Reactions of Nitroplatinum Complexes. 2. Reactions of K2[Pt(NO2)4] and Related Complexes with Aqueous Acids (CH3CO2H, HClO4, CF3SO3H, HNO3, and H2SO4): Pathways to Platinum(III) Complexes with Acetate Bridges. Crystal Structure of K2[{Pt(NO2)2(.mu.-CH3CO2)}2].cntdot.H2O

Abstract

Full title: Reactions of nitroplatinum complexes. 2. Reactions of K2[Pt(NO2)4] and related complexes with aqueous acids (CH3CO2H, HClO4, CF3SO3H, HNO3, and H2SO4): Pathways to platinum(III) complexes with acetate bridges. Crystal structure of K2[{Pt(NO2)22(μ-CH 3CO2)}2]·H2O. Reaction of K2[Pt(15NO2)4] under argon with 1 M HClO4 or CF3SO3H gave an initial blue solution (λmax = 627 nm), due to nitrosyl complexes of platinum(IV). With heating, the color faded, and 195Pt and 15N NMR peaks were observed from cis-[Pt(15NO2)2(H2O)2], [Pt(15NO2)(H2O)3]+, and fac-[Pt(15NO2)3(H2O) 3]+. In air or oxygen, reaction was faster, giving [Pt(H2O)4]2+ as well as mixed nitrito-N/aqua platinum(II) complexes, and larger proportions of platinum(IV) complexes, including [Pt(OH)6]2- in solution, and solid H2[Pt(OH)6]. With 0.5 M H2SO4, reactions were similar, but a greater variety of platinum(IV) complexes were formed, some probably containing coordinated sulfate. With 1 M HNO3, K2[Pt(NO2)6] formed. Reactions of K2[Pt(NO2]4] with aqueous acetic acid gave mixtures of Pt(II) and Pt(IV) mononuclear complexes and dinuclear Pt(III) complexes containing acetate bridges. The composition of the solution depended on the reaction conditions (heated for various times with argon, air, or oxygen above the solution or bubbled through). Crystals of K2[{PtII(NO2)2(μ-CH 3CO2)}2]·H2O were obtained from a reaction under argon, and the crystal structure was determined by X-ray diffraction: space group P1 (no. 2); a = 7.202(2) A; b = 8.987(2) A; c = 13.592(2) A; α = 94.01(2)°; β = 90.68(2)°; γ = 111.04(2)°; Z = 2; R = 0.0371, for 2875 reflections. The structure showed two acetate ligands bridging between cis-Pt(NO2)2 units, with the Pt-Pt distance 2.986(1) A. Reactions of cis-[Pt(NO2)2(H2O)2] with various oxidants in the presence of acetic acid were studied. [{(CH3CO2)PtIII(NO2) 2(μ-CH3CO2)}2]2- is formed by the oxidation of preformed [{PtII(NO2)2(μ-CH3CO 2)}2]2-. Under anaerobic conditions, the major oxidant is HNO3 formed in the reaction mixture. Oxidation of [{PtII(NO2)2(μ-CH3CO 2)}2]2- with NO2 formed in the reaction mixture in the presence of oxygen provides one route to [(O2N)PtIII(NO2)2(μ-CH 3CO2)2PtIII(NO2) 2(O2CCH3)]2-. Continued heating of solutions containing these Pt(III) complexes eventually gave solutions containing [{(CH3CO2)PtIII(NO2)} 2(μ-CH3CO2)3]-.