Z. anorg. allg. Chem. 621 (1995) 1322-1329 Zeitschrift fur anorganische und allgemeine Chemie 0 Johann Ambrosius Barth 1995 Na,B,S, and Li,B,S,: Two Novel Perthioborates with Planar 1,2,4-Trithia-3,5- Diborolane Rings Christoph Jansen, Jorn Kuper, and Bernt Krebs* Munster, Anorganisch-Chemisches Institut der Westfalischen Wilhelms-Universitat Received March 3rd, 1995. Abstract. For the first time perthioborates with trigonal planar contain exactly planar [B2SSl2- groups consisting of five- coordination pf boron wereo prepared. NatB2SS (Pnma, membered B,S, rings with one additional exocyclic sulfur on a = 12.545(2) A , b = 7.441(1) A , c = 8.271(1) A , Z = 4) and each of the boron atoms. The alkaline metal cations are four- Li2B,S5 (C-mcm, a = 15.864(1) A, b = 6.433(1) A, coordinate (lithium) and (four + four)-coordinate (sodium) c = 6.862(1) A, Z = 4) were obtained by reaction of the metal respectively. sulfides with stoichiometricamounts of boron and an excess of sulfur (effective molar ratio M : B : S = 1 : 1 : 4) at 600 "C Keywords: Lithium perthioborate; sodium perthioborate; syn- (650 "C) and subsequent annealing. The non-isotypic structures thesis, crystal structure Na,B,S, und Li,B,S,: Zwei neue Perthioborate mit planaren 1,2,4-Trithia-3,5-Diborolan- Ringen Inhaltsiibersicht. Na2B2SS (Pnma, a = 12,545(2) A, Reaktionstemperatur von 600 "C (650 "C) dargestellt werden. b = 7,441(1) A, c = 8,271(1) A, Z = 4) und Li2BzFS (Cmcm, Die Kristallstrukturen bestehen aus planaren, isolierten a = 15,864(1) A, b = 6,433(1) A, c = 6,862(1) A , Z = 4) [BzSS]Z--Funfringen, zwischen denen sich die (vier)- (Lithium) konnten durch Reaktion der Metallsulfide mit amorphem Bor bzw. (vier + vier)-fach (Natrium) koordinierten Kationen und elementarem Schwefel im Atomverhaltnis 1 : 1 : 4 bei einer befinden. Introduction Though only a relatively small number of thioborates and especially perthioborates are known to date, these com- pounds show a strikingly high variety of structures. Re- cent years have brought major improvements in their syn- thesis and crystallisation so that access to new ternary and quaternary boron sulfides has become easier. For a long time there had been only little progress in this field of solid state chemistry due to problems arising from the properties of boron chalcogenides (see below). In addi- tion to the binary compounds B,S, [l, 2, IS], (BS,), [3, 41 a n d B,S,, [3, 41, a number of ternary and quaternary thioborates have been synthesized and their structures determined (Table 1). Boron is found to be either trigonally or tetrahedrally surrounded by sulfur. In the binary compounds and in metal-rich phases containing small cations of high surface charge sulfur is not nucleophilic enough to establish four-coordinate boron. The anions formed are then relatively small ones like [BS,]'-, [B,S,]'- and [B,S,I3- (see upper part of Table 1). If enough sulfur is present, as is the case in the boron sulfide-rich phases, the cation charge can be distributed among more "ligands" so that the nucleophility of sulfur is sufficient to form a tetrahedral coordination of boron. This results in condensation to polymeric anions in chains, layers or even three-dimen- sional networks (see lower part of Table 1). Sample Preparation and Properties At temperatures applied for syntheses and annealing (300 to 800 O C) thioborates are extremely aggressive against silica and oxide ceramics. Under sulfur/oxygen exchange oxoborates and, in case of silica, thiosilicates are formed. Thus containers must either be made of boron nitride or graphite, or silica tubes coated with glassy carbon have to be used. The latter option is mostly applied. The reaction tubes can be prepared in a relatively simple way by slowly turning a fused silica ampoule filled with acetone vapour