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(μ‐sulfito‐1κS:2κO)bis[(ethane‐1,2‐diamine)platinum(II)] trihydrate [(en)Pt(SO 2 O) 2 Pt(en)]·3 H 2 O ( 1 ) with parallel μ‐(S:O) sulfite bridges, and of bis[(ethane‐1,2‐diamine)‐μ‐(S:O)‐sulfitopalladium(II)] trihydrate [(en)Pd(SO 2 O)(OO 2 S)Pd(en)]·3 H 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 ν (MN 2 ); the Raman spectrum of 1 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 PtN 2 group trans to sulfur are clearly lowered in frequency.