Eight new crystalline alpha-pyrrolidinonate-bridged homo- and mixed-valence cis-diammineplatinum dimers and tetramers, HT-[Pt(2.0+)(2)(NH3)(4)(mu-C4H6NO)(2)] (CLO4)(2) (2), HH-[Pt(2.25 +)(2)(NH3)(4)(mu-C4H6NO)(2)](2)(ClO4)(5) (4), HH-[Pt(2.25 +)(2)(NH3)(4)(mu-C4H6NO)(2)](2)(PF6)(3)(NO3)(2) (5), {HH-[Pt(2.25+)(2)(NH3)(4)(mu-C4H6NO)2](2)}{HH-[Pt(2.5 +)(2)(NH3)(4)(mu-C4H6NO)(2)(NO3)](2)}(PF6)(2)(NO3)(7). 6H(2)O (7), HH-[Pt(2.5+)(4)(NH3)(8)(mu-C4H6NO)(4)(Cl)](CLO4)(3)Cl-2 (9), HH-[Pt(3.0+)(2)(NH3)(4)(mu-C4H6NO)(2)(Cl)(2)](NO3)(2)(11), HH-[Pt(3.0+)(2)(NH3)(4)(mu-C4H6NO)(2)(Cl)(NO3)](NO3)(2). H2O (12), and HT-[(H2O)(H3N)(2)Pt(3.0+)(mu-C4H6NO)(2)Pt(3.0+)(NH3)(mu-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+)1 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 ...](infinity) 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 mu-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 alpha-pyrrolidinonate and the hexacyclic alpha-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 alpha-pyridonate Pt(2,5+)4 complex is also reported.