Bis(Dicarbollide) Complexes of Transition Metals: How Substituents in Dicarbollide Ligands Affect the Geometry and Properties of the Complexes.

The interaction between different types of substituents in dicarbollide ligands and their influence on the stabilization of various rotational conformers (rotamers) of transition metal bis(dicarbollide) complexes [3,3'-M(1,2-CBH)] are considered. It has been shown that the formation of intramolecular CH···X hydrogen bonds between dicarbollide ligands is determined by the size of the proton acceptor atom X rather than its electronegativity. Due to the stabilization of rotamers with different dipole moments, intramolecular hydrogen bonds between ligands in transition metal bis(dicarbollide) complexes can have a significant impact on the biological properties of their derivatives. In the presence of external complexing metals, weak intramolecular CH···X hydrogen bonds can be broken to form stronger X->M donor-acceptor bonds. This process is accompanied by the mutual rotation of dicarbollide ligands and can be used in sensors and molecular switches based on transition metal bis(dicarbollide) complexes.