Structural investigations of sulfite-bridged binuclear complexes of platinum(II) and palladium(II)

Although analogous platinum(II) and palladium(II) compounds usually show similar chemical behaviour, different reaction products have been obtained on reaction of ethane-1,2-diamine bissulfitometallates(II) with the diaqua ethane-1,2-diamine metal(II) complexes of Pt and Pd. - The crystal structures of bis(mu -sulfito-1 kappaS:2 kappaO)bis[(ethane-1,2-diamine)platinum(II)] trihydrate [(en)Pt(SO2O)(2)Pt(en)]. 3H(2)O (1) with parallel mu-(S:O) sulfite bridges, and of bis [(ethane-1,2-diamine)-mu-(S:O)-sulfitopalladium(II)] trihydrate [(en)Pd(SO2O)-(OO2S)Pd(en)]. 3H(2)O (2) with antiparallel bridges, have been determined by single-crystal X-ray structure analyses, In both compounds the complex units are held together mainly by a complicated network of hydrogen bonds including the hydrate water molecules, - In contrast to the complex molecules in 1 with parallel bridges, the complex units of 2 possess an inversion centre. As a result the mutual exclusion rule reduces the number of bands in each of the vibrational spectra of 2 to half that in the spectra of 1. This effect is most clearly seen in the number of the valence vibrations v(MN2); the Raman spectrum of I displays four relatively strong bands, whereas the Raman spectrum of 2 shows only two, as expected. Further, features of the vibrational spectra are in agreement with the findings of the crystal and molecular structures. Thus, the trans-influence exerted by the S-coordinated sulfites onto the M-N bonds in the trans-position induces a significant lengthening and weakening of these bonds relative to the M-N bonds trans to oxygen. In the Raman spectrum of 1 the valence vibrations of the PtN2 group trans to sulfur are clearly lowered in frequency.