Drei stereoisomere quadratisch-pyramidale [Ma3b2]-Komplexe: Untersuchungen zur Existenz und zur Struktur kristalliner Dimethylsulfoxid-Komplexe von Antimon- und Bismuttrichlorid

Three Stereoisomeric Square-Pyramidal Complexes Ma₃b₂]: Investigations of the Existence and the Structures of Crystalline Dimethyl Sulfoxide Complexes of Antimony and Bismuth Trichlorides The formation of solid complexes MCl₃ · n DMSO (M = Sb, Bi; n = 1–4) was reinvestigated. In each system, only two of four presumptive complexes could be isolated as crystalline solids: SbCl₃ · DMSO ( 1 a ) was prepared for the first time, SbCl₃ · 2 DMSO ( 1 b ), BiCl₃ · 2 DMSO ( 2 b ) and BiCl · 3 DMSO ( 2 c ) were reproduced according to literature data. Evidence is presented as to the non-existence of BiCl₃ · 4 DMSO, contrary to previous claims in the literature. A unit cell determination showed 2 c to be structurally identical with the monomeric fac-octahedral complex BiCl₃(DMSO)₃ obtained fortuitously and described elsewhere Z. anorg. allg. Chem. 620 (1994) 1037]. The compounds 1 a (monoclinic, space group P2₁/c), 1 b (monoclinic, space group P2₁/n) and 2 b (monoclinic, space group C2) represent examples of each of the three possible geometric isomers of a square-pyramidal complex Ma₃b₂]. In the formally 1/1 adduct 1 a , which is in fact Sb(1)Cl₃(DMSO)₂ · Sb(2)Cl₃], the Sb(1) atom of the complex unit displays square-pyramidal geometry with the DMSO ligands situated in the apical and one of the basal positions. These units are linked into chains by SbCl₃ molecules acting as Cl-acceptors. Sb(2) forms two chelating chloro-bridges with cis-Cl atoms of one neighbouring complex and a third chloro-bridge with the remaining Cl of the symmetry-related second neighbour. The resulting Cl₆-geometry around Sb(2) is distorted octahedral. 1 b consists of square-pyramidal molecules, in which the DMSO ligands occupy two basal cis-positions; the monomeric units are loosely linked through the apical Cl atoms to form a chain of octahedra sharing trans-vertices. The asymmetric unit of 2b is a square pyramid with trans-basal DMSO ligands. The pyramids are connected by symmetry-equivalent basal chlorine atoms into chains of octahedra sharing cis-vertices. 1a displays remarkably short Sb? O dative bonds (204.7/212.9 pm); the M? O bond distances of 1b and 2b are 223.0/234.6 and 234.5/238.7 pm, respectively.