The interplay of secondary Hg...S, Hg...N and Hg...π bonding interactions in supramolecular structures of phenylmercury(ii) dithiocarbamates

Article abstract of DOI:10.1039/c1ce05678f

Three new phenylmercury(ii) and one mercury(ii) dithiocarbamate complexes viz. PhHg S₂CN(PyCH₂)Bz (1), PhHg S ₂CN(PyCH₂)CH₃ (2), PhHg S₂CN(Bz) CH₃ (3), and [Hg (NCS₂(PyCH₂)Bz)₂] (4) (Py = pyridine; Bz = benzyl) have been synthesized and characterized by elemental analyses, IR, electronic absorption, ¹H and ¹³C NMR spectroscopy. The crystal structures of 1, 2 and 3 showed a linear S-Hg-C core at the centre of the molecule, in which the metal atom is bound to the sulfur atom of the dithiocarbamate ligand and a carbon atom of the aromatic ring. In contrast the crystal structure of 4 showed a linear S-Hg-S core at the Hg(ii) centre of the molecule. Weak intermolecular Hg...N (Py) interactions link molecules into a linear chain in the case of 1, whereas chains of dimers are formed in 2 through intermolecular Hg...N (Py) and Hg...S interactions. 3 forms a conventional face-to-edge dimeric structure through intermolecular Hg...S secondary bonding and 4 forms a linear chain of dimers through face-to-face Hg...S secondary bonding. In order to elucidate the nature of these secondary bonding interactions and the electronic absorption spectra of the complexes, ab initio quantum chemical calculations at the MP2 level and density functional theory calculations were carried out for 1-3. Complexes 1 and 2 exhibited photoluminescent properties in the solid state as well as in the solution phase. Studies indicate that Hg...S interactions decrease and Hg...N interactions increase the chances of photoluminescence in the solid phase The Royal Society of Chemistry 2011.

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PAPER
The interplay of secondary Hg/S, Hg/N and Hg/p bonding interactions
in supramolecular structures of phenylmercury(II) dithiocarbamates†
a
Vikram Singh, Abhinav Kumar, Rajendra Prasad, Gunjan Rajput, Michael G. B. Drew and Nanhai Singh
b
c
a
d
a
*
Received 4th June 2011, Accepted 15th August 2011
DOI: 10.1039/c1ce05678f
Three new phenylmercury(II) and one mercury(II) dithiocarbamate complexes viz. PhHg S2CN(PyCH2)
Bz (1), PhHg S2CN(PyCH2)CH3 (2), PhHg S2CN(Bz)CH3 (3), and [Hg (NCS2(PyCH2)Bz)2] (4) (Py ¼
pyridine; Bz ¼ benzyl) have been synthesized and characterized by elemental analyses, IR, electronic
absorption, 1H and 13C NMR spectroscopy. The crystal structures of 1, 2 and 3 showed a linear S–Hg–
C core at the centre of the molecule, in which the metal atom is bound to the sulfur atom of the
dithiocarbamate ligand and a carbon atom of the aromatic ring. In contrast the crystal structure of 4
showed a linear S–Hg–S core at the Hg(II) centre of the molecule. Weak intermolecular Hg/N (Py)
interactions link molecules into a linear chain in the case of 1, whereas chains of dimers are formed in 2
through intermolecular Hg/N (Py) and Hg/S interactions. 3 forms a conventional face-to-edge
dimeric structure through intermolecular Hg/S secondary bonding and 4 forms a linear chain of
dimers through face-to-face Hg/S secondary bonding. In order to elucidate the nature of these
secondary bonding interactions and the electronic absorption spectra of the complexes, ab initio
quantum chemical calculations at the MP2 level and density functional theory calculations were carried
out for 1–3. Complexes 1 and 2 exhibited photoluminescent properties in the solid state as well as in the
solution phase. Studies indicate that Hg/S interactions decrease and Hg/N interactions increase the
chances of photoluminescence in the solid phase
their relevance to mercury detoxification.9b Organomercury(II)
dithiocarbamates have been found to be extremely versatile
groups for construction of supramolecular arrays,11a exhibit
photoluminescence properties,11b,c and used as dyes for solar
energy harvesting.11d
Introduction
A great deal of interest in dithiocarbamate chemistry is
concentrated on the functionalisation of the dithiocarbamate
substituents which allows more complex architectures to be
developed and potentially gives rise to tuneable physical
properties.1–8 However, the pivotal challenge still faced by
crystal engineers is the rational assembly of the molecular
components into 3-D arrays controlling the full gamut of
intermolecular interactions.
Previous studies on phenylmercury(II) dithiocarbamate
complexes revealed the fact that the bulkiness of the pendant
group in the dithiocarbamate part of the compound plays an
important role in the construction of the supramolecular archi-
tecture through Hg/S interactions.11b Alcock termed such
contacts as ‘‘secondary interactions’’.12 Organomercury(II)
dithiocarbamates having an –NH2 group in the periphery of the
dithiocarbamate ligand have been reported,11a but, because of the
steric restrictions of these groups, the compounds have not
exhibited intermolecular Hg/N secondary interactions. These
weak Hg/N secondary interactions and other non-covalent
forces can also determine the solid state luminescent properties of
these organometallic compounds.13
Organomercury(II) compounds continue to attract significant
attention owing to their importance in the preparation of other
organometallics,9,10 as intermediates in organic chemistry9a and
aDepartment of Chemistry, Faculty of Science, Banaras Hindu University,
Varanasi, 221005, India. E-mail: nsingh@bhu.ac.in; Fax: +91 542
2368127; Tel: +91 542 2307321 ext. 108
bDepartment of Chemistry, Faculty of Science, University of Lucknow,
Lucknow, 226007, India
cDepartment of Chemistry, S.G.B. Amrawati University, Amrawati,
444602, India
dDepartment of Chemistry, University of Reading, Whiteknight, Reading,
RG6 6AD, UK
Hence, in the quest for new types of secondary interactions
containing the less common Hg/N and supramolecular motifs
we herein report the synthesis, characterization, x-ray structures
and photoluminescent properties of new phenylmercury(II) and
mercury(II) dithiocarbamates having pyridine in the pendant
group of the dithiocarbamate. The magnitude of intermolecular
interaction energies in supramolecular motifs of 1, 2, and 3 has
† Electronic supplementary information (ESI) available. CCDC
reference numbers 796965–796967, 828129. For ESI and
crystallographic data in CIF or other electronic format see
DOI:10/1039/c1ce05678f
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been estimated at the MP2 level of theory. The UV-Vis electronic
absorption spectra of these complexes have been assigned using
TD-DFT calculations.
in complexes reported earlier (Table 1). However, as compared
to the previously reported complexes, the deviation for the
linearity is considerably greater in the case of compound 1. This
may be attributed to some what stronger intermolecular Hg/N
(Py) secondary bonding in 1. Within the dithiocarbamate func-
Results and discussion
ꢀ
ꢀ
tion, C–N bond lengths of 1.33(3) A and 1.329(16) A for 1 and 2
respectively, indicate a substantial delocalization of the p-elec-
tron density in these bonds.15
General aspects
The secondary amines were obtained by the condensation of the
aldehyde functionalized pyridine and an amine to give the cor-
responding imine, followed by its subsequent reduction. From
these pyridyl containing secondary amines, the potassium salts of
the dithiocarbamates were prepared by addition of KOH and
CS2 in equimolar ratio in THF : acetonitrile medium.
The structure of 3 shows an interesting variation as the metal
atom is disordered over two sites in a 47 : 53 ratio (Fig. 3). The
two metal atoms Hg(1a) and Hg(1b) form strong bonds to the
ꢀ
phenyl carbon C1 at 2.135(8) and 2.212(9) A and also strong
ꢀ
bonds to one of the sulfur atoms S(11) at 2.190(2) A or S(13) at
ꢀ
2.260(2) A, in trans positions and weak bonds to S(11) at 3.113(2)
Complexes 1–4 were prepared by addition of phenylmercuric
acetate/mercuric acetate to methanolic solutions of dithiocar-
bamate salts in appropriate molar ratios to give white or light
yellow solids (Scheme 1). All the compounds are air-stable and
characterized by elemental analyses, IR, 1H and 13C NMR
spectroscopy and their structures elucidated by single crystal
x-ray diffraction. Single crystals of all complexes were obtained
by the slow evaporation of dichloromethane–methanol mixture
solutions.
ꢀ
ꢀ
A or S(13) at 3.126(2) A respectively. Thus both mercury posi-
tions offer environments that are equivalent to those found in 1
and 2 with linear arrangements, S(11)–Hg(1a)–C(1) being 173.7
(2)ꢁ and S(13)–Hg(1b)–C(1) 171.1(2)ꢁ.
In complex 4 the metal atom is positioned on a crystallographic
centre ofsymmetry andbondedtotwodithiocarbamate ligands. As
in the previous three structures the metal is in a 2-coordinate linear
ꢀ
environment being bonded to S(11) at 2.3901(9) A. In addition
ꢀ
there are weak interactions to S(13) at 2.9432(9) A (Fig. 4).
Our previous results showed that the bulkiness of the pendant
groups is often responsible for preventing the phenylmercury(II)
dithiocarbamates to exhibit additional molecular Hg/S
secondary interactions.11b,11c As reported for PhHgS2CNBz2 (Bz
¼ –CH2C6H5),11b because of the bulky benzyl group the orga-
nomercury complex forms only one Hg/S interaction instead of
two. Hence, in the quest for the new type of secondary bonding it
was decided to replace one of the benzyl (CH2C6H5) groups of
this compound by the methyl pyridyl (CH2C5H4N) group to
obtain complex 1. As anticipated complex 1 features interesting
intermolecular Hg/N (Py) secondary bonding leading to the
formation of a molecular chain (Fig. 5a). These Hg/N (Py)
Spectroscopy
The IR spectra of all the complexes show distinct vibrational
bands at 1003–1029 and 973–991 cmꢀ1 that can be assigned to the
n(CS2) vibration. The observed splitting of the n(CS2) in all the
four compounds may be attributed to monodentate coordination
of sulfur atom of the dithiocarbamate ligand to Hg and PhHg
moieties. The bands in the 1315–1425 cmꢀ1 region in all the
complexes are associated primarily with the thioureide vibration
and can be assigned to the n(C]N) which is appreciably higher
than the free ligand and thereby indicates a significant increase in
the partial double bond character in the C–N bond. The bands at
422–460 cmꢀ1 are assigned to the stretching vibration of the Hg–
C bond.
ꢀ
contacts of dimension 2.74(2) A are comparable to the sum of the
van der Waals radii of the respective elements (rvdw (Hg) ¼ 1.73–
ꢀ
ꢀ
2.00 A and rvdw (N) ¼ 1.55 A). The S–Hg/N bond angle is 108.3
(6)ꢁ. This intermolecular Hg/N (Py) secondary bonding is
important because it prevents 1 from forming head to tail dimers
through Hg/S secondary bonding, a characteristic feature of
the phenylmercury(II) dithiocarbamates.
The purity and composition of the compounds were checked
by NMR spectroscopy. All of the compounds display well
1
resolved H NMR signals which integrate well into the corre-
sponding hydrogens. A perceptible upfield shift of d z 10 ppm in
the 13C spectrum for C–S2 carbon as compared to the free
dithiocarbamate ligands is observed in all the complexes and
indicates the M–S bonding in the complexes.
Unlike complex 1, complex
2 comprising –CH3 and
–CH2C5H4N groups displays both intermolecular Hg/N (Py)
and Hg/S secondary bonding having distances 2.983(4) and
ꢀ
3.403(4) A, respectively, leading to the formation of chain of two
Molecular structures
dimers (Fig. 5b). The S–Hg/N bond angle is 87.6(3)ꢁ which
shows that the N position looks to be directly in a T position. It is
noteworthy here that on reducing the bulkiness of one of the
pendant groups from CH2C6H5 to CH3, the intermolecular Hg/
S secondary bonding is once again restored in complex 2
(Fig. 5b). Also, in contrast to the pyridyl analogue, the complex 3
possessing –CH3 and –CH2C6H5 groups forms head to tail
dimers through Hg(A) or Hg (B)/S interactions of length 3.126
The immediate coordination geometry about the Hg atom in 1
and 2 is defined by the ipso-C atom of the phenyl group and the
atom S(11) of the dithiocarbamate ligand as shown in Fig. 1 and
2. In addition there is a weak interaction from Hg(1) to S(13).
ꢀ
The Hg–S(11) bond lengths in 1 and 2 are 2.413(5) and 2.400(4) A
respectively, while the weak interactions Hg1/S(13) are 2.993(6)
ꢀ
and 2.981(4) A in 1 and 2 respectively, thereby reflecting the
ꢀ
propensity of Hg to exist in a linear coordination geometry. The
proximity of atom S(13) is partly responsible for the deviation
from the ideal linear geometry, as seen in the (Ph)C–Hg–S(11)
bond angles of 165.2(5)ꢁ and 176.6(4)ꢁ for 1 and 2 respectively.
These bond lengths and angles are in close agreement with those
(2) and 3.177(2) A (Fig. 5c). This can be attributed to the bulk-
iness of the benzyl group. In order to see the effect of the bulk-
iness of the phenyl group in the formation of new secondary
interactions, complex 4 was prepared with replacement of the
phenylmercury moiety by the mercury(II) ion.
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Scheme 1 Syntheses of the dithiocarbamate ligands and their organomercury(II) and mercury(II) complexes.
The crystal structures of the compounds 1, 2, 3 and 4 as dis-
cussed above are good examples of the interplay of different
molecular interactions that lead to interesting supramolecular
aggregates in the solid state (Fig. 5 and 6). It is obvious that Hg/
S, Hg/N (Py) and Hg/arene (p) interactions play an important
role if the structure is to be rationalized in terms of interactions
between the molecular fragments. However, the question as to
what kind of intermolecular interaction(s) contribute to the
binding energy between molecules and dimers in the structure
need to be investigated. It is known that the covalent, H-bond,
dipole–dipole, and van der Waals interaction energies are >1700,
70–50, 8–2, and <4 kJ molꢀ1, respectively. In order to analyze the
various interactions that lead to the crystal structure, interaction
energies and electrostatic potentials have been calculated for
dimer and trimer fragments keeping Hg/S and Hg/N(Py)
distances fixed at values obtained from the X-ray single-crystal
structure analyses.
This analysis of the interaction energy in the crystal structure
of 1 by means of dimer unit at the MP2 level of theory yields an
interaction energy in the Hg/N (Py) dimer of ꢀ14 kJ molꢀ1
.
While interaction energies in the crystal structure of 2 by means
of dimer and trimer units at the MP2 level of theory yields an
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Fig. 3 Perspective view of the molecular structure for compound 3.
ꢁ
ꢀ
Selected metric data (A, ): Hg(1a)–S(11) 2.190(2), Hg(1b)–S(13) 2.260(2)
ꢀ
A, Hg(1a)–S(13) 3.126(2), Hg(1a)–C(1) 2.212(9), Hg(1b)–C(1) 2.135(8), C
(12)–N(14) 1.327(7); C(1)–Hg(1a)–S(11) 173.7(4) C(1)–Hg(1b)–S(13)
171.1(2).
Fig. 1 Perspective view of the molecular structure for compound 1.
ꢁ
ꢀ
Selected metric data (A, ): Hg–S(11) 2.413(5), Hg–S(13) 2.993(6), Hg–C
(1) 2.074(15), C(12)–N(14) 1.33(3); C(1)–Hg–S(11) 165.2(5), C(1)–Hg–S
(13) 112.1(5).
Fig. 4 Perspective view of the molecular structure for compound 4.
ꢀ
Selected metric data (A): Hg(1)–S(11) 2.390(9), Hg(1)–S(13) 2.943(9), C
Fig. 2 Perspective view of the molecular structure for compound 2.
Selected metric data (A, ꢁ): Hg(1)–S(11) 2.400(4), Hg(1)–S(13) 2.981(4),
ꢀ
(12)–N(14) 1.334(4).
Hg(1)–C(1) 2.102(13), C(12)–N(14) 1.329(16); C(1)–Hg(1)–S(11) 176.6
(4), C(1)–Hg(1)–S(13) 116.9(4).
as a trimer formed by weak cooperative type Hg/N (Py) and
Hg/S interactions.
interaction energy in the Hg/N (Py) dimer of ꢀ59 kJ molꢀ1 (i.e.,
29.5 kJ molꢀ1 per Hg/N (Py) secondary bond), the interaction
energy of Hg/S is calculated to be ꢀ55 kJ molꢀ1 (i.e.,
27.5 kJ molꢀ1 per Hg/S secondary bond), and the interaction
energy in the trimer including the Hg/N (Py) and Hg/S
interactions is ꢀ109 kJ molꢀ1. The structure can be characterized
Analysis of the interaction energies in the crystal structure of 3
(Fig. 5c) by means of dimer units at the MP2 level of theory
yields an interaction energy of Hg/S that is calculated to be
ꢀ52 kJ molꢀ1 (i.e., 26 kJ molꢀ1 per Hg/S secondary bond). In
order to gain some insight into the Hg/p(Ar) interaction
Table 1 Selected geometric parameters for PhHg(dithiocarbamate) structures
a
f
C–Hg–S/ꢁ
Hg/S/A
ꢀ
Hg–S2/A
ꢀ
C–Hg–S/A
ꢀ
Compound
Ref.
PhHg(S2CN(Bun)2)
PhHg(S2CN(CH2)4O)
11b
11b
11b
11b
14a
14b
14c
14c
11c
11c
11c
11d
11d
2.402(2)
2.9465(19)
2.9725(13)
2.905(3)
170.60(19)
169.97(14)
176.1(3)
3.22; 3.87
3.17; 3.61
3.36
3.55
3.1178
3.1809
3.191; 3.398
3.133; 3.174
3.23
2.3979(12)
2.395(2)
2.392(2)
2.4009(13)
2.4033(9)
2.385(3)
2.387(3)
2.388(2)
2.412(12)
2.401(3), 2.400(3)
2.402(3)
PhHg(S2CNBz2)b
PhHg(S2CNBz2)c
PhHg(S2CN(CH2)4)
2.924(3)
174.0(3)
2.9056(13)
2.9093(10)
2.978(3)
2.923(3)
2.965(2)
2.9025(11)
2.876(3), 2.882(3)
2.958(3)
2.981(3)
172.22(14)
166.76(10)
171.3(3)
172.2(3)
168.5(3)
170.91(12)
175.8(3), 176.8(4)
168.5(3)
PhHg(S2CN(Prn)2)
PhHg(S2CNEt2)d
PhHg(S2CNEt2)e
PhHgS2CN(CH2Fc)CH2C6H5
PhHgS2CN(CH2Fc)CH2CH(CH3)2
[PhHgS2CN(CH2Fc)]2(CH2C6H4CH2)
PhHgS2CN(CH2Fc)CH2C5H4N
PhHgS2CN(CH2Fc)CH2C4H3O
3.08
3.303; 3.749; 3.640
3.181
3.174
2.397(3)
168.3(3)
a
The Hg/S2 distance refers to the ‘‘chelate’’ Hg/S2 interactions.b Two molecules in the asymmetric unit: molecule 1.c Two molecules in the
asymmetric unit: molecule 2.d Two molecules in the asymmetric unit: molecule 1.e Two molecules in the asymmetric unit: molecule 2.f Intermolecular
interactions.
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Fig. 5 (a) Molecular chain through intermolecular Hg/N interactions; (b) chains of dimers through intermolecular Hg/N and Hg/S interactions;
(c) head to tail dimer through intermolecular Hg/S interactions; (d) face to face dimers through intermolecular Hg/S interaction; (e) Hg/p and Hg/
S interaction in reported complex.11b
energy, an analysis of the interaction energies for the previously
11b
230 nm due to ligand centered charge transfer transitions. The
observed absorption bands of 1–3 have been explained with the
help of TD-DFT calculations. The vertical excitation energies,
oscillator strength, composition, and tentative nature of transi-
tions obtained at the TD-DFT level have been listed in Table 2.
Since each absorption line in a TD-DFT spectrum is due to
several single excitations, a description of the transition character
is generally not straightforward. However, approximate assign-
ments have been made, although they provide a simplified
representation of the transitions. The calculations reveal that in
all the three complexes the first energy band is dominated by the
HOMO / LUMO transition and can be assigned to transition
from the lone pairs of two sulfur atoms and some minimal charge
transfer from the Hg center to the thioureide group; however,
intensity is relatively weak; therefore this is a local transition
(Fig. S1–S3 in the ESI†). The next two higher energy transitions
reported complex, PhHgBz2NCS2 (5) exhibiting the Hg/p
(Ar) and Hg/S interaction was calculated at the MP2 level of
theory and yields an interaction energy of ꢀ26 kJ molꢀ1. These
combined interaction energies are significantly lower than the
single Hg/S interactions. This is basically because of the rela-
tively large Hg/p(Ar) and Hg/S interaction distances as
compared to those found in 2 and 3. The different intermolecular
interaction energies for all four compounds are in the range
between 30 and 15 kJ molꢀ1, which is well beyond the range of H-
bond or dipole–dipole interactions.
Electronic absorption spectra and photoluminescent properties
The electronic absorption spectra of complexes 1–4 in
dichloromethane solution display common bands at around 360–
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broad and red shifted luminescent emission in the case of 1 can be
attributed to the intermolecular Hg/N (Py) interactions oper-
ating in the solid phase which were absent in dichloromethane
solution.20 As evident from the photoluminescent emissions of 2
in both solution and solid phase it appears that Hg/N (Py)
intermolecular interactions may induce the red shift in photo-
luminescent emission, whilst the Hg/S interactions are sup-
pressing this effect. This can be further substantiated by the fact
that for a previously reported complex PhHgBz2dtc11b a medium
strong photoluminescent emission in dichloromethane solution
was observed at ꢂ420 nm when the complex was excited at
355 nm. The comparatively broad emission complex in the solid
state resulted in ꢂ40 nm bathochromic shift which may be
attributed to the Hg/C (p) intermolecular interactions present
in this complex.
Fig. 6 Electrostatic potentials plotted at the van der Waals surfaces for
the complexes 1, 2, 3 and 5 (PhHgBz2NCS2),11b calculated at the MP2
level of theory, yellow/blue denote areas of low/high charge density.
Conclusions
are ascribed to electron transfer from the lone pair of the sulfur
atoms and the p electrons of the dithiocarbamate nitrogen to the
thioureide group in the case of 1 and to the p orbital of the
aromatic ring in the case of 3. From the calculations it is
apparent that the incorporation of the pyridine ring in the
dithiocarbamate ligand does not alter the position of electronic
absorption bands.
In summary it can be concluded that replacing the aliphatic or
aromatic hydrocarbon groups by a heteroaromatic group like
pyridine, enables the PhHg(II) dithiocarbamates to undergo new
secondary bonding interactions and also alleviate the likelihood
of forming additional Hg/S interactions, a characteristic
feature of the PhHg(II) dithiocarbamtes. Hence, the incorpora-
tion of heteroaromatic rings into the dithiocarbamate ligands
leads to interesting supramolecular architectures. The solid state
emission studies demonstrated that the presence of sole Hg/S
interactions decreases the probability of photoluminescent
emission, whereas Hg/N (Py) intermolecular interaction
increases its probability. Quantum chemical calculations for 2
also indicated that the presence of both Hg/N (Py) and Hg/S
interactions in the same molecule induces cooperative effects.
In comparison to other metals ions, the photoluminescent
properties of the mercury(II) compounds are less explored.16–19
The photoluminescent spectra of the complexes were recorded in
dichloromethane solution as well as in the solid state in the form
of film. In dichloromethane solution (Fig. 7a), when excited at
336 nm the complexes 1 and 2 exhibited emissions at ꢂ400 and
465 nm, respectively. The photoluminescent quantum yield (F)
for 1 and 2 measured in dichloromethane versus pyridyl-2-amine
was found to be 0.305% and 0.167%, respectively. No photo-
luminescent emission was observed in the case of 3 and 4.
In the solid state when excited at 336 nm (Fig. 7b), the
complexes 1 and 2 display strong broad photoluminescent
emissions at ꢂ435 and 465 nm, respectively. It is noteworthy that
in the case of 2, the position of the photoluminescent emission in
both solution and solid phase does not show any change. The
Experimental details
General considerations
All chemicals were of analytical grade obtained from commercial
sources and used without further purification. The solvents were
purified in accordance with the standard methods.
Table 2 TD-DFT calculated excitations and approximate assignments for 1, 2 and 3
Oscillator
strength (f)
Nature of the
transition and approximate assignment
Excitation energy/eV
Wavelength/nm
Composition (%)
1
3.48
4.43
4.84
5.32
2
356
280
256
233
0.0005
0.0622
0.0332
0.0134
HOMO / LUMO (48%)
HOMO-1 / LUMO (35%)
HOMO-1 / LUMO (47%)
HOMO-6 / LUMO (29%)
lp (S) / NCS2
lp (S) + p (N) / NCS2
lp (S) + p (N) / NCS2
p (Py) / NCS2
3.67
4.37
4.75
338
284
261
0.0036
0.0513
0.1274
HOMO / LUMO (44%)
HOMO-1 / LUMO (37%)
HOMO-2 / LUMO (13%)
HOMO-6 / LUMO (12%)
HOMO-5 / LUMO (18%)
lp (S) / NCS2
lp (S) + p (N) / NCS2
lp (S) + p (N) / NCS2
5.15
3
240
0.1520
p (Py) / NCS2
3.61
4.27
4.94
5.29
343
290
251
234
0.0008
0.0334
0.2157
0.0096
HOMO / LUMO (48%)
HOMO-1 / LUMO (35%)
HOMO / LUMO + 3 (45%)
HOMO-4 / LUMO (23%)
lp (S) / NCS2
lp (S)+ p (N)/NCS2
lp (S)+ p (N)/p*
p (PhHg) + p (Bz) / NCS2
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NC5H5). 13C NMR (75.45 MHz, DMSO-d6): d 216.75CS2,
d 153.1, 149.5, 147.0, 146.0 (NC5H5), d 138.5, 138.3, 128.3, 127.9,
126.7 (C6H5), d 54.0 (NC5H5CH2–), d 53.2 (–CH2C6H5).
Synthesis of potassium N-methyl-N-methyl pyridine
dithiocarbamate
The method adopted for synthesis is similar as mentioned above
except that methyl amine (0.031 g, 1 mmol) was used instead of
benzyl amine.
1H NMR (300.40 MHz, DMSO-d6): d 8.51 (M, 2H,C5H5N),
d 7.17–7.41 (M, 6H, C6H5 and C5H5N), d 7.17–7.41 (M, 6H,
C6H5 and C5H5N), d 5.28 (S, 2H, –CH2NC5H5). 13C NMR (75.45
MHz, DMSO-d6): d 212.6 (CS2), 149.7, 149.6, 148.5 (NC5H5),
44.08 (–CH3), 59.42 (–C5H5CH2C5H5N).
Synthesis of potassium N-methyl-N-benzyl dithiocarbamate
The ligand was prepared in accordance with the reported
method.21 A 5 mL aqueous solution of KOH (0.056 g, 1 mmol)
was added to the N-benzyl-N-methylamine (0.121 g, 1 mmol).
The reaction mixture was stirred for 15 min and then kept in an
ice-bath and CS2 (0.0760 g, 1 mmol) was added to this in
a dropwise manner. The reaction mixture was stirred for another
1 h and vacuum evaporated to dryness to obtain off-white
precipitate (0.19 g, 88% yield).
1H NMR (300.40 MHz, DMSO-d6): d 7.27 (m, 5H, benzyl),
5.30 (s, 3H, CH3), 3.29 (s, 2H, PhCH2). 13C NMR (75.45 MHz,
DMSO-d6): d 215.9 (CS2), 132.8, 128.5, 128.3, 127.7 (–C6H5),
57.7 (–CH2Ar), 39.7 (–CH3).
Fig. 7 (a) Photoluminescent spectra for the complexes recorded in
dichloromethane solution; (b) photoluminescent spectra recorded as thin
solid film.
1H and 13C NMR spectra were recorded on a JEOL AL 300
Fourier transform (FT) NMR spectrophotometer. Chemical
shifts were reported in parts per million using TMS as internal
standard. Elemental analysis was performed on an Exeter
analytical Inc ‘‘Model CE-440 CHN analyzer’’. Electronic
absorption spectra were recorded on a Shimadzu UV-1700
pharma spec UV-Vis spectrophotometer. Photoluminescent
spectra in solution and solid phase were recorded on a Varian
Cary Eclipse fluorescence spectrophotometer having a slit width
of 5 nm and a Horiba Jobin Yvon Fluorolog-3, respectively.
Synthesis of PhHgC5H4NCH2NCS2CH2C6H5 (1)
The potassium N-benzyl-N-methyl pyridine dithiocarbamate
(0.312 g, 1 mmol) was dissolved in 5 mL methanol and phenyl-
mercuric acetate (0.335 g, 1 mmol) was added in portions. The
reaction mixture was stirred overnight and the solvent was
removed to obtain a light yellow solid product (0.482 g, 87%
ꢁ
yield), mp 140 C.
1H NMR (300.40 MHz, CDCl3): d 8.62 (M, 2H, C5H4N),
d 7.38–7.20 (M, 6H, C6H5 and NC5H5), d 5.07 (S, 4H, –CH2Ar).
13C NMR (75.45 MHz, CDCl3): d 206.7 (CS2), 153.8, 150.3
(NC5H5), 137.6, 137.0, 134.4, 129.0, 128.8, 128.7, 128.5, 128.4,
128.3, 127.8, 122.2 (–C5H5), 58.0 (–CH2C6H5N), 55.0 (–CH2Ar).
nmax (KBr)/cmꢀ1 1412 (C]N), 1026 and 1074 (C–S), 454 (C–Hg).
Anal. Calc. for C20H18N2S2Hg C, 43.59; H, 3.29; N, 5.08; S,
11.64%. Found: C, 43.55; H, 3.35; N, 5.03; S, 11.45%.
Synthesis of potassium N-benzyl-N-methyl pyridine
dithiocarbamate
Pyridine-4-carboxaldehyde (0.107 g, 1 mmol) and benzyl amine
(0.108 g, 1 mmol) were dissolved in 5 mL ethanol and the mixture
was refluxed for 5 h. The reaction mixture was kept in an ice bath
and reduced with NaBH4 in methanol and the product was
extracted with dichloromethane (50 mL) and washed with water
(2 ꢃ 25 mL). An oily yellow solid was collected on solvent
removal. The resulting N-benzyl-N-methylpyridylamine ligand
(0.198 g) was dissolved in 10 mL THF : acetonitrile (50 : 50 v/v)
and then KOH (0.056 g, 1 mmol), followed by CS2 (0.076 g,
1 mmol) was added. The mixture was stirred for 2 h. The solvent
was removed under vacuum and the product was washed with
diethyl ether (3 ꢃ 15 mL). The light yellow solid product
(0.312 g) was obtained.
Synthesis of PhHgC5H4NCH2NCS2CH3 (2)
The ligand potassium N-methyl-N-methyl pyridine dithiocarba-
mate (0.236 g, 1 mmol) was dissolved in 5 mL methanol and
phenylmercuric acetate (0.335 g, 1 mmol) was added in portions.
The reaction mixture was stirred overnight and the solvent was
removed. The residue was extracted in DCM and the organic
solution was washed thrice with water followed with brine. The
organic layer was dried over anhydrous sodium sulfate and then
filtered to collect the filtrate. The solvent was removed to give
1H NMR (300.40 MHz, DMSO-d6): d 8.53 (2H, m, C5H5N),
ꢁ
7.18–7.40 (6H, m, C6H5 and C5H5N), d 5.37 (4H, s, ArCH2,
a light yellow solid product (0.412 g, 89% yield), mp 173 C.
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CrystEngComm, 2011, 13, 6817–6826 | 6823

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1H NMR (300.40 MHz, CDCl3): d 8.63 (M, 2H, C5H5), 7.21,
7.23, 7.25, 7.36, 7.38, 7.42, 7.44 (M, 6H, C6Hs and NC5H5), d 2.16
(S, 3H, CH3). 13C NMR (75.45 MHz, CDCl3) d 205.70 (CS2),
150.35, 143.9, 137.6, 137.03 (NC5H4), 128.78, 128.68, 128.49,
128.3, 122.07 (C5H5), 59.79 (–CH2C5H5N), 43.2 (–CH3). nmax
(KBr)/cmꢀ1 1420 (C]N), 1032 and 1086 (C–S), 462 (C–Hg).
Anal. Calc. for C13H14N2S2Hg, C, 33.73; H, 3.05; N, 6.05; S,
13.85%. Found: C, 33.70; H, 3.25; N, 5.99; S, 13.75%.
122.09 (–C6H5), 59.67 (–CH2C5H4N), 57.69 (–CH2Ar). nmax
(KBr)/cmꢀ1 1420 (C]N), 1028 and 1076 (C–S), Anal. Calc. for
C28H26N4S4Hg C, 45.00; H, 3.51; N, 7.50; S, 17.16%. Found: C,
44.98; H, 3.51; N, 7.42; S, 16.92%
Crystallography
Intensity data for the colorless crystals 1 and 3 were collected at
150(2) and 298(2) K, respectively on a Bruker SMART diffrac-
tometer system equipped with graphite monochromated Mo Ka
Synthesis of PhHgCH3NCH2C6H5CS2 (3)
ꢀ
radiation l ¼ 0.71073 A. The final unit cell determination, scaling
To a stirring methanol solution (30 mL) of PhHgO2CCH3 (0.335
g, 1 mmol) was added a methanol solution (20 mL) of Na
(C6H5CH2)(CH3)NCS2 (0.219 g, 1 mmol). The white precipitate
3 (0.389 g, 82%) formed was additionally stirred for 30 min. This
was filtered and washed twice with diethyl ether and vacuum
dried, mp 184 ꢁC.
1H NMR (300.40 MHz, CDCl3): d 7.27 (m, 5H, benzyl), d 5.30
(S, 3H, CH3), d 3.29 (s, 2H, PhCH2). 13C NMR (75.45 MHz,
CDCl3): d 209.9, 132.8, 128.5, 128.3, 127.7, 57.7, 39.7. nmax
(KBr)/cmꢀ1 1416 (C]N), 1029 and 1078 (C–S), 460 (C–Hg).
Anal. Calc. for C15H15NS2Hg C, 38.01; H, 3.19; N, 2.95; S,
13.53%. Found: C, 37.98; H, 3.20; N, 2.91; S, 13.42%.
of the data, and corrections for Lorentz and polarization effects
were performed with Bruker SAINT.22 A symmetry-related
(multi-scan) absorption correction had been applied. The data
for the colorless crystals 2 and 4 were collected at 298(2) K on
a Sapphire2-CCD, Oxford diffractometer system equipped with
ꢀ
graphite monochromated Mo Ka radiation l ¼ 0.71073 A and
correct empirically for absorption effects. The final unit cell
determination, scaling of the data, and corrections for Lorentz
and polarization effects were performed with CrysAlis RED.23
Structure solution followed by full-matrix least squares refine-
ment was performed using the WINGX-1.70 suite24 of programs
for 1 and 3 and the SHELX suite for compounds 2 and 4. While
the phenyl ring in 3 is likely to be disordered, in common with the
Hg position, we were unable to refine a suitable model. In 4, the
ligand contained a phenyl and a pyridine ring but the position of
the nitrogen was disordered between the two rings with pop-
ulation parameters of x and 1 ꢀ x, x refining to 0.63(4).
Empirical absorption corrections were carried out with
ABSPACK.25 All non-hydrogen atoms were refined anisotropi-
cally and located at calculated positions and refined using
a riding model with isotropic thermal parameters fixed at 1.2
times the Ueq value of the appropriate carrier atom.
Synthesis of Hg(C6H5CH2CS2CH2C5H4N)2 (4)
To a 5 mL methanolic solution of the ligand potassium N-benzyl-
N-methyl pyridine dithiocarbamate (0.312 g, 1 mmol) was added
slowly a 5 mL solution of mercuric acetate (0.159 g, 0.5 mmol) in
same solvent. The reaction mixture was stirred for 6 h the light
yellow precipitate thus forms was filtered off washed with dieth-
ylether and dried under vaccum (0.645 g, 82% yield), mp 172 ꢁC.
1H NMR (300.40 MHz, CDCl3): d 8.32 (m, 4H, C5H5N),
d 7.27–7.16 (m, 10H, –C6H5), d 7.36 (m, 4H, C5H4N), d 5.09 (s,
4H, –CH2Ar). 13C NMR (75.45 MHz, CDCl3): d 205.60 (CS2),
149.56, 142.32, 136.23, 135.38 (NC5H4), 127.45, 126.32, 124.65,
In the case of 1, the largest difference between the peak and
hole were 3.22 and ꢀ5.29 e Aꢀ3, respectively both close to the
ꢀ
Table 3 Crystallographic data and structure refinements for 1, 2, 3 and 4a
1
2
3
4
Empirical formula
Formula weight/g molꢀ1
Crystal system
C20H18HgN2S2
551.07
Monoclinic
P21
9.559(4)
9.846(4)
10.043(4)
101.732(6)
925.5(6)
2
C14H14HgN2S2
478.98
Monoclinic
P21/n
8.4029(3)
15.5076(6)
11.8130(4)
102.430(4)
1503.26(9)
4
C15H15HgNS2
474.00
Monoclinic
P21/n
6.0864(7)
14.1681(15)
18.7008(18)
108.658(3)
1527.9(3)
4
C28H26HgN4S4
747.37
Monoclinic
C2/c
33.05804(18)
4.6030(4)
19.1970(9)
109.660(10)
2750.0(3)
4
Space group
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
b/deg
3
ꢀ
V/A
Z
Dcalc/g cmꢀ3
1.978
8.546
2.099
10.503
2.061
10.332
1.805
5.922
Absorption coefficient/mmꢀ1
F(000)
528
0.37 ꢃ 0.21 ꢃ 0.05
896
0.47 ꢃ 0.32 ꢃ 0.20
896
0.42 ꢃ 0.18 ꢃ 0.16
1464
0.45 ꢃ 0.43 ꢃ 0.40
Crystal size/mm3
Reflections collected
Independent reflections
Reflections with I > 2s(I)]
Final R indices [I > 2s(I)]
R indices (all data)
Goodness-of-fit on F2
5933
4004 [Rint ¼ 0.043]
3460
5879
3242 [Rint ¼ 0.042]
2322
11762
2960 [Rint ¼ 0.033]
2090
11896
3081 [Rint ¼ 0.034]
2481
R1 ¼ 0.061 wR2 ¼ 0.152 R1 ¼ 0.079 wR2 ¼ 0.213 R1 ¼ 0.040 wR2 ¼ 0.089 R1 ¼ 0.035 wR2 ¼ 0.063
R1 ¼ 0.084 wR2 ¼ 0.219 R1 ¼ 0.106 wR2 ¼ 0.229 R1 ¼ 0.062 wR2 ¼ 0.098 R1 ¼ 0.049 wR2 ¼ 0.067
1.25
3.22 and ꢀ5.29
1.03
5.07 and ꢀ4.63
1.04
1.18 and ꢀ0.68
1.09
0.61 and ꢀ0.47
ꢀ3
ꢀ
Largest difference peak and hole/e A
a
R1 ¼ SkF0| ꢀ |Fck/S|F0|. R2 ¼ {[Sw(F0 ꢀ Fc )/Sw(F0 )2]}1/2, w ¼ 1/[s2(F0 ) + (xP)2], where P ¼ (F02 + 2Fc )/3.
2
2
2
2
2
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5 (a) G. Hogarth, E.-J. C.-R. C. R. Rainford-Brent and I. Richards,
Inorg. Chim. Acta, 2009, 362, 1361; (b) C. Anastasiadis, G. Hogarth
and J. D. E. T. Wilton-Ely, Inorg. Chim. Acta, 2010, 363, 3222.
6 (a) P. D. Beer, N. Berry, M. G. B. Drew, O. D. Fox, M. E. Padilla-
Tosta and S. Patell, Chem. Commun., 2001, 199; (b) O. D. Fox,
M. G. B. Drew and P. D. Beer, Angew. Chem., Int. Ed., 2003, 39, 135.
7 (a) R. E. Benson, C. A. Ellis, C. E. Lewis and E. R. T. Tiekink,
CrystEngComm, 2007, 9, 930; (b) R. A. Howie, G. M. de Lima,
D. C. Menezes, J. L. Wardell, S. M. S. V. Wardell, D. J. Young
and E. R. T. Tiekink, CrystEngComm, 2008, 10, 1626; (c)
S. Naeem, E. Ogilvie, A. J. P. White, G. Hogarth and
J. D. E. T. Wilton-Ely, Dalton Trans., 2010, 39, 4080; (d)
E. R. T. Tiekink and J. Zukerman-Schpector, Coord. Chem. Rev.,
2010, 254, 46; (e) E. R. T. Tiekink and D. J. Young, J. Chem.
Crystallogr., 2008, 38, 419; (f) I. Haiduc, in Comprehensive
Coordination Chemistry II, ed. J. A. McCleverty and T. J. Meyer,
Elsevier Ltd, Oxford, UK, 2004, vol. 1, p. 349.
metal atom and the absolute structure parameter was ꢀ0.05(3)
confirming the refined absolute structure. Whereas in 2, the
largest difference peak and hole 5.07 and ꢀ4.63 e Aꢀ3 both close
ꢀ
to the metal atom. The crystallographic data are presented in
Table 3.
Computational details
Molecular geometries were optimized at the level of density
functional theory (DFT) using the B3LYP exchange-correlation
functional.26 The split valence basis sets, 6-31G**, were used at
all C, N, and H atom centers whereas basis set, 6-311G**, was
used at S atom centers. Stephens–Basch–Krauss ECP triple-split
basis set, CEP-121G, was used for Hg atom. The optimized
structures of the complexes at DFT level were used for molecular
orbital analyses and vertical electronic absorption spectra
calculations. Solvent effects on the vertical electronic spectra
were investigated by using polarized continuum model (PCM).27
The solvent parameters were those of dichloromethane. The
excitation energies and intensities of the six lowest-energy spin
allowed electronic transitions were calculated using the time
dependent density functional theory (TD-DFT). The intermo-
lecular interaction energies have been estimated at the MP2 level
of theory. For the interaction energy calculations, the Hg/S,
Hg/N and Hg/C (p) distances have been fixed for the dimers
and trimers while all other degrees of freedom were relaxed in the
geometry optimization. The magnitudes of energies corre-
sponding to these dimers and trimers were subtracted from twice
the energy of monomer in the cases of dimers or three times for
trimers. The intermolecular interaction strengths are significantly
weaker than either ionic or covalent bonding, therefore it was
essential to do basis set superposition error (BSSE) corrections.
The BSSE corrections in the interaction energies were done using
the Boys–Bernardi Scheme.28 In this paper all interaction ener-
gies have been reported after BSSE correction. All computa-
tional experiments have been performed using the Gaussian 03
programme.29 The electrostatic potential at van der Waals
surface plots was obtained with the MOLDEN program.30
8 (a) G. M. de Lima, D. C. Menezes, C. A. Cavalcanti, J. A. F. dos
Santos, I. P. Ferreira, E. B. Paniago, J. L. Wardell,
S. M. S. V. Wardell, K. Krambrock, I. C. Mendes and H. Beraldo,
J. Mol. Struct., 2011, 988, 1; (b) A. Mederos, A. Cachapa,
ꢁ
R. Hernandez-Molina, M. T. Armas, P. Gili, M. Sokolov,
J. Gonzalez-Platas and F. Brito, Inorg. Chem. Commun., 2003, 6, 498.
ꢁ
9 (a) E. Wehman, G. van Koten and J. T. B. H. Jastrzebski, J. Chem.
Soc., Dalton Trans., 1988, 2975; (b) A. F. M. J. van der Ploeg,
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J. Chem. Soc., Dalton Trans., 1981, 933; (h) W. J. Scott and
J. K. Stille, J. Am. Chem. Soc., 1986, 108, 3033.
10 (a) R. C. Larock, Angew. Chem., Int. Ed. Engl., 1978, 17, 27; (b)
J. G. Melnick, K. Yurkerwich and G. Parkin, Inorg. Chem., 2009,
48, 6763.
11 (a) C. S. Lai and E. R. T. Tiekink, CrystEngComm, 2003, 5, 253; (b)
N. Singh, A. Kumar, K. C. Molloy and M. F. Mahon, Dalton Trans.,
2008, 4999; (c) N. Singh, A. Kumar, R. Prasad, K. C. Molloy and
M. F. Mahon, Dalton Trans., 2010, 39, 2667; (d) V. Singh,
R. Chauhan, A. Kumar, L. Bahadur and N. Singh, Dalton Trans.,
2010, 39, 9779.
12 (a) N. W. Alcock, Adv. Inorg. Chem. Radiochem., 1972, 15, 1; (b)
N. W. Alcock, Bonding and Structure: Structural Principles in
Inorganic and Organic Chemistry, Ellis Horwood, New York, 1990;
(c) I. Haiduc and F. T. Edelmann, Supramolecular Organometallic
Chemistry, Wiley-VCH, Weinheim, 1999; (d) I. Haiduc, Secondary
Bonding, in Encyclopedia of Supramolecular Chemistry, ed. J. L.
Atwood and J. Steed, Marcel Dekker Inc., New York, 2004,
p. 1215.
13 (a) R. J. Pudephatt, Chem. Commun., 1998, 1055; (b) R. J. Pudephatt,
Coord. Chem. Rev., 2001, 216–217, 313; (c) H. Schumidbaur, Chem.
Soc. Rev., 1995, 24, 391; (d) M. I. Bruce, B. C. Hall,
B. W. Skeleton, M. E. Smith and A. H. White, J. Chem. Soc.,
Dalton Trans., 2002, 995; (e) P. Li, B. Ahrens, K.-H. Choi,
M. S. Khan, P. R. Raithby, P. J. Khan, M. S. Wilson and
W.-Y. Wong, CrystEngComm, 2002, 4, 405.
14 (a) C. S. Lai and E. R. T. Tiekink, Acta Crystallogr., Sect. E: Struct.
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Acknowledgements
We are grateful to Council of Scientific and Industrial Research,
New Delhi for financial assistance in the form of Senior Research
Fellowship (VS) and Project no. 01(2290)/09/EMR-II and SAP,
Department of Chemistry, Banaras Hindu University, Varanasi
for providing computational facility. AK is grateful to Professor
William S. Sheldrick and Mrs Heike Mayer-Figge for solving the
X-ray data and also for their immense support and
encouragement.
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