BIS(CARBOXYLATO) COMPLEXES OF PLATINUM(II) - STRUCTURAL AND BONDING ANALYSIS OF [PT(O(2)CR)(2)(L-L)] [L-L=2PPH(3), PH(2)PCH(2)PPH(2) OR FE(C(5)H(4)PPH(2))(2), R=ME, CF3, PR-I OR PH]

Treatment of [PtCl2(L-L)] [L-L = 2 PPh(3), Ph(2)PCH(2)PPh(2)(dppm) or Fe(C(5)H(4)PPh(2))(2)(dppf)] with Ag(O(2)CR) (R = Me, CF3, Pr-i or Ph) at room temperature generally gave [Pt(O(2)CR)(2)(L-L)] in moderate t o good yields. The crystal and molecular structures of [Pt(O(2)CMe)(2) (dppf)]. H2O, [Pt(O(2)CPh)(2)(dppf)]. CH2Cl2 and [Pt(O2CCF3)(2)(dppm)] have been determined by single-crystal X-ray diffractometry. All thes e complexes show a mononuclear square-planar structure with a chelatin g diphosphine and two neighbouring (cis) carboxylates in a monodentate mode. These structures contrast those of the parent [Pt-4(mu-O(2)CMe) (8)] and its derivative [Pt-4(en)(4)(mu-O(2)CMe)(4)](4+) (en = ethylen ediamine) which are tetrameric, based on octahedral Pt-II, and contain bridging acetates and direct Pt-Pt bonds. Fenske-Hall molecular orbit al calculations of these structures confirmed the existence of Pt-Pt b onding interactions. The presence of hard and electronegative ligands like en and acetate incurs a deficiency in sigma-electron density, com pared to virtually filled non-bonding orbitals; the former is alleviat ed by Pt-Pt bonding. d(8) Complexes with ligands like phosphines posse ssing both sigma-donating and pi-accepting qualities appear to favour the usual square-planar geometry.