Comproportionation of the platinum(0) complex Pt(PMe3)(4) with the platinum(II) hexafluoroacetylacetonate complexes Pt(hfac)(2) or [Pt(hfac)(PMe3)(2)][hfac] yields diplatinum species of stoichiometry [Pt-2(mu-hfac)(PMe3)(4)][hfac], 1, and [Pt-2(PMe3)(6)][hfac](2), 2, respectively. The NMR spectra and X-ray crystal structure of 1 show that the two platinum centers are chemically inequivalent; one is a square-planar platinum(II) center, and the other is trigonal planar platinum(0) center. One of the hfac groups is anionic while the other bridges between the two platinum atoms. Each platinum center bears two PMe3 ligands, and the bridging hfac group is bound to one platinum center in the usual fashion through its two oxygen atoms. The bridging hfac group, however, is bound to the other platinum center as an eta(2) alkene ligand via its methine carbon and one of the two carbonyl carbons. The two platinum atoms do not interact directly with one another and are separated by 3.786(1) Angstrom. The H-1 NMR spectra of the hexakis(trimethylphosphine)diplatinum complex 2 are consistent with a structure in which the two platinum centers are connected by a Pt-Pt bond and the six PMe3 groups complete two mutually perpendicular square-planar coordination environments. Treatment of Pt(PMe3)(4) with [Pt(Pt(PMe3))(4)][[hfac]2 in tetrahydrofuran gives the platinum(II) hydride [PtH(PMe3)(4)][hfac], 3. The H-1 and P-31{H-1} NMR data of 3 are consistent with a trigonal bipyramidal structure; the hydride ligand occupies an axial position. The hydride ligand evidently arises from adventitious water. Thermolysis of 1 and 2 under vacuum gives the platinum(II) methyl complex [PtMe(PMe3)(3)][hfac] as a result of the cleavage of one of the P-C bonds in the PMe3 ligands. Crystal data for 1 at -75 degrees C : triclinic, space group P (1) over bar, a 9.848(2) Angstrom, b = 12.079(3) Angstrom, c = 15.373(3) Angstrom alpha= 84.70(2)degrees, beta = 78.57(2)0, gamma = 80.30(2)degrees, V = 1763(7) Angstrom(3), Z = 2, R-F = 0.043, R-WF = 0.044 for 400 variables and 3360 reflections with I > 2.58 sigma(I).