Two new examples of very short thallium-transition metal contacts: Tl3Ag3Sb2S6 and Tl3Ag3As2S6

Article abstract of DOI:10.1016/j.jallcom.2007.03.014

Two new sulphosalts Tl₃Ag₃Sb₂S₆, (1) and Tl₃Ag₃As₂S₆, (2) were prepared in reaction of synthetic binary sulfides: argentite (Ag₂S), carlinite (Tl₂S) and orpiment (As₂S₃) or stibnite (Sb₂S₃), and their crystal structures have been determined using single-crystal data. The compounds are isostructural and crystallize in the space group P2₁/c (Z = 4), with a = 11.6854(17) ?, b = 11.8602(17) ?, c = 12.1294(18) ?, β = 123.356(2)°, V = 1404.1(4) ?³ for 1, and a = 11.4415(14) ?, b = 11.7530(15) ?, c = 11.9880(16) ?, β = 123.516(3)°, V = 1344.0(3) ?³ for 2. Refinements involving anisotropic displacement parameters for all atoms converged to the conventional R-factors: R₁ = 0.0496 for 1 and R₁ = 0.0372 for 2. The structures consist of two kinds of slabs alternately situated along [1 0 0] direction and sharing S atoms located between them. The first slab is built up of Tl1S₈, Tl2S₆, Tl3S₅Ag3 coordination polyhedra and Ag3S₃Tl3 distorted trigonal pyramid (the average 〈Ag3-S〉 distance is 2.542 for 1 and 2.539 ? for 2) combined with trigonal Sb1S₃ or As1S₃ coordination pyramids (〈Sb1-S〉 and 〈As1-S〉 are 2.438 and 2.259 ?, respectively). The thallium atom Tl1 is surrounded by eight S atoms forming a square anti-prism (〈Tl1-S〉: 3.393 for 1 and 3.356 ? for 2), while the coordination polyhedron of Tl2 can be described as a significantly distorted trigonal prism or as an extremely distorted octahedron (〈Tl2-S〉: 3.236 ? for 1 and 3.238 ? for 2). Thallium Tl3 is surrounded by six atoms (one Ag, four S at shorter and one S at longer distance), which form a distorted trigonal prism (〈Tl3-S〉: 3.165 ? in 1 and 3.155 ? in 2). The second slab consists of trigonal Sb2S₃ or As2S₃ coordination pyramids combined with Ag1S₄ and Ag2S₄ coordination tetrahedra (〈Sb2-S〉 and 〈As2-S〉 are 2.433 and 2.251 ?, respectively; 〈Ag1-S〉: 2.623 ? for 1 and 2.612 ? for 2; 〈Ag2-S〉: 2.623 ? for 1 and 2.630 ? for 2). The most interesting feature of both structures is the existence of short Tl3-Ag3 contacts of 2.959(2) ? in 1 and 2.922(1) ? in 2. These contacts are the shortest found so far and indicate very strong Tl-Ag interactions. They are discussed in terms of metallophilicity principle and relativistic effects. It is also pointed out that if only valence shell electrons are considered (Tl-Ag)²⁺ group is isoelectronic with the (Hg-Hg)²⁺ ion, therefore new examples of short Tl-Ag contacts could be expected.

Full text of DOI:10.1016/j.jallcom.2007.03.014

Journal of Alloys and Compounds 457 (2008) 66–74
Two new examples of very short thallium–transition
metal contacts: Tl3Ag3Sb2S6 and Tl3Ag3As2S6
a
b,∗
c
ˇ
´
ˇ
´
´
Ljiljana Karanovic , Dejan Poleti , Tonci Balic-Zunic ,
c
ˇ ´ d
Emil Makovicky , Ivan Grzetic
a Faculty of Mining and Geology, University of Belgrade, Ðusˇina 7, 11000 Belgrade, Serbia
b Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia
c Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
d Faculty of Chemistry, University of Belgrade, P.O. Box 158, 11001 Belgrade, Serbia
Received 9 January 2007; received in revised form 27 February 2007; accepted 5 March 2007
Available online 12 March 2007
Abstract
Two new sulphosalts Tl3Ag3Sb2S6, (1) and Tl3Ag3As2S6, (2) were prepared in reaction of synthetic binary sulfides: argentite (Ag2S), carlinite
(Tl2S) and orpiment (As2S3) or stibnite (Sb2S3), and their crystal structures have been determined using single-crystal data. The compounds
◦
˚
˚
˚
are isostructural and crystallize in the space group P21/c (Z = 4), with a = 11.6854(17) A, b = 11.8602(17) A, c = 12.1294(18) A, β = 123.356(2) ,
3
◦
3
˚
˚
˚
˚
˚
V = 1404.1(4) A for1, anda = 11.4415(14) A, b = 11.7530(15) A, c = 11.9880(16) A, β = 123.516(3) , V = 1344.0(3) A for2. Refinementsinvolving
anisotropic displacement parameters for all atoms converged to the conventional R-factors: R1 = 0.0496 for 1 and R1 = 0.0372 for 2. The structures
consist of two kinds of slabs alternately situated along [1 0 0] direction and sharing S atoms located between them. The first slab is built up of Tl1S8,
˚
Tl2S6, Tl3S5Ag3 coordination polyhedra and Ag3S3Tl3 distorted trigonal pyramid (the average ꢀAg3–Sꢁ distance is 2.542 for 1 and 2.539 A for 2)
˚
combined with trigonal Sb1S3 or As1S3 coordination pyramids (ꢀSb1–Sꢁ and ꢀAs1–Sꢁ are 2.438 and 2.259 A, respectively). The thallium atom Tl1
˚
is surrounded by eight S atoms forming a square anti-prism (ꢀTl1–Sꢁ: 3.393 for 1 and 3.356 A for 2), while the coordination polyhedron of Tl2 can
˚
˚
be described as a significantly distorted trigonal prism or as an extremely distorted octahedron (ꢀTl2–Sꢁ: 3.236 A for 1 and 3.238 A for 2). Thallium
˚
Tl3 is surrounded by six atoms (one Ag, four S at shorter and one S at longer distance), which form a distorted trigonal prism (ꢀTl3–Sꢁ: 3.165 A in
˚
1 and 3.155 A in 2). The second slab consists of trigonal Sb2S3 or As2S3 coordination pyramids combined with Ag1S4 and Ag2S4 coordination
˚
˚
˚
˚
tetrahedra (ꢀSb2–Sꢁ and ꢀAs2–Sꢁ are 2.433 and 2.251 A, respectively; ꢀAg1–Sꢁ: 2.623 A for 1 and 2.612 A for 2; ꢀAg2–Sꢁ: 2.623 A for 1 and
˚
˚
˚
2.630 A for 2). The most interesting feature of both structures is the existence of short Tl3–Ag3 contacts of 2.959(2) A in 1 and 2.922(1) A in 2.
These contacts are the shortest found so far and indicate very strong Tl–Ag interactions. They are discussed in terms of metallophilicity principle
and relativistic effects. It is also pointed out that if only valence shell electrons are considered (Tl–Ag)2+ group is isoelectronic with the (Hg–Hg)2+
ion, therefore new examples of short Tl–Ag contacts could be expected.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Sulphosalts; Crystal structure; Thallium; Silver; Short metal–metal contacts
1. Introduction
- in reaction of synthetic proustite (Ag3AsS3) and ellisite
(Tl3AsS3) giving 1, or pyrargyrite (Ag3SbS3) and “stibioel-
lisite” (Tl3SbS3) giving 2:
Tl3Ag3Sb2S6 (1) and Tl3Ag3As2S6 (2) are quasi-ternary
compounds which belong to the corresponding Ag2S–Tl2
S–As2S3–Sb2S3 system (Fig. 1). They can be prepared in three
different ways [1]:
Ag3AsS3 + Tl3AsS3 = Tl3Ag3As2S6
(1)
Ag3SbS3 + Tl3SbS3 = Tl3Ag3Sb2S6
(2)
- in reaction of synthetic binary sulfides argentite (Ag2S), car-
linite (Tl2S) and orpiment (As2S3) or stibnite (Sb2S3):
3Ag2S + 2As2S3 + 3Tl2S = 2Tl3Ag3As2S6
3Ag2S + 2Sb2S3 + 3Tl2S = 2Tl3Ag3Sb2S6
(3)
(4)
∗
Corresponding author. Tel.: +381 11 3370477; fax: +381 11 3370847.
E-mail address: dejan@tmf.bg.ac.yu (D. Poleti).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2007.03.014

L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
67
Fig. 2. Part of Ag2S–Tl2S–As2S3–Sb2S3 system describing Tl3Ag3As2S6 and
Tl3Ag3Sb2S6 relations to the particular end-members.
It has been reported that 1 and 2 decompose incon-
gruently at 278 and 293 ◦C, respectively [2], but both are
stable at 200 ◦C [3]. 2 is in equilibrium with Ag3TlS3,
Ag35Tl5S20–Ag34Tl6S20(ss), lorandite, proustite, ellisite, pyrar-
gyrite, Ag9Tl3As4S12 and Tl3Ag3Sb2S6. 1 is in equilibrium with
Ag3TlS3, Ag35Tl5S20–Ag34Tl6S20(ss), weissbergite, proustite,
“stibioellisite” and Tl3Ag3As2S6 (Figs. 1 and 2).
Both compounds have not been found in nature yet, but the
complex Ag2S–Tl2S–As2S3–Sb2S3 system [1] is closely related
to the polymetallic ore deposits. Therefore, the appearance of 1
and 2 could be expected under proper geothermal conditions.
In this paper crystal structures of 1 and 2 are reported and
related to the congenial sulphides and sulphosalts. Very short
Tl–Ag contacts found in both structures are discussed in terms
of metalophilic attractions.
Fig. 1. Ag2S–Tl2S–As2S3–Sb2S3 system [3]. Legend: el—ellisite
(Tl3AsS3), get—getchellite (AsSbS3), lo—lorandite (TlAsS2),
my—miargyrite (AgSbS2), p—pierrotite (Tl2Sb6As4S16), pp—parapierrotite
(Tl(Sb,As)5S8), pr—pyrargyrite (Ag3SbS3), pu—proustite (Ag3AsS3),
re—rebulite (Tl5Sb5As8S22), tm—trechmannite (AgAsS2), u—(TlSb3S5),
ws—weissbergite (TlSbS2), Q—Ag9Tl3As4S12, R—Ag3Tl3As2S6, P—Ag11
Tl2As7S17, O—AgTlAs2S4, X—AgTlAsSbS4.
- in reaction of elements silver, thallium, sulfur, and arsenic or
antimony:
2. Experimental
2.1. Synthesis
3Ag + 2As + 3Tl + 6S = Tl3Ag3As2S6
3Ag + 2Sb + 3Tl + 6S = Tl3Ag3Sb2S6
(5)
(6)
For our purpose, four binary sulfides: Ag2S, Tl2S, As2S3 and Sb2S3 presyn-
thesized from the corresponding high purity elements (>99.99%) were used as
Table 1
Crystal data, data collection and refinement details for Tl3Ag3Sb2S6 (1) and Tl3Ag3As2S6 (2)
1
2
Formula weight, Mr
1372.58
1278.92
Crystal system, space group
Monoclinic, P21/c
◦
˚
Unit cell dimensions (A, )
a = 11.6854(17),
b = 11.8602(17),
a = 11.4415(14),
b = 11.7530(15),
c = 12.1294(18), β = 123.356(2)
1404.1(4)
4, 6.493
c = 11.9880(16), β = 123.516(3)
1344.0(3)
4, 6.320
3
˚
Unit cell volume (A )
Z, calculated density (g cm−3
)
F(0 0 0)
2328
43.020
2184
45.896
Absorption coefficient (mm−1
Transmission factors
)
Tmin = 0.3896, Tmax = 0.3065
2.09–25.68
Tmin = 0.1368, Tmax = 0.1907
2.13–26.37
Range for data collection (o)
Limiting indices
Reflections collected/unique
Observed reflections [I > 2σ(I)]
Rint
Extinction coefficient
Refined parameters
R-indices [I > 2σ(I)]
R-indices (all data)
Goodness-of-fit, S
−14 ≤ h ≤ 14, −14 ≤ k ≤ 14, −14 ≤ l ≤ 14
9081/2646
1487
0.0984
0.00089(7)a
10217/2741
1857
0.0922
0.00057(5)a
128
R1 = 0.0496, wR2 = 0.0886b
R1 = 0.0855, wR2 = 0.0969
0.971
R1 = 0.0372, wR2 = 0.0673b
R1 = 0.0691, wR2 = 0.0744
0.899
Fc∗ = kFc[1 + 0.001 × Fc2λ3/sin(2θ)]−1/4
.
a
w = 1/[σ2(Fo2) + (0.0346P)2 + 0.0000P] for 1, and w = 1/[σ2(Fo2) + (0.0241P)2 + 0.0000P] for 2, where P = (Fo2 + 2Fc2)/3.
b

68
L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
starting materials. The sulphosalts were prepared by reactions (3) and (4) during
the above-mentioned study [1] of the Ag2S–Tl2S–As2S3–Sb2S3 system. The
syntheses were performed as described by Kullerud [4] in evacuated and sealed
silica glass tubes with a minimum vapour space by heating below the melting
points of the corresponding compounds. An electronically controlled wound
horizontal furnace with a temperature accuracy of 2 ◦C was used for heating
experiments.
The individual charges were repeatedly ground and reheated at 200 ◦C
over 4–6 weeks until the equilibrium was attained. After that the samples
were quenched in ice water and the reaction products were characterized
at room temperature. Small polished sections from different charges were
prepared for homogeneity examination under the reflecting microscope in
an oil immersion. For purity determination X-ray diffraction patterns were
obtained on a Philips PW 1710 diffractometer employing Ni-filtered Cu K␣
radiation.
and Lp correction. The software SMART was used for data collection, SAINT
for integration of intensities and Lp correction [5]. The empirical absorption
correction was also applied (program XPREP from the SHELXTL package [6]).
Selected crystal and experimental data are given in Table 1.
The structures were solved by direct methods [7], which revealed positions
of Tl and Ag, as well as of some Sb (or As) and S atoms. The remaining atoms
were found in difference Fourier maps during the subsequent isotropic and
finally anisotropic refinements for all atoms by full-matrix least-squares on F2
[8]. The highest residual maxima and minima in the last difference Fourier
˚
˚
˚
−3
˚
˚
map were 2.29 A (1.02 A from Tl1) and −1.79 A (1.05 A from Sb2) for 1,
˚
˚
as well as 2.77 (0.96 A from Tl3) and −1.22e A (0.79 A from Ag3) for 2.
The final atomic coordinates and anisotropic displacement parameters are listed
in Tables 2 and 3 .
3. Results and discussion
2.2. Structure determination
3.1. Structure description
Several crystal fragments of 1 and 2, coloured steel grey with metal-
lic lustre were checked on a single crystal diffractometer. Two irregular
fragments with dimensions of 0.03 mm × 0.03 mm × 0.04 mm for 1 and
0.05 mm × 0.05 mm × 0.07 mm for 2 were selected as suitable for the crystal
structure analysis. Room temperature data (298 1 K) were collected using
Because investigated compounds are isostructural only com-
pound 1 will be used for illustrations in all figures. The crystal
structures of 1 and 2 can be divided into two types of slabs
parallel to the (1 0 0) plane (Fig. 3).
A slab is placed between the relative heights a from about
−0.33 to about 0.33. This slab is composed of Tl1S8, Tl2S6,
Tl3S5Ag3 coordination polyhedra and Ag3S3Tl3 distorted
trigonal pyramid combined with trigonal Sb1S3 or As1S3 coor-
dination pyramids. The thickness of the A slab is approximately
as the double thickness of the B slab.
B slab is built of Sb2S3 (As2S3) trigonal pyramids combined
with Ag1S4 and Ag2S4 coordination tetrahedra. Its boundaries
lie between a about 0.33 and 0.67.
A and B slabs are linked to each other by (semi)metal–sulphur
bonds created by (semi)metals from A and B slabs and S atoms
positioned between them, i.e. S3 from A slab and triangular
S1S2S6-net from B slab.
In the central part of the A slab, two S atoms (S4 and S5)
are arranged in triangles and distorted squares (Fig. 4(a)) form-
ing a net related to the two-dimensional net found in tetragonal
Tl2S2, i.e., Tl+Tl3+S2− (Tl2Se2-type structure) [9], and some
other compounds [10]. The main difference is that the four-fold
symmetry found in tetragonal Tl2S2 (Fig. 4(b)) is transformed
to the two-fold symmetry in 1 and 2.
All Tl atoms are sitting in the holes of two-dimensional
S4S5-net: Tl1 and Tl2 in distorted triangles and Tl3 in very
deformed squares (Fig. 4(a)). They are positioned a little above
and below the plane of S4S5-net forming two similar and paral-
lel metal–semimetal sheets with Ag3 and Sb1. The distribution
of Tl1-Tl3 is also closely related to the distribution in tetrago-
nal Tl2S2 [9]: the (1 0 0) plane corresponds to the (0 0 1) plane
of the Tl2S2 structure (Fig. 4). Although observed distortion is
large in comparison to the Tl2S2 structure, Tl atoms are princi-
pally located in similar positions relative to S atoms. Fig. 4(a)
shows two kinds of distorted triangles in which Tl atoms are
positioned: Tl1 in a less deformed, and Tl2 in the other, more
deformed triangle. There is one Tl atom per triangle, opposing to
the Tl2S2 structure, where only one trivalent Tl “belongs” to two
triangles. The analogous position of monovalent Tl in Tl2S2 [9]
is the Tl3-site. In Fig. 5 one metal–semimetal sheet is presented
together with S atoms included in creating Tl–S, Ag–S and Sb–S
˚
Mo K␣ radiation (λ = 0.71073 A) on a Bruker-AXS four circle diffractometer
equipped with 1K area detector and a flat graphite monochromator. The sample-
to-detector distance and collimator diameter were 40 and 0.5 mm, respectively.
The data collections were performed by a combination of ω and ϕ scans using
six sets of exposures and 1680 frames; each 60 s exposure for 1 and 50 s for 2
covered an ω-rotation of 0.3◦. The final unit cell parameters were determined
from 2066 for 1 and 2239 for 2 strong reflections [I > 10σ(I)] after integration
Table 2
Fractional atomic coordinates and equivalent isotropic displacement parameters
for 1 and 2
2
˚
Atom
x
y
z
Ueq (A )
1
Tl1
Tl2
Tl3
Ag1
Ag2
Ag3
Sb1
Sb2
S1
S2
S3
S4
S5
0.2146(1)
0.88373(7)
1.01213(7)
0.75889(7)
0.8755(2)
0.8657(2)
1.1567(1)
0.9155(1)
0.6479(1)
0.8394(4)
0.5762(4)
0.7520(4)
0.9673(4)
0.8278(4)
0.5834(4)
0.10108(8)
0.27209(8)
0.57430(9)
0.4229(2)
0.0479(2)
0.1737(2)
0.4086(1)
0.2462(1)
0.2969(5)
0.4708(5)
0.3684(5)
0.1807(5)
0.4533(5)
0.1719(5)
0.0389(3)
0.0374(3)
0.0426(3)
0.0428(5)
0.0470(5)
0.0481(5)
0.0255(3)
0.0251(3)
0.029(1)
0.030(1)
0.033(1)
0.032(1)
0.030(1)
0.027(1)
−0.1981(1)
0.8431(1)
0.4749(2)
0.4753(2)
0.1084(2)
0.1689(1)
0.4988(1)
0.5869(6)
0.6317(6)
0.2647(6)
0.0023(6)
0.0068(6)
0.6441(5)
S6
2
Tl1
Tl2
Tl3
Ag1
Ag2
Ag3
As1
As2
S1
S2
S3
S4
S5
0.21445(6)
−0.20582(6)
0.84388(7)
0.4690(1)
0.4716(1)
0.1108(1)
0.1590(1)
0.5043(1)
0.5781(4)
0.6252(4)
0.2502(4)
0.0016(4)
0.0091(4)
0.6375(3)
0.88283(5)
1.01576(5)
0.75947(6)
0.8755(1)
0.8606(1)
1.1568(1)
0.9094(1)
0.6465(1)
0.8275(3)
0.5778(3)
0.7565(3)
0.9678(3)
0.8311(3)
0.5853(3)
0.10078(6)
0.27670(6)
0.57238(7)
0.4215(1)
0.0425(1)
0.1771(1)
0.4014(1)
0.2493(1)
0.2919(4)
0.4597(4)
0.3635(4)
0.1913(4)
0.4496(4)
0.1755(3)
0.0398(2)
0.0393(2)
0.0458(2)
0.0422(3)
0.0491(3)
0.0475(3)
0.0268(3)
0.0267(3)
0.0314(8)
0.0302(8)
0.0310(8)
0.0347(9)
0.0309(8)
0.0289(8)
S6
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.

L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
69
Table 3
Anisotropic displacement parameters (A ) for 1 and 2
2
˚
Atom
U11
U22
U33
U23
U13
U12
1
Tl1
Tl2
Tl3
Ag1
Ag2
Ag3
Sb1
Sb2
S1
S2
S3
S4
S5
0.0388(6)
0.0352(5)
0.0526(7)
0.044(1)
0.060(1)
0.060(1)
0.0269(8)
0.0217(8)
0.038(3)
0.034(3)
0.034(3)
0.024(3)
0.031(3)
0.027(3)
0.0374(5)
0.0383(5)
0.0399(5)
0.046(1)
0.044(1)
0.039(1)
0.0207(6)
0.0253(7)
0.025(2)
0.026(2)
0.026(3)
0.033(3)
0.024(3)
0.025(2)
0.0385(5)
0.0377(5)
0.0424(5)
0.045(1)
0.038(1)
0.045(1)
0.0281(7)
0.0268(7)
0.028(3)
0.027(3)
0.037(3)
0.035(3)
0.041(3)
0.030(3)
−0.0047(4)
0.0006(4)
−0.0070(4)
−0.0069(8)
0.0022(7)
0.0083(8)
−0.0001(5)
0.0002(5)
0.001(2)
0.0200(4)
0.0195(4)
0.0307(5)
0.0288(9)
0.028(1)
0.028(1)
0.0146(6)
0.0124(6)
0.022(3)
0.015(2)
0.019(3)
0.013(3)
0.024(3)
0.015(2)
−0.0029(4)
0.0047(4)
−0.0082(4)
−0.0037(9)
−0.0060(9)
0.0139(9)
−0.0008(6)
−0.0010(6)
0.003(2)
0.001(2)
0.001(2)
0.007(2)
0.004(2)
0.004(2)
−0.002(2)
−0.001(2)
0.000(2)
S6
−0.004(2)
−0.001(2)
2
Tl1
Tl2
Tl3
Ag1
Ag2
Ag3
As1
As2
S1
S2
S3
S4
S5
0.0392(4)
0.0363(3)
0.0544(4)
0.0446(7)
0.0625(8)
0.0535(8)
0.0273(7)
0.0245(7)
0.041(2)
0.037(2)
0.035(2)
0.030(2)
0.033(2)
0.032(2)
0.0406(4)
0.0397(4)
0.0475(4)
0.0453(8)
0.0508(9)
0.0453(8)
0.0240(8)
0.0288(8)
0.028(2)
0.026(2)
0.028(2)
0.037(2)
0.031(2)
0.027(2)
0.0369(4)
0.0392(4)
0.0424(4)
0.0414(7)
0.0351(7)
0.0408(8)
0.0266(8)
0.0259(8)
0.032(2)
0.029(2)
0.032(2)
0.031(2)
0.033(2)
0.028(2)
−0.0040(3)
0.0008(3)
−0.0058(3)
−0.0040(6)
0.0008(5)
0.0072(6)
−0.0008(6)
0.0003(6)
−0.001(1)
−0.001(1)
−0.000(1)
0.008(2)
0.0193(3)
0.0191(3)
0.0310(3)
0.0267(6)
0.0276(6)
0.0243(6)
0.0134(6)
0.0133(6)
0.024(2)
0.019(2)
0.019(2)
0.014(2)
0.020(2)
0.016(2)
−0.0045(3)
0.0035(3)
−0.0082(3)
−0.0017(5)
−0.0072(6)
0.0128(6)
−0.0016(5)
−0.0011(5)
−0.001(1)
−0.002(1)
0.004(1)
0.005(1)
−0.001(1)
−0.002(1)
S6
−0.002(1)
−0.001(1)
(As–S) bonds. The Sb1S3 (As1S3) trigonal pyramids are framed
by pentagons formed by five Tl atoms. These pentagons share
two edges with neighbouring pentagons forming zigzag chains
parallel to c-axis.
In the central part of B slab two distinct, Ag1 and Ag2, and
one Sb2 (As2) sites are present forming a new metal–semimetal
sheet shown in Fig. 3. Above and below the plane of this sheet,
three S atoms (S1, S2 and S6) produce an irregular triangular net
(Fig. 6(a)), which closely corresponds to the S-net (Fig. 6(b))
found in sulphosalts ellisite (Tl3AsS3) [11] and “stibioellisite”
(Tl3SbS3) [12]. The Sb2 (As2) atom exhibits a usual three-
fold coordination by S with Sb2 (As2) situated on one vertex
of a trigonal pyramid (Fig. 6(a)). In this slab all SbS3 (AsS3)
pyramids are enclosed in a distorted hexagonal Ag1Ag2-net,
Fig. 3. The projection of the Tl3Ag3Sb2S6 structure along b-axis showing two types of slabs parallel to (1 0 0).

70
L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
Fig. 4. The difference between Tl-S-net and positions of Tl atoms found in 1 (a) and Tl2S2 (b). For an easier comparison a unique set of square and triangles (bottom
right) is shaded.
Fig. 5. The projection of Tl3Ag3Sb2S6 perpendicular to the A slab showing one metal–semimetal sheet and S atoms included in building the corresponding polyhedra.

L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
71
Fig. 6. The corrugated sheet of S atoms (S1, S2 and S6) showing irregular net viewed along the a-axis (a), and triangular net of S atoms in “stibioellisite” viewed
along the c-axis (b).
which is similar to a type of graphene layer (Fig. 7(a)). Ag1S4-
and Ag2S4-tetrahedra (Fig. 7(b)) in six-membered rings share
edges when Ag atoms are in crystallographicaly the same posi-
tions (two Ag1S4- or two Ag2S4-tetrahedra), but only vertices
when they are in different sites (one Ag1S4- and one Ag2S4-
tetrahedron).
The coordination polyhedron of Tl1 is completed by eight S
atoms (2S4 + 1S5 from triangle of S4S5-net, 3S from S1S2S6-
net and additional two S3 atoms). Tl1–S distances (Table 4) are
a significantly distorted trigonal prism with one base completed
by S4 + 2S5 from S4S5-net, and another by S1 + S2 atoms from
triangular S1S2S6-net and one S3 (Fig. 5). Alternatively, it can
be described as an extremely distorted octahedron. The average
˚
˚
ꢀTl2–Sꢁ distances are very similar: 3.236 A for 1 and 3.238 A
for 2, and slightly longer than the sum of the ionic radii for Tl+
2−
˚
˚
with CN = 6 (1.45 A) and S (1.70 A [13]).
Thallium Tl3 is surrounded by five nearest atoms (one
˚
Ag and four S) at distances 2.959(2)–3.181(5) A for 1 and
˚
˚
˚
2.922(1)–3.147(4) A for 2 (Table 4). The distance Tl3–Ag3 is
in the range 3.259(5)–3.672(6) A for 1 and 3.228(4)–3.529(4) A
for 2. The coordination is a square antiprism with a quasi-four-
fold axis close to the [0 1 0] direction (Fig. 5). The average
˚
˚
2.959(2) A in 1 and 2.922(1) A in 2. (The short Tl–Ag contacts
will be discussed latter in detail.) The fifth S atom is at a longer
˚
˚
˚
ꢀTl1–Sꢁ distance in 1 (3.393 A) is almost identical to the sum
distance of 3.652(5) A for 1 and 3.695(4) A for 2. These six
atoms form a distorted trigonal prism around Tl3. A similar
coordination of Tl atoms, but with six S atoms, was observed
in the structure of synthetic Tl3SbS4 [14]. The average ꢀTl3–Sꢁ
+
2−
˚
˚
of Tl (1.69 A) and S (1.70 A) ionic radii [13], while in 2
˚
this distance (3.356 A) is somewhat shorter and very close to
3.35 A found for Tl with CN = 8 in the tetragonal Tl2S2 [9].
+
˚
˚
The Tl2 atom is surrounded by six S atoms at distances
distances in both structures are almost identical (3.206 A for
1 and 3.202 A for 2) and somewhat shorter than the average
ꢀTl2–Sꢁ distances, but slightly longer than 3.15 A, i.e. than the
˚
˚
˚
between 3.091(5) and 3.392(5) A for 1 and 3.070(4)–3.397(4) A
for 2 (Table 4). The coordination polyhedron can be described as
˚
Fig. 7. The B slab from above in 1 with S3 atoms from A slab included because of polyhedra completion (a), and the same slab showing connections of AgS4-tetrahedra
(b).

72
L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
Table 4
Ag2S4-tetrahedra are connected and form zigzag chains parallel
to the [0 1 0] direction (Fig. 7(b)).
˚
Selected bond distances (A) for 1 and 2
In 1 the average tetrahedral ꢀAg1/Ag2–Sꢁ distances (Table 4)
and ꢀS–Ag1/Ag2–Sꢁ angles (107.6◦ and 108.3◦) are very simi-
lar to the corresponding values found in 2 (108.9◦ and 108.2◦).
1
2
Bond
distance
Average bond
distance
Bond
distance
Average bond
distance
˚
The distances are also very close to the 2.62 A, i.e. the sum of
Tl1–S5I
3.259(5)
3.272(6)
3.303(5)
3.304(5)
3.348(5)
3.421(5)
3.566(5)
3.672(6)
3.091(5)
3.138(6)
3.185(5)
3.228(5)
3.381(5)
3.392(5)
2.994(5)
3.093(5)
3.111(5)
3.181(5)
3.652(5)
2.537(5)
2.589(5)
2.613(6)
2.752(5)
2.564(6)
2.566(5)
2.618(6)
2.745(5)
2.454(5)
2.583(6)
2.590(5)
2.959(2)
2.419(5)
2.427(5)
2.468(5)
3.470(5)
2.429(5)
2.429(5)
2.442(5)
3.228(4)
3.321(4)
3.272(4)
3.257(4)
3.297(4)
3.449(4)
3.496(4)
3.529(4)
3.070(4)
3.111(4)
3.185(4)
3.358(4)
3.397(4)
3.304(4)
2.986(4)
3.086(4)
3.095(4)
3.147(4)
3.695(4)
2.536(4)
2.593(4)
2.606(4)
2.712(4)
2.555(4)
2.559(4)
2.629(4)
2.777(4)
2.466(4)
2.550(4)
2.601(4)
2.922(1)
2.247(4)
2.246(4)
2.284(4)
3.593(4)
2.241(4)
2.252(4)
2.261(4)
3.831(4)
+
2−
˚
Ag with CN = 4 (0.92 A) and S ionic radii [13]. The aver-
Tl1–S4
˚
Tl1–S6II
age triangular ꢀAg3–Sꢁ distances (2.542 in 1 and 2.539 A in 2)
and ꢀS–Ag3–Sꢁ angles (120.0◦ in both) are very similar too.
The fourth, Ag3–Tl3 contact is approximately perpendicular to
the triangular Ag3S3-group. Similar coordinations for Ag with
Tl1–S2II
Tl1–S3
Tl1–S4III
Tl1–S3I
Tl1–S1
Tl2–S5
˚
˚
three S atoms at ≈2.5 A and one S instead of Tl at ≈2.9 A
were found in structures of freieslebenite, PbAgSbS3 [15], mar-
rite, PbAgAsS3 [16], hatchite, PbTlAgAs2S5 [17], and smithite,
AgAsS2 [18].
ꢀ3.393ꢁ
ꢀ3.236ꢁ
ꢀ3.356ꢁ
ꢀ3.238ꢁ
Tl2–S4
Tl2–S3V
Tl2–S2IV
Tl2–S1VII
Tl2–S5VI
Tl3–S2
The three nearest S atoms of Sb1 and Sb2 are at average
˚
˚
distances of 2.438 and 2.433 A in 1 and at 2.259 and 2.252 A for
As1 and As2 in 2. The average ꢀS–Sb–Sꢁ angles are 99.0◦ and
97.3◦ for trigonal Sb1S3- and Sb2S3-pyramids in 1, but 101.1◦
and 99.6◦ for As1S3- and As2S3-pyramids in 2. Three additional
S atoms (S1 from slab B and two S3 from slab A; Fig. 3) are
Tl3–S5IX
Tl3–S4X
Tl3–S1
Tl3–S6XI
Ag1–S1
ꢀ3.206ꢁ
ꢀ2.623ꢁ
ꢀ3.202ꢁ
ꢀ2.612ꢁ
˚
at much longer distances (about 3.75–4.05 A) from Sb2/As2
Ag1–S6XI
Ag1–S3
making an irregular trigonal antiprism and clearly indicating
direction of the Sb/As lone electron pair. On the other hand,
Ag1–S6II
Ag2–S2I
Ag2–S1
˚
up to 4 A only one additional S atom (S6) lying opposite to S5
(Fig. 5) exists close to Sb1/As1. Thus, in the case of Sb1/As1 all
S atoms are concentrated in one hemisphere leaving the space
for the Sb/As lone electron pair in another hemisphere.
As already stated, compounds 1 and 2 are structurally iden-
tical and their geometrical features are very similar in many
aspects. The main difference are a shorter distances around As
than around Sb ions, which is as expected because of different
As3+ and Sb3+ radii; consequently, the unit cell volume of 2 is
smaller for about 4 %.
Only few Tl sulphosalts are structurally characterized
so far and no other compounds with the same combi-
nation of the elements are present in ICSD [19]. The
closest chemical compositions found in some minerals:
hatchite, PbTlAgAs2S5 [17], sicherite, TlAg2(As2.03Sb0.97)S6
[20], rathite, Pb8Pb4−x(Tl2As2)x(Ag2As2)As16S40 [21],
wallisite, PbTl(Cu0.65Ag0.35)(As2S5) [22], and gabrielite,
Tl2AgCu2As3S7 [23] always contain some additional elements.
No simple structural relationships between these minerals and
here described compounds exist.
Different kinds of layers and slabs are characteristic for
many natural and synthetic sulphides and sulphosalts involv-
ing Tl-containing ones (see, for example, refs. [24,25]). Two
recent examples are above-mentioned sicherite and gabrielite.
In sicherite there are slabs containing polyhedra of Tl and Ag,
and slabs with As/SbS3-pyramids [20]. In gabrielite three differ-
ent slabs sharing layers of common S atoms exist. Tl atoms are
present in two slabs, one of them hosts coordination polyhedra
of As and Tl and another of Tl only [23].
Ag2–S3I
Ag2–S2II
Ag3–S5V
Ag3–S6II
Ag3–S4
ꢀ2.623ꢁ
ꢀ2.542ꢁ
ꢀ2.630ꢁ
ꢀ2.539ꢁ
Ag3–Tl3VIII
Sb1(As1)–S3
Sb1(As1)–S4
Sb1(As1)–S5
Sb1(As1)–S6II
Sb2(As2)–S1
Sb2(As2)–S2
Sb2(As2)–S6
ꢀ2.438ꢁ
ꢀ2.696ꢁ
ꢀ2.259ꢁ
ꢀ2.593ꢁ
ꢀ2.433ꢁ
ꢀ2.764ꢁ
ꢀ2.251ꢁ
ꢀ2.646ꢁ
Sb2(As2)–S1XII 3.754(5)
Symmetry transformations used to generate equivalent atoms: Ix, −y + 3/2,
z − 1/2; II−x + 1, y + 1/2, −z + 1/2; III−x, −y + 2, −z; IVx − 1, −y + 3/2, z − 1/2;
−x, y + 1/2, −z + 1/2; −x, −y + 2, −z + 1; VIIx − 1, y, z;
−x + 1, −y + 2,
XII
V
VI
VIII
−z + 1; IXx + 1, y, z; Xx + 1, −y + 3/2, z + 1/2; XIx, −y + 3/2, z + 1/2; −x + 1,
y − 1/2, −z + 1/2.
sum of Tl+ and S2− ionic radii. If the short Tl3–Ag3 contact
is included, the average bond distances around Tl3 decrease to
3.165 A in 1 and 3.155 A in 2.
Only Tl2 and Tl3 display stereochemical activity of their lone
electron pairs, which are directed opposite to the short Tl–S
bonds (Tl2–S5, as well as Tl3–S2 and Tl3–S4; see Table 4).
In both structures Ag1–Ag3 have three nearest S neighbours
˚
˚
˚
at distances ≈2.5–2.6 A (Table 4). The fourth atom in coordina-
tion polyhedra of Ag1 and Ag2 is S at a slightly longer distance
˚
of ≈2.7 A, but in coordination polyhedron of Ag3 the fourth
3.2. Short metal–metal contacts
˚
atom is Tl3 at distance of ≈2.9 A for both structures. These
coordination polyhedra can be described as distorted tetrahedra
for Ag1 and Ag2, or a trigonal pyramid for Ag3. All Ag1S4- and
The most striking feature of structures 1 and 2 is the short
˚
Tl–Ag distance of 2.959(2) and 2.922(1) A, respectively. To best

L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
73
of our knowledge these distances are shorter than any Tl+–Ag+
distance reported previously. For example, the shortest Tl–Ag
contact found so far in an inorganic compound is 3.250 A in
Table 5
˚
Selected Tl–Ag and Ag–Ag contacts (A) for 1 and 2
˚
Contacts
TlAg3S2 [26]. A search of the Cambridge Structural Database
[27] also did not reveal any Tl–Ag contact shorter than 3.25 A.
1
2
˚
Tl1–Ag1
3.382(2)
3.428(2)
3.450(2)
3.683(2)
3.719(2)
2.959(2)
3.566(2)
3.237(2)
3.369(3)
3.302(1)
3.387(2)
3.389(2)
3.659(2)
3.627(2)
2.922(2)
3.518(2)
3.124(2)
3.337(2)
The significance of Tl–Ag interactions in 1 and 2 is further
manifested by the deviation in planarity of the Ag3S3-units: Ag3
atoms are displaced outward their respective S4S5S6-planes by
Tl1–Ag3III
Tl1–Ag2
Tl2–Ag2I
Tl2–Ag2III
Tl3–Ag3III
Tl3–Ag3II
Ag1–Ag2IV
Ag1–Ag1III
˚
0.048 in 1 and 0.031 A in 2.
The tendency of Tl+ ions to make Tl–metal contacts that
are (sometimes much) shorter than the sum of corresponding
van der Waals (vdW) radii is well documented in literature.
˚
First of all, Tl–Tl contacts shorter than 3.92 A (i.e. 2 × rvdW(Tl)
Symmetry transformations used to generate equivalent atoms: Ix, −y + 3/2,
z − 1/2; II−x + 1, y + 1/2, −z + 1/2; III−x, −y + 2, −z; IVx − 1, −y + 3/2, z − 1/2.
[28]) are found in many classes of compounds, as simple inor-
˚
ganic salts, e.g., TlF (the shortest Tl–Tl distance: 2.59 A) [29]
˚
and TlNO3 (Tl–Tl: 3.05 A) [30], some organometallics, e.g.,
˚
Tl4(OR)4, R = Me, Et, n-Pr (Tl–Tl: 3.83 A) [31], some inter-
getic stabilization of s and p shells, as well as shortening of
corresponding bond lengths. The relativistic effects are very pro-
nounced for the sixth row elements (W to Bi) with the maximum
at Au, but they could be relevant for fifth (e.g., Ag) and even
fourth (e.g., Cu) row elements [44].
˚
metallics, e.g., Li5Tl2 (Tl–Tl: 3.01 A) [32] and KTl (Tl–Tl:
˚
3.06–3.08 A) [33], as well as in many coordination compounds,
e.g., [As(C6H5)4][Tl2{μ-Mn(CO)4(μ-H)Mn3(CO12}2] (Tl–Tl
˚
3.632 A) [34] and a series of pyrazolate complexes (Tl–Tl:
˚
It is interesting that (Tl–Au)2+ group is isoelectronic with the
(Hg–Hg)2+ ion. The same is true for (Tl–Ag)2+ group if only
the valence-shell electrons are considered. From this point of
view, the appearance of (Tl–Au/Ag)2+ groups and their further
arrangement in more complicated clusters is not surprising at
all. However, these facts are entirely overlooked in previous
studies and discussions. Since, as stated above, the relativistic
effects are less prominent for Ag than for Au, a number of known
compounds with short Tl–Ag contacts is still very small, but new
examples of similar compounds should be expected.
In addition to the above-discussed very short Tl3–Ag3 con-
tacts, several Tl–Ag interactions with longer separations (up
to 3.566(2) A) were also found in the present sulphosalts
(Table 5). They are also shorter than the sum of vdW radii
(rTl + rAg = 1.96 + 1.72 = 3.68 A [28]). Besides, there are four
3.53 A) [35].
On the other hand, short thallium–transition metal (TM) con-
tacts (sometimes described as metal–metal ␴ bonds), where TMs
typically are some heavier transition metals, as Rh, Pt, Pd and
Re, or even Mn, are present in many polynuclear complexes and
complexes containing metallic chains or clusters [36]. The most
suchcomplexeswerepreparedinsolutiononlyandcharacterized
by different spectroscopic techniques, whereas the existence of
Tl–TM contacts was, for example, confirmed by the determi-
nation of the spin-spin coupling constants. However, a short
˚
Tl(I)–Pd(II) distance of 2.897(2) A was also proved by the crys-
tal structure determination [36(c)]. This distance is very close
˚
to the sum of Tl(I) and Pd(II) covalent radii (2.89 A) strongly
˚
supporting the existence of Tl–Pd bond.
Of special importance here is a class of polynuclear, Tl+-
containing complexes of the sixth row elements with a special
role of Tl–Au compounds. Such complexes often exhibit the
luminescent properties, which have been attributed to the nature
of ligands, to the coordination geometry and to the presence
of metal–metal interactions [37]. For example, Tl(I)–Au(I) dis-
˚
˚
Tl–Ag distances, which are very close to 3.68 A or slightly above
this value.
Furthermore, some Ag–Ag interactions were determined to
˚
be significant. Three of them in the range ≈3.2–3.4 A (Table 5)
indicate a weak Ag–Ag interaction, but the Ag1–Ag2 distance
˚
˚
˚
tances as short as 2.911 A [38], 2.971 A [39] and 3.122 A [40]
have been reported recently. They are comparable with the
Tl–Ag distances found in the present compounds.
˚
of 3.124(2) A in 2 corresponds to the presence of significant
argentophilic attraction. For comparison, the crystal structure
of above-mentioned Tl[Ag(CN)2] shows Ag–Ag distances of
3.110(3) A [43], but even shorter distances, e.g., 2.857 [45]
and 2.997 A [46], exist within some other complex compounds.
In addition, short Ag–Ag distances (2.915–3.256 A) are char-
acteristic for minerals pyrargyrite, Ag3SbS3, and stephanite,
Ag5SbS4 [19].
Although some properties of Ag and Au should be simi-
lar and their radii are practically identical, really short Tl–Ag
contacts have not been found so far. A significant metal-metal
˚
˚
˚
˚
attraction and Tl–Ag separation of 3.13 A were predicted in an
isolatedTl[Ag(CN)2]species[41]. However, boththetheoretical
study and crystal structure determination of Tl[Ag(CN)2] have
not confirmed an importance of Tl–Ag contacts in this example
[42,43].
Acknowledgements
Short Tl–Au/Ag bonds could be attributed to the closed-shell
metal–metal interactions often described as metallophilicity
(aurophilicity, argentophilicity, etc.) principle [37]. This is at
least partially related to the relativistic effects which influence
many heavy metal properties, including contraction and ener-
We thank the Ministry for Science and Environmental Pro-
tection of the Republic of Serbia (Project No. 142030) and the
DanishNaturalScienceResearchCouncil(ProjectNo. 9901772,
KU 56347) for the financial support. The authors gratefully
acknowledge the critical reviews of the manuscript by two

74
L. Karanovic´ et al. / Journal of Alloys and Compounds 457 (2008) 66–74
anonymous referees, whose comments and suggestions have
notably improved the quality of the paper.
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