(HgBr2)3(As4S4)2: An adduct of HgBr2 molecules and undistorted as4S 4 cages

Article abstract of DOI:10.1002/zaac.200600363

(HgBr₂)₃(As₄S₄)₂ is obtained by high temperature reaction of stoichiometric amounts of HgBr ₂ and As₄S₄. It crystallizes in the monoclinic space group P2₁/c with the lattice constants a = 9.593(5) A, b = 11.395(5) A, c = 13.402(5) A, β= 107.27(3)°, V = 1399(1) A³, and Z = 2. The crystal structure consists of molecular units built from two undistorted As₄S₄ cages which are coordinated weakly by three almost linear HgBr₂ units. Raman spectra clearly indicate minor bonding interactions between HgBr₂ and As ₄S₄.

Full text of DOI:10.1002/zaac.200600363

Short Communications
DOI: 10.1002/zaac.200600363
(
HgBr ) (As S ) : An Adduct of HgBr Molecules and Undistorted As S Cages
2
3
4 4 2
2
4 4
Michael F. Bräu and Arno Pfitzner*
Regensburg, Universität, Institut für Anorganische Chemie
Received December 20th, 2006.
Abstract. (HgBr
tion of stoichiometric amounts of HgBr
2
)
3
(As
4
S
4
)
2
is obtained by high temperature reac-
and As . It crystallizes
weakly by three almost linear HgBr
indicate minor bonding interactions between HgBr and As S .
2 4 4
2
units. Raman spectra clearly
2
4
S
4
in the monoclinic space group P2
1
/c with the lattice constants a ϭ
˚
˚
˚
9
1
.593(5) A, b ϭ 11.395(5) A, c ϭ 13.402(5) A, β ϭ 107.27(3)°, V ϭ
399(1) A , and Z ϭ 2. The crystal structure consists of molecular
cages which are coordinated
˚
3
Keywords: Mercury halides; Molecular adducts; Arsenic sulfides;
Crystal structures; Raman spectroscopy
units built from two undistorted As
4
S
4
Copper(I) halides are well established as a preparative tool to ob-
tain new molecular or polymeric compounds of group 15 and 16
elements [1]. Inspired by early investigations of Rabenau et al. [2],
and Möller and Jeitschko [3] many molecules or polymers of phos-
phorus [4], phosphorus chalcogenides [5], and heteroatomic chal-
cogen polymers [6] were synthesized. Extraction of CuI from the
3 2 2 3 4
Hg Q X (Q ϭ S, Se, Te; X ϭ F, Cl, Br, I) and Hg AsQ X (Q ϭ
S, Se, X ϭ Cl, Br, I) [11]. Also, a whole family of mercury chalco-
genometalate halides is described in the literature [12]. These
materials are usually prepared by high temperature syntheses from
stoichiometric amounts of the corresponding mercury halide and
the chalcogens, respectively. They can be described as polycationic
adducts (CuI)
8
P12 and (CuI)
3
P12 leaves the pure phosphorus
3
frameworks of QHg pyramids (Q ϭ S, Se) which are linked to
polymers behind [7]. Even mixed arsenic-phosphorus polymers are
accessible using this experimental approach [8]. A reason for the
stability of these compounds is the structural flexibility of the cop-
per halide framework, which is obviously able to host various mole-
cules. In addition, the d10 ion Cu seems to form strong bonds to
phosphorus and thus helps to stabilize the embedded main group
molecules.
one-, two- or three dimensional networks. The anions occupy layers
in between the cationic networks. Bonding between mercury and
chalcogen atoms is assumed to be mainly covalent with distances
d(Hg-S) ഠ 2.4 A and d(Hg-Se) ഠ 2.55 A. These compounds are
very stable and some of them are known as minerals. However,
˚
˚
ϩ
during the synthesis of (HgI
fur none of these compounds were observed. In contrast, almost
linear HgI molecules and As cages remain and form the dimeric
molecular adduct [10]. Herein, we report about the mercury bro-
mide adduct (HgBr (As
2 2 4 4 2 2
) (As S ) from HgI , arsenic and sul-
2
4 4
S
Extending this approach, the next goal is to get access to adduct
compounds of binary cage molecules or polymers of arsenic and
sulfur or selenium. The reaction of copper(I) halides with arsenic
2
)
3
4 4 2
S ) .
3 4
and sulfur reveals Cu AsS , known as the mineral enargite, CuAsS,
known as the mineral lautite, and other binary phases. Obviously,
these are the preferred products in high temperature syntheses. In
Experimental Details
low temperature syntheses a reaction of As
transition metals ends in fragmentation of the cages [9].
4 4 4 4
S or As Se cages with
(
2 3 4 4 2 2
HgBr ) (As S ) is obtained by melting a mixture of HgBr , As
and S at 400 °C in evacuated silica ampoules and subsequent an-
nealing at 190 °C for two weeks. The main products of this reaction
are Hg S Br and As S . Besides these small amounts of
2 4 4
Recently, a molecular adduct of linear HgI moieties and As S
cages was described [10]. This shows that the d10 ion Hg is also
able to form adducts with main group element cages. The structure
consists of mercury iodide molecules with the mercury atoms are
2ϩ
3
2
2
4 4
(HgBr
2
)
3
(As
4
S
4
)
2
are obtained as well shaped single crystals by this
high temperature route. Higher yields are obtained by reaction of
a mixture of HgBr and As in CS at 160 °C for two weeks.
This solvothermal route results in (HgBr
product. The main byproduct again is Hg
2
4
S
4
2
weakly coordinated to the sulfur atoms of As cages. In case of
4 4
S
2
)
3
(As
Br
4 4 2
S ) as the major
HgI and As , dimeric units (HgI (As S ) are formed.
2
4
S
4
2
)
2
4 4 2
3
S
2
2
.
A wide spectrum of these compounds forming polycationic net-
works of mercury and chalcogen atoms is known in the compounds
Single crystals of (HgBr ) (As S ) were selected under a micro-
2
3
4 4 2
scope, mounted on a glass fiber and checked for their quality by
Weissenberg photographs. Diffraction data were collected on a Stoe
IPDS at room temperature applying MoKͰ radiation. Cell con-
stants were determined from powder patterns of the pure product
*
Prof. Dr. Arno Pfitzner
Universität Regensburg
Institut für Anorganische Chemie
Universitätsstraße 31
D-93040 Regensburg /Germany
Fax: (ϩ49)941/943 4983
(STOE STADI P, CuKͰ
1
, Ge(111) monochromator).
Raman spectra were recorded on
a
Bruker RFS100/S FT
spectrometer equipped with a Nd:YAG laser (λ ϭ 1064 nm) and
E-mail: arno.pfitzner@chemie.uni-regensburg.de
Ge-detector cooled by liquid nitrogen.
Z. Anorg. Allg. Chem. 2007, 633, 935Ϫ937
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
935

M. F. Bräu, A. Pfitzner
2 3 4 4 2 4 4 2
Fig. 1 In (HgBr ) (As S ) As S cages are connected by HgBr
units. Ellipsoids are drawn at the 70 % probability level. Selected
interatomic distances in A:
Fig. 2 Section of the crystal structure of (HgBr
As cages (shown as polyhedra) are arranged in columns along
[0 0 1]. Ellipsoids are drawn at the 70 % probability level.
2 3 4 4 2
) (As S ) . The
˚
4 4
S
Hg1-Br1: 2.457(2), Hg2-Br2: 2.410(2), Hg2-Br3: 2.515(2), Hg1-S1: 3.15(3),
Hg1-S4: 3.12(2), Hg2-S2: 3.19(6), Hg2-S3: 3.07(1), As1-As2: 2.552(2), As3-
As4: 2.572(2), As1-S2: 2.250(3), As1-S3: 2.245(3), As2-S1: 2.244(3), As2-S4:
2
2
.247(3), As3-S2: 2.239(3), As3-S4: 2.244(4), As4-S1: 2.241(3), As4-S3:
.249(3).
Table 1 Vibrational frequencies in cmϪ1 for (HgBr
a tentative assignment. Most of the frequencies correspond to the
2 3 4 4 2
) (As S ) and
4 4
cages in binary As S .
Results and Discussion
Assignment
Intensity
(HgBr
2
)
3
(As
4
S
4
)
2
4 4
As S [17]
(
2 3 4 4 2 2 4 4
HgBr ) (As S ) is a reaction product of HgBr and As S , for-
As-S stretch
As-S stretch
As-S stretch
Ϫ
very weak
very strong
very weak
very weak
very weak
very strong
very strong
strong
374
359
344
279
248
225
198
191
183
164
148
376
355
345
Ϫ
ming yellow transparent crystals of irregular shape. The crystal
structure was determined from single crystal diffraction data. Data
were corrected numerically for absorption after refining the de-
scription of the shape of the crystal with X-SHAPE [13] using 500
independent reflections selected within X-RED [14]. Extinction
conditions allowed the space groups P2
able solution and refinement of the crystal structure was possible
in P2 /c. The refinement converged to final R-values R1 ϭ 0.0525
and wR2 ϭ 0.0863 for all data [15]. The structure consists of ad-
ducts of three HgBr units with two As cages. Figure 1 shows
the arrangement of the HgBr and As molecules with Hg and
Ϫ
Ϫ
As-S wag
As-S-As bend
Ϫ
As-As stretch
As-S-As wag
As-S-As bend
222
196
Ϫ
184
167
144
1
/c, P2
1
and Pc. A reason-
strong
weak
weak
1
2
4 4
S
4 4 4 4
can be assigned to the As S cage in binary As S . Since the shifts
of the frequencies are within two times the experimental resolution
it can be assumed that the bonds within the coordinated cage are
2
4 4
S
Br atoms forming more or less linear units. Mercury atoms are
additionally coordinating sulfur atoms in comparably long dis-
tances. Thus, one exactly linear HgBr in the centre of the adduct
2
4 4
very similar to the non-coordinated cage in binary As S . The ques-
tion whether the weak bands, cf. Table 1, have to be assigned to
Hg-Br vibrational modes or to weak vibrations of the slightly dis-
torted cages is subject of further investigations. The vibrational
and two slightly bent HgBr
2
molecules (;wk(Br2-Hg2-Br3) ϭ
˚
162.5°) at both ends result. The distance d(Hg1-Br1) ϭ 2.457(2) A
of the central HgBr
2
unit corresponds to binary HgBr
2
, d(Hg-Br) ϭ
˚
2
modes of the HgBr molecule depend on the angle Br-Hg-Br and
2.445(3) A, whereas the terminating HgBr
2
units differ slightly with
˚
˚
the chemical environment. Thus, in solid HgBr containing molecu-
d(Hg2-Br2) ϭ 2.410(2) A and d(Hg2-Br3) ϭ 2.515(2) A, respec-
2
˚
lar units with an angle Մ(Br1-Hg-Br2) ϭ 179.9(1)° only one Ra-
tively. The distances d(Hg2-S2) ϭ 3.19(2) A and d(Hg2-S3) ϭ
Ϫ1
˚
˚
˚
1 2
man resonance at ν ϭ 184 cm is observed. In molten HgBr this
3
3
.07(1) A (terminal) and d(Hg1-S1) ϭ 3.15(3) A and d(Hg1-S4) ϭ
Ϫ1
1 3
line shifts to ν ϭ 195 cm and an additional line appears at ν ϭ
.12(2) A (center) of the molecule are all in the same range, but
cage corre-
and the isostructural cage in the
mineral Realgar. The shape of the As cage is not restricted by
Ϫ1
2
71 cm [18]. These frequencies are in the same range as the not
vary significantly. The distances and angles in the As
spond to those in (HgI (As
4 4
S
assigned frequencies observed for (HgBr (As . Especially the
2
)
3
4 4 2
S )
2
)
2
4 4 2
S )
finding that all vibrational frequencies of the cage molecules re-
main unchanged shows that the bonding interactions between mer-
4 4
S
the space group symmetry. Nevertheless, it has nearly the ideal sym-
metry of the point group D4d within the standard deviations.
cury and the As
4 4
S cages are extremely small. Otherwise one would
find significant shifts for these frequencies.
The arrangement of the resulting adduct molecules
(
2 3 4 4 2
HgBr ) (As S ) is the second example for an adduct compound
(HgBr
2
)
3
(As
4
S
4
)
2
is displayed in Figure 2. The As
4
S
4
cages are
1
0
10
of a d ion and a main group cage molecule with the d ion being
Hg . Obviously, this family of compounds contains examples for
the coinage metals Cu and Ag and now also for the group 12 cation
Hg . However, the arrangement of the “ionic part” of the com-
pounds, i.e. the MX or the MX part (M ϭ metal, X ϭ halide) and
also the composition and the structures of the main group elemen-
arranged in stacks along the c-axis with HgBr
2
molecules located
2
ϩ
between these stacks.
2
ϩ
In order to get some more insight in the bonding situation between
Hg and S, and As and S, respectively, we recorded Raman spectra
of (HgBr ) (As S ) . Table 1 shows that most of the frequencies
2 3 4 4 2
2
936
www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 935Ϫ937

2 3 4 4 2
(HgBr ) (As S )
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2
2 3 4 4 2
Fig. 3 Raman spectrum of (HgBr ) (As S ) recorded at room
Ϫ1
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.
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2
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are found.
7
I
12
Q
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Q
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I
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Acknowledgement. We thank Prof. Dr. H. Haeuseler and Regina
Stötzel, Universität Siegen, for recording the Raman spectra.
[
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[
[
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2
)
3
(As
4 4 2
S ) : M ϭ 1937.1 g/mol, mono-
clinic, space group P2
1
/c, lattice constants (refined from X-ray
[
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Ϫ1
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Karlsruhe,
76344
Eggenstein-
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Z. Anorg. Allg. Chem. 2007, 935Ϫ937
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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