Mode of binding of dimethyl sulphoxide in platinum(II) and palladium(II) cationic complexes containing a chelated diamine. X-Ray crystal structures of (2,2′-bipyridyl)chloro(dimethyl sulphoxide-O)palladium(II) tetrafluoroborate and chloro(dimethyl sulphoxide-S)(ethylenediamine)palladium(II) perchlorate

Abstract

The mode of binding of dimethyl sulphoxide (dmso) in cations of the type [M(N–N)(dmso)Cl]+[M = Pd or Pt; N–N = 2,2′-bipyridyl (bipy), 1, 10-phenanthroline (phen), or ethylenediamine (en)] has been examined by i.r. and 1H n.m.r. spectroscopy. Infrared spectra of the complexes in the solid state indicate that dmso binds through oxygen in the palladium(II) adducts containing bipy and phen, and through sulphur in the other cases. Proton n.m.r. spectra in CD3NO2 solution show that the complexes in which dmso is S-bonded in the solid state retain their structure in solution, while those containing O-bonded dmso equilibrate to a mixture of O- and S-bonded isomers whose composition depends upon the nature of the chelated diamine. Interconversion between the two isomers is slow on the n.m.r. time-scale, while exchange of S- and O-bonded dmso is fast. The crystal and molecular structures of [Pd(bipy)(dmso)Cl][BF4], (1), and [Pd(en)(dmso)Cl][ClO4], (2), have been determined by X-ray diffraction: (1) crystallizes in the triclinic space group P with Z= 2, a= 10.318(1), b= 12.503(1), c= 7.436(1)A, and α= 95.40(1), β= 109.10(1), γ= 109.75(1)°; (2) crystallizes in the monoclinic space group P21/n with Z= 4, a= 9.960(1), b= 8.652(1), c= 14.152(2)A, and β= 92.25(1)°. The structures were solved by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.026 and 0.024 for (1) and (2), respectively. The co-ordination geometry of the metal atom is square planar in both cases; in complex (1) the dmso ligand is oxygen bonded, while in (2) it is sulphur bonded. The geometries of O- and S-bonded dmso differ considerably: in (2) the SO distance, O–S–C and C–S–C angles correspond to the geometry of free dmso; in (1) the SO distance is intermediate between single and double bond lengths, the two O–S–C angles increase by some 7° with respect to S-bonded dmso, while the C–S–C angle increases only by 3.6°.