G. Gomathi et al. / Polyhedron 102 (2015) 424–433
429
bonded to the two sulfur atoms of the dithiocarbamate ligand at
distances of Tl1-S1 = 3.062(3) and Tl1-S2 = 3.082(3) Å in complex
1
2
and Tl1-S1 = 3.0909(14) and Tl1-S2 = 3.0205(13) Å in complex
. Each thallium center in the asymmetric unit is bonded with
two sulfur atoms of another centrosymmetrically related
dithiocarbamate ligand at distances of 3.114 (3) and 3.055 (3) Å
in complex 1, and 3.0647(13) and 3.1492(14) Å in complex 2, lead-
ing to a dimer. In addition, two monohapto interactions involving
thallium and the C atom of the CS
at distances of Tlꢀ ꢀ ꢀC1S = 3.376 and Tlꢀ ꢀ ꢀC1 S
and Tlꢀ ꢀ ꢀC1S = 3.422 and Tlꢀ ꢀ ꢀC1 S
2
moiety are observed to occur
i
2
2
= 3.386 Å for 1,
2
= 3.391 Å for 2, with the car-
i
2
bon atom of dithiocarbamate ligands of an asymmetric unit and
centro symmetrically related unit, respectively. In the dimeric unit,
the thallium atoms are situated on either side of a sulfur parallel-
ogram (Fig. 3) with edges of ꢃ2.9 and ꢃ3.9 Å, forming a bicapped
parallelogram. In the dimer, the Tlꢀ ꢀ ꢀTl distances for 1 and 2 are
3
.6451(8) and 3.7195(4) Å, respectively, which are shorter than
the sum of the van der Waals radii (3.92 Å), exhibiting the presence
of a Tlꢀ ꢀ ꢀTl interaction.
In the case of complex 1, each thallium atom in the binuclear
molecule is bonded to four sulfur atoms and there is a cation–
interaction (the arene -system counts as a single donor), thus
forming a distorted square pyramid. The centroid of the aryl ring
p
p
+
Fig. 4. Tl -arene interaction in complex 1.
+
(
C3–C8) is situated 3.237 Å from the Tl ion. Since Carene–Tl dis-
tances vary only slightly within a narrow range from 3.462 to
+
6
3
.571 Å, the Tl –arene interaction can be regarded as true
g –coor-
dination, Fig. 4. Two intramolecular C–Hꢀ ꢀ ꢀS (C9–H9ꢀ ꢀ ꢀS2 = 2.517
(
11) Å) and C2–H2ꢀ ꢀ ꢀS1 = 2.572(11) Å) interactions take place
between methylene hydrogen atoms (of benzyl and furfuryl
groups) and the thioureide sulfur atom. This complex also displays
a weak intermolecular C–Hꢀ ꢀ ꢀS interaction (Fig. 5, Table 3).
In complex 2, a C–Hꢀ ꢀ ꢀTl interaction is observed (Fig. 6).
Generally, three types of C–Hꢀ ꢀ ꢀM interactions are found, i.e. (i)
hydrogen ion (ii) agostic and (iii) anagostic interactions [41–61].
Hydrogen bonds are 3-center-4-electron interactions within an
almost linear geometry. Agostic interactions are usually referred
to as 3-centered-2-electron interactions and characterized by
Mꢀ ꢀ ꢀH distances of ꢃ1.8–2.2 Å and C–Hꢀ ꢀ ꢀM bond angles of ꢃ90–
1
30°. Anagostic interactions are characterized by Mꢀ ꢀ ꢀH distances
of 2.3–2.9 Å and large Mꢀ ꢀ ꢀH–C bond angles ꢃ110–170°. Anagostic
8
interactions are stabilized by d complexes. C–Hꢀ ꢀ ꢀTl interactions
are rare [62–65]. In the present study, an intermolecular C–Hꢀ ꢀ ꢀTl
(
2
Hꢀ ꢀ ꢀTl = 3.198 Å and \C–Hꢀ ꢀ ꢀTl = 131.91°) is observed in complex
. The Hꢀ ꢀ ꢀTl distance is larger than the values found in complexes
8
of d metal ions (Mꢀ ꢀ ꢀH ꢃ2.3–2.9 Å) [66]. This is due to the
+
larger size of the Tl ion. Further stabilization of the complex is
provided by intramolecular C–Hꢀ ꢀ ꢀS (H2Aꢀ ꢀ ꢀS1 = 2.633(11) and
H6Aꢀ ꢀ ꢀS2 = 2.531(10) Å) interactions with the hydrogen atoms of
the dithiocarbamate methylene group and O–Hꢀ ꢀ ꢀS (Hꢀ ꢀ ꢀS 2.467
(
10) Å) interactions (Fig. 7, Table 3).
3.6. Characterization of thallium sulfide nanoparticles
Tl S synthesized from complex 1 using conventional heating
2
and microwave irradiation methods are represented as samples 3
and 4, respectively. The PXRD patterns for samples 3 and 4 are
given in Fig. 8. In the case of sample 3, the sharp diffraction peaks
reveal that the obtained Tl S nanoparticles are well crystalline. The
2
diffraction peaks located at 2h = 29.3°, 32.9°, 39.1°, 44.6° and 54.4°
Fig. 5. Intramolecular and intermolecular C–Hꢀ ꢀ ꢀS interactions in 1.
irreversible and one electron processes. A one electron reduction
process with the formation of Tl has been already proposed [66]:
+
ꢁ
Tl + e ? Tl. This indicates that the oxidation state of thallium
can be indexed respectively as (033), (116), (306), (330) and
in both the complexes is +1.
(
229) planes of the rhombohedral phase with lattice constants
a = 12.2(7) and c = 18.17(6), which are in good agreement with
the Joint Committee on Powder Diffraction Standards JCPDS file
No 89-2013 [67]. The presence of (012), (113) and (122) planes
in the diffraction patterns of sample 4 is characteristic of the
3
.5. Single crystal X-ray structural analysis of complexes 1 and 2
ORTEP diagrams of complexes 1 and 2 are shown in Figs. 1 and
2, respectively. In the asymmetric unit, the thallium center is
2
hexagonal phase of Tl S. This is in good agreement with the JCPDS