Molecular structure of dinuclear complexes of platinum(II). Part III. Dichloro-bis-µ-ethanethiolato-bis(tripropylphosphine)diplatinum(II)

Abstract

The title compound is orthorhombic, space group Pbca, a= 20·02(1), b= 21·73(1), c= 15·72(1)Å, Z= 4. Least-squares refinement of X-ray diffractometer data using 2115 independent structure amplitudes converged with R 0·05.

The co-ordination round each platinum atom is strained square-planar, but the two co-ordination planes are not coplanar, having a dihedral angle of 130° between them. This conformation is partly attributed to severe steric repulsion between the alkyl groups on the phosphorus and on the sulphur atoms. The non-planarity of the (Pt₂S₂) bridge and the pyramidal configuration at the sulphur atoms are unfavourable to d_π–p_π aromatic bonding in the bridge while allowing d_π–d_π overlap. The Pt–S bonds trans to P have approximately normal lengths for single bonds [2·37(1)Å], whilst those cis to P and trans to Cl are much shorter [2·27(1)Å]; the Pt–P bonds are also short [2·26(1)Å]. The stability of the cis-isomer is attributed to the continuous zig-zag chain of strong cis-bonds P–Pt–S–Pt–P in which one of the bridging sulphur atoms is held by two strong bonds; the trans-isomer is inherently less stable because one Pt–S bond to each bridging sulphur atom will be weakened by the trans-influence of the phosphines. The bonds in the zig-zag chain in the cis-isomer all have appreciable π-character, and a multiple overlap of d_π orbitals resembling conjugation may be present.