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

Mössbauer spectroscopy of iron(III) bis(dicarbollide) (1) and its adduct (2) revealed low spin Fe in 1 and surprisingly Fe in 2. In 1, the (CBH) groups rotate at room temperature with a frequency of 10 Hz, getting across the energy barrier of 24 meV. Numerical simulations showed a gradient of electric charge in 2, which may explain the Fe-like character in 2.