Magnetic moments and electron spin resonance spectra of some iron–sulphur–molybdenum and –tungsten cubane-like cluster dimers

Abstract

The variation of the effective magnetic moment, _m, with temperature in the range 1.9–300 K, and with applied magnetic field (1.25–20.0 kG), is reported for [NEt₄]₃[Fe₆M₂S₈(SPh)₆(OMe)₃][M = Mo (1) or W (2)], [NBuⁿ₄]₃[Fe₆Mo₂S₈(SPh)₉](3), and [NEt₄]₃[Fe₆W₂S₈(SEt)₉](4). The e.s.r. spectra at 4.2 K for powders of (2), (3), and (4), and a frozen glass in MeCN for (2) are also reported. An interpretation of these data is presented in terms of antiferromagnetic spin coupling between two Fe^II ions and an Fe^III ion within a Fe₃MS₄ sub-unit, with an additional much weaker couping between the sub-units.