Synthesis, characterization, and photochemistry of a dinuclear cyanide-bridged iron(II)-platinum(IV) mixed-valence compound and its implications for the corresponding iron(II)-platinum(IV)-iron(II) complex

The mixed-valence compound [(NH3)(5)Pt-IV(mu-NC)Fe-II(CN)(5)]. 6H(2)O was synthesized by the substitution reaction of [Pt-IV(NH3)(5)OSO2CF3](OSO2CF3)(3) and [Fe-II(CN)(6)](4-) in aqueous solution and was characterized by UV/vis, IR, and resonance Raman spectroscopies, cyclic voltammetry, and single-crystal X-ray diffractometry. The monoclinic crystal (space group P2(1)/m (No. 11)) consists of a dinuclear, cyanide-bridged Fe(II)-Pt(IV) moiety with unit cell dimensions of a = 9.3241(5) Angstrom, b = 14.0466(7) Angstrom, c = 9.6938(4) Angstrom, beta = 111.467(2)degrees, and Z = 2. There are also an average of six waters of hydration per unit cell. The R-factors for this structure are R = 3.66% and R-w = 7.90%. The electronic spectrum reveals a broad intervalent (IT) charge-transfer absorption at approximately 420 nm (epsilon = 540 M-1 cm(-1)). Both the ground-state spectroscopy and the electrochemistry of this compound are very similar to those of the corresponding trinuclear adduct [(NC)(5)Fe-II(mu-CN)Pt-IV(NH3)(4)(mu-NC)Fe-II(CN)(5)](4-), which has been reported previously. Classical Marcus-Hush theory has been applied in the analysis of the IT band of the dinuclear compound in an effort to elucidate a fuller understanding of the photophysics of the trinuclear complex. The data suggest that this latter, centrosymmetric species can be treated theoretically as two back-to-back dinuclear donor-acceptor (D-A) compounds of the form D-A/A-D, where the Pt(IV) inversion center acts as the acceptor for both halves of the molecule. The photochemistry of the dinuclear complex was also investigated.