Influence of halogen bonding interaction on supramolecular assembly of coordination compounds; Head-to-tail N···X synthon repetitivity

Article abstract of DOI:10.1021/ic3021113

In this study, N-(3-halophenyl)-2-pyrazinecarboxamide ligands, L ^3-F, L^3-Cl, L^3-Br, and L^3-I, carrying a different halogen atom on the phenyl meta-position and N-phenyl-2-pyrazinecarboxamide ligand, L^H, have been employed for the synthesis of 12 mercury(II) complexes, [HgCl₂(L^H)] _n, 1, [HgCl₂(L^3-Cl)]_n, 2, [Hg ₂Cl₄(L^3-Br)₂], 3, [Hg ₂Cl₄(L^3-I)₂], 4, [Hg ₂Br₄(L^H)₂], 5, [HgBr ₂(L^3-F)], 6, [HgBr₂(L^3-Cl)], 7, [HgBr₂(L^3-Br)], 8, [HgBr₂(L^3-I)], 9, [Hg₂I₄(L^H)₂], 10, [HgI ₂(L^3-Br)], 11, and [HgI₂(L^3-I)] _n, 12. Interestingly, structural analysis clearly shows that, by the replacing of coordinated anions from chloride with bromide and iodide in each series containing the same ligand, the coordination geometry and structural motif of the resulting compounds have been dramatically affected. One of the common features in the crystal structures of these complexes is that there is a strong tendency to form halogen bonding synthons between adjacent halophenyl and pyrazine rings. The influence of these halogen bonding interactions on the supramolecular assemblies has been discussed with the help of geometrical analysis and theoretical calculations. The X···N halogen bonding distances are 2.5-9.4% shorter than the sum of the van der Waals radii of nitrogen and halogen atoms. Theoretical methods also show the halogen bonding energies within a range of -27.86 to -46.15 kJ·mol^-1. In all complexes synthesized here, the pyrazine ring is coordinated to the mercury(II) ion through the N atom syn to the carbonyl. Therefore, the second common feature of the crystal structures for complexes studied here is the selectivity of the metal ion coordination site. The halogen bond synthon repetitivity across these compounds and selectivity in the mercury(II) ion coordination site further point to application in the coordination crystal engineering research field.

Full text of DOI:10.1021/ic3021113

Article
pubs.acs.org/IC
Influence of Halogen Bonding Interaction on Supramolecular
Assembly of Coordination Compounds; Head-to-Tail N···X Synthon
Repetitivity
Hamid Reza Khavasi* and Alireza Azhdari Tehrani
Faculty of Chemistry, Shahid Beheshti University, General Campus, Evin, Tehran 1983963113, Iran
S
* Supporting Information
ABSTRACT: In this study, N-(3-halophenyl)-2-pyrazinecarboxamide ligands, L3‑F, L3‑Cl, L3‑Br, and L3‑I, carrying a different
halogen atom on the phenyl meta-position and N-phenyl-2-pyrazinecarboxamide ligand, LH, have been employed for the
synthesis of 12 mercury(II) complexes, [HgCl2(LH)]n, 1, [HgCl2(L3‑Cl)]n, 2, [Hg2Cl4(L3‑Br)2], 3, [Hg2Cl4(L3‑I)2], 4,
[Hg2Br4(LH)2], 5, [HgBr2(L3‑F)], 6, [HgBr2(L3‑Cl)], 7, [HgBr2(L3‑Br)], 8, [HgBr2(L3‑I)], 9, [Hg2I4(LH)2], 10, [HgI2(L3‑Br)],
11, and [HgI2(L3‑I)]n, 12. Interestingly, structural analysis clearly shows that, by the replacing of coordinated anions from
chloride with bromide and iodide in each series containing the same ligand, the coordination geometry and structural motif of the
resulting compounds have been dramatically affected. One of the common features in the crystal structures of these complexes is
that there is a strong tendency to form halogen bonding synthons between adjacent halophenyl and pyrazine rings. The influence
of these halogen bonding interactions on the supramolecular assemblies has been discussed with the help of geometrical analysis
and theoretical calculations. The X···N halogen bonding distances are 2.5−9.4% shorter than the sum of the van der Waals radii
of nitrogen and halogen atoms. Theoretical methods also show the halogen bonding energies within a range of −27.86 to −46.15
kJ·mol−1. In all complexes synthesized here, the pyrazine ring is coordinated to the mercury(II) ion through the N atom syn to
the carbonyl. Therefore, the second common feature of the crystal structures for complexes studied here is the selectivity of the
metal ion coordination site. The halogen bond synthon repetitivity across these compounds and selectivity in the mercury(II) ion
coordination site further point to application in the coordination crystal engineering research field.
refers to any noncovalent interaction involving a halogen as the
acceptor of electron density, a Lewis acid, and an electron-
donating atom, D, as a Lewis base.3 Various types of XB,
including R-X···Nu, X2···Nu, R-X1···X2-R, R-X1···X2-M, and R-
X1···X2−, where Nu is a nucleophile, R-Xi is a haloalkyl group, X2
is a dihalogen molecule, Xi− is a halide anion, and M is a metal,
have been studied in detail.4 Although the role of XB in metal-
containing crystal structures and analogies and differences with
respect to hydrogen bonds have been reviewed by Brammer5 and
INTRODUCTION
■
Structural assemblies in coordination compounds rely on a range
of directional and nondirectional intermolecular interactions to
hold the components together. The most extensively exploited of
these interactions is highly directional hydrogen bonding.1 The
influence of π···π, cation···π, anion···π, lone-pair···π, and
metal···π interactions is also well accepted among supra-
molecular coordination chemists.2 Another interaction that has
more recently become of interest as a construction tool in the
field of crystal engineering is directional attractive halogen
bonding interaction (hereafter referred to as XB). The XB,
denoted in the general form D···X−Y (Y = C, N, halogen, etc.),
Received: September 28, 2012
© XXXX American Chemical Society
A
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Inorganic Chemistry
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Bertani and co-workers,6 compared to organic systems, to our
knowledge, far less attention has been paid to systematic studies
that examine the effect of halogen bonding on the supra-
molecular aggregation of coordination complexes. To make
progress in controlling specific interactions in the solid state of
coordination compounds, it is desirable to synthesize a series of
coordination compounds of predetermined chemical structure,
allowing for a comparison between assemblies with specific and
controllable changes to their molecular structure.
Scheme 1. Synthetic Route of 1−12 and Presence of Halogen
Bond Synthons (Red Band)
Recently, the possibility of using CO···X (X = Cl, Br, I)
halogen bonds for directed assembly in copper(II) coordination
compounds containing β-diketonate moieties bearing chloro,
bromo, and iodo substituents has been systematically studied by
Aakeroy and co-workers.7 In 2008, competition between
̈
coordination network formation and halogen bond network
formation using copper(II) iodobenzoate units was reported by
Brammer and co-workers.8
On the other hand, with the exploration of how weak
interactions work individually or cooperatively in the supra-
molecular structure, the identification of reproducible synthons
in the supramolecular structures is an important line of research.9
In this regard, even failed attempts at supramolecular assembly
can offer some insight into discovering how intermolecular
interactions can be ranked in terms of structural effectiveness.
Assembly of discrete copper(II) and cobalt(II) coordination
compounds into 1D linear chains using halogen bond
interactions has been investigated by Aakeroy, and the results
̈
showed that attempts at creating desired architectures had
failed.10 In Ward and co-worker’s paper, the repetitivity of C−
I···NC(Ru) halogen bonds in [Ru(bipy)(CN)4]2− salts contain-
ing iodinated cations has been shown, while the analogous
brominated cations do not exhibit halogen bond interactions.11
During our research effort on π−π stacking,12a C−H···π12b
interaction, and ligand substituent effect12c in the crystal packing
of mercury coordination compounds containing pyrazine
carboxamide ligands, that the authors are developing, the effect
of halogen bonding on the three-dimensional supramolecular
architecture of coordination compounds has herein been
reported. In this Article, a series of N-(3-halophenyl)-2-
pyrazinecarboxamide ligands, L3‑F, L3‑Cl, L3‑Br, and L3‑I, and N-
phenyl-2-pyrazinecarboxamide ligand, LH (Scheme 1), carrying a
different halogen atom in the phenyl meta-position, have been
employed for the synthesis of mercury(II) complexes in order to
get insights into the effect of halogen bonding interactions on the
structural assembly of the complexes. Because of the freedom of
C−C and C−N single bond rotations in these ligands, the
pyrazine and halophenyl rings can be freely twisted to meet the
requirements of the coordination geometries of metal atoms and
intermolecular interactions in the assembly process. Twelve
Hg(II) complexes of these ligands, [HgCl2(LH)]n, 1, [HgCl2-
(L3‑Cl)]n, 2, [Hg2Cl4(L3‑Br)2], 3, [Hg2Cl4(L3‑I)2], 4, [Hg2Br4-
(LH)2], 5, [HgBr2(L3‑F)], 6, [HgBr2(L3‑Cl)], 7, [HgBr2(L3‑Br)], 8,
[HgBr2(L3‑I)], 9, [Hg2I4(LH)2], 10, [HgI2(L3‑Br)], 11, and
[HgI2(L3‑I)]n, 12, have been prepared by the reaction of
equimolar quantities of mercury(II) halides (chloride, bromide,
and iodide) in a methanol solution (Scheme 1). The structural
details show that the presence of Cl, Br, and I atoms in the meta-
position of the N-phenyl ring significantly influences the
structural assembly of the resulting mercury(II) complexes and
the ligands are pointed toward the adjacent molecules to
generate simple or head-to-tail N···X (X = Cl, Br, I) halogen
bond synthons.
RESULTS AND DISCUSSION
■
Synthesis. The ligands LH, L3‑F, L3‑Cl, L3‑Br, and L3‑I were
prepared by simply mixing the same equivalents of meta-
haloaniline or aniline and pyrazinecarboxylic acid in pyridine in
the presence of triphenyl phosphite.13 The reaction of equimolar
B
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Table 1. Structural Data and Refinement Parameters for Compounds 1−12
1
2
3
4
5
6
formula
fw
C11H9Cl2HgN3O
470.70
C11H8Cl3HgN3O
505.14
C22H16Br2Cl4Hg2N6O2
1099.18
monoclinic
P21/c
C22H16Cl4Hg2I2N6O2
1193.18
monoclinic
P21/c
C22H18Br4Hg2N6O2
1119.20
monoclinic
P21/n
C11H8Br2FHgN3O
577.59
orthorhombic
Pbca
cryst syst
space group
a (Å)
monoclinic
P21/c
triclinic
P1
̅
7.1019(11)
11.2071(19)
16.435(2)
90
3.9330(8)
12.012(2)
15.803(3)
109.56(3)
96.68(3)
98.47(3)
684.8(2)
2.450
16.4086(2)
13.2074(2)
13.1793(2)
90
16.5955(12)
13.4945(7)
13.4342(9)
90
7.2762(10)
15.4995(14)
12.0093(16)
90
6.7945(4)
12.5409(12)
33.507(2)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
91.144(12)
90
104.4990(10)
90
104.954(6)
90
92.121(11)
90
90
90
1307.8(3)
2.391
2765.19(7)
2.640
2906.7(3)
2.727
1353.5(3)
2.746
2855.1(4)
2.688
D
calc (Mg·m−3
)
Z
4
2
4
4
2
8
μ (mm−1
F(000)
)
12.167
11.816
468
14.402
13.076
17.266
16.385
2096
872
2016
2160
1016
2θ (deg)
R (int)
58.40
54.00
58.60
58.60
58.42
58.66
0.0616
0.1097
1.08
0.0519
0.0729
0.1008
0.2859
1.38
GOF
1.12
1.04
1.12
1.20
a
R1 (I > 2σ(I))
0.044
0.047
0.029
0.052
0.054
0.179
b
wR2 (I > 2σ(I))
0.140
0.115
0.053
0.124
0.139
0.360
final electron
1.86, −1.97
1.63, −1.66
1.26, −1.20
2.06, −2.22
1.77, −3.76
1.74, −1.44
density (e·Å−3
)
CCDC No.
901972
901975
901970
912465
901971
901981
7
8
9
10
11
12
formula
fw
C11H8Br2ClHgN3O
594.04
C11H8Br3HgN3O
638.49
C11H8Br2HgIN3O
C22H18Hg2I4N6O2
1307.20
monoclinic
C2/c
C11H8BrHgI2N3O
732.49
C11H8HgI3N3O
779.49
685.49
cryst syst
space group
a (Å)
orthorhombic
Cmca
monoclinic
C2/m
monoclinic
C2/m
monoclinic
C2/m
monoclinic
C2/m
6.6796(13)
13.257(3)
33.744(7)
90
13.3681(17)
6.6595(9)
17.1358(18)
103.551(9)
1483.0(3)
2.860
13.681(13)
6.6901(17)
17.162(4)
104.740(18)
1519.0(6)
2.997
7.2849(11)
12.5265(14)
33.5265(4)
91.415(11)
3043.7(7)
2.853
13.609(2)
6.9070(10)
17.596(3)
102.494(12)
1614.8(4)
3.013
13.9063(13)
6.9034(7)
17.5611(17)
103.402(7)
1640.0(3)
3.157
b (Å)
c (Å)
β (deg)
V (Å3)
Dcalc (Mg·m−3
2988.1(10)
2.641
)
Z
8
4
4
4
4
4
μ (mm−1
)
15.823
18.455
17.419
14.162
15.824
15.028
F(000)
2160
1152
1224
2320
1296
1368
2θ (deg)
R (int)
58.50
58.64
58.74
58.56
58.44
58.34
0.1265
0.1275
0.1489
0.1118
0.1049
0.0725
GOF
1.17
1.15
1.19
1.07
1.26
1.09
a
R1 (I > 2σ(I))
0.059
0.094
0.077
0.131
0.063
0.047
b
wR2 (I > 2σ(I))
0.141
0.239
0.193
0.358
0.175
0.126
final electron density (e·Å−3
)
2.27, −2.54
901978
2.19, −2.71
901973
3.25, −2.12
901974
1.70, −1.31
901980
2.12, −4.86
901979
2.56, −2.30
901977
CCDC No.
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = [∑(w(Fo − Fc2)2)/∑w(Fo )2]1/2
.
amounts of these ligands and HgX2 (X = Cl, Br, and I) in
methanol gave the corresponding complexes. Slow evaporation
of the solvent resulted in air-stable block crystals of 1, 3−5, 8, and
10−12; prism crystals of 2, 7, and 9; and needle crystals of 6, after
a few days. Attempts were made to form complexes with HgCl2
and HgI2 using the L3‑F ligand and HgI2 using the L3‑Cl ligand. Yet
unfortunately, no mercury-containing species were isolated from
the reaction mixtures. Crystallographic data for compounds 1−
12 are listed in Table 1. Selected bond distances and angles are
summarized in Table 2.
unit of 1 consists of one crystallographically independent Hg2+
ion, one N-phenyl-2-pyrazinecarboxamide, LH, and two chloride
ions. As depicted in Figure 1a, in this compound, the highly
distorted tetrahedral geometry of the Hg(II) center can be better
described as a seesaw structure. The Cl−Hg−Cl angle is
176.17(10)°, where the two Hg−Cl bonds form the plank (Table
2). The angle between the other two bonds (Table 2), which
form the pivot, is 90.0(2)°. The Cl−Hg−Cl and N−Hg−O
planes are nearly perpendicular, with a dihedral angle of 87.0(4)°.
For this complex, the four-coordinate geometry index, τ4, of 0.64
fits with a seesaw description.14
Structural Analysis of HgCl2 Complexes, [HgCl2(LH)]n, 1,
[HgCl2(L3‑Cl)]n, 2, [Hg2Cl4(L3‑Br)2], 3, and [Hg2Cl4(L3‑I)2], 4. A
simple reaction between HgCl2 and LH, L3‑Cl, L3‑Br, and L3‑I in
methanol afforded well-formed crystals of 1−4. The asymmetric
Compound 2 crystallizes in the P1 space group. The
̅
asymmetric unit of 2 consists of one Hg2+ ion, two halogen
anions, and one crystallographically independent ligand. As
C
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Table 2. Selected Bond Lengths (Å) and Angles (deg) around Mercury(II) for Complexes 1−12
complex
1
2
3
4
5
6
bond distance
Hg1−X1
Hg1−X1
2.289(2)
2.3464(18)
2.3106(6)
2.295(2)
2.4147(10)
2.443(4)
a
3.047(2)
Hg1−X2
Hg1−X2
Hg1−O1
Hg1−N2
Hg2−X3
Hg2−X4
Hg2−O1
Hg2−N5
X1−Hg1−X2
X1−Hg1−X2
X1−Hg1−X1
X2−Hg1−X2
X1−Hg1−O1
X2−Hg1−O1
X1−Hg1−N2
X2−Hg1−N2
X1−Hg1−N2
X2−Hg1−N2
N1−Hg1−O1
Hg1−O1C5
X3−Hg2−X4
X3−Hg2-N5
X3−Hg2−O1
X4−Hg2−N5
X4−Hg2−O1
N5−Hg2−O1
Hg2−O1C5
2.303(2)
2.3375(19)
2.3089(7)
2.294(2)
2.4293(0)
2.462(4)
b
3.044(2)
a
c
2.748(6)
2.656(8)
2.949(7)
2.575(5)
2.573(2)
2.3340(7)
2.3088(7)
2.815(2)
2.516(2)
169.44(2)
2.599(7)
2.300(2)
2.325(2)
2.822(7)
2.551(9)
169.81(9)
2.514(7)
2.49(3)
bond angle
176.17(10)
173.26(6)
161.93(4)
163.90(15)
a
92.71(6)
b
86.82(6)
b
92.98(6)
a
92.0(1)
105.8(1)
82.8(1)
101.3(2)
95.8(2)
a
86.6(1)
93.18(18)
90.40(17)
93.01(15)
93.73(14)
94.30(5)
95.36(5)
94.34(17)
95.12(17)
98.2(7)
97.9(7)
a
91.5(5)
b
93.7(1)
a
c
90.0(2)
79.4(2)
a
c
125.4(5)
114.8(5)
166.36(3)
93.57(6)
98.53(5)
99.15(6)
88.49(5)
80.48(7)
106.8(2)
166.00(9)
99.32(17)
89.4(1)
93.77(17)
97.3(1)
82.34(16)
109.0(5)
complex
7
8
9
10
11
12
bond distance
bond angle
Hg1−X1
Hg1−X1
Hg1-X2
2.4639(12)
2.459(2)
2.4569(18)
2.622(2)
2.6381(10)
2.6394(8)
d
e
f
3.512(3)
3.4957(5)
3.5182(4)
25953(8)
2.484(7)
155.95(3)
2.4287(14)
2.469(10)
161.05(5)
2.424(2)
2.480(13)
160.26(9)
2.420(2)
2.449(13)
159.07(8)
2.602(2)
2.54(3)
2.5950(11)
2.474(10)
156.92(4)
Hg1−N2
X1−Hg1−X2
X1−Hg1−X2
X1−Hg1−X1
X1−Hg1−N2
X2−Hg1−N2
163.17(10)
e
f
93.63(3)
94.46(2)
d
e
f
92.61(8)
89.84(3)
90.06(2)
98.3(3)
98.2(4)
98.8(3)
98.4(7)
97.6(7)
102.0(2)
101.0(2)
102.3(2)
101.8(2)
100.6(2)
101.6(4)
102.1(3)
e
f
X1−Hg1-N2
94.24(8)
81.3(2)
79.1(2)
a
b
c
d
Symmetry codes: 1 + x, y, z. Symmetry codes: −1 + x, y, z. Symmetry codes: −x, 2 − y, 2 − z. Symmetry codes: 1/2 − x, 1/2 − y, −z.
Symmetry codes: 3/2 − x, −1/2 + y, −z. Symmetry codes: 1/2 − x, −1/2 + y, 1 − z.
e
f
depicted in Figure 1b, the coordination geometry around the
metal center is a square-based pyramid (SBP) (Table 2) with a
trigonality index, τ5,15 of 0.03. In this structure, the plane of the
square-based pyramid is occupied by four halogen anions (Table
2). The apical position is occupied by a nitrogen atom from the
pyrazine ring of the L3‑Cl ligand at a normal distance of 2.575(5)
Å. As it is clear from the τ5 value and geometrical parameters
around the central metal atom (Table 2), the coordination
geometry around Hg(II) is almost perfect SBP.
Dinuclear isostructural compounds 3 and 4 consist of two
different mercury environments. In these compounds, each
asymmetric unit consists of two crystallographically independent
mercury centers, four chloride ions, and two neutral L3‑Br or L3‑I
ligands (Figure 1c,d). The Hg1 atom is located in a three
coordination environment, chelating with two chloride atoms
and one pyrazine nitrogen atom from the ligand L3‑X (X = Br, I)
(Table 2). The Cl−Hg−Cl angle of 169.44(2)° and 169.81(9)°
for 3 and 4, respectively, shows that the geometry around the
metal center is slightly distorted T-shaped. In these compounds,
the L3‑X ligand acts as an angular bridge via the carbonyl oxygen
and the pyrazine nitrogen atoms to link Hg1 and Hg2 ions. The
coordination geometry around the Hg2 atom in compounds 3
and 4 can be described as a seesaw structure with a τ4 index of
0.67 for both complexes, with nearly linear Cl−Hg−Cl (Table 2)
forming the plank, and N−Hg−O (Table 2) for 3 and 4 forming
the pivot. The dihedral angles between the Cl−Hg−Cl and N−
Hg−O planes are 83.78(6)° and 84.91(7)° for 3 and 4,
D
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In 1, the adjacent mercury atoms are linked by CO−Hg
bonds to form a 1D linear polymeric chain spanning along the a
axis (Figure 2a). In this compound, the phenyl ring involved in
Figure 2. Representation of 1D linear polymeric chain in 1 (a), and a
side view representation of 1 in the a direction showing the association
of the adjacent molecules in the chain, through an additional head-to-tail
Cphen−H···Cl−Hg and CO···H−Cphen nonclassical hydrogen bonds
and Hg···Cl contacts and Hg···πphen intermolecular interactions (b). In
(b), different colors show different adjacent linear chains.
the intramolecular π−π stacking interaction with the adjecent
pyrazine rings is arranged in such a way that the angle between
the plane (containing C−CO−N fragment) normal and the O−
Hg vector (for geometrical definition, see ref 12a) reaches about
36.81(6)°. In πphen···πpyz interactions, the centroid−centroid
distance is 3.569(5) Å. Such π−π interaction effects on the
primary structure directing the coordination geometry around
Hg(II), which contain similar ligands to those discussed in this
paper, have previously been reported in detail by some of us.12a
As shown in Figure 2b, these 1D linear chains are further linked
Figure 1. Portion of the structure of coordination compounds formed
between HgCl2 and LH, 1 (a), L3‑Cl, 2 (b), L3‑Br, 3 (c), and L3‑I, 4 (d),
showing coordination geometry around the central metal. Displacement
ellipsoids are shown at 30% probability level. Symmetry codes: (a) (i) 1
+ x, y, z; (b) (i) 1 + x, y, z; (ii) −1 + x, y, z.
to each other from one side by head-to-tail dimeric Cphen
−
H···Hg−Cl and Cphen−H···OC nonclassical hydrogen bonds
(Table S1, Supporting Information), and from the other side by
head-to-tail Hg···Cl contacts and Hg···πphen intermolecular
interactions (Table 3). Coordination geometry and intermo-
lecular interactions of compound 1 are illustrated in Scheme 2.
Within the asymmetric unit of 2, each mercury coordinates to
the nitrogen donor atom of the pyrazine ring, the N atom syn to
the carbonyl, of the L3‑Cl ligand, while each chloride atom in the
basal plane bridges two adjacent metal centers to generate a 1D
double-chain motif in the a direction (Figure 3a). The planar
organic ligands stack along both sides of the HgCl skeleton, and
the distance between their mean planes is 3.933(1) Å (Figure
3a). These 1D chains are further linked to adjacent ones by
Hg···Cl contacts to generate a double chain in the a direction
(Table 3). The resulting double chains are further linked to
respectively. We propose a simple geometry index for almost
planar three-coordinate complexes, trigonal-planar index, τ3, eq 1
τ3 = |[(α + β + γ)/360] − |(α − 120)/60||
(1)
inspired by Houser’s four-cooordinate τ4 index14 and Addison
and Reedijk’s five-coordinate τ5 index.15 In this equation, α is the
largest angle in the three-coordinated complex. The values of τ3
will range from 1.00 for a perfect trigonal-planar geometry, since
[(120 + 120 + 120)/360] − [(120 − 120)/60] = 1 − 0 = 1, to
zero for a perfect T-shaped geometry, since [(180 + 90 + 90)/
360] − [(180 − 120)/60] = 1.00 − 1.00 = 0. Therefore, this
parameter can be used for almost planar three-coordinate
complexes since trigonal-planar and T-shaped geometries are the
extremes. Trigonal-planar index, τ3, for Hg1 in compound 3 and
4 is 0.17 for both complexes.
adjacent chains from one side by head-to-tail dimeric Cphen
−
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H···OC and Cpyz−H···Cl−Hg nonclassical hydrogen bonds
(Figure 3b; Table S1, Supporting Information). The coordina-
tion geometry and the intermolecular interactions of compound
2 are illustrated in Scheme 2.
In isostructural 3 and 4, the two independent dinuclear
moieties are closely packed through head-to-tail Hg···Cl contacts
(Table 3) to generate dimeric units (Figure 4a). Adjacent dimeric
units are further linked to each other by head-to-tail N···Br/I
halogen bonds (Figure 4b). In the packing of these complexes,
the overall supramolecular structure results from the linkage of
Table 3. Hg···X, Hg···π, Amide···π, and π···π Distances for
Compounds 1−10
complex
D−H···A
d(D···A) (Å)
symmetry
1
Hg1···Cl2
Hg1···πphen
Hg1···Cl1
Hg1···Cl2
Hg2···Cl4
πphen···πpyz
Hg1···πphen
Hg1···Cl3
Hg2···Cl2
πphen···πpyz
Hg1···πphen
πphen···πphen
Hg1···Br2
Hg1···Br2
amide···πphen
Hg1···Br1
amide···πphen
Hg1···Br1
amide···πphen
Hg1···Br1
amide···πphen
πphen···πpyz
3.203(2)
3.548(2)
3.198(2)
3.288(1)
3.247(1)
3.449(4)
3.452(1)
3.324(3)
3.324(3)
3.516(6)
3.517(4)
3.847(7)
3.378(4)
3.454(4)
3.475(5)
3.401(1)
3.373(1)
3.411(1)
3.363(1)
3.443(1)
3.390(1)
3.661(8)
1 − x, 2 − y, −z
1 + x, 3/2 − y, 1/2 + z
2 − x, 2 − y, 1 − z
−x, 1 − y, −z
2
3
−x, 1 − y, −z
1-x, y, z
neighboring units of Hg···πphen, Cphen−H···OC, and Cphen
−
4
1 − x, 1 − y, 1 − z
1 − x, 1 − y, 1 − z
H···Cl−Hg with nonclassical hydrogen bonds (Figure 4c).
Coordination geometries and intermolecular interactions of
compounds 3 and 4 are illustrated in Scheme 2.
x, y, −1 + z
Structural Analysis of HgBr2 Complexes, [Hg2Br4(LH)2],
5, [HgBr2(L3‑F)], 6, [HgBr2(L3‑Cl)], 7, [HgBr2(L3‑Br)], 8,
[HgBr2(L3‑I)], 9. The reaction of 1 equiv of HgBr2 with 1 equiv
of LH in methanol produces a dinuclear mercury complex, 5, with
a 12-membered ring (Figure 5a). This compound displays 2/m
point symmetry in the solid state, making half of the molecules
crystallographically unique. Metal is in a seesaw geometry, with a
four-coordinate geometry index, τ4, of 0.64, coordinated by two
Br atoms (Table 2) at the plank and one pyrazine nitrogen atom
of the LH ligand and one carbonyl oxygen atom of the second LH
ligand (Table 2), which form the pivot. The recent LH ligand acts
as an angular bridge via carbonyl oxygen and pyrazine nitrogen
5
6
1/2 − x, 1/2 + y, 5/2 − z
1/2 + x, 1/2 − y, 2 − z
−1/2 + x, 1/2 − y, 2 − z
1/2 + x, y, 5/2 − z
−1/2 + x, 1/2 − y, −z
1/2 − x, y, 1/2 − z
1/2 − x, −1/2 + y, 1 − z
1/2 − x, −1/2 + y, 2 − z
1/2 − x, −1/2 + y, −z
1/2 − x, −1/2 + y, 1 − z
−x, y, 1/2 − z
7
8
9
10
Scheme 2. Representation of Coordination Geometry and Intermolecular Interactions of Compounds 1−12
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Table 3). In 6, these chains are further linked to adjacent chains
by Cphen−H···Br−Hg and Cpyz−H···F−C intermolecular inter-
actions (Table S1, Supporting Information), while in 7−9,
cooperation of Npyz···Cl/Br/I halogen bonds and Cphen
−
H···OC nonclassical hydrogen bonds are main factors in the
generation of supramolecular assemblies (Figures 7b, 8b, and
9b). It is notable that compounds 8 and 9 have isostructural
coordination geometries, and intermolecular interactions of
compounds 6−9 are illustrated in Scheme 2.
Structural Analysis of HgI2 Complexes, [Hg2I4(LH)2], 10,
[HgI2(L3‑Br)]n, 11, and [HgI2(L3‑I)]n, 12. In compound 10, the
metal center has the same seesaw geometry observed in
compounds 1 and 5, with two iodide atoms as the plank, and
one iodide and one pyrazine nitrogen atom in the pivot position
(Table 2). For this complex, the four-coordinate geometry index,
τ4, is 0.70. In this compound, each discrete molecular unit
consists of a centrosymmetric dinuclear iodo-bridge Hg2I2
fragment. This bridged Hg2I2 forms a unsymmetric tetra-atomic
rhombohedral plane (Figure 10a).
In 1D structures of 11 and 12, each asymmetric unit consists of
one crystallographically independent Hg center, two iodide ions,
and one neutral L3‑Br or L3‑I ligand. In both structures, the
coordination geometry around the Hg center is square-based
pyramid (SBP) (Figure 10b,c), respectively, with a trigonality
index, τ5, of 0.09 and 0.03, respectively. In both structures of 11
and 12, the plane of square-based pyramid is occupied by iodide
anions (Table 2). The apical position in both structures is
occupied by a nitrogen atom from the pyrazine ring of the L
ligand at a normal distance of 2.474(10) and 2.484(7) Å for 11
and 12, respectively. As it is clear from the τ5 values and
geometrical parameters around the central metal atoms (Table
2), Hg has a slightly distorted SBP environment in both
compouds.
In 10, the dinuclear units are further linked to adjacent ones
from one side by Cphen−H···I−Hg nonclassical hydrogen bonds
(Figure 11a) and from the other side by πpyz···πphen
intermolecular interactions (Figure 11b and Table 3). The
coordination geometry and intermolecular interactions of
compound 10 are illustrated in Scheme 2.
In 11 and 12, the arrangement of the asymmetric units defines
the well-known double-stranded stair motif16 (Figure 12a). In
this stair 1D polymer, the translation axis is parallel to the b
direction. In these compounds, the Hg−I bond distance of
3.4957(5) and 3.5182(4) Å is comparable to that previously
reported (3.3773(5) Å) by Popovic et al.16b The I1 atom adopts a
μ3 mode to bridge three Hg atoms, while I2 is coordinated to
metal centers as a terminal ligand. The iodide anion in the stair is
tricoordinated with distorted T-shaped geometry (diagonal I···I
= 4.3733(9) and 4.4005(6) Å for 11 and 12, respectively). The
organic ligand moieties approximately preserve their planarity
and stack along both sides of the HgI skeleton (Figure 12a).
These 1D chains are further linked by head-to-tail Npyz···Br/I
halogen bonds in the other direction (Figure 12b). Coordination
geometries and intermolecular interactions of compounds 11
and 12 are illustrated in Scheme 2.
Figure 3. Representation of 1D double chain (a), and a side view
representation of 2 (b), showing the association of the adjacent
molecules in the chains, through head-to-tail Cphen−H···OC and
Cpyz−H···Cl−Hg nonclassical hydrogen bonds and head-to-tail N···Cl
halogen bonds. Different colors show different adjacent linear chains.
Halogen bonds are shown in red (b).
atoms to link Hg1 and Hg1i (symmetry code: (i) x, 2 − y, 2 − z)
ions. The Br−Hg−Br and N−Hg−O planes are nearly
perpendicular, with a dihedral angle of 80.17(9)°.
The coordination geometries around the Hg atom in 6−9 are
similar and made up of discrete neutral HgBr2L3‑X units. Figure
5b−e depicts the representative molecular structure showing the
arrangement about the Hg(II) center for 6−9, and selected bond
distances and angles are listed in Table 2. The Hg atom lies in a
T-shaped structure defined by two bromide atoms and one the
pyrazine nitrogen atom of the L3‑X ligand (Table 2). Trigonal-
planar indexes, τ3, for these compounds are 0.27, 0.32, 0.33, and
0.35, respectively (Table 4). The angle between the Br−Hg−Br
plane and the pyrazine ring for 6 is 6.87(9)° and for 7−9 is
almost 0.00°.
In 5, the structure is stabilized by an ordered network of
intermolecular π···π interactions that exist between the pyrazine
and phenyl rings (Figure 6, Table 3). In these πphen···πpyz
interactions, the centroid−centroid distance is 3.847(5) Å. As
shown in Figure 6, these π···π interactions cooperate with Cphen
−
H···Br−Hg and Cpyz−H···Br−Hg to further link to each other
from one side by head-to-tail dimeric Hg−Cl···H−Cphen
nonclassical hydrogen bonds (Table S1, Supporting Informa-
tion). The coordination geometry and intermolecular inter-
actions of compound 4 are illustrated in Scheme 2.
Influence of Halide Counteranion and Halogen
Bonding on Coordination Geometry and Supramolecular
Assembly. Progress in controlling the structural assemblies of
coordination complexes in the solid state requires investigation
of the families of compounds designed so that the effects of
different factors on the resultant supramolecular and structural
properties may be systematically delineated. In this regard, the
effect of halogen bonding and the effect of different halogen
In compounds 6−9, discrete units are linked to adjacent ones
by Hg···Br contacts to generate a double-stranded stair motif
(Figures 7a, 8a, and 9a). In these compounds, the Hg···Br
contacts of 3.378(4) and 3.454(4) Å for 6 and 3.401(1),
3.411(1), and 3.443(1) Å for 7−9, respectively (Table 3), are
comparable to those previously reported (3.385(1) Å) by Wu et
al.16a The resulting double chains are further linked to adjacent
chains by πphen···−NHCO− interactions (Figures 7a and 8a and
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Figure 4. Side view representation of 3, showing the generation of dimeric moieties through the Hg···Cl short contacts (a), and head-to-tail N···Br
halogen bonds between adjacent dimeric units; halogen bonds are shown in red (b). A representation of part of 3 (c), showing the cooperation of head-
to-tail N···Br halogen bonds, Hg···πphen, Cphen−H···OC, and Cphen−H···Cl−Hg nonclassical hydrogen bonds in generation of three-dimensional
packing. Different colors show different adjacent moieties; halogen bonds are shown in red.
anions on the coordination geometry and supramolecular
architecture of the 12 coordination compound of mercury(II)
have been studied. Much of the difference in the structural motifs
can be explained by the changing of the halogen atom on the
halophenyl ring, but the role of the different halogen ions should
not be neglected. Therefore, in the following discussion, first, we
will focus on controlling the effect of the coordinated anion on
the structural motif of the resulting coordination compounds.
Influence of Halide Anion on Coordination Geometry and
Supramolecular Assembly. It is well-known that anions play an
important role in the crystal engineering of self-assembled
coordination polymers.17 Some of us have recently demonstrated
that cooperative noncovalent interactions can lead to the
formation of one- or two-dimensional architectures under
anion-directed self-assembly.18
Interestingly, structural analysis clearly shows that, by the
replacing of coordinated anions from chloride with bromide and
iodide in each series containing the same ligand, the coordination
geometry and structural motif of the resulting compounds have
been dramatically affected. It seems that the size of the
coordinated halides would make a substantial contribution to
the local mercury coordination environment and can also affect
the extended structures.17a,18,19 In compounds 1, 5, and 10,
where the carboxamide ligand, LH, is similar, all complexes have
the same seesaw coordination geometries (Table 4, Scheme 2).
Compound 1 shows a 1D linear chain structure. The situation for
compounds 5 and 10 (where the chloride anion is replaced by
bromide and iodide) is quite different from that of compound 1.
The different structural motifs between 1, 5, and 10 are
seemingly attributed to the anion size effect. Unlike the
formation of the 1D linear chain in 1, the bulkier Br and I ions
in 5 and 10 are sterically hindered to form a larger aggregate. By
replacing the coordinated anion from chloride to bromide and
iodide, the supramolecular structure changed from 1D linear
chains to dinuclear units (Table 4). Similar results were also
observed for complexes 2 and 7. For complexes containing the
L3‑Cl ligand with HgCl2 and HgBr2, 2 and 7, the coordination
sphere changes from SBP for 2 to T-shape for 7 (Table 4, Scheme
2). The structural motifs in these compounds are also quite
different, and the 1D double chain in 2 is changed to a discrete
monomer structure in 7.
For HgX2 adducts, while the carboxamide ligand is L3‑Br, from
3 to 8 and to 11 (where counteranions are chloride, bromide, and
iodide, resepectively), the coordination sphere changes from the
seesaw/T-shape (for two crystallographically independent metal
ions) in 3, to a T-shape in 8 and SBP in 11 (Table 4, Scheme 2).
As listed in this table, compounds 3 and 8 show dinuclear and
monuclear structures, respectievely, whereas compound 11 has a
1D ladder chain structure. In the case of 11, although increasing
the size of the anion results in the formation of a larger molecular
complex, the study of Hg−I distances indicates that two of the
four Hg−I bond lengths in the basal plane, connecting Hg metal
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As compounds 3 and 4, 8 and 9, and 11 and 12 are
isostructural, for HgX2 adducts, while the carboxamide ligand is
L3‑I (compounds 4, 9, and 12), the same trend as L3‑Br
(compounds 3, 8, and 11) is observed (Table 4, Scheme 2).
Influence of N···X Halogen Bonding Interaction on
Supramolecular Assembly. The compounds studied here were
designed to probe the influence of halogen bonding interactions
on the supramolecular assembly of similar coordination
compounds. Organic ligands with flexible torsions can indeed
generate dissimilar conformations with different halogen bond
patterns and packing modes. The common feature in the crystal
structures of complexes obtained from the reaction between
HgX2 and L3‑Cl, L3‑Br and L3‑I ligands is the existence of a N···X
halogen bond. Thus, a systematic evaluation of supramolecular
synthons consisting of N···X halogen bonding interactions in a
series of conformationally flexible mercury complexes containing
halophenyl pyridazinamides is interesting.
In these compounds, since the halophenyl ring is flexible in
rotation around the Namide−Cphen bond, this allows subtle
conformational adaptation of L3‑X to produce additional
synthons via the rotation of the halophenyl ring. In all Hg(II)
complexes reported here, the coordination of the pyrazine ring
occurred through the N atom syn to the carbonyl and the N atom
anti to the carbonyl is involved in classical intramolecular N−
H···N hydrogen bonds. Because of the presence of such
intramolecular hydrogen bonds, the pyrazine-CONH moiety is
approximately planar, and C5O1 and C4−N1 bonds are in the
anti position. Therefore, the conformational variation of L3‑X can
be discussed by a dihedral angle of O1C5−C8−X, which is
listed in Table 5 for compounds 1−12. As in compounds 3 and 4,
each asymmetric unit consists of two crystallographically
independent L3‑X ligands; two different values for this angle are
listed in Table 5. According to the direction of the CO and C−
X bonds, the L3‑X ligands can be arranged in anti and syn
conformations (Scheme 3). In the presence of this flexibility, the
halogen atom of the halophenyl ring is pointed toward the
adjacent molecule to generate different synthons. Two basic
halogen bond synthons (Scheme 3) were observed in the
mercury complexes examined. Compound 7 adopts the syn
conformation while the others, 2, 3, 4, 8, 9, 11, and 12, adopt anti
conformations. It is notable that these two different con-
formations play different roles in the formation of packing. The
syn-conformational L3‑Cl ligand generates a single Cl···N halogen
bond in 7, whereas in the complexes of HgX2 with L3‑Br and L3‑I,
and also HgCl2 with L3‑Cl, the anti-conformational ligands
generate a head-to-tail halogen bond synthon (Table 5).
Table 5 provides a summary of the geometrical parameter of
the halogen bonding synthons observed in 2−4, 7−9, 11, and 12.
These results show that there is a strong tendency to form
halogen bonding synthons between adjacent halophenyl and
pyrazine rings, in order to stabilize the packing of these
compounds. As it is clear from Table 5, halogen bonds show
geometries consistent with a donor−acceptor binding model in
which the pyrazine nitrogen atom serves as the electron donor
and the halocarbon C−X bond serves as the acceptor. In
complexes containing the L3‑Cl ligand, 2 and 7, contact distances
of Cl···N were 3.190(6) and 3.217(5) Å, respectively (Table 5),
indicating a 3.3% and 2.5% reduction of the sum of van der Waals
radii.21 The Br···N halogen bonding distances in compounds 3, 8,
and 11, complexes containing the L3‑Br ligand, were found
between 3.100(3) and 3.251(9) Å, which are 8.8−4.4% shorter
than the sum of the van der Waals radii of nitrogen and bromide
atoms.21
Figure 5. Structure of coordination compounds formed between HgBr2
and LH, 5 (a), L3‑F, 6 (b), L3‑Cl, 7 (c), L3‑Br, 8 (d), and L3‑I, 9 (e), showing
coordination geometry around the central metal. Displacement
ellipsoids are shown at 30% probability level. Symmetry codes: (i) −x,
2 − y, 2 − z.
centers through a Hg−I−Hg bridge, are much longer than the
others, 3.496(1) Å, compared to the remaining Hg−I bond
lengths, and deviate considerably from the average bond length
(Table 2). It is noteworthy that a search of the Cambridge
Structural Database20 for the Hg−I distance shows that there are
only 8 out of a total of 468 hits that have values longer than 3.496
Å. In the recent series, the structural analysis confirms that, as the
size of the counteranion increases, the extended structures
change significantly. It can be anticipated that the halide steric
factor cannot be the only factor dictating the coordination
environment and extended structures but certainly plays an
important role in this regard.
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Table 4. Coordination Geometries and τi Values of Compounds 1−12
compound
coordination geometry
τi
τ4 = 0.64
polymeric/nonpolymeric
1, [HgCl2(LH)]n
2, [HgCl2(L3‑Cl)]n
3, [Hg2Cl4(L3‑Br)2]
4, [Hg2Cl4(L3‑I)2]
5, [Hg2Br4(LH)2]
6, [HgBr2(L3‑F)]
7, [HgBr2(L3‑Cl)]
8, [HgBr2(L3‑Br)]
9, [HgBr2(L3‑I)]
10, [Hg2I4(LH)2]
11, [HgI2(L3‑Br)]n
12, [HgI2(L3‑I)]n
seesaw
1D linear chain
1D double chain
dinuclear
SBP
τ5 = 0.03
T-shape/seesaw
T-shape/seesaw
seesaw
τ3 = 0.17/τ4 = 0.67
τ3 = 0.17/τ4 = 0.67
τ4 = 0.64
dinuclear
cyclic dinuclear
monomer
T-shape
T-shape
T-shape
T-shape
seesaw
τ3 = 0.27
τ3 = 0.32
monomer
τ3 = 0.33
monomer
τ3 = 0.35
monomer
τ4 = 0.70
dinuclear
SBP
τ5 = 0.09
1D ladder chain
1D ladder chain
SBP
τ5 = 0.03
Figure 6. Side view representation of 5, showing the cooperation of
πpyz···πphen interactions and Cphen−H···Br−Hg and Cpyz−H···Br−Hg
nonclassical hydrogen bonds in generation of three-dimensional
packing. Different colors show different adjacent moieties.
Figure 8. Side view representation of 7, showing the generation of
double-stranded stair motifs through the Hg···Br short contacts, and
head-to-tail πphen···amide interactions between adjacent chains (a). A
representation of part of 7 in the a direction (b), showing the
cooperation of Npyz···Cl halogen bond and Cphen−H···OC non-
classical hydrogen bonds in generation of three-dimensional packing.
Different colors show different adjacent moieties; halogen bonds are
shown in red.
Since iodide is the most polarizable atom, it would have a
higher positive charge than bromide and chloride. This should
also affect the intermolecular bond strength, which is indeed
reflected in the observed distance between I and N (of C−I···N)
(Table 5). The C−I···N intermolecular distances in compounds
4, 9, and 12, containing the L3‑I ligand, were found to be between
3.198(7) and 3.300(9) Å, which are 9.4−6.5% shorther than the
sum of the van der Waals radii of nitrogen and iodide atoms.21
As expected,22 Table 5 shows that the strength of the halogen
bond increases from chloride to bromide and further to iodide.
Besides the N···X distance, another contributing factor to
halogen bond strength is the halogen bond angle C−X···N. The
C−X···N angles are all close to linearity, which is consistent with
the theory of electron donation into the C−X σ* orbitals of the
X-bond donor.23
Figure 7. Side view representation of 6, showing the generation of
double-stranded stair motifs through the Hg···Br short contacts, and
πphen···amide interactions between adjacent chains (a). A representation
of part of 6 in the a direction (b), showing the cooperation of Cphen
−
H···Br−Hg and Cpyz−H···F−C intermolecular interactions in gener-
ation of three-dimensional packing. Different colors show different
adjacent moieties.
The Cambridge Structural Database (CSD) was analyzed for
halogen bonding of 2−4, 7−9, 11, and 12 to determine the
common range of NM−X···N interactions, where NM is a
nonmetal and nonhalogen and X is Cl, Br, or I (Figure 13).20
J
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Figure 11. Side view representation of 10 showing the association via
C−Hphen···I−Hg nonclassical hydrogen bonds (a), and πpyz···πphen
intermolecular interactions (b), in the generation of three-dimensional
packing. Different colors show different adjacent linear moieties.
Figure 9. Side view representation of 8 and 9, showing the generation of
double-stranded stair motifs through the Hg···Br short contacts (a), and
cooperation of Npyz···Br/I halogen bond and Cphen−H···OC
nonclassical hydrogen bonds in generation of three-dimensional packing
(b). Different colors show different adjacent moieties; halogen bonds
are shown in red.
Figure 12. Side view representation of 11 and 12, showing the
generation of double-stranded stair motifs through the Hg−I bonds (a),
and Npyz···Br/I halogen bond in generation of three-dimensional
packing (b). Different colors show different adjacent moieties; halogen
bonds are shown in red.
Similar plot correlations have been reported for C−I···N halogen
bonds.24 This figure reveals that all parameters for determining
these interactions are in the normal range. Therefore, it seems
that the driving force for the crystal formation of these
compounds is a halogen bond between the pyrazine nitrogen
atom and the halogen atom on the halophenyl ring. It was
thought of interest to further investigate the XB energy in these
compounds by using theoretical methods. The binding energies
obtained from DFT on two relative fragments (from complexes
2−4, 7−9, 11, and 12) provide us an opportunity to evaluate the
complexes involving XB interactions. Calculations were
performed with the experimental structures as the starting
point at the LDA-ZORA-TZP level. The outcomes obtained
from DFT methods are listed in Table 5. From these data, it is
explicit that halogen bonding energies vary within a range of
−27.86 to −46.15 kJ·mol−1. In view of the directionality and
Figure 10. Portion of the structure of coordination compounds formed
between HgI2 and LH, 10 (a), L3‑Br, 11 (b), and L3‑I, 12 (c), showing
coordination geometry around the central metal. Displacement
ellipsoids are shown at 30% probability level. Symmetry codes: (a) (i)
1/2 − x, 1/2 − y, −z; (b) (i) 3/2 − x, −1/2 + y, −z; (ii) 3/2 − x, 1/2 + y,
−z; (c) (i) 1/2 − x, −1/2 + y, 1 − z; (ii) 1/2 − x, 1/2 + y, 1 − z.
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Table 5. Halogen Bond, Conformational Parameters, and Calculated XB Binding Energies for Compounds 2−4, 7−9, 11, and 12
reduction
of the sum
of the van
der Waals
calculated XB
energy (kJ/mol)
XB
L3‑X
O1C5−C8−X
complex
X···N
X···N (Å) C−X···N (deg) radii (%)
symmetry code
X = Cl
synthon conformation torsion angle (deg) (LDA-Zora-TZP)
2, [HgCl2(L3‑Cl)]n
7, [HgBr2(L3‑Cl)]
Cl···N
Cl···N
3.190(6)
3.217(5)
172.7(3)
163.5(5)
3.3
2.5
1 − x, −y, −z
1 − x, 1/2 + y, 1/2 − z
X = Br
I
anti
syn
4.16(6)
0.00
−46.15
−27.86
II
3, [Hg2Cl4(L3‑Br)2]
Br···N
3.100(3)
3.188(3)
3.201(17)
3.251(9)
173.6(1)
170.9(1)
171.0(8)
173.1(5)
8.8
6.2
6.1
4.4
−x, 1 − y, 1 − z
−x, 1 − y, 1 − z
−x, y, 2 − z
1 − x, y, 1 − z
X = I
I
I
I
I
anti
anti
anti
anti
6.64(5)
29.72(8)
0.00
−39.84
8, [HgBr2(L3‑Br)]
11, [HgI2(L3‑Br)]
Br···N
Br···N
−34.06
−32.35
0.00
4, [Hg2Cl4(L3‑I)2]
I···N
3.198(7)
3.288(7)
3.248(18)
3.300(9)
175.3(2)
170.7(2)
174.3(5)
174.2(3)
9.4
6.9
8.0
6.5
−x, 1 − y, 2 − z
−x, 1 − y, 2 − z
−x, y, 1 − z
I
I
I
I
anti
anti
anti
anti
6.49(8)
32.44(9)
0.00
−44.02
9, [HgBr2(L3‑I)]
12, [HgI2(L3‑I)]
I···N
I···N
−41.59
−39.48
1 − x, y, −z
0.00
thermogravimetric analyses reveal that these compounds have
identical single-step decomposition patterns.
Scheme 3. Halogen Bonding Synthons Exhibited in Hg(II)
Complexes
CONCLUSION
■
The coordination geometry and supramolecular architecture of
the 12 coordination compounds of mercury(II) halides based on
L3‑X ligands (L = N-(3-halophenyl)-2-pyrazinecarboxamide)
carrying a different halogen atom in the phenyl meta-position
and LH (L = N-phenyl-2-pyrazinecarboxamide) have been
studied. Structural analysis clearly shows that the size of the
coordinated halides would make a substantial contribution to the
local mercury coordination environment and can also affect the
extended structures. In each series containing the same ligand,
the bulkier Br and I ions are sterically hindered to form a larger
molecule. The crystal packing of the studied compounds is
determined mostly by C−H···O/X (X = F, Cl, Br, I) nonclassical
hydrogen bonds and π···π/Hg/amide and Hg···X intermolecular
interactions. Since the halophenyl ring is flexible in rotation
around the Namide−Cphen bond, it allows for subtle conforma-
tional adaptation of L3‑X (X = Cl, Br, I) to produce additional
halogen bond synthons via the rotation of the halophenyl ring. In
view of the directionality and strength of the halogen bonds, the
Npyz···Cl/Br/I interaction can be recognized as an effective
strength of the halogen bonds, the Npyz···Cl/Br/I interaction can
be recognized as an effective driving force to determine the
alignment of molecules in supramolecular assemblies, which
enables the design and development of new functional solid
material.
The decomposition behavior of these compounds was also
investigated in a static air atmosphere from ambient conditions
to 500 °C. Stacked TG curves of compounds 2, 3, 4, 7, 8, 9, 11,
and 12 are given in Figure S1 (Supporting Information). The
Figure 13. Scatter plot of the halogen bonding distance X···N versus the angle of NM−X···N (where NM is a nonmetal and nonhalogen). X is Cl, Br, or I
shown in deep green, brown, and purple, respectively. Reported data were obtained from CSD, version 2011, filtered to include only error-free,
nondisordered structures with R, 0.075. Correlation values: chloride, 0.243; bromide, 0.438; iodide, 0.489.
L
dx.doi.org/10.1021/ic3021113 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
2. As expected, the highest peaks and deepest holes for these mercury
complexes are slightly high, but the residual densities are close to heavy
mercury atoms (with a maximum distance of 1.21 Å from Hg1 in
complex 1). For compounds 5 and 11, which have high residual
densities, the highest peaks and deepest holes are close to the Hg atoms
with a distance of 0.86 and 0.79 Å for the highest peaks and 0.89 and 0.85
Å for deepest holes, respectively.
Synthesis of N-(3-Halophenyl)pyrazine-2-carboxamide li-
gands, LH, L3‑F, L3‑Cl, L3‑Br, and L3‑I. These ligands were prepared by
using the previously reported method.13
driving force to determine the alignment of molecules in
supramolecular assemblies. The N···X halogen bonding
distances are 2.5−3.3, 4.4−8.8, and 6.5−9.4% shorter than the
sum of the van der Waals radii of nitrogen and halogen in
complexes containing L3‑Cl, L3‑Br, and L3‑I ligands, respectively.
Theoretical methods show that the halogen bonding energies
within a range of −27.86 to −46.15 kJ·mol−1 are comparable to
classical hydrogen bonding. The presence of a strong tendency to
form halogen bonding synthons between adjacent halophenyl
and pyrazine rings is one of the common features in the crystal
structures of these complexes. Structural analysis of complexes
studied here has clearly resulted in new sets of ligands that have
been especially developed for selective and efficient metal
coordination. Designing ligands that can provide capabilities for
selective metal ion coordination is one of the important factors in
controlling the architecture of self-assembled species. In all
complexes synthesized here, the pyrazine ring is coordinated to
the mercury(II) ion through the N atom syn to the carbonyl.
Accordingly, the second nitrogen of the pyrazine ring, the N
atom anti to the carbonyl, is now available to serve as a halogen
bond acceptor to interact with the halogen atom. Therefore, the
second common feature of the crystal structures of complexes
studied here is the selectivity of the metal ion coordination site.
The similarity of the halogen bond synthon across these
compounds and selectivity in the mercury(II) ion coordination
site further point to their application in coordination crystal
engineering especially in the clever design of such special metal
species and the crystal structure prediction research field.
Synthesis of [HgCl2(LH)]n, 1. To a solution of HgCl2 (0.027 g, 0.1
mmol) in 3 mL of methanol was added a solution of LH (0.019 g, 0.1
mmol) in 3 mL of methanol while stirring. The mixture was heated at 40
°C for about 1 h and then filtered. Upon slow evaporation of the filtrate
at room temperature, suitable yellow cystals of complex 1 for X-ray
analysis were obtained after 5 days (yield 41%, mp = 153−155 °C). Anal.
Calcd for C11H9Cl2HgN3O: C, 28.07; H, 1.93; N, 8.93. Found: C, 28.05;
H, 1.95; N, 8.94. FT-IR (CsI pellet, cm−1): 3337 (N-H str. vib.), 1666
(CO amide str. vib.), 1606, 1540 (C-N str. and N-H bend vib.),
1434(CC str. vib.), 1387 (C-N str. vib.), 1016, 877, 685 (OC-N
group bend vib.), 572 (OC-N group bend vib), 439. 1H NMR
(CD3OD, δ from TMS): 10.71 (s, 1H-pyrazine), 9.30 (s, amidic H),
8.93 (d, 1H-pyrazine), 8.81−8.83 (m, 1H-pyrazine), 7.89 (d, 2H-
phenyl), 7.37 (t, 2H-phenyl), and 7.14 (t, 1H-phenyl).
Synthesis of [HgCl2(L3‑Cl)]n, 2. The procedure was similar to the
synthesis of 1 except that L3‑Cl (0.023 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 2 were formed after 5 days (yield 72%, mp =
184−186 °C). Anal. Calcd for C11H8Cl3HgN3O: C, 26.15; H, 1.60; N,
8.32. Found: C, 26.13; H, 1.58; N, 8.30. FT-IR (CsI pellet, cm−1): 3356
(N-H str. vib.), 1692 (CO amide str. vib.), 1600, 1527 (C-N str. and
N-H bend vib.), 1474 (CC str. vib.), 1420, 1394 (C-N str. vib.), 1122
(C-Cl str. vib.), 1049, 844, 777, 678 (OC-N group bend vib.), 579
1
(OC-N group bend vib), 426. H NMR (CD3OD, δ from TMS):
EXPERIMENTAL SECTION
10.96 (s, 1H-pyrazine), 9.30 (s, amidic H), 8.95 (d, 1H-pyrazine), 8.82−
8.84 (m, 1H-pyrazine), 8.09 (s, 1H-phenyl), 7.86 (d, 1H-phenyl), 7.40
(t, 1H-phenyl), and 7.20 (d, 1H-phenyl).
■
General. All chemicals were purchased from Aldrich or Merck and
used without further purification. The synthesis and recrystallization of
LH, L3‑F, L3‑Cl, L3‑Br, and L3‑I, and mercury(II) complexes 1−12 were
carried out in air. The 1H NMR spectrum was recorded on a Bruker AC-
300 MHz spectrometer at ambient temperature in CD3OD. All chemical
shifts are quoted in parts per million (ppm) relative to tetramethylsilane.
Infrared spectra (4000−250 cm−1) of the solid sample were taken as 1%
dispersion in CsI pellets using a BOMEM-MB102 spectrometer.
Elemental analysis was performed using a Heraeus CHN-O Rapid
analyzer. Melting points were obtained by a Bamstead Electrothermal
type 9200 melting point apparatus and corrected. All ligands were
prepared according to the reported procedure.13
Synthesis of [Hg2Cl4(L3‑Br)2], 3. The procedure was similar to the
synthesis of 1 except that L3‑Br (0.027 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 3 were formed after 7 days (yield 69%, mp =
196−198 °C). The complex 3 is relatively stable in the solid state when
stored in the mother liquor, but decomposes slowly when exposed to
open air. Therefore, the diffraction data for this compound were
collected at 173 K. Anal. Calcd for C22H16Br2Cl4Hg2N6O2: C, 24.04; H,
1.47; N, 7.65. Found: C, 24.01; H, 1.45; N, 7.63. FT-IR (CsI pellet,
cm−1): 3350 (N-H str. vib.), 1692 (CO amide str. vib.), 1659 (CO
amide str. vib.), 1573 (C-N str. and N-H bend vib.), 1467 (CC str.
vib.), 1394 (C-N str. vib.), 1122 (C-Br str. vib.), 857, 685 (OC-N
group bend vib.), 579 (OC-N group bend vib), 433. 1H NMR
(CD3OD, δ from TMS): 10.91 (s, 1H-pyrazine), 9.29 (s, amidic H),
8.95 (d, 1H-pyrazine), 8.81−8.84 (m, 1H-pyrazine), 8.24 (s, 1H-
phenyl), 7.90 (d, 1H-phenyl), 7.56 (d, 1H-phenyl), and 7.35 (t, 1H-
phenyl).
Single-Crystal Diffraction Studies. For crystals 1−9, 11, and 12,
intensity data were collected using a Bruker SMART APEX-II CCD
diffractometer, equipped with a fine focus 1.75 kW sealed tube with Mo
Kα radiation (λ, 0.71073 Å). The total number of images was based on
the results from the program COSMO.25a Cell parameters were
retrieved using APEX II software25b and refined using SAINT on all
observed reflections. Data reduction was performed using the SAINT
software,25c which corrects for the Lorentz and polarizing effects. Scaling
and absorption corrections were applied using the SADABS25d
multiscan technique, supplied by George Sheldrick. X-ray data for
compound 10 were collected on a STOE IPDS-II diffractometer with
graphite monochromated Mo Kα radiation (λ, 0.71073 Å). Data were
collected in a series of ω scans in 1° oscillations and integrated using the
Synthesis of [Hg2Cl4(L3‑I)2], 4. The procedure was similar to the
synthesis of 1 except that L3‑I (0.032 g, 0.1 mmol) was used instead of
LH. Light yellow crystals of 4 were formed after 2 weeks (yield 55%, mp
= 200−202 °C). Anal. Calcd for C22H16Cl4Hg2I2N6O2: C, 22.15; H,
1.35; N, 7.04. Found: C, 22.14; H, 1.35; N, 7.04. FT-IR (CsI pellet,
cm−1): 3337 (N-H str. vib.), 1692 (CO amide str. vib.), 1675 (CO
amide str. vib.), 1573 (C-N str. and N-H bend vib.), 1533, 1467 (CC
str. vib.), 1394 (C−N str. vib.), 1116 (C-I str. vib), 1016, 850, 685 (O
C-N group bend vib.), 585 (OC-N group bend vib), 435. 1H NMR
(CD3OD, δ from TMS): 10.83 (s, 1H-pyrazine), 9.28 (s, amidic H),
8.93 (d, 1H-pyrazine), 8.79−8.82 (m, 1H-pyrazine), 8.38 (s, 1H-
phenyl), 7.90 (d, 1H-phenyl), 7.50 (d, 1H-phenyl), and 7.17 (t, 1H-
phenyl).
Stoe X-AREA26a software package. A numerical absorption correction
̈
was applied using the X-RED26b and X-SHAPE26c software. All
structures were solved by direct methods using SHELXS-9727 and
refined with full-matrix least-squares on F2 using the SHELXL-9727
program package. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were added at ideal positions and constrained to ride
on their parent atoms, with Uiso(H) = 1.2Ueq. All refinements were
performed using the X-STEP32 crystallographic software package.28
Structural illustrations have been drawn with ORTEP-329 and
MERCURY.30 Crystallographic data for compounds 1−12 are listed
in Table 1. Selected bond distances and angles are summarized in Table
Synthesis of [Hg2Br4(LH)2], 5. The procedure was similar to the
synthesis of 1 except that HgBr2 (0.036 g, 0.1 mmol) was used instead of
HgCl2. Colorless crystals of 5 were formed after 5 weeks (yield 69%, mp
= 146−148 °C). Anal. Calcd for C22H18Br4Hg2N6O2: C, 23.61; H, 1.62;
N, 7.51. Found: C, 23.60; H, 1.60; N, 7.50. FT-IR (CsI pellet, cm−1):
M
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3343 (N-H str. vib.), 1672 (CO amide str. vib.), 1546 (C-N str. and
N-H bend vib.), 1447 (CC str. vib.), 1401 (C-N str. vib.), 1016, 744,
685 (OC-N group bend vib.), 579 (OC-N group bend vib), 453.
1H NMR (CD3OD, δ from TMS): 10.72 (s, 1H-pyrazine), 9.29 (s,
amidic H), 8.91 (d, 1H-pyrazine), 8.79−8.83 (m, 1H-pyrazine), 7.88 (d,
2H-phenyl), 7.36 (t, 2H-phenyl), and 7.16 (t, 1H-phenyl).
(N-H str. vib.), 1692 (CO amide str. vib.), 1540 (C-N str. and N-H
bend vib.), 1474 (CC str. vib.), 1401 (C-N str. vib.), 1175, 1122 (C-
Br str. vib.), 1056, 850, 671 (OC-N group bend vib.), 585 (OC-N
group bend vib), 433. 1H NMR (CD3OD, δ from TMS): 10.93 (s, 1H-
pyrazine), 9.29 (s, amidic H), 8.95 (d, 1H-pyrazine), 8.79−8.83 (m, 1H-
pyrazine), 8.23 (s, 1H-phenyl), 7.88 (d, 1H-phenyl), 7.56 (d, 1H-
phenyl), and 7.33 (t, 1H-phenyl).
Synthesis of [HgBr2(L3‑F)], 6. The procedure was similar to the
synthesis of 5 except that L3‑F (0.021 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 6 were formed after 7 days (yield 48%, mp =
156−158 °C). Anal. Calcd for C11H8Br2FHgN3O: C, 22.87; H, 1.40; N,
7.27. Found: C, 22.87; H, 1.40; N, 7.29. FT-IR (CsI pellet, cm−1): 3339
(N-H str. vib.), 1694 (CO amide str. vib.), 1617, 1544 (C-N str. and
N-H bend vib.), 1445 (CC str. vib.), 1407 (C-N str. vib.), 1272, 1146
(C-F str. vib), 860, 680 (OC-N group bend vib.), 580 (OC-N
group bend vib), 459. 1H NMR (CD3OD, δ from TMS): 10.98 (s, 1H-
pyrazine), 9.31 (s, amidic H), 8.95 (d, 1H-pyrazine), 8.81−8.83 (m, 1H-
pyrazine), 7.85 (d, 1H-phenyl), 7.75 (d, 1H-phenyl), 7.41 (dd, 1H-
phenyl), and 6.97 (t, 1H-phenyl).
Synthesis of [HgI2(L3‑I)], 12. The procedure was similar to the
synthesis of 10 except that L3‑I (0.032 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 11 were formed after 2 weeks (yield 42%, mp =
207−209 °C). Anal. Calcd for C11H8HgI3N3O: C, 16.95; H, 1.03; N,
5.39. Found: C, 16.95; H, 1.02; N, 5.37. FT-IR (CsI pellet, cm−1): 3343
(N-H str. vib.), 1692 (CO amide str. vib.), 1540 (C-N str. and N-H
bend vib.), 1467 (CC str. vib.), 1381 (C-N str. vib.), 1122 (C-I str.
vib.), 850, 777, 671 (OC-N group bend vib.), 585 (OC-N group
1
bend vib), 459. H NMR (CD3OD, δ from TMS): 10.86 (s, 1H-
pyrazine), 9.29 (s, amidic H), 8.94 (d, 1H-pyrazine), 8.79−8.82 (m, 1H-
pyrazine), 8.32 (s, 1H-phenyl), 7.90 (d, 1H-phenyl), 7.50 (d, 1H-
phenyl), and 7.17 (t, 1H-phenyl).
Synthesis of [HgBr2(L3‑Cl)], 7. The procedure was similar to the
synthesis of 5 except that L3‑Cl (0.023 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 7 were formed after 5 days (yield 45%, mp =
185−187 °C). Anal. Calcd for C11H8Br2ClHgN3O: C, 22.24; H, 1.36; N,
7.07. Found: C, 22.23; H, 1.36; N, 7.06. FT-IR (CsI pellet, cm−1): 3350
(N-H str. vib.), 1686 (CO amide str. vib.), 1586, 1533 (C-N str. and
N-H bend vib.), 1440 (CC str. vib.), 1414 (C-N str. vib.), 1129 (C-Cl
str. vib.), 1049, 857, 784, 685 (OC-N group bend vib.), 572 (OC-N
group bend vib), 453. 1H NMR (CD3OD, δ from TMS): 10.95 (s, 1H-
pyrazine), 9.31 (s, amidic H), 8.95 (d, 1H-pyrazine), 8.81−8.83 (m, 1H-
pyrazine), 8.09 (s, 1H-phenyl), 7.85 (d, 1H-phenyl), 7.40 (t, 1H-
phenyl), and 7.20 (d, 1H-phenyl).
Computational Details. DFT calculations were performed using
the ORCA quantum chemistry suite.31 The local density approximation
(LDA) exchange correlation potential was used with the local density
approximation of the correlation energy.32 Gradient-corrected geometry
optimizations33 were performed by using the generalized gradient
approximation.34 Large atom basis sets TZP were used to ascribe all of
the atoms. Scalar relativistic effects were taken into account by using the
zeroth-order regular approximation (ZORA).35
Thermal Analysis (TG). TG experiments were carried out using a
Rheometric Scientific (STA/1500) with a heating rate of 10 °C/min in
the range of 25−500 °C, under an air atmosphere. The measurements
were carried out using around 10 mg of a powdered sample sealed in
aluminum pans with a mechanical crimp.
Synthesis of [HgBr2(L3‑Br)], 8. The procedure was similar to the
synthesis of 5 except that L3‑Br (0.027 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 8 were formed after 2 weeks (yield 63%, mp =
190−192 °C). Anal. Calcd for C11H8Br3HgN3O: C, 20.69; H, 1.26; N,
6.58. Found: C, 20.69; H, 1.26; N, 6.58. FT-IR (CsI pellet, cm−1): 3350
(N-H str. vib.), 1699 (CO amide str. vib.), 1573, 1540 (C-N str. and
N-H bend vib.), 1474 (CC str. vib.), 1410 (C-N str. vib.), 1129 (C-Br
str. vib), 850, 771, 681 (OC-N group bend vib.), 579 (OC-N group
ASSOCIATED CONTENT
* Supporting Information
■
S
TG curves for compounds 2, 3, 4, 7, 8, 9, 11, and 12; hydrogen
bond geometries, and X-ray crystallographic files in CIF format
for structural determination of 1 (CCDC No. 901972), 2
(CCDC No. 901975), 3 (CCDC No. 901970), 4 (CCDC No.
901976), 5 (CCDC No. 901971), 6 (CCDC No. 901981), 7
(CCDC No. 901978), 8 (CCDC No. 901973), 9 (CCDC No.
901974), 10 (CCDC No. 901980), 11 (CCDC No. 901979),
and 12 (CCDC No. 901977). This material is available free of
charge via the Internet at http://pubs.acs.org.
1
bend vib), 433. H NMR (CD3OD, δ from TMS): 10.96 (s, 1H-
pyrazine), 9.30 (s, amidic H), 8.94 (d, 1H-pyrazine), 8.80−8.83 (m, 1H-
pyrazine), 8.23 (s, 1H-phenyl), 7.89 (d, 1H-phenyl), 7.56 (d, 1H-
phenyl), and 7.34 (t, 1H-phenyl).
Synthesis of [HgBr2(L3‑I)], 9. The procedure was similar to the
synthesis of 5 except that L3‑I (0.032 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 9 were formed after 5 days (yield 61%, mp =
191−193 °C). Anal. Calcd for C11H8Br2HgIN3O: C, 19.27; H, 1.18; N,
6.13. Found: C, 19.27; H, 1.17; N, 6.13. FT-IR (CsI pellet, cm−1): 3337
(N-H str. vib.), 1686 (CO amide str. vib.), 1586, 1533 (C-N str. and
N−H bend vib.), 1460 (CC str. vib.), 1402 (C-N str. vib.), 1122 (C-I
str. vib), 1009, 850, 784, 685 (OC-N group bend vib.), 585 (OC-N
group bend vib), 413. 1H NMR (CD3OD, δ from TMS): 10.88 (s, 1H-
pyrazine), 9.31 (s, amidic H), 8.95 (d, 1H-pyrazine), 8.79−8.83 (m, 1H-
pyrazine), 8.31 (s, 1H-phenyl), 7.89 (d, 1H-phenyl), 7.51 (d, 1H-
phenyl), and 7.18 (t, 1H-phenyl).
AUTHOR INFORMATION
Corresponding Author
*Phone: +98 21 29903105. Fax: +98 21 22431661. E-mail: h-
khavasi@sbu.ac.ir.
■
Notes
The authors declare no competing financial interest.
Synthesis of [Hg2I4(LH)2], 10. The procedure was similar to the
synthesis of 1 except that HgI2 (0.045 g, 0.1 mmol) was used instead of
HgCl2. Colorless crystals of 10 were formed after 4 days (yield 59%, mp
= 140−142 °C). Anal. Calcd for C22H18Hg2I4N6O2: C, 20.21; H, 1.39;
N, 6.43. Found: C, 20.19; H, 1.38; N, 6.42. FT-IR (CsI pellet, cm−1):
3360 (N-H str. vib.), 1695 (CO amide str. vib.), 1533 (C-N str. and
N-H bend vib.), 1445 (CC str. vib.), 1387 (C-N str. vib.), 1308, 1155,
883, 685 (OC-N group bend vib.), 587 (OC-N group bend vib),
433. 1H NMR (CD3OD, δ from TMS): 10.73 (s, 1H-pyrazine), 9.28 (s,
amidic H), 9.28 (d, 1H-pyrazine), 8.79−8.83 (m, 1H-pyrazine), 7.87 (d,
2H-phenyl), 7.37 (t, 2H-phenyl), and 7.15 (t, 1H-phenyl).
ACKNOWLEDGMENTS
■
We would like to thank the Graduate Study Councils of Shahid
Beheshti University, General Campus, for financial support and
Prof. Richard J. Staples from the Department of Chemistry,
Michigan State University, for data collection on some of single
crystals studied here.
REFERENCES
■
(1) (a) Ali, A.; Hundal, G.; Gupta, R. Cryst. Growth Des. 2012, 12,
1308−1319. (b) Duong, A.; Maris, T.; Wuest, J. D. Inorg. Chem. 2011,
50, 5605−5618. (c) Natale, D.; Mareque-Rivas, J. C. Chem. Commun.
2008, 425−437. (d) Desiraju, G. R. J. Chem. Soc., Dalton Trans. 2000,
3745−3751. (e) Nishio, M. CrystEngComm 2004, 6, 130−158.
(f) Brammer, L. Dalton Trans. 2003, 3145−3157.
Synthesis of [HgI2(L3‑Br)], 11. The procedure was similar to the
synthesis of 10 except that L3‑Br (0.027 g, 0.1 mmol) was used instead of
LH. Colorless crystals of 11 were formed after 2 weeks (yield 51%, mp =
200−202 °C). Anal. Calcd for C11H8BrHgI2N3O: C, 18.04; H, 1.10; N,
5.74. Found: C, 18.03; H, 1.10; N, 5.72. FT-IR (CsI pellet, cm−1): 3350
N
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(2) (a) Janssen, F. F. B. J.; Gelder, R. G.; Rowan, A. E. Cryst. Growth
Des. 2011, 11, 4326−4333. (b) Field, J. S.; Munro, O. Q.; Waldron, B. P.
Dalton Trans. 2012, 41, 5486−5496. (c) Tiekink, E. R. T.; Zukerman-
Schpector, J. CrystEngComm 2009, 11, 1176−1186. (d) He, L.; Ma, D.;
Duan, L.; Wei, Y.; Qiao, J.; Zhang, D.; Dong, G.; Wang, L.; Qiu, Y. Inorg.
Chem. 2012, 51, 4502−4510. (e) Semeniuc, R. F.; Reamer, T. J.; Smith,
M. D. New J. Chem. 2010, 34, 439−452. (f) Hay, B. P.; Bryantsev, V. S.
Chem. Commun. 2008, 2417−2428. (g) Mooibroek, T. J.; Gamez, P.;
Reedijk, J. CrystEngComm 2008, 10, 1501−1515. (h) Schottel, B. L.;
Chifotides, H. T.; Dunbar, K. R. Chem. Soc. Rev. 2008, 37, 68−83.
(3) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. . Acc. Chem. Res.
2005, 38, 386−395.
2006, 45, 1617−1626. (k) Farnum, G. A.; LaDuca, R. L. Cryst. Growth
Des. 2010, 10, 1897−1903. (l) Seward, C.; Chan, J.; Song, D.; Wang, S.
Inorg. Chem. 2003, 42, 1112−1120. (m) Dobrzan
2011, 13, 2303−2309.
́
ska, L. CrystEngComm
(18) Notash, B.; Safari, N.; Khavasi, H. R. Inorg. Chem. 2010, 49,
11415−11420.
(19) (a) Hu, C.; Li, Q.; Englert, U. CrystEngComm 2003, 5, 519−529.
(b) Lee, S. Y.; Park, S.; Kim, H. J.; Jung, J. H.; Lee, S. S. Inorg. Chem.
2008, 47, 1913−1915. (c) Wang, X.-F.; Lv, Y.; Okamura, T.-A.;
Kawaguchi, H.; Wu, G.; Sun, W.-Y.; Ueyama, N. Cryst. Growth Des.
2007, 7, 1125−1133. (d) Zhou, H.-P.; Gan, X.-P.; Li, X.-L.; Liu, Z.-D.;
Geng, W.-Q.; Zhou, F.-X.; Ke, W.-Z.; Wang, P.; Kong, L.; Hao, F.-Y.;
Wu, J.-Y.; Tian, Y.-P. Cryst. Growth Des. 2010, 10, 1767−1776.
(20) Cambridge Structural Database, version 5.33; CCDC: Cambridge,
U.K., November 2011.
(4) (a) Desiraju, G. R.; Parthasarathy, R. J. Am. Chem. Soc. 1989, 111,
8725−8727. (b) Jagarlapudi, A. R.; Sarma, P.; Desiraju, G. R. Acc. Chem.
Res. 1986, 19, 222−228. (c) Awwadi, F. F.; Willett, R. D.; Twamley, B.;
Schneider, R.; Landee, C. Inorg. Chem. 2008, 47, 9327−9332.
(d) Awwadi, F. F.; Willett, R. D.; Twamley, B. Cryst. Growth Des.
2007, 7, 624−632. (e) Brammer, L.; Espallargas, G. M.; Adams, H.
CrystEngComm 2003, 5, 343−345. (f) Zordan, F.; Brammer, L.;
Sherwood, P. J. Am. Chem. Soc. 2005, 127, 5979−5989. (g) Karpfen, A. J.
Phys. Chem. A 2001, 105, 2064−2072. (h) Willett, R. D.; Awwadi, F. F.;
Butcher, R.; Haddad, S. F.; Twamley, B. Cryst. Growth Des. 2003, 3,
301−311. (i) Rosokha, S. V.; Lu, J.; Rosokha, T. Y.; Kochi, J. k. Chem.
Commun. 2007, 3383−3385. (j) Awwadi, F. F.; Willett, R. D.; Haddad, S.
(21) Bondi, A. J. Phys. Chem. 1964, 68, 441−451.
(22) (a) Metrangolo, G.; Resnati, G. Halogen Bonding: Fundamentals
and Applications; Springer: Berlin, 2008. (b) Metrangolo, P.; Meyer, F.;
Pilati, T.; Resnati, G.; Terraneo, G. Angew. Chem., Int. Ed. 2008, 47,
̀
6114−6121. (c) Formigue, M.; Batail, P. Chem. Rev. 2004, 104, 5379−
5418. (d) Politzer, P.; Murray, J. S.; Clark, T. Phys. Chem. Chem. Phys.
2010, 12, 7748−7757. (e) Legon, A. C. Angew. Chem., Int. Ed. 1999, 38,
2686−2714. (f) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc.
Chem. Res. 2005, 38, 386−395. (g) Cavallo, G.; Metrangolo, P.; Pilati,
T.; Resnati, G.; Sansoteraa, M.; Terraneo, G. Chem. Soc. Rev. 2010, 39,
3772−3783. (h) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc.
Chem. Res. 2005, 38, 386−395. (i) Metrangolo, P.; Resnati, G. Science
2008, 321, 918−919. (j) Murray, J. S.; Riley, K. E.; Politzer, P.; Clark, T.
Aust. J. Chem. 2010, 63, 1598−1607.
F.; Twamley, B. Cryst. Growth Des. 2006, 6, 1833−1838. (k) Aakeroy, C.
̈
B.; Desper, J.; Helfrich, B. A.; Metrangolo, P.; Pilati, T.; Resnati, G.;
Stevennazzi, A. Chem. Commun. 2007, 4236−4238.
(5) (a) Brammer, L.; Espallargas, G. M.; Libri, S. CrystEngComm 2008,
10, 1712. (b) Mareque Rivas, J. C.; Brammer, L. Coord. Chem. Rev. 1999,
183, 43−80.
(23) Ananthavel, S. P.; Manoharan, M. Chem. Phys. 2001, 269, 49−57.
(24) Rissanen, K. CrystEngComm 2008, 10, 1107−1113.
(6) Bertani, R.; Sgarbossa, P.; Venzo, A.; Lelj, F.; Amati, M.; Resnati,
G.; Pilati, T.; Metrangolo, P.; Terraneo, G. Coord. Chem. Rev. 2010, 254,
677−695.
(25) (a) COSMO V1.58: Software for the CCD Detector Systems for
Determining DataCollection Parameters; Bruker Analytical X-ray
Systems: Madison, WI, 2008. (b) APEX2 V2008.5-0: Software for the
CCD Detector System; Bruker Analytical X-ray Systems: Madison, WI,
2008. (c) SAINT V 7.34: Software for the Integration of CCD Detector
System; Bruker Analytical X-ray Systems: Madison, WI, 2008. (d)
SADABS V2.008/2, program for absorption corrections using Bruker-
AXS CCD based on the method of Robert Blessing. Blessing, R. H. Acta
Crystallogr. 1995, A51, 33−38.
(7) Aakeroy, C. B.; Sinha, A. S.; Chopade, P. D.; Desper, J. Dalton
̈
Trans. 2011, 40, 12160−12168.
(8) Smart, P.; Espallargas, G. M.; Brammer, L. CrystEngComm 2008,
10, 1335−1344.
(9) Desiraju, G. R. Angew. Chem., Int. Ed. 1995, 34, 2311−2327.
(10) Aakeroy, C. B.; Schultheiss, N.; Desper, J.; Moore, C.
̈
CrystEngComm 2007, 9, 421−426.
(26) (a) X-AREA: Program for the Acquisition and Analysis of Data,
vesion 1.30; Stoe & Cie GmbH: Darmstadt, Germany, 2005. (b) X-
RED: Program for Data Reduction and Absorption Correction, version
1.28b; Stoe & Cie GmbH: Darmstadt, Germany, 2005. (c) X-SHAPE:
Program for Crystal Optimization for Numerical Absorption Correction,
vesion 2.05; Stoe & Cie GmbH: Darmstadt, Germany, 2004.
(27) Sheldrick, G. M. SHELX97: Program for Crystal Structure Solution
(11) Derossi, S.; Brammer, L.; Hunter, C. A.; Ward, M. D. Inorg. Chem.
2009, 48, 1666−1677.
(12) (a) Khavasi, H. R.; Azizpoor Fard, M. Cryst. Growth Des. 2010, 10,
1892−1896. (b) Khavasi, H. R.; Salimi, A. R.; Eshtiagh-Hosseini, H.;
Amini, M. M. CrystEngComm 2011, 13, 3710−3717. (c) Khavasi, H. R.;
Mehdizadeh Barforoush, M.; Azizpoor Fard, M. CrystEngComm 2012,
14, 7236−7244.
and Refinement; University of Gottingen: Gottingen, Germany, 1997.
̈
̈
(13) Sasan, K.; Khavasi, H. R.; Davari, M. D. Monatsh. Chem. 2008,
139, 773−780.
(14) Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955−
964.
(15) Addison, A. W.; Rao, T. N.; Reedijk, J.; Van Rijn, J.; Verschoor, G.
C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356.
(16) (a) Wu, J.-Y.; Hsu, H.-Y.; Chan, C.-C.; Wen, Y.-S.; Tsai, C.; Lu, K.-
L. Cryst. Growth Des. 2009, 9, 258−262. (b) Popovic, Z.; Soldin, Z.;
Matkovic-Calogovic, D.; Pavlovic, G.; Rajic, M.; Giester, G. Eur. J. Inorg.
Chem. 2002, 171−180.
(28) X-STEP32: Crystallographic Package, version 1.07b; Stoe & Cie
GmbH: Darmstadt, Germany, 2000.
(29) Farrugia, L. J. J. Appl. Crystallogr. 2012, 45, 849−854.
(30) Mercury 2.3, supplied with cambridge structural database; CCDC:
Cambridge, U.K., 2003−2004.
(31) Neese, F.; Becker, U.; Ganyushin, D.; Liakos, D. G.; Kossmann, S.;
Petrenko, T.; Riplinger, C.; Wennmohs, F. ORCA, 2.7.0; University of
Bonn: Bonn, Germany, 2009.
(32) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys 1980, 58, 1200−
1211.
(17) (a) Custelcean, R. Chem. Soc. Rev. 2010, 39, 3675−3685.
(b) Mondal, R.; Basu, T.; Sadhukhan, D.; Chattopadhyay, T.; Bhunia, K.
Cryst. Growth Des. 2009, 9, 1095−1105. (c) Reger, D. L.; Semeniuc, R.
F.; Rassolov, V.; Smith, M. D. Inorg. Chem. 2004, 43, 537−554.
(d) Schultheiss, N.; Powell, D. R.; Bosch, E. Inorg. Chem. 2003, 42,
8886−8890. (e) Bai, H.-Y.; Ma, J.-F.; Yang, J.; Liu, Y.-Y.; Wu, H.; Ma, J.-
C. Cryst. Growth Des. 2010, 10, 995−1016. (f) Shatruk, M.; Chouai, A.;
Dunbar, K. R. Dalton Trans. 2006, 2184−2191. (g) Zhang, X.; Zhou, X.-
P.; Li, D. Cryst. Growth Des. 2006, 6, 1440−1444. (h) Ni, J.; Wei, K.-J.;
Liu, Y.; Huang, X.-C.; Li, D. Cryst. Growth Des. 2010, 10, 3964−3976.
(i) Zhang, G.; Yang, G.; Ma, J. S. Cryst. Growth Des. 2006, 6, 1897−1902.
(j) Díaz, P.; Benet-Buchholz, J.; Vilar, R.; White, A. J. P. Inorg. Chem.
(33) (a) Versluis, L.; Ziegler, T. J. Chem. Phys. 1988, 88, 322−328.
(b) Fan, L.; Ziegler, T. J. Chem. Phys. 1991, 95, 7401−7405.
(34) Perdew, J. P.; Chevary, J. A.; Vosko, S. H.; Jackson, K. A.;
Pederson, M. R.; Singh, D. J.; Fiolhais, C. Phys. Rev. 1992, 46, 6671−
6687.
(35) (a) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys.
1993, 99, 4597−4610. (b) van Lenthe, E.; Baerends, E. J.; Snijders, J. G.
J. Chem. Phys. 1994, 101, 9783−9792. (c) van Lenthe, E.; van Leeuwen,
R.; Baerends, E. J.; Snijders, J. G. Int. J. Quantum Chem. 1996, 57, 281−
293.
O
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