New Structural Aspects of α-Pyrrolidinonate- and α-Pyridonate-Bridged, Homo- and Mixed-Valence, Di- and Tetranuclear cis-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

Eight new crystalline α-pyrrolidinonate-bridged homo- and mixed-valence cis -diammineplatinum dimers and tetramers, HT-[Pt(2.0+) 2 (NH 3 ) 4 (μ-C 4 H 6 NO) 2 ](ClO 4 ) 2 ( 2 ), HH-[Pt(2.25+) 2 (NH 3 ) 4 (μ-C 4 H 6 NO) 2 ] 2 (ClO 4 ) 5 ( 4 ), HH-[Pt(2.25+) 2 (NH 3 ) 4 (μ-C 4 H 6 NO) 2 ] 2 (PF 6 ) 3 (NO 3 ) 2 ( 5 ), {HH-[Pt(2.25+) 2 (NH 3 ) 4 (μ-C 4 H 6 NO) 2 ] 2 }{HH-[Pt(2.5+) 2 (NH 3 ) 4 (μ-C 4 H 6 NO) 2 (NO 3 )] 2 }(PF 6 ) 2 (NO 3 ) 7 ·6H 2 O ( 7 ), HH-[Pt(2.5+) 4 (NH 3 ) 8 (μ-C 4 H 6 NO) 4 (Cl)](ClO 4 ) 3 Cl 2 ( 9 ), HH-[Pt(3.0+) 2 (NH 3 ) 4 (μ-C 4 H 6 NO) 2 (Cl) 2 ](NO 3 ) 2 ( 11 ), HH-[Pt(3.0+) 2 (NH 3 ) 4 (μ-C 4 H 6 NO) 2 (Cl)(NO 3 )](NO 3 ) 2 ·H 2 O ( 12 ), and HT-[(H 2 O)(H 3 N) 2 Pt(3.0+)(μ-C 4 H 6 NO) 2 Pt(3.0+)(NH 3 )(μ-OH)] 2 (NO 3 ) 6 ·4H 2 O ( 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 NH 3 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.