Synthesis and characterization of liquid platinum compounds

Liquid platinum complexes were obtained with a ligand with alkyl chains that attach to the coordination plane perpendicularly and herewith render a close packing of the molecules difficult for certain chain lengths. Bis(O,O′-dialkyldithiophosphato)platinum(II) complexes, Pt(Cxdtp)2, where the alkyl chains are methyl (x=1), ethyl (x=2), propyl (x=3), butyl (x=4), pentyl (x=5), hexyl (x=6), heptyl (x=7), dodecyl (x=12), and octadecyl (x=18), were investigated. The platinum compounds were synthesized via two routes: reaction of tetrachloroplatinate(II) with ammonium-O,O′-dialkyldithiophosphates or oxidative addition of (O,O′-dialkylthiophosphoryl)disulfides to tris(styrene)platinum(0). The melting temperatures as a function of the alkyl chain length show a minimum for the complex with pentyl groups. The complexes with pentyl and hexyl groups are liquid at room temperature, and the complexes with butyl and heptyl groups melt only slightly above room temperature. Depending on the complex, the low melting temperatures are induced by an unfavorable packing of the molecules in the solid state, reflected in a low melting enthalpy, or melting entropy. The molecular weights of the liquid complexes are between 700 and 800 and, therefore, extraordinarily high for liquid metal compounds. Depending on the alkyl groups, the complexes decompose at 172–241°C. Crystals of bis(O,O′-diethyldithiophosphato)platinum(II), Pt(C2dtp)2, are monoclinic, space group P21/n, a=8.90, b=8.70, c=12.45 Å, α=γ=90°, β=100.89°, and Z=4.