Steric influence on hapto interactions in supramolecularly linked thallium dithiocarbamates

Article abstract of DOI:10.1007/s00706-013-0974-y

Spectral and structural characterization of diallyl and dibenzyl dithiocarbamates of thallium(I) indicated increased thalliocarbon hapto interactions in dibenzyl dithiocarbamate due to increased steric effects. Proton magnetic resonance spectra of the compounds showed that the protons in the vicinity of the thioureide nitrogen are highly deshielded and the corresponding ¹³C spectra showed large chemical shifts of the thioureide carbons due to decreased electron density. Cyclic voltammetry and bond valence calculations established that the oxidation number of thallium was +1. The Tl-S bond distances in both compounds did not vary significantly. η¹-Tl···C(S₂) supramolecular interactions were observed in both compounds. A nonclassical S···H bond (2.841 A) was also observed in the dibenzyl compound. Aside from the two noncovalent interactions mentioned, additional hapto interactions such as Tl(1)S₂η¹Cη ¹Cη²C₂ and Tl(2)S₂η ¹Cη³C₃ were observed. Both compounds formed polymeric chains through hapto interactions.

Full text of DOI:10.1007/s00706-013-0974-y

Monatsh Chem (2013) 144:1329–1334
DOI 10.1007/s00706-013-0974-y
ORIGINAL PAPER
Steric influence on hapto interactions in supramolecularly linked
thallium dithiocarbamates
•
Kuppukkannu Ramalingam Corrado Rizzoli
•
Nagarajan Alexander
Received: 2 June 2012 / Accepted: 19 March 2013 / Published online: 25 April 2013
Ó Springer-Verlag Wien 2013
Abstract Spectral and structural characterization of
diallyl and dibenzyl dithiocarbamates of thallium(I) indi-
cated increased thalliocarbon hapto interactions in dibenzyl
dithiocarbamate due to increased steric effects. Proton
magnetic resonance spectra of the compounds showed that
the protons in the vicinity of the thioureide nitrogen are
highly deshielded and the corresponding 13C spectra
showed large chemical shifts of the thioureide carbons due
to decreased electron density. Cyclic voltammetry and
bond valence calculations established that the oxidation
number of thallium was ?1. The Tl–S bond distances in
both compounds did not vary significantly. g1–TlꢀꢀꢀC(S2)
supramolecular interactions were observed in both com-
Introduction
Thallium, a group 12 element, shows interesting structural
variations in its compounds and is useful in many biomedical
applications. Neuronal activity in rats has been analyzed
using thallium diethyldithiocarbamate [1]. The utilization of
thallium(I) acetate in the TlAMG technique and the appli-
cation of 201Tl in single-photon emission computed
tomography (SPECT) imaging in humans are well docu-
mented [2, 3]. Thallium compounds find use in the
production of optical glasses, lenses for IR equipment,
scintillation sensors, high-temperature superconductors,
OLED materials, and related nanoparticles [4–7]. Dithio-
carbamates are highly versatile ligands that interact with
main-group metals and stabilize a variety of oxidation states
in different coordination geometries [8, 9]. A limited number
of Tl(I) and Tl(III) dithiocarbamates have been structurally
characterized [10–25]. In the work described in the present
paper, the synthesis and the spectroscopic and single-crystal
X-ray structural characterization of [Tl(dadtc)]2 (1) and
[Tl(dbdtc)]2 (2) (dadtc = diallyldithiocarbamate, dbdtc =
dibenzyldithiocarbamate) were achieved. The characteris-
tics of thalliocarbon hapto interactions and the steric effects
of substituents on the supramolecular interactions that pre-
vail in the compounds were analyzed.
˚
pounds. A nonclassical SꢀꢀꢀH bond (2.841 A) was also
observed in the dibenzyl compound. Aside from the two
noncovalent interactions mentioned, additional hapto
interactions such as Tl(1)S2g1Cg1Cg2C2 and Tl(2)S2g1
Cg3C3 were observed. Both compounds formed polymeric
chains through hapto interactions.
Keywords Main group compounds ꢀ Thallium(I) ꢀ
Hapto ꢀ Supramolecular ꢀ X-ray structure determination ꢀ
NMR spectroscopy
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-013-0974-y) contains supplementary
material, which is available to authorized users.
Results and discussion
K. Ramalingam (&) ꢀ N. Alexander
Department of Chemistry, Annamalai University,
Annamalainagar, 608 002 Chidambaram, Tamilnadu, India
e-mail: krauchem@yahoo.com
Electronic, fluorescence, and IR spectra
Charge-transfer transitions are observed with maximum
intensity, and the characteristic absorption bands appear at
around 437 nm for the complexes. Intraligand transitions
for the dithiocarbamate are observed at around 280 nm.
C. Rizzoli
Dipartimento di Chimica ed Inorganica Chimica Analitica
Chimica Fisica, Universita di Parma, Viale G.P. Usberti 17/A,
43100 Parma, Italy
123

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K. Ramalingam et al.
Low-intensity fluorescence maxima are observed at 407
and 410 nm for the compounds.
coordination environments are different. The electro-
chemical process envisaged is Tl? ? e- ? Tl. A small
current observed at -0.60 V corresponds to the stripping
of thallium. The observed cyclic voltammetric processes
confirmed that the oxidation state of the thallium in the
compounds is ?1. Upon the application of a positive
potential, no significant rise in current was observed for
either compound, indicating that there was no observable
oxidation to ?3, probably due to the chemical instability
associated with the electrochemically oxidized species.
In the IR spectra of the compounds, characteristic
thioureide bands are observed at 1,462 and 1,489 cm-1 for
1 and 2, respectively, indicating that the partially double-
bonded polar thioureide resonance structures provide a
smaller contribution than they do in transition metal
compounds [26, 27]. The mC–S band appears in the range
1,053–1,073 cm-1
.
1H NMR and 13C NMR spectral studies
Crystal structures
1
For compound 1, the H NMR spectrum shows a signal
due to a-CH2 at 4.63 ppm. The b- and c-protons are de-
shielded and appear in the ranges 5.85–5.95 ppm and
5.16–5.28 ppm, respectively. Chemical shifts for the thio-
ureide carbon (N13CS2) were observed at 205.2 and 206.7
for compounds 1 and 2, respectively, and serve as a fin-
gerprint for the dithiocarbamate in the compounds [28, 29].
In compound 1, the a-carbon appears slightly deshielded
and is found at 54.75 ppm. However, the b- and c-carbons
are highly deshielded and appear at 132.0 and 117.9 ppm,
respectively.
Table 1 shows the data collection and refinement parame-
ters and Table 2 shows important bond parameters of
compounds 1 and 2. An ORTEP diagram for [Tl(dadtc)]2
(1) is shown in Fig. 2. In 1, each thallium is primarily
bonded to the two sulfur atoms of one dithiocarbamate with
˚
bond lengths of 2.968(2) and 2.988(2) A. However, each
thallium also shows nonbonded interactions with the two
sulfurs of another (centrosymmetrically related) dithiocar-
˚
bamate at distances of 3.165(2) and 3.287(2) A, leading to
a dimer (see Fig. 2). In addition, a fifth sulfur of the
adjacent dithiocarbamate also shows a nonbonded Tl–S
˚
interaction at 3.506(2) A. The dimer depicted in the OR-
Cyclic voltammetry
TEP is part of the polymeric chain formed by the
supramolecular interactions. The bond angle S–Tl–S
between each thallium atom and the sulfur atoms that it is
primarily bonded to is 59.46(5)°. The thioureide bond
A representative cyclic voltammogram of 1 is shown in
Fig. 1, and compound 2 showed a similar reduction pattern.
The reduction potentials are -1.136 and -1.013 V for 1
and 2. The voltammograms are well-defined irreversible
one-electron reduction processes. One-electron reduction
processes for Tl?1 have been reported to occur in aqueous
medium (TlClO4) at -1.100 V [30, 31]. The characteristics
of the reduction observed in the present study are similar to
those reported in aqueous medium, although the
˚
distance observed in the compound, 1.336(8) A, clearly
indicates the partially double-bonded nature of that bond.
The four sulfur atoms in the dimer form a parallelogram,
with the two thallium atoms occupying the axial positions.
Effectively, each thallium is at the vertex of a pyramidal
structure involving the two dithiocarbamates, considering
the four relatively strong Tl–S interactions. The fifth sulfur
occupies the apical position in the pyramid.
The ORTEP diagram of [Tl(dbdtc)]2 (2) is shown in
Fig. 3. Two formula units are present in the asymmetric
unit of 2. Each thallium is bound to two sulfurs of a
dithiocarbamate unit at distances of 2.976(1) and
˚
3.070(1) A in one of the formula units (and at 2.960(1) and
˚
3.046(1) A in the other formula unit). In addition, thallium
is bonded to two other sulfur atoms of another dithiocar-
˚
bamate unit at distances of 3.053(1) and 3.167(1) A in one
˚
formula unit (and at 3.098(1) and 3.214(1) A in the other).
The coordination environment around thallium is similar to
that observed in 1. The four sulfur atoms and thallium are
arranged in an approximately pyramidal geometry. The
˚
thioureide C–N length in the molecule is 1.330(5) A (or
˚
1.348(5) A in the other formula unit), which indicates its
partially double-bonded nature. The bond angle S1–T11–
Fig. 1 Cyclic voltammogram of [Tl(dadtc)]2
S2 is 58.71(3)° (or 59.07(3)°) in the compound.
123

Steric influence on hapto interactions
1331
Table 1 Crystal data, data collection, and refinement parameters for 1 and 2
[Tl(dadtc)]2 (1)
[Tl(dbdtc)]2 (2)
Empirical formula C14H20N2S4Tl2
C30H28N2S4Tl2
Formula weight
Dimensions/mm3
Crystal system
Space group
753.3
953.5
0.32 9 0.09 9 0.08
0.14 9 0.12 9 0.05
Monoclinic
Triclinic
P21/C
P-1
˚
a/A
6.3136(6)
6.9562(5)
˚
b/A
18.1021(19)
12.6650(9)
˚
c/A
9.0382(9)
17.6744(12)
a/°
b/°
c/°
90.00
89.4864(11)
95.9554(18)
85.7503(11)
90.00
76.6911(11)
3
˚
V/A
1027.40(18)
1511.08(18)
Z
2
2
Dcalc /g cm-3
l/cm-1
F (000)
2.435
2.096
16.068
10.950
688
896
˚
k/A
0.71673
0.71073
Index ranges
Reflections
Reflections
-7 B h B 7; -12 B k B 12; -11 B l B 11
-9 B h B 9;-18 B k B 18; -25 B l B 25
2,018
9,180
6,206
1,665
2
2
2
2
2
Weighting scheme w = 1/[S2 (Fo 2) ? (0.0.492P) ] where P = (F ? 2 Fc )/3 w = 1/[r2(Fo2) ? 0.0397P)2] where P = (Fo ? 2Fc )/3
o
Parameters refined 100
343
Final R, Rw
0.0282, 0.0806
1.050
0.0606, 0.0846
1.003
Goof
˚
Table 2 Selected bond distances/A and bond angles/°
[Tl(dadtc)]2
[Tl(dbdtc)]2
Tl1–S1
2.9679 (18)
2.9876 (19)
3.1652 (18)
3.7256 (5)
1.697 (6)
1.724 (6)
1.336 (8)
1.458 (8)
1.465 (8)
1.472 (10)
59.46 (5)
81.19 (5)
105.53 (4)
57.49 (4)
54.94 (3)
89.3 (2)
Tl(1)–S(2)
2.976 (1)
3.053 (1)
3.070 (1)
3.167 (1)
3.6132 (4)
2.9603 (13)
3.0459 (14)
3.0982 (12)
3.6962 (4)
1.727 (4)
56.91 (3)
79.12(3)
Tl1–S2
Tl1–S20
Tl1–Tl10
Tl(1)–S(1)
Tl(1)0–S(1)
Tl(1)0–S(2)
S1–C1
Tl(1)–Tl(1)0
S2–C1
Tl(2)–S(4)
N1–C1
Tl(2)–S(3)
N1–C2
Tl(2)–S(4)
Tl(2)–Tl(2)0
Fig. 2 ORTEP of [Tl(dadtc)]2
N1–C5
Supramolecular interactions
C2–C3
S(1)–C(1)
S1–Tl1–S2
S1–Tl1–S20
S2–Tl1–S20
S1–Tl1–Tl10
S2–Tl1–Tl10
C1–S1–Tl1
S(1)–Tl(1)–S(2)
S(1)–Tl(1)–S(2)
S(4)–Tl(2)–S(3)
S(4)–Tl(2)–S(4)
S(3)–Tl(2)–S(4)
C(1)–S(1)–Tl(1)
[Tl(dadtc)]2 (1) shows a TlꢀꢀꢀC(S2) hapto interaction, which
˚
occurs at a distance of 3.335 A. An additional mono hapto
59.07 (3)
104.85 (3)
79.80 (3)
85.34 (13)
interaction involving thallium is observed to occur at a
˚
distance of 3.469 A with the carbon of the dithiocarbamate
group of the next dimeric unit. The compound shows a
supramolecularly linked polymeric chain which is
123

1332
K. Ramalingam et al.
Fig. 4 Supramolecular interactions in [Tl(dadtc)]2
Fig. 3 ORTEP of [Tl(dbdtc)]2
connected via Tl1ꢀꢀꢀS2 interactions (distance of interaction:
˚
3.506 A) and is stacked along the a axis, as depicted in
Fig. 4.
The T12ꢀꢀꢀCl6 distance in one formula unit of 2 is
˚
˚
3.383 A (or 3.412 A in the other formula unit), which is
significantly less than the sum of the van der Waals radii of
˚
Tl and C, 3.73 A, indicating a significant hapto interaction.
A nonclassical hydrogen-bonded S4ꢀꢀꢀH5 interaction at a
Fig. 5 Supramolecular interactions in [Tl(dbdtc)]2
˚
distance of 2.841 A is observed (note that the sum of the
3
˚
van der Waals radii in this case is 3.0 A). Tl2 shows a g
interaction with the benzene ring involving C3, C4, and C5
˚
at distances of 3.656, 3.473, and 3.555 A, respectively. T11
is also bound to two of the carbons (C22 and C23) of the
second molecular unit through a dihapto (g2) interaction at
˚
distances of 3.483 and 3.607 A. The TlꢀꢀꢀTl distance in the
˚
dimer is 3.613 A. Each dimer is flanked on either side by
two other dimers, and this trimeric unit of dimers is held
together by supramolecular interactions (g3 involving C3,
C4, and C5). Therefore, each thallium is directly bonded to
two sulfur atoms of the dithiocarbamate, but is also bonded
to two more sulfur atoms of the other dithiocarbamate at a
longer distance. The two coordination environments may
be described as Tl1(S)2 g1C g1C g2C2 and Tl2(S2) g1C
g3C3, and the hapto interactions in the dimer are shown in
Fig. 5. In the dimeric unit, the four sulfur atoms form a
parallelogram and the thallium atoms occupy the apical
positions of a bicapped parallelogram, as shown in Fig. 6.
The axial distance between the thallium atoms in the
dimeric unit reflects its stability.
Fig. 6 Bicapped Tl2S4 parallelogram
g1–TlꢀꢀꢀC(S2) supramolecular interactions are observed in
both compounds. Perusal of the nonbonded distances
indicates that the diallyl complex shows a relatively long
˚
TlꢀꢀꢀTl (3.726 A) distance compared to that observed in 2
˚
(3.613 A), due to steric effects. A comparison of the dis-
tances associated with methyl and ethyl analogs reported
previously [14] shows that the TlꢀꢀꢀTl distances in those
analogs are shorter than those observed in 1 and 2, indi-
cating decreased stability due to increased steric effects.
Bond valence sum (BVS) calculations yielded 1.1877 and
0.9664 as the valence sums for 1 and 2, respectively [32].
The increased hapto interactions in 2 cause its relatively
low BVS. These bond valence sums are in line with the
crystal structures and the results of cyclovoltammetric
studies of the compounds, confirming that the formal oxi-
dation state of thallium is ?1.
Important structural parameters of the compounds are
compared in Table 3. The Tl–S bond lengths in 1 and 2
barely change when different substituents are considered,
though the dibenzyl analog shows an increasing bond
length. In compound 1, a weak supramolecular interaction
prevails between thallium and hydrogen, leading to one of
˚
the shortest interaction distances reported so far (2.962 A).
123

Steric influence on hapto interactions
1333
Table 3 Comparison of structural parameters
C–N thioureide/A S–C–S/8 TlꢀꢀꢀTl/A SꢀꢀꢀH g1–TlꢀꢀꢀC(S2)/g2/g3–TlꢀꢀꢀC
˚
Bonded Tl–S/A
˚
˚
˚
Complex
Nonbonded TlꢀꢀꢀS/A
[Tl (dadtc)]2 2.968(2); 2.988(2) 3.165(2); 3.287(2); 3.506(2) 1.336(8)
[Tl (dbdtc)]a2 2.976(1); 3.070(1) 3.053(1); 3.167(1)
119.4(3) 3.726
118.9(2) 3.613
–
3.335, 3.469
1.348(5)
2.841 3.383, 3.636, 3.473, 3.555
a
One set of parameters is given
Diallyldithiocarbamatothallium(I) [Tl(dadtc)]2
Conclusions
(1, C14H20N2S4Tl2)
Diallylamine (0.18 cm3, 2 mmol) and 0.12 cm3 carbon
disulfide (2 mmol) in ethanol were mixed under ice-cold
conditions (5 °C) to obtain a yellow dithiocarbamic acid
solution. To the freshly prepared dithiocarbamic acid
solution, an aqueous solution of 0.446 g TlF (2 mmol)
was added with constant stirring. A pale yellow solid
separated from the solution, which was filtered, washed
with alcohol, and dried in air. Pale yellow solid; m.p.:
170 °C; yield 67 %; IR (KBr): v = 1,462 (thioureide C–N),
An IR spectral investigation confirmed the important con-
tribution of the thioureide bonds to the dithiocarbamate.
NMR spectral data on diallyl and dibenzyl dithiocarba-
mates of thallium(I) showed that the protons and carbons in
the immediate vicinity of the thioureide nitrogen are
strongly affected by the bonding to thallium. CV and BVS
calculations established that the formal oxidation state of
thallium is ?1. In the present study, a comparison of the
nonbonded covalent interactions in 1 and 2 clearly showed
increased thalliocarbon hapto interactions in the dibenzyl
dithiocarbamate 2 analog due to the presence of bulky
phenyl groups.
1
1,053 (C–S) cm-1; H NMR (CDCl3): d = 4.63 (a-CH2),
5.85–5.93 (b-CH), 5.16–5.28 (c-CH2) ppm; 13C
NMR(CDCl3): d = 54.75 (a-CH2), 132.0 (b-CH), 117.9
(c-CH2), 205.2 (thioureide C–N) ppm.
Dibenzyldithiocarbamatothallium(I) [Tl(dbdtc)]2
Experimental
(2, C30H28N2S4Tl2)
Dibenzylamine (0.39 cm3, 2 mmol) and 0.12 cm3 carbon
disulfide (2 mmol) in ethanol were mixed under ice-cold
conditions (5 °C) to obtain a yellow dithiocarbamic acid
solution. To the freshly prepared dithiocarbamic acid
solution, an aqueous solution of 0.446 g TlF (2 mmol)
was added with constant stirring. A pale yellow solid
separated from the solution, which was filtered, washed
with alcohol, and dried in air. Yellow solid; m.p.: 164 °C;
yield 72 %; IR (KBr): v = 1,489 (thioureide C–N), 1073
All reagents and solvents employed were commercially
available analytical grade materials and were used as
supplied, without further purification. IR spectra were
recorded on ABB Bomem (Quebec, Canada) MB 104
spectrometer (range: 4,000–400 cm-1) as KBr pellets.
Electronic spectra were recorded in ethanol on a Hitachi
(Tokyo, Japan) U-2001 spectrometer. Fluorescence spectra
were recorded in ethanol. To prevent any nonlinearity of
the fluorescent intensity, 350 nm was chosen as the exci-
tation wavelength. NMR spectra were recorded on a Bruker
(Rheinstetten, Germany) 400 MHz spectrometer at room
temperature using CDCl3 as solvent.
1
(C–S) cm-1; H NMR (CDCl3): d = 5.26 (benzyl CH2),
7.17–7.42 (aromatic) ppm; 13C NMR (CDCl3): d = 54.73
(benzylic CH2), 206.7 (thioureide C–N).
Intensity data were collected at ambient temperature
(295 K) on a Bruker SMART 1000 CCD diffrac-
tometer using graphite monochromated MoKa radiation
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