A New One-Dimensional Platinum System Consisting of Carboxylate-Bridged <i>cis</i>-Diammineplatinum Dimers¹

Abstract

With the aim of developing new 1D platinum chain solids having infinite Pt−Pt bonds, several carboxylate-bridged cis-diammineplatinum dimers have been prepared and structurally characterized. For a dimer doubly bridged with acetates, five different salts [Pt2(NH3)4(μ-CH3CO2)2]X2·nH2O (X2, n = (ClO4)2, 2, 1; (NO3)2, 1, 2; (BF4)2, 4, 3; (PF6)2, 2, 4; (SiF6), 4, 5) have been prepared. The crystal structure of 5 has revealed that an infinite dimer chain [Pt2(NH3)4(μ-CH3CO2)2]n2n+ can be given as a result of hydrogen bond formation between the ammines and the oxygen atoms of acetates, demonstrating our prediction that the N2O2 coordination sphere may serve as a hydrogen-bonding moiety to assist formation of an infinite dimer chain. An asymmetric dimer bridged by both acetate and hydroxide ligands, [Pt2(NH3)4(μ-CH3CO2)(μ-OH)](SiF6) (6), has also been isolated as a byproduct of 5, and a similar 1D framework, [Pt2(NH3)4(μ-CH3CO2)(μ-OH)]n2n+, has been characterized by X-ray diffraction. In addition, some glycolate-bridged analogues of similar frameworks have been synthesized and characterized: [Pt2(NH3)4(μ-CH2(OH)CO2)2](SiF6)·4H2O (7), [Pt2(NH3)4(μ-CH2(OH)CO2)2](ClO4)2·H2O (8), and [Pt2(NH3)4(μ-CH2(OH)CO2)(μ-OH)](NO3)2 (9). To obtain partially oxidized systems, benzoate derivatives have been selected as bridging ligands. Although a benzoate system gave dark blue solids ascribable to mixed-valence Pt(2.25+) compounds, a crystallographically analyzed complex has turned out to be a double complex involving both a Pt(II) monomer and a dinuclear Pt(II) complex, [Pt2(NH3)4(μ-C6H5CO2)2]2(SiF6) (BF4)2·[cis-Pt(NH3)2(C6H5CO2)2]·3H2O (10). Nevertheless, our final efforts in this work have revealed that a p-hydroxybenzoate system, [Pt(2.25+)2(NH3)4(μ-p-C6H4(OH)CO2)2]2X5·nH2O (X5, n = (SO4)2.25(p-C6H4(OH)CO2)0.5, 5, 12a; (PF6)2(SO4)(p-C6H4(OH)CO2), 6, 12b; (PF6)2(NO3)2(p-C6H4(OH)CO2), 7, 12c), may be suited to achieve a 1D platinum blue system. The compounds display a blue chromophore at 630 nm ascribable to the Pt(2.25+)4 species. Moreover, the compounds have been judged to be diamagnetic, and therefore the S = 1/2 spins derived from the Pt(2.25+)4 units must be diamagnetically coupled in the solid state, suggesting that the repeating unit should be expressed as [Pt(2.25+)8]n (n is undetermined).