Intramolecular rotations and electronic states of iron in the iron bis(dicarbollide) complex Fe[(C2B9H11)2] studied by a 57Fe nuclear probe and computational methods.

Mössbauer spectroscopy of iron(III) bis(dicarbollide) (1) and its adduct (2) revealed low spin Fe^III in 1 and surprisingly Fe^II in 2. In 1, the (C₂B₉H₁₁) groups rotate at room temperature with a frequency of 10⁷ Hz, getting across the energy barrier of 24 meV. Numerical simulations showed a gradient of electric charge in 2, which may explain the Fe^II-like character in 2. [ABSTRACT FROM AUTHOR]