(HgBr₂)₃(As₄S₄)₂: An Adduct of HgBr₂ Molecules and Undistorted As₄S₄ Cages.

Abstract

Abstract. (HgBr 2 ) 3 (As 4 S 4 ) 2 is obtained by high temperature reaction of stoichiometric amounts of HgBr 2 and As 4 S 4 . It crystallizes in the monoclinic space group P2 1 /c with the lattice constants a ϭ 9.593(5) Å , b ϭ 11.395(5) Å , c ϭ 13.402(5) Å , β ϭ 107.27(3)°, V ϭ 1399(1) Å 3 , and Z ϭ 2. The crystal structure consists of molecular units built from two undistorted As 4 S 4 cages which are coordinated [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 copper halide framework, which is obviously able to host various molecules. In addition, the d 10 ion Cu ϩ seems to form strong bonds to phosphorus and thus helps to stabilize the embedded main group molecules.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 and sulfur reveals Cu 3 AsS 4 , 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 low temperature syntheses a reaction of As 4 S 4 or As 4 Se 4 cages with transition metals ends in fragmentation of the cages [9].Recently, a molecular adduct of linear HgI 2 moieties and As 4 S 4 cages was described [10]. This shows that the d 10 ion Hg 2ϩ is also able to form adducts with main group element cages. The structure consists of mercury iodide molecules with the mercury atoms are weakly coordinated to the sulfur atoms of As 4 S 4 cages. In case of HgI 2 and As 4 S 4 , dimeric units (HgI 2 ) 2 (As 4 S 4 ) 2 are formed.A wide spectrum of these compounds forming polycationic networks of mercury and chalcogen atoms is known in the compounds . Also, a whole family of mercury chalcogenometalate 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 frameworks of QHg 3 pyramids (Q ϭ S, Se) which are linked to 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 Å and d(Hg-Se) ഠ 2.55 Å . These compounds are very stable and some of them are known as minerals. However, during the synthesis of (HgI 2 ) 2 (As 4 S 4 ) 2 from HgI 2 , arsenic and sulfur none of these compounds were observed. In contrast, almost linear HgI 2 molecules and As 4 S 4 cages remain and form the dimeric molecular adduct [10]. Herein, we report about the mercury bromide adduct (HgBr 2 ) 3 (As 4 S 4 ) 2 . Experimental Details(HgBr 2 ) 3 (As 4 S 4 ) 2 is obtained by melting a mixture of HgBr 2 , As and S at 400°C in evacuated silica ampoules and subsequent annealing at 190°C for two weeks. The main products of this...