Solid-state structures of triarylantimony dihalides; the isolation of some mixed-halide species and crystal structures of Ph3SbI2 and [Ph4Sb]I3

Abstract

Fifteen compounds of stoichiometry R₃SbX₂(R = Ph or substituted aryl; X₂= Br₂, I₂ or IBr) were synthesised and studied by Raman spectroscopy. The crystal structure of Ph₃SbI₂ has been determined, which shows it to be a distorted trigonal-bipyramidal molecule. The distortion from regular trigonal-bipyramidal geometry may be explained by a pseudorotation process towards a rectangular pyramid. Moreover, there are two independent molecules within the unit cell and its distorted structure is in direct contrast to the known Ph₃SbX₂(X = Cl or Br) which both adopt regular trigonal-bipyramidal geometry. The interhalogen compounds R₃SbIBr also have trigonal-bipyramidal geometry. In direct contrast to the molecules Ph₃EI₂(E = P or As), which ionise in solution to form [Ph₃EI]I, Ph₃SbI₂ is chemically changed in acetonitrile solution and forms the ionic [Ph₄Sb]I₃, there being no evidence for [Ph₃SbI]I. The crystal structure of [Ph₄Sb]I₃ has also been determined.