New Structural Aspects of α-Pyrrolidinonate- and α-Pyridonate-Bridged, Homo- and Mixed-Valence, Di- and Tetranuclear <i>cis-</i>Diammineplatinum Complexes: Eight New Crystal Structures, Stoichiometric 1:1 Mixture of Pt(2.25+)₄ and Pt(2.5+)₄, New Quasi-One-Dimensional Halide-Bridged [Pt(2.5+)₄-Cl···]_∞ System, and Consideration of Solution Properties

Abstract

Eight new crystalline α-pyrrolidinonate-bridged homo- and mixed-valence cis-diammineplatinum dimers and tetramers, HT-[Pt(2.0+)2(NH3)4(μ-C4H6NO)2](ClO4)2 (2), HH-[Pt(2.25+)2(NH3)4(μ-C4H6NO)2]2(ClO4)5 (4), HH-[Pt(2.25+)2(NH3)4(μ-C4H6NO)2]2(PF6)3(NO3)2 (5), {HH-[Pt(2.25+)2(NH3)4(μ-C4H6NO)2]2}{HH-[Pt(2.5+)2(NH3)4(μ-C4H6NO)2(NO3)]2}(PF6)2(NO3)7·6H2O (7), HH-[Pt(2.5+)4(NH3)8(μ-C4H6NO)4(Cl)](ClO4)3Cl2 (9), HH-[Pt(3.0+)2(NH3)4(μ-C4H6NO)2(Cl)2](NO3)2 (11), HH-[Pt(3.0+)2(NH3)4(μ-C4H6NO)2(Cl)(NO3)](NO3)2·H2O (12), and HT-[(H2O)(H3N)2Pt(3.0+)(μ-C4H6NO)2Pt(3.0+)(NH3)(μ-OH)]2(NO3)6·4H2O (14), have been isolated and characterized by X-ray diffraction, where HH and HT correspond to the head-to-head and head-to-tail isomers, respectively. The first spontaneous resolution has been observed for the chiral HT-Pt(2.0+)2 molecules (2). 7 has turned out to be the first 1:1 “stoichiometric” mixture of blue and tan (Pt(2.25+)4 and Pt(2.5+)4). The structural evidence supporting the axial coordination behaviors of the Pt(2.5+)4 tetramer has been obtained (7 and 9). A very unique quasi-one-dimensional halide-bridged system having a chain definition of [Pt(2.5+)4−Cl···]∞ has been characterized (9). The HT-Pt(3.0+)2 dimer has been found to release an NH3 group in aqueous media to form a dimer of dimers linked by μ-OH bridges (14). Relationships between the structural parameters and the average Pt oxidation state have been examined in detail to better understand the structure-transformation properties of the platinum-blue family. Remarkable structural differences observed between the pentacyclic α-pyrrolidinonate and the hexacyclic α-pyridonate systems are rationally interpreted in terms of differences in both the N−C−O bite angle and the Pt−N−C angle around the bridging geometry. In addition, spectrophotometric studies reveal that an outer-sphere electron-transfer process between two Pt(2.25+)4 molecules takes place to afford a Pt(2.0+)4 and a Pt(2.5+)4 molecule. General consideration for the solution properties of this family is also described. The synthesis of an α-pyridonate Pt(2.5+)4 complex is also reported.