A Crystallographic Study of Platinum(II) Complexes

Abstract: Single crystal structural data have been used to estimate the influence of the X, Y and Z ligands on the Pt‹L bond length in [PtLXYZ] complexes, i.e. the ground state cis- and trans-influence. Cl or S were selected as indicator ligands, L, for these studies. Ligands with soft donor atoms, such as sulfur, carbon and silicon have been used to study their trans-influence on halides. The effects of experimental errors and packing have been evaluated and taken into account in the discussion of the cis- and trans-influence. X-ray diffraction data for structural analysis were collected on a four-circle diffractometer with MoKa radiation. Comparisons of related structures were performed with statistical methods such as half-normal probability plot analysis and calculations of average bond distances and their dispersions. These comparisons reveal that particularly the packing effects can affect the bond distances to a significant extent. A "noise level" for the combined outcome of experimental errors and packing effects is proposed. Differences in corresponding Pt‹Cl as well as Pt‹S distances in different compounds are considered possibly significant (above the noise level) in the range 0.01-0.02 Å and as significant if the difference is larger than 0.02 Å. These levels of significance are sometimes too optimistic but in most cases they can be considered as guide-lines. Some trans-complexes with a biological activity have been structurally characterized and their cytotoxicity investigated.