TRIOCTAHEDRAL HALOARSENATES(III) [AS3X12]3- (X = BR,I) WITH VERTEX AND FACE SHARING - STRUCTURAL CORRELATION FOR IODOARSENATES(III)

The haloarsenates(III) [Et3NH]3[As3Br12] (1) and [Me3NH]3[As3I12] (2) have been prepared and their structures established by X-ray analysis. Both trioctahedral anions display a novel structure in which a central AsX6 octahedron shares two faces with a common vertex with two terminal AsX6 octahedra. The bridging As-X-bonds in the latter building units are markedly longer than the opposite terminal As-X-bonds in both anions. For example, the former As-I-bonds in [As3I12]3- lie in the range 3.154(1)-3.400(1) angstrom, the latter As-I-bonds between 2.581(1) and 2.656(1) angstrom. The distortion of the central ASX6 octahedron is less marked for both anions, e.g. the As-I distances in [As3I12]3- lie in this central polyhedron between 2.706(1) and 3.048(1) angstrom. Using the results for (2) and for other characterised anions, a structural correlation is presented for 28 trans-sited As-I bond distances in iodoarsenates(III).