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A New One-Dimensional Platinum System Consisting of Carboxylate-Bridged cis-Diammineplatinum Dimers1

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posted on 27.10.1998, 00:00 by Ken Sakai, Masao Takeshita, Yuko Tanaka, Takuma Ue, Masayuki Yanagisawa, Masaya Kosaka, Taro Tsubomura, Masamichi Ato, Takeo Nakano
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).