Treatment of bis(phosphine)platinum(II) carbonate complexes (LL)Pt(CO3) (e.g., LL = 1,3-bis(diphenylphosphino)propane) with vicinal diols (i.e., HOCR(1)R(2)CR(3)R(4)OH) gives equilibrium conversion to the corresponding diolate complexes (LL)Pt(OCR(1)R(2)CR(3)R(4)O), which are readily isolated in good yield. From competition experiments, relative diol complexation constants were determined as a function of both the diol and the phosphine substituents and found to span a range of over 10(4). Corresponding triolate and alditolate complexes were similarly prepared, for which very distinct equilibrium isomeric regioselectivities are observed, favoring complexation of gamma,delta-threo diols. An X-ray structure of (dppp)Pt(D-mannitolate) shows that the mannitol is bonded to the platinum as its dianion via the oxygens on C3 and C4 to form a 2,5-dioxaplatinacyclopentane chelate ring and that three different strong intramolecular hydrogen-bonding interactions are present between the hydroxyl hydrogens and the metallacycle oxygens (O...O (av) = 2,65(2) A), forming five-, six-, and seven-membered rings. Crystal data for PtP2O6C33H38.CH2Cl2 : P2(1)2(1)2(1), Z = 4, T approximate to 20 degrees C, a = 11.225(2) Angstrom, b = 15.875(3) Angstrom, c 19.964(4) Angstrom, R(F-o) = 0.058, R(w)(F-o) = 0.062.