The complexes M(3)[Pt(SnX(3))(5)] (M = Bu(4)N(+), PhCH(2)PPh(3)(+); X = Cl, Br), cis-M(2)[PtX(2)(SnX(3))(2)] (M = Bu(4)N(+), PhCH(2)PPh(3)(+), CH(3)PPh(3)(+), Pr4N+; X = Cl, Br), and [PhCH(2)PPh(3)](2)[PtBr3(SnBr3)] have been prepared and characterized by Sn-119 and Pt-195 NMR, far-infrared, and electronic absorption and emission spectroscopies. In acetone solutions the [Pt(SnX(3))(5)](3-) ions retain their trigonal bipyramidal structures but are stereochemically nonrigid as evidenced by Sn-119 and Pt-195 NMR spectroscopy. For [Pt(SnCl3)(5)](3-) spin correlation is preserved between 183 and 363 K establishing that the nonrigidity is due to intramolecular tin site exchange, probably via Berry pseudorotation. Whereas, [Pt(SnCl3)(5)](3-) does not undergo loss of SnCl3- or SnCl2 to form either [Pt(SnCl3)(4)](2-) or [PtCl2(SnCl3)(2)](2-), [Pt(SnBr3)(5)](3-) is not stable in acetone solution in the absence of excess SnBr2 and forms [PtBr2(SnBr3)(2)](2-) and [PtBr3(SnBr3)](2-) by loss of SnBr2. Similarly, [PtCl2(SnCl3)(2)](2-) is stable in acetone at ambient temperatures but disproportionates at elevated temperatures and [PtBr2(SnBr3)(2)](2-) loses SnBr2 in acetone to form [PtBr3(SnBr3)](2-). The crystal structures of methyltriphenylphosphonium cis-dibromobis(tribromostannyl)platinate(II) and benzyltriphenylphosphonium tribromo(tribromostannyl)platinate(II) have been determined.