Packing effects in palladium(II) and platinum(II) compounds, X-ray crystallography

Sammanfattning: This thesis focuses on i) the effect of packing on the molecular geometry ii) packing arrangements of neutral Pd(II) and Pt(II) complexes iii) the trans influence in Pt(II) complexes iv) the differences in bonding in corresponding Pd(II) and Pt(II) complexes and v) the geometry of Pd(II) complexes with potential catalytic properties. Detailed three-dimensional structural information at the atomic level can be obtained from X-ray crystallography. Such information is fundamental for an understanding of for example reactivity, stability and physical properties for a compound. The observed molecular geometry in the solid state is the result of a compromise of intra- and intermolecular forces. A study of the same molecular complex in different crystallographic surroundings makes it possible to get information about the effect of the intermolecular forces. The crystallographic environment have for neutral complexes been changed by co-crystallisation with different solvent molecules and for charged complexes by changing the counter ions. Packing effects for similar structures with small differences have been analysed by half-normal probability plots and Root Mean Square calculations. It is concluded that packing effects may have a large impact on, not only torsion and bond angles but also on bond distances. However, conclusions regarding this should be based on several compounds. Sulfoxides give shorter bond lengths and thus stronger bonds to palladium than thioethers. A trans influence series based on Pt-Cl distances is proposed. The PPh3, AsPh3 and PBz3 ligands are found to have a preferable orientation around the coordination plane with one P/As-C bond close to the coordination plane. With one exception these benzyl carbons are all anti along the P-P and As-As axes, respectively. Centrosymmetric neutral Pd(II) and Pt(II) complexes prefer the space groups adequate for close packing, P21/c, P-1 and Pbca and among these P21/c and P-1 dominates strongly. The metal coordination in potential palladium catalysts mainly influences the geometry around the X atom in P-X bidentate ligands, where X is an ether, a keton or an amin. In most of the phosphine complexes, but not the arsine complexes, C-H---Pd interactions, < 3.0 Å, is found. These interactions may interfere with substrates entering the coordination sphere for associative reactions.