Organometallic Oxides:  Oxidation of the Cubane [(η-C5R5)Cr(μ3-O)]4 and the Structures and Magnetic Properties of the Salts {[(η-C5R5)Cr(μ3-O)]4}{tcnq} and {[(η-C5R5)Cr(μ3-O)]4}{BF4}

• Published in: Organometallics Vol. 20; no. 9; pp. 1840 - 1848
• Main Authors: Allen, Daryl P., Bottomley, Frank, Day, Robert W., Decken, Andreas, Sanchez, Victor, Summers, David A., Thompson, Robert C.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 30.04.2001
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om001067y

Differential pulse and current voltammetry for the cubane-like clusters [(η-C5R5)Cr(μ3-O)]4 (R = H, Me; R5 = H4Me) showed that [(η-C5H4Me)Cr(μ3-O)]4 and [(η-C5Me5)Cr(μ3-O)]4 were oxidized to {[(η-C5R5)Cr(μ3-O)]4}+ and then to {[(η-C5R5)Cr(μ3-O)]4}2+, but [(η-C5H5)Cr(μ3-O)]4 was oxidized only to {[(η-C5H5)Cr(μ3-O)]4}+. Oxidation of [(η-C5Me5)Cr(μ3-O)]4 (1) by AgBF4 or tcnq gave {[(η-C5Me5)Cr(μ3-O)]4}{BF4} (2) or {[(η-C5Me5)Cr(μ3-O)]4}{tcnq} (3). It was shown by X-ray diffraction that the average Cr−Cr, Cr−O, and Cr−Cp* distances in 2 and 3 were 0.034(2), 0.007(5), and 0.02(1) Å shorter than those in 1, respectively. Compounds 1, 2, and 3 were antiferromagnetic, with similar intracluster exchange coupling constants, J (−262(23), −211(34), and −266(46) cm-1, respectively). There was coupling between unpaired electrons on {[(η-C5Me5)Cr(μ3-O)]4}+ and {tcnq}- in 3 at temperatures below 110 K.