Solvent Molecules as Ligands in Coordination Compounds of Metals with Boron Cluster Anions and Their Derivatives (A Review)

This study summarizes the literature data on the synthesis and structure of coordination compounds of alkali and alkaline earth metals, a series of M(I), M(II) transition metals, and rare earth elements with solvent molecules and boron cluster anions and their derivatives as ligands. The considered group of compounds has been classified in view of the nature of the coordinating solvent molecules as well as the position of boron cluster anions and their derivatives in the inner coordination sphere of the metal or the outer sphere. It has been shown that boron cluster anions and their derivatives are coordinated by metal atoms along with the solvent molecules via the three-center two-electron bonds in the presence of the Pearson’s soft acid metals [copper(I), silver(II), and lead(II)], forming the coordination polyhedrons. The possibility of the formation of mixed-ligand complexes due to the completion of the metal coordination polyhedron with the BH groups of the boron cluster has been revealed for the nonclassical complex-forming metals during the thermal treatment of the aqua complexes or the complexes with alcohol molecules as ligands, [ML 6 ][B n H n ] (M = Ca, Mg, Co, and Ni).