Syntheses, crystal and molecular structures, and properties of some new phenylmercury(ii) dithiolate complexes

Article abstract of DOI:10.1039/b804635b

A series of new phenylmercury(ii) dithio complexes [PhHg(Bu ⁿ₂dtc)] (1; Buⁿ₂dtc^- = di-n-butyldithiocarbamate), [PhHg(morphdtc)] (2; morphdtc^- = morpholinedithiocarbamate), [PhHg(Bz₂dtc)] (3; Bz₂dtc ^- = dibenzyldithiocarbamate), [PhHg(methoxethxant)] (4; methoxethxant^- = 2-methoxyethylxanthate) [(PhHg)₂NED] (5; NED^2- = 1-nitroethylene-2,2-dithiolate) and [(PhHg)₂CDC] (6; CDC^2- = cyanodithioimidocarbonate) have been prepared and characterized by elemental analysis, UV-Vis, IR, ¹H and ¹³C NMR spectra and mass spectrometry. The crystal structures of 1, 2 and 3 showed a linear Hg(ii) core at the center of the molecules. The weak intra- and intermolecular Hg-S interactions provide a molecular chain framework. The reaction of PhHgO₂CCH₃ with Bu ⁿ₂dtcH gave the known dimeric complex Hg(Bu ⁿ₂dtc)₂ while the Ni(O₂CCH ₃)₂ mediated reaction gave 1 instead of the expected heterobimetallic complex [PhHgNi(Buⁿ₂CS₂) ₂]O₂CCH₃ which has been corroborated by natural charges at each atom obtained at the density functional level (DFT) of theory. Upon excitation at 358 nm 3 exhibited a medium strong photoluminescence emission at 420 nm as a consequence of intraligand π → π* transitions. The electronic absorption bands of 3 were assigned from time dependent density functional theory (TD-DFT) calculations. Geometrical configurations of 4, 5 and 6 have been optimized using the DFT method. All of the complexes are weakly conducting (σ_rt ～ 10^-12 S cm^-1). However 2 and 6 exhibited semiconductivity with band gaps of 0.39 and 0.94 eV respectively. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b804635b

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PAPER
www.rsc.org/dalton | Dalton Transactions
Syntheses, crystal and molecular structures, and properties of some new
phenylmercury(II) dithiolate complexes†
b
Nanhai Singh,*‡a Abhinav Kumar,a Kieran C. Molloyb and Mary F. Mahon*§
Received 18th March 2008, Accepted 4th July 2008
First published as an Advance Article on the web 1st August 2008
DOI: 10.1039/b804635b
A series of new phenylmercury(II) dithio complexes [PhHg(Bun dtc)] (1; Bun dtc− =
2
2
di-n-butyldithiocarbamate), [PhHg(morphdtc)] (2; morphdtc− = morpholinedithiocarbamate),
[PhHg(Bz2dtc)] (3; Bz2dtc− = dibenzyldithiocarbamate), [PhHg(methoxethxant)] (4; methoxethxant− =
2-methoxyethylxanthate) [(PhHg)2NED] (5; NED2− = 1-nitroethylene-2,2-dithiolate) and
[(PhHg)2CDC] (6; CDC2− = cyanodithioimidocarbonate) have been prepared and characterized by
elemental analysis, UV-Vis, IR, 1H and 13C NMR spectra and mass spectrometry. The crystal structures
of 1, 2 and 3 showed a linear Hg(II) core at the center of the molecules. The weak intra- and
intermolecular Hg · · · S interactions provide a molecular chain framework. The reaction of
PhHgO2CCH3 with Bun dtcH gave the known dimeric complex Hg(Bun dtc)2 while the Ni(O2CCH3)2
2
2
mediated reaction gave 1 instead of the expected heterobimetallic complex
[PhHgNi(Bun CS2)2]O2CCH3 which has been corroborated by natural charges at each atom obtained at
2
the density functional level (DFT) of theory. Upon excitation at 358 nm 3 exhibited a medium strong
photoluminescence emission at 420 nm as a consequence of intraligand p → p* transitions. The
electronic absorption bands of 3 were assigned from time dependent density functional theory
(TD-DFT) calculations. Geometrical configurations of 4, 5 and 6 have been optimized using the DFT
method. All of the complexes are weakly conducting (rrt ∼ 10−12 S cm−1). However 2 and 6 exhibited
semiconductivity with band gaps of 0.39 and 0.94 eV respectively.
reaction of the organomercurials which allows the simultaneous
Introduction
formation of symmetric diorganomercurials HgR2 and Hg(II)
complexes.7 Such reactions, involving the cleavage of an Hg–C
bond, are promoted by strong complexing agents such as sulfur
donors.7
Organomercury(II) compounds of the type R2Hg and RHgX (R =
alkyl or aryl; X = halide or acetate)1 have received considerable
attention over the last three decades mainly related to the search for
biologically active compounds and versatile reagents in controlled
transmetallation reactions.2 These compounds have been used
for many years as intermediates in organic chemistry3 and in
the preparation of other organometallics.4 Their convenience lies
in the ease with which they transfer their organic groups to
other atoms, usually replacing a halide or other anionic group.
In this way, many new cyclometallated complexes otherwise
inaccessible by classical Grignard or lithiation reactions have been
prepared.4a,i,5 Recent studies have indicated that the coordination
of organomercury(II) ions by the donors so as to increase the
metal coordination from the usual linear dicoordination to a
higher coordination number is quite important in the activation
of the Hg–C bond, both in the enzymatic degradation processes
and laboratory chemical reactions.6 Symmetrization is a general
The xanthate and dithiocarbamate ligands have been found
to be extremely versatile moieties for metal directed self as-
sembly leading to supramolecular arrays.8 In recent years some
organomercury dithiocarbamates, xanthates and dithiophos-
phates have been prepared and their structures investigated.8–10
These possess a linear geometry with significant intra- and inter-
molecular Hg · · · S interactions.11 Organomercury(II) compounds
provide Lewis acidic metal centers having greater propensity for
soft sulfur donors, which can provide intra- and intermolecular
Hg · · · S secondary or hypervalent interactions12–14 with diverse
and fascinating structural motifs required for crystal engineering.
Mono anionic 1,1-dithioligands such as dithiocarbamate
and xanthate as well as dianionic 1,1-dithioligands e.g.
cyanodithioimidocarbonate (CDC2−)15 and 1-nitroethylene-2,2-
dithiolate (NED2−), where thio functions are on the same car-
bon, differ appreciably in behaviour.16–18 The dinegative CDC2−
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*108
and NED2− may exhibit greater electron delocalization in their
2−
=
≡
complexes through C–S, C N and N–C N bonds in CDC
bDepartment of Chemistry, University of Bath, Bath, UK BA2 7AY.
E-mail: m.f.mahon@bath.ac.uk
and C–S, C C and NO2 bonds in NED2−, while no such
dominant delocalizations are envisaged in the case of xanthate
and dithiocarbamate ligands (Chart 1).
=
† Electronic supplementary information (ESI) available: Fragmentation
pattern for 1 and 2, electronic absorption spectra, selected orbital
transitions. CCDC reference numbers 681258–681260 (1, 2 and 3). For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/b804635b
‡ For general correspondence.
§ For crystallographic correspondence.
Further, the ligand dithiocarbamates and xanthate discussed
herein differ from those reported with regards to differing bulky
functionalities.19 This difference in behaviour may provide varying
degrees of strain thereby influencing inter- and intra-ligand S · · · S
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Scheme 1
Chart 1
negative charges while the nickel possesses the positive charge as
expected, whereas in the phenyl mercuric acetate the mercury atom
and the carboxylic carbon bear the positive charge and the two
oxygen atoms possess negative charges, which indicates that the
ionic interaction is dominating between the Hg and the acetate O
atom.
Due to the positive charge on the mercury(II), the coordinated
sulfur atom of the nickel complex attacks the thiophilic mercury
center to form the preferred linear organomercury(II) dithio
complex. The remaining unstable part of the nickel complex gives
nickel sulfide. From the calculated natural charges on various
atoms, we propose the expected reaction pathway for the formation
of 1 (Scheme 1).
and Hg · · · S and other weaker interactions such as hydrogen
bonding affecting the overall geometry and molecular stacking
in the solid phase.
Despite their synthetic versatility16–18 and wide range of appli-
cations, to the best of our knowledge no work is reported on
the organomercury complexes with the dinegative ligands CDC2−
and NED2−. Bearing in mind the above facts and our interest in
the solid state structure and properties of the organomercury(II)
dithio complexes, we herein report the synthesis, characteriza-
tion, solid state conductivity and photoluminescent properties
of a series of complexes formed with PhHg(II) and the ligands
Bun dtc−, morphdtc−, Bz2dtc−, methoxethxant−, NED2− and
2
All of the compounds are air stable. Crystals of 2 suitable for
X-ray analysis were obtained by slow evaporation of acetone–
acetonitrile solution while that of 3 was obtained by slow diffusion
of methanol in chloroform solution. While the crystals of 1 were
obtained directly from the reaction mixture.
CDC2−. Density functional theory (DFT) and time dependent
density functional theory (TD-DFT) calculations have been
performed in order to obtain insights into the reaction mechanisms
and electronic spectral properties respectively.
Results and discussion
Spectroscopy
General aspects
The IR spectra of all the complexes show distinct vibrational
bands at 1003–1029 and 973–991 cm−1 that can be assigned to
m(CS2) vibration. The observed splitting of the m(CS2), especially
in 1, 2, 3 and 4, may be attributed to monodentate coordination
of the sulfur atom of the ligand to the PhHg moiety. In 5 and 6,
the presence of only one strong absorption suggests symmetrical
bidentate behaviour of the dithiolate groups. The bands in the
1315–1425 cm−1 region in 1, 2, 3 and 6 are associated primarily
Excepting 1, all the other phenylmercury(II) dithio complexes were
synthesized by reacting a methanolic solution of phenylmercuric
acetate and the dithio ligands in methanol–water in appropriate
stoichiometric ratios as shown in eqn 1 and 2.
=
with the thioureide vibration and is assigned to m(C N), which is
appreciably higher than the free ligand and indicates a significant
increase in the partial double bond character in the C–N bond.
In the case of 4 the m(C–O) frequency also noticeably increases
because of the greater electron delocalization over the O–CS2
group. The bands at 422–460 cm−1 are assigned to the stretching
vibration of Hg–C.
The purity and composition of the compounds were checked by
NMR spectroscopy. All of the compounds display well-resolved
1H NMR signals which integrate to the corresponding hydrogens.
A perceptible shift of ∼10 ppm in the 13C spectrum for the C–S2
carbon in all the complexes as compared to the free dithio ligands
indicates the M–S bonding in the complexes. The ES-MS spectra
of 1, 2 and 3 are summarized in the Experimental section.
(1)
(2)
The synthetic procedure for 1 was entirely different in compar-
ison to the other above mentioned compounds. An attempt was
made to prepare 1 by reacting Bun NCS2H and PhHgO2CCH3
in stoichiometric ratio but it resulted in the formation of the
dimeric Hg(Bun NCS2)2 complex20 which we have also charac-
2
2
terized crystallographically. However, in an attempt to isolate the
heterobimetallic complex [PhHgNi(Bun NCS2)2]O2CCH3 by the
2
reaction of Ni(Bun NCS2)2 and PhHgO2CCH3, the crystals of 1
2
were obtained leaving a black precipitate of nickel sulfide.
The natural charges over various atoms of interest are displayed
in Scheme 1. In the case of the nickel complex, the coordinated
sulfur and nitrogen atoms of the dithiocarbamate ligand possess
Crystal structure
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
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S(1) of the dithiocarbamate ligand (Fig. 1 and 2). The Hg–S(1)
˚
bond lengths for 1 and 2 are 2.402(2) and 2.3979(12) A respectively.
These are significantly shorter than the Hg · · · S(2) distances of
˚
2.9465(19) and 2.9725(13) A for 1 and 2 respectively, thereby
reflecting the propensity of Hg to exist in linear coordination
geometry. The proximity of atom S(2) is partly responsible for
the deviation from the ideal linear geometry, as seen in the C(1)–
Hg–S(1) bond angle of 170.60(19)◦ and 169.97(14)◦ for 1 and 2
respectively. The deviations from planarity of atoms Hg, S(1), S(2)
˚
and C(7), defining the chelate ring are 0.03, 0.06, 0.05 and 0.08 A
˚
respectively for 1, while for 2 these are 0.02, 0.03, 0.03 and 0.04 A
respectively. For 1, the angle between the least-squares plane, i.e.
Hg, S(1), S(2) and C(7), and that through the Hg-bound phenyl
ring is 23.2◦, and for 2 it is 23.1◦, thereby indicating a certain degree
of coplanarity. The C(7)–N bond length in 1 and 2 are 1.322(9) and
˚
1.332(6) A respectively. These values are intermediate to that of C–
˚
˚
=
N (1.47 A) and C N (1.28 A), thereby indicating the partial double
bond character between the C(7)–N bond of the ligand moiety. In
Fig. 3 ORTEP diagram of a molecule of 3 at 50% probability with
the atom numbering scheme; H atoms are omitted for clarity. The
asymmetric unit comprises two independent molecules.
4
2 the morpholine ring adopts a normal C chair conformation.
Selected bond lengths and bond angles are given in Table 1.
C(7), which defines the chelate ring, are 0.02, 0.03, 0.04 and
˚
0.05 A respectively. For Hg(2), S(3), S(4) and C(28) these are 0.02,
˚
0.03, 0.03 and 0.04 A respectively. The angle between these least-
squares planes and those through the Hg-bound phenyl rings are
37.9◦ and 35.0◦ respectively, thereby indicating a certain degree of
coplanarity in the two molecules present in the asymmetric unit.
The intermolecular S(2) · · · Hgꢀ interactions in 1 and 2 have
˚
distances of 3.22 and 3.17 A respectively (sym. op: 1 − x, −y, 1 −
z) and join the molecules into dimers (Fig. 4 and 5). These Hg · · · S
contacts are comparable to the sum of the van der Waals radii
˚
of the respective elements (rvdw(Hg) = 1.73–2.00 A and rvdw(S) =
8
˚
1.80 A) and are in the range for organomercury dithiocarbamates.
These dimers are almost orthogonal to each other so there are also
weak Hgꢀꢀ · · · S(1) interactions in both 1 and 2, having distances
˚
of 3.87 and 3.61 A respectively (sym. op.: x − 1/2, 1/2 − y, z),
joining the dimers together and thus give rise to chains of dimers
in both 1 and 2.
Fig. 1 ORTEP diagram of a molecule of 1 with 50% probability, together
with the atom numbering scheme; H atoms are omitted for clarity.
Fig. 2 ORTEP diagram of a molecule of 2 at 50% probability with the
atom numbering scheme; H atoms are omitted for clarity.
Like 1 and 2, the crystal structure of 3 has two molecules in
the asymmetric unit (Fig. 3 and Table 1) and a mercury core at
the center of the linear coordination sphere. The Hg(1)–S(2) and
˚
Hg(2)–S(3) bond lengths are 2.395(2) and 2.392(2) A respectively
Fig. 4 Molecular chain for 1 showing weak intra- and intermolecular
Hg · · · S interactions. Symmetry operation: Hgꢀ = 1 − x, −y, 1 − z; Hgꢀꢀ =
x − 1/2, 1/2 − y, z.
which are shorter than Hg(1) · · · S(1) and Hg(2) · · · S(4) distances
˚
having dimensions 2.905(3) and 2.924(3) A respectively. There is
considerable difference between the two C–S bond distances of
the ligand, which is the possible cause for the slight deviation
from ideal linear geometry as seen in the C(1)–Hg(1)–S(2) and
C(22)–Hg(2)–S(3) bond angles 176.1◦ and 174.0◦ respectively.
The deviation from planarity of atoms Hg(1), S(1), S(2) and
Unlike 1 and 2, in 3 there are only chains of molecules, not chains
of dimers, (Fig. 6) due to weak bonds between S(3)ꢀ · · · Hg(1)
ꢀ
˚
˚
(3.42 A) and S(2) · · · Hg (3.41 A) (sym. op: 1 + x, y, z). Also in
3, each Hg atom has two short interactions with the neighboring
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Table 1 Selected bond lengths and angles for complexes 1, 2 and 3
˚
Bond lengths/A
1
2
3
Hg–C(1)
Hg–S(1)
Hg–S(2)
S(1)–C(7)
S(2)–C(7)
N–C(7)
2.085(8)
2.402(2)
2.9465(19)
1.754(7)
1.712(7)
1.322(9)
Hg–C(1)
Hg–S(1)
Hg–S(2)
S(1)–C(7)
S(2)–C(7)
N–C(7)
2.078(5)
2.3979(12)
2.9725(13)
1.750(5)
1.699(5)
1.332(6)
Hg(1)–C(1)
Hg(1)–S(2)
Hg(1)–S(1)
Hg(2)–C(22)
Hg(2)–S(3)
Hg(2)–S(4)
S(1)–C(7)
2.079(10)
2.395(2)
2.905(3)
2.098(9)
2.392(2)
2.924(3)
1.665(9)
1.726(10)
1.789(12)
1.699(11)
1.399(14)
1.296(13)
S(2)–C(7)
S(3)–C(28)
S(4)–C(28)
N(1)–C(7)
N(2)–C(28)
Bond angles/◦
1
2
3
C(1)–Hg–S(1)
C(1)–Hg–S(2)
S(1)–Hg–S(2)
C(7)–S(1)–Hg
C(7)–S(2)–Hg
C(7)–N–C(8)
C(7)–N–C(12)
C(12)–N–C(8)
170.60(19)
118.6(2)
67.17(5)
94.5(2)
C(1)–Hg–S(1)
C(1)–Hg–S(2)
S(1)–Hg–S(2)
C(7)–S(1)–Hg
C(7)–S(2)–Hg
C(9)–O–C(10)
C(7)–N–C(8)
C(7)–N–C(11)
C(11)–N–C(8)
169.97(14)
114.32(14)
66.66(4)
95.19(16)
77.70(16)
108.9(3)
123.9(4)
121.8(4)
113.4(4)
C(1)–Hg(1)–S(2)
C(1)–Hg(1)–S(1)
S(2)–Hg(1)–S(1)
C(22)–Hg(2)–S(3)
C(22)–Hg(2)–S(4)
S(3)–Hg(2)–S(4)
C(7)–S(1)–Hg(1)
C(7)–S(2)–Hg(1)
C(28)–S(3)–Hg(2)
C(28)–S(4)–Hg(2)
C(7)–N(1)–C(8)
C(7)–N(1)–C(15)
C(8)–N(1)–C(15)
C(28)–N(2)–C(29)
C(28)–N(2)–C(36)
C(29)–N(2)–C(36)
176.1(3)
116.5(3)
67.26(7)
174.0(3)
117.4(3)
67.40(8)
77.6(4)
92.9(4)
95.0(3)
79.8(4)
121.8(7)
123.8(8)
114.4(7)
125.0(9)
120.7(9)
114.2(8)
77.9(2)
122.5(6)
122.5(6)
114.9(6)
Fig. 6 Molecular chain for 3 showing weak intra- and intermolecular
Hg · · · S and intermolecular Hg · · · C interactions. Symmetry operation:
1 + x, y, z.
Fig. 5 Molecular chain for 2 showing weak intra- and intermolecular
Hg · · · S interactions. Symmetry operation: Hgꢀ = 1 − x, −y, 1 − z; Hgꢀꢀ =
x − 1/2, 1/2 − y, z.
˚
˚
phenyl ring. Hg(1) · · · C(23) (3.36 A), Hg(1) · · · C(24) (3.55 A);
˚
˚
Hg(2) · · · C(5) (3.51 A), Hg(2) · · · C(6) (3.37 A) which are absent
in the case of 1 and 2. These distances fall within the sum of the
˚
van der Waals radii of the element (rvdw(Hg) = 1.73–2.00 A and
˚
r
vdw(C) = 1.70 A) and are comparable to those found in several
mercurials that features Hg · · · C(p) interactions.21
Fig. 7 Optimised molecular structures for 4, 5 and 6.
Despite our best efforts we could not grow single crystals of 4,
5 and 6. The optimized structure of all these are shown in Fig. 7.
In all the three optimized structures, the mercury core lies at the
center of the almost linear coordination sphere. In 4, the Hg
lying at the center of the linear coordination sphere exhibits
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Table 2 Selected bond lengths and angles for complexes 4, 5 and 6
˚
Bond lengths/A
4
5
6
Hg–S(1)
Hg–S(2)
C(2)–S(1)
C(3)–S(2)
Hg–C(1)
2.501
2.935
1.921
1.875
2.058
Hg(1)–S(1)
Hg(2)–S(2)
C(3)–S(1)
C(3)–S(2)
Hg(1)–C(1)
Hg(2)–C(2)
2.465
2.435
1.743
1.795
2.112
2.113
Hg(1)–S(1)
Hg(2)–S(2)
C(3)–S(1)
C(3)–S(2)
Hg(1)–C(1)
Hg(2)–C(2)
2.503
2.508
1.903
1.900
2.056
2.048
Bond angles/◦
4
5
6
S(1)–Hg–C(1)
S(2)–Hg–C(1)
S(1)–C(2)–S(2)
171.99
112.36
123.98
S(2)–Hg(2)–C(2)
S(1)–Hg(1)–C(1)
S(1)–C(3)–S(2)
177.83
174.22
109.27
S(2)–Hg(2)–C(2)
S(1)–Hg(1)–C(1)
S(1)–C(3)–S(2)
C(4)–N–C(3)
175.11
160.11
120.32
114.95
intramolecular Hg · · · S interactions. In the case of 5, only one Hg
is involved in an Hg · · · O interaction with the nitro group while
the other remains free. In 6, one Hg is showing an intramolecular
Hg · · · N interaction with the nitrile group, while the other Hg
displays an intramolecular Hg · · · N interaction with the imido
nitrogen of the CDC2− ligand. The selected bond lengths and
bond angles for 4, 5 and 6 are given in Table 2.
Electronic absorption spectra and photoluminescent properties
As compared to other metal ions, studies on the photoluminescent
properties of mercury(II) compounds are scarce.22–25 Compounds
1, 2 and 3 display very similar electronic absorption spectra in
chloroform and exhibit bands near 250, 300 and 350 nm which
may be assigned to intraligand transitions.
In CHCl3 solution, 3 exhibits three bands at 358, 300 and
260 nm in the ultraviolet region (Fig. 8). The TD-DFT calculation
indicates that the low energy band (calculated at 356 nm with
oscillator strength of 0.0014) is due to the HOMO → LUMO
electron excitation and attributed to the electron transfer from the
uncoordinated sulfur atom of the ligand to the imido nitrogen
(Fig. 9). The next two bands (calculated at 288 and 263 nm
with oscillator strengths of 0.0547 and 0.2137 respectively) are
assigned to the charge transfer transitions from the coordi-
nated and uncoordinated sulfur atoms to the imido group of
the ligand dibenzyldithiocarbamate and to the aromatic ring
of the organomercury (Fig. 9). Additionally, the absorptions
calculated at 259 and 253 nm with oscillator strengths of 0.0466
and 0.0261 respectively are ascribed to ligand-to-metal charge
Fig. 9 Selected molecular orbitals for 3 (orbital contour values are 0.05).
transfer (LMCT) transitions (Fig. 9). The absorption wavelength
values, oscillator strengths and major contributions are listed in
Table 3.
When excited at its maximum wavelength for absorption, i.e.
at 358 nm, only 3 shows a medium-strong photoluminescence
emission at 420 nm (Fig. 8). These bands are mainly associated
with the intraligand (p → p*)25 transitions, possibly with some
admixture of the metal orbitals.
Fig. 8 Electronic absorption ( ) and fluorescence spectra (---) of 3.
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Table 3 Computed absorption wavelength (k/nm), oscillator strengths
(f ), and transition nature of 3
by conventional reaction of the reactants. The complexes 2 and
6 exhibited semiconductivity, whereas 3 showed photolumines-
cent properties because of the significant intraligand p → p*
transitions. The TD-DFT calculations show that the electronic
absorption spectrum of 3 exhibits charge transfer transitions
mainly from the coordinated and uncoordinated sulfur atoms
to the imido group of the ligand dibenzyldithiocarbamate. The
k
Energy/eV
Oscillator strength
Major contribution
356
288
272
263
259
254
253
252
252
249
3.4821
4.2982
4.5614
4.7156
4.7809
4.8849
4.9093
4.9140
4.9162
4.9735
0.0014
0.0547
0.0024
0.2137
0.0466
0.0261
0.0014
0.0221
0.0106
0.0039
n → p*
n → p*
n → p*
n → p* (ILCT)
LMCT
n
unsuccessful synthesis of 1 by the reaction of Bu2 NCS2H and
LMCT
PhHgO2CCH3, which led to the formation of known dimeric
n
p → p*
n → p*
p → p*
n → p*
[Hg(Bu2 CS2)2]2, confirms the group transferring property of the
organomercury compounds.
Experimental
General considerations
Pressed pellet conductivity
All the compounds are very weakly conducting with rrt
All manipulations were conducted under open atmosphere. Sol-
vents were dried in accordance with the literature procedures. IR as
KBr pellets and 1H and 13C NMR spectra were recorded on Varian
3100 FTIR and JEOL AL300 FTNMR spectrophotometers re-
spectively. Chemical shifts were reported in parts per million using
TMS as internal standard. Electronic absorption and fluorescence
spectra were collected on Shimadzu UV-1700 PharmaSpec UV-
Vis Spectrophotometer and Perkin Elmer LS-45 fluorescence
spectrometer respectively. Elemental analyses and ESI-MS were
performed by Sophisticated Analytical Instrumentation Facility,
Central Drug Research Institute, Lucknow. The pressed pellet
conductivity of the complexes was recorded on a Keithley
236 Source Measure Unit by employing a conventional two
probe technique. Cyanamide, potassium hydroxide, phenylmer-
curic acetate (Aldrich), carbon disulfide (Merck), di-n-butylamine,
dibenzylamine (BDH), morpholine (Qualigens), nitromethane
(Spectrochem) and methoxyglycol (Riedel) were used as received.
Dipotassium cyanodithioimidocarbonato26 and dipotassium 1-
nitroethylene-2,2-dithiolate27 were synthesized according to the
literature procedure. The dithioxanthate CH3OCH2CH2OCS2K
was prepared by reacting the methoxyglycol, carbon disulfide and
KOH in equimolar ratio.
=
10−12 S cm−1. Nevertheless 2 and 6 exhibit semiconductivity
with band gaps of 0.39 and 0.94 eV respectively (Fig. 10).
The solid-state electronic absorption spectra of 2 and 6 display
bands between 230–500 nm region which indicates intramolecular
delocalisation.† However, the absence of bands in the visible
region is indicative of the fact that there is no intermolecular
conjugation between the molecules in the solid state. The absence
of intermolecular conjugation, along with the irregular stacked
structures, is the probable cause of the extremely weak conducting
behaviour of the compounds. Also, with an increase in temperature
the enhancement in r may be attributed to the thermal activation
of electrons.
Synthesis of [PhHg(Bun dtc)] (1). Di-n-butylamine (0.34 ml,
2
2 mmol) in w◦ater (4 ml) was added gradually to CS2 (0.12 ml,
2 mmol) at 0 C with continuous stirring. This was additionally
stirred at room temperature for 1 h. Ni(O2CCH3)2·6H2O (0.249 g,
1 mmol) dissolved in water (4 ml) was added to this reaction
mixture slowly and was continually stirred for 4 h at room
temperature. To this diethyl ether (20 ml) was added to separate
the organic phase which was washed thrice with water. The dark
green coloured ethereal solution was filtered and to this was
added a methanolic solution (30 ml) of PhHgO2CCH3 (0.336 g,
1 mmol) and stirred for another 2 h. The resulting solution was
filtered to obtain a clear light green solution which was kept for
evaporation. After 24 h the colour of the solution changed to
black and thereafter keeping it for 3 d colourless crystals of 1
(0.130 g, 27%) (instead of anticipated heterobimetallic complex)
were separated along with the black precipitate presumably of
nickel sulfide. Found: C, 37.14; H, 4.78; N, 2.87; S, 13.30%.
C15H23NS2Hg requires: C, 37.26; H, 4.80; N, 2.90; S, 13.24%.
Fig. 10 Temperature dependence pressed pellet conductivity for 2 and 6.
Conclusions
In summary, we have synthesized and characterized six phenylmer-
cury(II) complexes with some mono- and di-negative 1,1-
dithioligands. The weak Hg · · · S interactions exhibited by the
complexes 1, 2 and 3 lead to supramolecular aggregation. Unlike
other phenylmercury(II) dithiocarbamates, 3 exhibited only one
Hg · · · S interaction because of bulkiness of the ligand and, exclu-
sively, also shows Hg · · · C(p) interactions. Addition of nickel(II)
promoted the synthesis of 1 which was not isolated otherwise
mmax(KBr)/cm−1 1420 cm−1 (C N), 1018 and 973 (C–S), 453 (Hg–
=
C). kmax(CHCl3)/nm 299 and 349. dH(300 MHz; CDCl3; Me4Si)
0.97 (t, 6H, –CH3), 1.38 (q, 4H, –CH2–), 1.79 (t, 4H, –CH2–), 3.76
5004 | Dalton Trans., 2008, 4999–5007
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=
(t, 4H, –CH2–N), 7.38 (m, 5H, –C6H5). dC(75.45 MHz; CDCl3;
Me4Si) 12.8 (–CH3), 19.1 (–CH2–), 28.0 (–CH2–), 54.6 (–CH2–N),
126.4, 127.1, 128.8, 135.5, 136.2, 153.7 (–C6H5), 200.9 (C–S). m/z
(EI) 172.0 (40%), 412.3 (42), 452.6 (100), 483.1 (8). rrt 9.24 × 10−12
S cm−1.
4.15; S, 9.47%. mmax(KBr)/cm−1 1591 (C C), 1291 and 1508 (N–
O), 905 (C–N), 1021 (C–S), 422 (C–Hg). kmax(DMSO)/nm 286 and
=
410. dH(300 MHz; DMSO-d6; Me4Si) 4.22 (s, 1H, –C C–H), 7.35
(m, 10H, –C6H5). dC(75.45 MHz; DMSO-d6; Me4Si) 127.1 (H–
C C), 127.9, 128.4, 136.7, 138.2 (–C6H5), 171.0 (C–S). rrt 11.09 ×
=
10−12 S cm−1.
Synthesis of [PhHg(morphdtc)] (2). To a stirring aqueous
solution (4 ml) of morpholine (0.87 ml, 1 mmol) was added
CS2 (0.06 ml, 1 mmol) at 0 C and then stirred for 1 h at room
Synthesis of [(PhHg)2CDC] (6). To a methanolic solution
(30 ml) of PhHgO2CCH3 (0.676 g, 2 mmol) was added dropwise a
methanolic solution (45 ml) of K2C2N2S2 (0.194 g, 1 mmol) with
vigorous stirring. This was additionally stirred for another 1 h to
obtain the yellow product 6 (0.559 g, 83%). This was filtered and
treated in accordance with 2. Found: C, 24.82; H, 1.45; N, 4.18;
S, 9.52%. C14H10N2S2Hg2 requires: C, 24.93; H, 1.50; N, 4.16; S,
◦
temperature. To this was added a methanolic solution (15 ml) of
PhHgO2CCH3 (0.338 g, 1 mmol) which yielded white precipitate
2 (0.343 g, 78%) immediately. This was stirred for another 30 min
and the compound formed was suction filtered, washed 5 times
with methanol, followed by diethyl ether and dried in vacuo over
anhydrous calcium chloride. Found: C, 29.89; H, 2.96; N, 3.16;
S, 14.48%. C11H13NOS2Hg requires: C, 29.93; H, 2.97; N, 3.18; S,
9.49%. mmax(KBr)/cm−1 2167 (C N), 1313 (C N), 1020 (C–S),
447 (Hg–C). kmax(DMSO)/nm 220, 360 and 460. dH(300 MHz;
DMSO-d6, Me4Si) 7.35 (m, –C6H5). dC(75.45 MHz; DMSO-d6;
≡
=
14.50%. mmax(KBr)/cm−1 1425 (C N), 1024 and 991 (C–S), 1425
=
(C–O), 450 (C–Hg). kmax(CHCl3)/nm 296 and 354. dH(300 MHz;
DMSO-d6; Me4Si) 3.66 (t, 4H, –CH2O–), 4.04 (t, 4H, –CH2N–),
7.20 (t, 1H, –C6H5), 7.31 (t, 2H, –C6H5), 7.38 (t, 2H, –C6H5).
dC(75.45 MHz; DMSO-d6; Me4Si) 51.6 (–O–CH2), 65.5 (–N–CH2),
127.2, 128.3, 137.1, 138.2, 155.6 (–C6H5), 201.0 (C–S). m/z (EI)
88.1 (6%), 130.1(12), 279.4 (11), 370.3 (28), 410.7 (100), 439.0 (4).
rrt 12.01 × 10−12 S cm−1.
≡
Me4Si) 118.4 (–C N), 127.8, 128.3, 136.8, 138.2 (–C6H5), 210.2
(–C–S). rrt 2.04 × 10−12 S cm−1.
Crystallography
Details about data collection and solution refinement are given in
Table 4. Intensity data for the colourless crystals 1, 2 and 3 were
collected at 150(2) K on a Nonius Kappa CCD diffractometer
system equipped with graphite monochromated Mo Ka radiation
Synthesis of [PhHg(Bz2dtc)] (3). To a stirring methanolic
solution (30 ml) of PhHgO2CCH3 (0.337 g, 1 mmol) was added
a methanolic solution (20 ml) of Na(C6H5CH2)2NCS2 (0.297 g,
1 mmol). The white precipitate 3 (0.479 g, 87%) formed was
additionally stirred for 30 min. This was filtered and treated as for
2. Found: C, 45.84; H, 3.45; N, 2.58; S, 11.67%. C21H19NS2Hg re-
quires: C, 45.87; H, 3.47; N, 2.56; S, 11.70%. mmax(KBr)/cm−1 1416
˚
k = 0.71073 A. The final unit cell determination, scaling of
the data, and corrections for Lorentz and polarization effects
were performed with Denzo-SMN.28 The structures were solved
by direct methods (SIR9729) and refined by a full-matrix least-
squares procedure based on F2.30 All non-hydrogen atoms were
refined anisotropically; hydrogen atoms were 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. Figures for 1, 2 and 3 were prepared using ORTEP.31
The asymmetric unit in 3 consists of 2 molecules. While the
final residuals are acceptable, they are somewhat larger than
desirable, a reflection of crystal twinning. Modelling of this
pseudo-merohedral twinning (47% for a 100◦ rotation about the
0 4 1 reciprocal lattice direction) which led to a reduction of
R1 [based on data for which I > 2r(I)] from 15% to the value
reported here (7.11%). Concomitant with the convergence of the
refinement factor was a reduction in size of the largest peak/hole
=
(C N), 1029 and 1078 (C–S), 460 (C–Hg). kmax(CHCl3)/nm 260,
300 and 358. dH(300 MHz; CDCl3; Me4Si) 5.06 (s, 4H,–CH2–), 7.38
(m, 15H, –C6H5). dC(75.45 MHz, CDCl3, Me4Si) 56.8 (–CH2–),
127.8, 128.4, 128.8, 134.8, 137.1, 154.1 (–C6H5), 205.5 (–C–S).
m/z (EI) 181.2 (8%), 240.1 (100), 411.5 (12), 443.3 (6), 550.0 (2),
600.3 (16). rrt 8.47 × 10−12 S cm−1.
Synthesis of [PhHg(methoxethxant)] (4). A methanolic solu-
tion (20 ml) of PhHgO2CCH3 (0.337 g, 1 mmol) was added drop-
wise to a methanolic solution (20 ml) of KCH3O–CH2CH2OCS2
(0.189 g, 1 mmol) with continuous stirring. Yellow compound 4
(0.339 g,79%) was immediately precipitated. This was stirred for
an additional 30 min and isolated in a similar fashion to 2. Found:
C, 27.87; H, 2.80; S, 14.89%. C10H12O2S2Hg requires: C, 27.91; H,
2.81; S, 14.87%. mmax(KBr)/cm−1 1137 (C–O), 1022 and 1055 (C–
S), 443 (C–Hg). kmax(CHCl3)/nm 425, 350 and 265. dH(300 MHz;
CDCl3; Me4Si) 3.42 (s, 3H, –OCH3), 3.77 (t, 2H, O–CH2), 4.65 (t,
2H,–CH2–N), 7.39 (m, 5H, –C6H5). dC(75.45 MHz; CDCl3; Me4Si)
59.1 (CH3–O), 69.7 (–OCH2–), 74.2 (–CH2–O), 128.7, 129.0, 129.1,
136.8, 137.6 (–C6H5), 223.8 (C–S). rrt insulating.
−3
˚
in the difference map from 28 and −5.06 e A , respectively, to
the values reported in Table 4. Residual electron density, while
chemically non-significant, remains larger than desirable. Overall
however, the structure is unambiguous and is being presented on
this basis.
Computational details
Geometry optimizations were carried out at the level of density
functional theory (DFT) using B3LYP32 functional. Natural
charges at each atom have been computed using Kohn–Sham33 or-
bitals obtained from DFT calculations. The electronic absorption
energies and oscillator strengths for 3 were computed using time
dependent density functional theory (TD-DFT) methods using its
single crystal X-ray geometry. The 6-31G* basis set was used for
C, H, N, O and S atoms. The CEP34 basis set was used for Hg.
All calculations were performed using the Gaussian 0335 program.
Synthesis of [(PhHg)2NED] (5). To a methanolic solution
(30 ml) of PhHgO2CCH3 (0.676 g, 2 mmol), was added dropwise
a K2NED (0.213 g, 1 mmol) solution (30 ml) in 90 : 10 v/v
CH3OH : H2O mixture over a period of 15 min with vigorous
stirring. Brown yellow compound 5 (0.540 g, 80%) immediately
precipitated. This was stirred for another 3 h and thereafter
isolated in the same manner as 2. Found: C, 24.83; H, 1.62; N,
4.12; S, 9.45%. C14H11NO2S2Hg2 requires: C, 24.89; H, 1.64; N,
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Table 4 Crystallographic data and structure refinements for 1, 2 and 3
1
2
3
Empirical formula
Formula weight/g mol−1
Temperature/K
Crystal system
C15H23HgNS2
482.05
150(2)
C11H13HgNOS2
439.93
150(2)
C21H19HgNS2
550.08
150(2)
Triclinic
¯
P1
Monoclinic
Orthorhombic
Space group
P21/aa
Pcabb
˚
a/A
9.4107(5)
12.8145(6)
14.1706(8)
9.4300(10)
12.031(2)
21.6724(3)
8.8490(3)
˚
b/A
11.6810(5)
18.5340(7)
80.935(2)
85.358(2)
90.025(2)
1885.47(13)
4
1.938
8.388
1056
˚
c/A
a/◦
b/◦
c /◦
95.681(2)
3
˚
V/A
1700.49(15)
4
1.883
9.285
2458.78(6)
8
2.377
12.836
Z
D
calc/g cm−3
Absorption coefficient/mm−1
F(000)
928
1648
Crystal size/mm
0.25 × 0.20 × 0.10
0.35 × 0.35 × 0.35
0.25 × 0.23 × 0.10
h (min.–max.)/◦
3.2–27.4
3.3–27.5
5.2–27.4
Reflections collected
Independent reflections
Data/restraints/parameters
Final R indices [I > 2r(I)]
R indices (all data)
23 174
31 979
23 996
23 996
23 996/0/453
R1 = 0.071, wR2 = 0.183
R1 = 0.101, wR2 = 0.202
1.05
3847 [Rint = 0.118]
3847/0/174
R1 = 0.043, wR2 = 0.091
R1 = 0.078, wR2 = 0.104
1.02
2817 [Rint = 0.095]
2817/0/145
R1 = 0.031, wR2 = 0.076
R1 = 0.041, wR2 = 0.081
1.01
Goodness-of-fit on F2
−3
˚
Largest difference peak and hole/e A
1.862 and −2.030
0.968 and −1.013
3.594 and −3.044
ꢀ
ꢀ
ꢀ
ꢀ
R1 = ꢁFo| − |Fcꢁ/ |Fo|. R2 = {[ w(Fo − Fc2)/ w(Fo2)2]}1/2, w = 1/[r2(Fo2) + (xP)2], where P = (Fo2 + 2Fc2)/3.a Non-standard setting of P21/c,
2
no. 14. b Non-standard setting of Pbca, no. 61.
Molecular orbital diagrams were constructed with the MOLDEN
program.36
Koten and K. Vrieze, J. Organomet. Chem., 1981, 222, 115; (c) G. K.
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K. Kundu and A. Pidcock, J. Chem. Soc., Dalton Trans., 1981, 933;
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Acknowledgements
The authors are thankful to CSIR, New Delhi for the financial
assistance in the form of JRF (A K) and CSIR Project No.
01(2032)/06/EMR-II (N S). SAP, Department of Chemistry,
Banaras Hindu University, Varanasi is gratefully acknowledged
for providing the computational facility. The authors are grateful
to Dr Subrato Bhattacharya, Dr Rajendra Prasad, Dr Guochun
Yang and Prof. Zhongmin Su for fruitful discussions, and Prof.
Lallan Mishra for recording fluorescence spectra.
6 M. J. Moore, M. D. Distefano, L. D. Zydowsky, R. J. Cummings and
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J. A. McCleverty, T. J. Meyer and A. B. P. Lever, Elsevier, Amsterdam,
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