Solution studies of complexes of the types trans-PtCl2L(1,4-diazine) and trans-LCl2Pt(μ-1,4-diazine)PtCl2L (L=phosphine and C2H4). The X-ray structures of PtCl4L2(2,5-dimethylpyrazine) (L= C2H4 and PEt3) and the relative trans-influence of alkene and tertiary phosphine ligands.