New pentacyano complexes of tri- and tetravalent platinum were obtained in aqueous solution and characterized by multinuclear NMR (Pt-195, C-13) supported by Raman spectroscopy. The complexes form as products of redox decomposition of metal-metal bonded platinum-thallium compounds. The trimetallic [(NC)(5)Pt-Tl-Pt(CN)(5)](3-) yields a new dimeric compound of Pt(III), [(NC)(5)Pt-Pt(CN)(5)](4-). The latter is a rare representative of unbridged dimeric complexes of trivalent platinum; it was obtained through an oxidation of monomeric square-planar platinum(IT) species by a metal complex. From the bimetallic compounds [(NC)(5)Pt-Tl(CN)(n)](n-) (n = 0-2) tetravalent platinum complexes are formed. Depending on the Pt-Tl species, electron transfer is initiated either by heat or by exposition to light; it results in [Pt(CN)(6)](2-) Or in the hitherto unknown complexes [Pt(CN)(5)(OH)](2-) and [Pt(CN)(5)(H2O)](-), with the Pt-195 NMR chemical shift values 1638.7 (+/-0.6) and 1766.7 (+/- 0.6), respectively. Proton dissociation constant of [Pt(CN)(5)(H2O)](-) has been determined, pK(a) = 2.51 (+/-0.01). In both Pt-III and Pt-IV pentacyano complexes platinum is hexacoordinated forming a pseudo-octahedron with two types of cyano ligands : four equivalent equatorial cyanides and one apical. Related platinum(IV) species, [Pt(CN)(5)X](2-) (X = Cl, Br, I), have also been studied. In all the pentacyano complexes a pronounced trans influence is reflected in a substantial difference between the Pt-195-C-13 spin-spin coupling constant for the epical (trans) and the equatorial (cis) carbon sites. In this respect, the studied X ligands can be ordered in a series of decreasing Pt-195-C-13(trans), coupling constant : H2O > Cl- > Br- > I- > OH- > CN-.