On the Question of Mixed-Valent States in Ligand-Bridged Dinuclear Organoplatinum Compounds RkPt(m-L)PtRkn, k = 2 or 4
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Organometallics 17 (16): 3532--3538 (1998)

Sym. dinuclear complexes between the bis-bidentate bridging ligands m-L (m-L = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) or 2,5-bis(1-phenyliminoethyl)pyrazine (bpip)) and the organoplatinum fragments PtMes2 (Mes = mesityl), PtMe2, or PtMe4 were synthesized as deeply colored compds. Low-energy charge-transfer transitions from metal d orbitals (PtII) or metal-carbon s bond combinations (PtIV) to low-lying p* orbitals of the p acceptor ligands are responsible for long-wavelength absorption maxima lmax(CT) \textgreater 700 nm. UV/Vis and EPR spectroelectrochem. results for reversible redn. processes indicate the formation of PtIV2(m-L.bul.-) and PtII2(m-L.bul.-) species, however, the latter exhibit a significant metal contribution according to a PtII/PtI formulation. Cyclic voltammetry reveals that the remarkable system Mes2Pt(m-bptz)PtMes2n forms an enormously stabilized radical anion (n = 1-) with DE1/2 = 1250 V and Kc = 1021.2 and a PtIII/PtII mixed-valent state (n = 1+) with DE1/2 = 80 mV and Kc = 23. This small Kc value is attributed to the predominantly ds orbital character of the redox orbitals on the Pt(II) centers. on SciFinder(R)
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