Electronic and molecular structure of 2,2'-bipyrimidine-bridged bis(organoplatinum) complexes in various oxidation states. Radical-bridged diplatinum species and the absence of a Pt(III)/Pt(II) mixed-valent intermediate
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Inorganica Chimica Acta 264 (1-2): 269--278 (1997)

Dinuclear organoplatinum compds. RnPt(bpym)PtRn (R = Me, n = 2, 4; R = mesityl, n = 2; bpym = 2,2'-bipyrimidine) were prepd. and characterized. The neutral compds. and their neighboring oxidn. states were studied using cyclic voltammetry, 1H NMR or EPR spectroscopy and UV-Vis spectroelectrochem. Oxidn. state assignments based on these data could be made for the following compds.: R2PtII(bpym)PtIIR2, R2PtII(bpym-I)PtIIR2·-, R2PtII(bpym-II)PtIIR22-, Mes2PtIII(bpym)PtIIIMes22+, Me4PtIV(bpym)PtIVMe4, Me4PtIV(bpym-I)PtIVMe4·-. The two-electron oxidn. of Mes2Pt(bpym)PtMes2, i.e. the absence of a stable Pt(III)/Pt(II) mixed-valent state, confirms that the highest-lying occupied metal orbitals (dz2) do not communicate via the p system of the bridging ligand. A crystal structure anal. of photoreactive Me4PtIV(bpym)PtIVMe4 was obtained: space group Pbca, a = 12.830(2) \AA, b = 11.502(2) \AA, c = 12.877(2) \AA, V = 1900.3(5) \AA3, Z = 4. The structural refinement revealed elongated axial Pt-Me bonds of about 2.13 \AA. The structural features could be well reproduced by a DFT calcn. of H4PtIV(bpym)PtIVH4 which also confirmed the s character of the HOMO. Of the ligand-reduced systems, the Pt(II) species exhibits a higher degree of g anisotropy than the Pt(IV) species. Low-lying excited states of the species generated were assigned through information from vibrational structuring, solvatochromic behavior and from (spectro)electrochem. results. on SciFinder(R)
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