NUCLEAR-MAGNETIC-RESONANCE INVESTIGATION OF THE FORMATION OF OXALATO, MALONATO, AND 2-METHYLMALONATO COMPLEXES OF PLATINUM(II) - CRYSTAL AND MOLECULAR-STRUCTURES OF POTASSIUM ANTI-BIS(2-METHYLMALONATO)PLATINATE(II) DIHYDRATE AND POTASSIUM DICHLORO(OXALATO)PLATINATE(II) HYDRATE

Nuclear magnetic resonance techniques utilizing Pt-195 and C-13 have been employed to study the formation of Pt(II) complexes of the dicarboxylic acids, oxalic (OxH2), malonic (MalH2), and 2-methylmalonic (MmalH2) acid. Oxalic acid reacts with K2[PtCl4] to form the monodentate [Pt(OxH-O)Cl3]2-, which reacts to form bidentate [Pt(Ox)Cl2]2-, then [Pt(Ox)(OxH-O)Cl]2- with one bidentate and one monodentate oxalato ligand, and, ultimately, the bis bidentate [Pt(Ox)2]2-. The structure of potassium dichloro(oxalato)platinate(II) hydrate has been determined by X-ray crystallography: P1BAR, a = 7.136 (2) angstrom, b = 7.308 (2) angstrom, c = 10.130 (4) angstrom, alpha = 86.75 (3)-degrees, beta = 74.58 (3)-degrees, gamma = 64.28 (2)-degrees, V = 457.7 (3) angstrom 3, Z = 2, R = 0.0526, R(w) = 0.0518. When the starting material is [Pt(H2O)4]2+, similar complexes are observed. Analogous complexes are observed with both malonic and 2-methylmalonic acids. Monodentate malonato and 2-methylmalonato complexes are observed in solution and are more stable than monodentate oxalato complexes. Monodentate complexes are demonstrated by nonequivalence of their carboxylate and carboxylato C-13 resonances and by their chemical shifts in Pt-195 NMR spectra. Two Pt-195 resonances are observed for [Pt(Mmal)(MmalH-O)Cl]2-, with one bidenate and one monodentate 2-methylmalonato ligand. Chirality at both alpha-carbon atoms results in two diastereomers of [Pt(Mmal)(MmalH-O)Cl]2-. Separate Pt-195 resonances are observed for [Pt(Mmal)2]2-, in which methyl groups are syn or anti with respect to the Pt coordination plane. The structure of potassium anti-bis(2-methylmalonato)platinate(II) dihydrate has been determined by X-ray crystallography: P1BAR, a = 4.059 (1) angstrom, b = 9.107 (2) angstrom, c = 10.111 (2) angstrom, alpha = 98.49 (1)-degrees, beta = 101.28 (1)-degrees, gamma = 101.84 (1)-degrees, V = 351.8 (1) angstrom, Z = 1, R = 0.0456, R(w) = 0.0451.