Crystal Structure of Nonstoichiometric Tetranuclear Platinum Compound, cis-Diammineplatinum α-Pyrrolidone Violet, [Pt4(NH3)8(C4H6NO)4](PF6)2(NO3)2.56·5H2O

Nonstoichiometric platinum tetranuclear compound, cis-Diammineplatinum α-Pyrrolidone Violet, [Pt4(NH3)8(C4H6NO)4)(PF6)2(NO3)2.56·5H2O, has been synthesized and the crystal structure has been solved with X-ray diffraction analysis. The crystal is triclinic with the space group of P1 and cell dimensions of a=13.530(8), b=19.242(9), c=10.222(3) Å, α=96.56(9), β=93.82(9), γ=74.64(8)°, V=2547.4 Å3, and Z=2. The structure have been solved by heavy atom method and the final discrepancy index R1 was 0.094 and R2 was 0.090. The cation is structurally identical with those of cis-Diammineplatinum α-Pyridone Yellow(PPY), [Pt4(NH3)8(C5H4NO)4]4+, cis-Diammineplatinum α-Pyridone Blue(PPB), [Pt4(NH3)8((C5H4NO)4]5+, and cis-Diammineplatinum α-Pyrrolidone Tan(PPT), [Pt4(NH3)8(C4H6NO)4]6+, and consists of four platinum atoms linked in a chain with bridging pyrrolidone ligands. Each platinum atom is cis coordinated by two ammine ligands and either two exocyclic oxygen atoms or two deprotonated ring nitrogen atoms of α-pyrrolidone ligands. The Pt-Pt bond distances are 2.848(2), 2.875(2), 2.839(2), and 2.875(2) Å, which are intermediate between those of PPY and PPB, indicating that the average platinum oxidation state is between 2.0 and 2.25. According to the potentiometric: oxidative titration of the compound using Ce(IV), the average platinum oxidation state is 2.14 and therefore the compound is considered to consist of 44% of [Pt4(NH3)8(C4H6NO)4]4+ and 56% of [Pt4(NH3)8(C4H6NO)4]5+.