Mixed-Valent Cations of Dinuclear Chromium Aryl Complexes: Electrochemical, Spectroscopic, and Structural Considerations

Article abstract of DOI:10.1021/ja00253a019

The oxidation of a series of six dinuclear chromium carbonyl complexes linked by a biphenyl ligand and/or a diphosphino- (or arsino-) methane moiety has been studied by electrochemistry, infrared spectroscopy, electron spin resonance spectroscopy, and X-ray crystallography.Comparison is made with four mononuclear analogues.Each dinuclear complex shows two successive one-electron oxidations, with the separation of E^o values varying from a low of 160 mV for <(benzene)Cr(CO)2>2(μ-dppm) (11, dppm=(diphenylphosphino)methane) to a high of 550 mV for (biphenyl)2(μ-dmpm) (10, dmpm=(dimethylphosphino)methane).The monocation derived from (biphenyl)2 (7⁺) displays IR and ESR spectra indicative of a charge- and spin-localized mixed-valent complex.Complexes 8⁺-10⁺ with both a biphenyl and diphosphino- or arsinomethane linkage are valence-delocalized, judging from IR and ESR spectra.Neutral (biphenyl)2(μ-dppm) (8) has a severe twisting of the phenyl rings, the torsion angle being 50.8 deg.However, the torsion angle relaxes to 3.7 deg in the monocation 8⁺.Neutral 8 crystallizes in the space group P1 with a=9.606(3) Angstroem, b=13.530(3) Angstroem, c=18.774(8) Angstroem, α=76.57(3) deg, β=78.88(3) deg, γ=70.04(3) deg, and z=2.Cationic 8^+- crystallizes in the space group C2/c with a=34.353(9) Angstroem, b=11.185(2) Angstroem, c=31.011(9) Angstroem, β=126.18(2) deg, and Z=8.