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Issue 12, 1989
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Dramatic tensor-axis non-coincidence effects in the electron spin resonance spectra of some low-spin manganese(II) complexes

Abstract

ESR spectra are reported for frozen CH2Cl2/ClCH2CH2Cl solutions of 14 low-spin manganese(II) cations: [(η5-C5H5)Mn(CO)L2]+, L = 1/2 Ph2PCH2CH2PPh2(dppe), 1/2 Me2PCH2CH2PMe2(dmpe), 1/2 Ph2PCH2PPh2(dppm), PMe3, PPh3; [(η5-MeC5H4)Mn(CO)dppe]+; [(η5-6-exo-PhC6H6)Mn(CO)L2]+, L = 1/2 dppe, 1/2 dmpe, PMe3; [(η5-6-exo-PhC6HMe5)Mn(CO)dppe]+; [(η5-6-exo-PhC7H8)Mn(CO)dppe]+; [(η5-C5H5-Mn(CO)2PPh3]+; and [(η5-6-exo-PhC6H6)Mn(CO)2L]+, L = PMe3, PnBu3. The spectra show anisotropic 55Mn hyperfine coupling and nearly isotropic 31P hyperfine coupling. There are dramatic departures from first-order line spacings which result from non-coincidence of the X and Z principal axes of the g and the 55Mn hyperfine tensors. In most cases, the ESR parameters can be interpreted in terms of a semi-occupied molecular orbital (SOMO) primarily dx2y2 in character, but rotated about the y axis to avoid an antibonding interaction with the dienyl ring. The spectrum of [(η5-6-exo-PhC6H6)Mn(CO)(PMe3)2]+ shows non-equivalent 31P couplings, suggesting an unsymmetrical dienyl ring conformation. This spectrum, and those of the monophosphine cations, are best explained in terms of a SOMO primarily dyz in character.

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Article type: Paper
DOI: 10.1039/F19898503913
Citation: J. Chem. Soc., Faraday Trans. 1, 1989,85, 3913-3925
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    Dramatic tensor-axis non-coincidence effects in the electron spin resonance spectra of some low-spin manganese(II) complexes

    R. D. Pike, A. L. Rieger and P. H. Rieger, J. Chem. Soc., Faraday Trans. 1, 1989, 85, 3913
    DOI: 10.1039/F19898503913

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