢁ1. IR (cmꢁ1): 1712
m
asym(OCO), 1622
m
asym(C(H)@N); 1593,
1
1427
m
(C@N)py. H NMR (DMSO-d6): 8.92 [d, J = 4.0 Hz, 1H, H-30],
8.90 [s, 1H, H-7], 8.13 [t, J = 8.0 Hz, 1H, H-60], 8.05 [d, J = 8.0 Hz,
1H, H-50], 7.80 [t, J = 6.4 Hz, 1H, H-40], 7.59 [d, 2H, J = 8.0 Hz, H-
3,5], 6.64 [d, 2H, J = 8.0 Hz, H-2,6], 3.94 [s, 3H, CO2CH3] ppm.
4.2.6. HgBr2L5 (9)
A similar synthetic procedure as for 4 was used except that
HgCl2 and p-ethylaniline were replaced by HgBr2 and methyl p-
aminobenzoate, giving pale yellow crystals. Yield 52%. Crystals of
compound [HgBr2L5]2: 9a and HgBr2L5: 9b (both prism type, gave
similar microanalytical and spectroscopic data and were indistin-
guishable) were obtained from acetonitrile from two different
batches of samples (see X-ray discussion for structural details).
M.p.: 9a 218–220 °C; 9b 143–145 °C. Anal. Calc. for C28H24Br4Hg2-
N4O4: C, 27.98; H, 2.01; N, 4.66. Found: C, 28.50; H, 2.10; N,
5.80%. dm (CH3CN):
(C(H)@N); 1592, 1485, 1439
6
X
ꢁ1 cm2 molꢁ1
.
IR (cmꢁ1): 1622 masym
m
(C@N)py. 1H NMR (DMSO-d6): 8.93
[s, 1H, H-7], 8.55 [d, J = 4.0 Hz, 1H, H-3’], 8.11 [t, J = 8.0 Hz, 1H,
H-60], 8.02 [d, J = 8.0 Hz, 1H, H-50], 7.72 [t, J = 6.4 Hz, 1H, H-40],
7.53 [d, J = 8.0 Hz, 2H, H-3,5], 7.31 [d, J = 8.0 Hz, 2H, H-2,6], 2.67
[q, 2H, CH2], 1.26 [t, 3H, CH3] ppm.
Compounds 5–10 were prepared as yellow crystals in a manner
similar to that described for the preparation of 4, using appropriate
anilines and mercury(II) halides as starting materials.
4.80%. dm (CH3CN): 6
X
ꢁ1 cm2 molꢁ1. IR (cmꢁ1): 1712
(C@N)py. 1H NMR (DMSO-d6):
masym(OCO),
1646 asym(C(H)@N); 1593, 1434
m
m
9.02 [s, 1H, H-7], 8.89 [d, J = 4.0 Hz, 1H, H-30], 8.15 [m, 4H, H-
50,60,3,5], 7.79 [t, J = 6.4 Hz, 1H, H-40], 7.61 [d, J = 8.0 Hz, 2H, H-
2,6], 3.94 [s, 3H, CO2CH3] ppm.
4.2.7. [HgI2L5]2 (10)
4.2.2. [HgCl2L2]2 (5)
A similar synthetic procedure as for 4 was used except that
HgCl2 and p-ethylaniline were replaced by HgI2 and methyl p-ami-
nobenzoate, giving pale yellow crystals. Yield 49%. M.p. 198–
200 °C. Found: C, 24.40; H, 1.52; N, 4.17%. Calc. for C14H12I2HgN2-
A similar synthetic procedure as for 4 was used except that p-
ethylaniline was replaced by p-ethoxylaniline, giving pale yellow
crystals from acetonitrile solution. Yield 46%. M.p. 194–195 °C.
Anal. Calc. for C28H28Cl4Hg2N4O2: C, 33.76; H, 2.84; N, 5.63. Found:
O2: C, 24.19; H, 1.74; N, 4.03%. dm (CH3CN): 7
X
ꢁ1 cm2 molꢁ1. IR
C, 33.85; H, 2.99; N, 5.80%. dm (CH3CN): 6
X
ꢁ1 cm2 molꢁ1. IR
(C@N)py. 1H
(cmꢁ1):1712
m
asym(OCO), 1639 asym(C(H)@N); 1553, 1434
m
(cmꢁ1): 1623
masym(C(H)@N); 1588, 1476, 1445
m
m
(C@N)py. 1H NMR (DMSO-d6): 9.11 [s, 1H, H-7], 8.81 [d,
NMR (DMSO-d6): 8.97 [s, 1H, H-7], 8.88 [d, J = 4.0 Hz, 1H, H-30],
8.10 [m, 2H, H-50,60], 7.70 [t, br, 1H, H-40], 7.59 [d, J = 8.0 Hz, 2H,
H-3,5], 6.68 [d, J = 8.0 Hz, 2H, H-2,6], 4.08 [q, 2H, CH2], 1.42 [t,
3H, CH3] ppm.
J = 4.0 Hz, 1H, H-30], 8.18 [t, br, 1H, H-60], 8.13 [d, J = 8.0 Hz, 2H,
H-3,5], 7.96 [d, br, 1H, H-50], 7.80 [t, br, 1H, H-40], 7.65 [d,
J = 8.0 Hz, 2H, H-2,6], 3.93 [s, 3H, CO2CH3] ppm.
4.3. X-ray data collection and structure determinations
4.2.3. [HgCl2L3]2 (6)
A similar synthetic procedure as for 4 was used except that p-
ethylaniline was replaced by p-chloroaniline, giving pale yellow
crystals from acetonitrile solution. Yield 40%. M.p. 243–245 °C.
Anal. Calc. for C24H18Cl6Hg2N4: C, 29.51; H, 1.86; N, 5.74. Found:
Crystals of compounds suitable for an X-ray crystal-structure
determination were obtained from acetonitrile (4, 6, 9a, 9b and
10), acetonitrile/acetone (7) and acetonitrile/methanol (5 and 8)
by slow evaporation of the solvent at room temperature. In the
case of compound 9, two crystalline polymorphs (9a and 9b) were
isolated from two different batches of crystals obtained from ace-
tonitrile solution. The measurements for 5, 7 and 10 were made at
low temperature on a Nonius KappaCCD diffractometer [25] with
C, 29.60; H, 1.68; N, 5.79%. dm (CH3CN): 8
X
ꢁ1 cm2 molꢁ1. IR
(C@N)py. 1H
(cmꢁ1): 1618
masym(C(H)@N); 1589, 1482, 1436
m
NMR (DMSO-d6): 8.89 [d, J = 4.0 Hz, 1H, H-30], 8.87 [s, 1H, H-7],
8.10 [m, 2H, H-50,60], 7.70 [t, br, 1H, H-40], 7.50 [d, J = 8.0 Hz, 2H,
H-3,5], 7.44 [d, J = 8.0 Hz, 2H, H-2,6] ppm.
graphite-monochromated Mo Ka radiation (k = 0.71073 Å) and an
Oxford Cryosystems Cryostream 700 cooler. The data for 8, 9a
and 9b were recorded on an Agilent Technologies SuperNova
4.2.4. [HgCl2L4]2 (7)
A similar synthetic procedure as for 4 was used except that p-
ethylaniline was replaced by methylanthranilate and reaction
was conducted under ice-cold conditions, giving pale yellow single
crystals from acetonitrile solution. Yield 50%. M.p.158–160 °C.
Anal. Calc. for C28H24Cl4Hg2N4O4: C, 32.84; H, 2.36; N, 5.47. Found:
area-detector diffractometer [26] using Mo Ka radiation from a mi-
cro-focus X-ray source and an Oxford Instruments Cryojet XL cooler,
while the data for 4 and 6 were recorded on a Bruker-APEX diffrac-
tometer equipped with a CCD area detector and Mo Ka radiation.
Data reduction on 5, 7 and 10 was performed with HKL Denzo
and Scalepack [27], with CrysAlisPro [26] for 8, 9a and 9b, and with
SAINT [28] for 4 and 6. The intensities were corrected for Lorentz and
polarization effects. An empirical absorption correction based on
the multi-scan method [29,30] using spherical harmonics was ap-
plied for 4–8, an analytical absorption correction [31] was applied
for 9a and 9b and a numerical absorption correction [32] was ap-
plied for 10. Equivalent reflections were merged. The structures
of compounds 5, 7 and 10 were solved by heavy-atom Patterson
methods [33], which initially revealed the position of the mercury
atom, while all remaining non-hydrogen atoms were located in a
Fourier expansion of the Patterson solution, which was performed
by DIRDIF94 [34]. The structures of 4, 6, 8, 9a and 9b were solved
by direct methods using SHELXS97 [35], which revealed the positions
C, 33.85; H, 2.42; N, 5.57%. dm (CH3CN): 8
(cmꢁ1): 1700
asym(OCO), 1620 asym(C(H)@N); 1592, 1485, 1438
(C@N)py. 1H NMR (DMSO-d6): 10.14 [s, 1H, H-7], 8.83 [d,
X
ꢁ1 cm2 molꢁ1. IR
m
m
m
J = 4.0 Hz, 1H, H-30], 7.95 [m, 2H, H-3,4], 7.83 [d, J = 8.0 Hz, 1H,
H-60], 7.60 [t, J = 8.0 Hz, 1H, H-50], 7.26 [t, J = 6.4 Hz, 1H, H-5],
6.70 [d, J = 6.4 Hz, 1H, H-6], 6.62 [t, J = 6.4 Hz, 1H, H-40], 3.86 [s,
3H, OCOCH3] ppm.
4.2.5. [HgCl2L5]2 (8)
A similar synthetic procedure as for 4 was used except that p-
ethylaniline was replaced by methyl p-aminobenzoate, giving pale
yellow crystals from acetonitrile solution. Yield 50%. M.p. 208–
210 °C. Anal. Calc. for C28H24Cl4Hg2N4O4: C, 32.84; H, 2.36; N,

282
T.S. Basu Baul et al. / Polyhedron 55 (2013) 270–282
of all non-hydrogen atoms. The non-hydrogen atoms in each struc-
ture were refined anisotropically. All of the H-atoms were placed in
geometrically calculated positions and refined by using a riding
model where each H-atom was assigned an isotropic displacement
parameter with a value equal to 1.2 Ueq of its parent atom (1.5 Ueq
for methyl–H). The refinement of each structure was carried out on
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.poly.2013.03.025.
F2 by using full-matrix least-squares procedures, which minimized
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The financial support of the Department of Science & Technol-
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Appendix A. Supplementary data
CCDC 915973–915980 contains the supplementary crystallo-
graphic data for 10, 4–8, 9a and 9b. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or