New Rhenium Octahedral Cluster Sulfido-cyanide Chain Polymer: The Synthesis and Crystal Structure of Cs4[{Re6S8}(CN)4S2/2]

Abstract

The chemistry of rhenium octahedral cluster chalcogenides demonstrates a rich diversity of types of chain-like, layered and framework structures as well as bridging ligands between clusters. The clusters can be connected via μ3 inner ligands of cluster units, apical halogenide ligands, complex telluride Te6 or Te7 3,4 and halogen-telluride Te8Q18 groups, Q=Cl, Br, chalcogenides, dichalcogenide and trichalcogenide ligands. The latter family described by Prof. W. Bronger (so called “Bronger phases”) seems to be most numerous and complete family of polymeric rhenium octahedral cluster chalcogenides with various bridges and connectivity between clusters. For example, Li4Re6S11 7 contains Re6S8 cluster units connected by six bridging m2 sulfido ligands that gave Li4[{Re6S8}(S)6/2]∞∞∞ framework according to Schafer notation. Recently it was shown that reaction of ReS2 with KCN at elevated temperature leads to formation an unique layered compound K4Re6S10(CN)2. In this polymer the Re6S8 units are linked into two-dimensional grids by sharing four apical sulphide ligands. Additionally two “trans” rhenium atoms in cluster core are coordinated by terminal cyano-groups. Thus, crystallographic formula of this compound may be written according to Schafer notation as K4[{Re6S8}(CN)2(S)4/2]∞∞. From formal point of view this compound could be presented as cleavage of two Re-μ2S-Re bridges in [{Re6S8}(S)6/2] and substitution of them by terminal cyano-ligands. In present work we report the synthesis and crystal structure of new chain polymer Cs4[{Re6S8}(CN)4(S)2/2]∞ which is the next member of a series M4[{Re6S8}(CN)2x(S)(6-2x)/2], where M is alkali metal. This compound was obtained with high yield by high temperature reaction of ReS2 with KCN in presence of CsCl excess. X-ray structural analysis revealed that compound Cs4[Re6S8(CN)4S2/2] is built from octahedral rhenium cluster units {Re6S8}. All atoms in the unit cell are lying in general Wyckoff 2i positions. Six crystallographically independent rhenium atoms and eight sulfur atoms form two centrosymmetric cluster units Re6(μ3–S)8 (Figure 1). Interatomic distances Re–Re are: mean: 2.606[9] A, min–max: 2.5924(11) ÷2.6201(11) A that are comparable within the Re–Re single bonds usually observed in octahedral rhenium clusters with Re6(μ3–S)8 cluster cores, e.g. in Li4Re6S11, in K4[Re6S10(CN)2] and in Cs3K[Re6S8(CN)6]. Re–μ3–S vary from 2.384(6) to 2.422(6), mean 2.406(10) A. These values are also typical for Re6(μ3–S)8 cluster unit. These cluster units are linked via two trans-μ2-S ligands to form the infinite chains running along a axis (Figure 2). The Figure 1. Two independent Re6S8 cluster units bridged by μ2-S ligand in the structure of Cs4[Re6S8(CN)4S2/2].