Structures of indium trihalide complexes with phosphine oxides and dimethyl sulphoxide, with comments on the metal–oxygen bonding

Abstract

The crystal structures of several phosphine oxide and dimethyl sulphoxide complexes of indium trihalides have been determined. The compounds [InCl₃(Me₃PO)₂(MeOH)], [InCl₃-(Me₃PO)₂(H₂O)]·H₂O, [InCl₃(PhMe₂PO)₃]·H₂O, [InCl₃(Me₂SO)₃], and [InBr₃(Me₂SO)₃] are all fac octahedral, but [InCl₃(Me₃PO)₃] has the mer configuration. Triphenylphosphine oxide yields ionic derivatives of the type [InX₂(Ph₃PO)₄]⁺[InX₄]^–(X = Cl or Br). Methyldiphenylphosphine oxide gives covalent [InCl₃(Ph₂MePO)₃], but ionic [InBr₂(Ph₂MePO)₄]⁺[InBr₄]^–. The general development of six-co-ordination is possible through enlargement of the In–O–P bond angles, with individual values (range 135–160°) dependent upon steric interactions. The behaviour is consistent with a predominantly electrostatic metal–oxygen bonding. For the methanol and aqua complexes, determination of the positions of the hydroxylic protons established the ligand orientation with respect to the In–O vector. A quasi-ionic metal–ligand interaction is again in evidence.