Boron cluster anions and their derivatives in complexation reactions

Abstract

Boron cluster anions attract the interest of chemists because of their electronic structures, geometry, and chemical behavior. These weak coordinating ligands allow one to vary their structure and properties of the final compounds. Here, we discuss the coordination ability of unsubstituted anions [BnHn]2− (n = 6, 10, 12), a number of their mono- and disubstituted derivatives of different compoition and perhalogenated anions [BnHaln]2− (Hal = F, Cl, Br, I; n = 10, 12), as well as dimeric boron cluster [B20H18]2− in the presence of solvents and organic ligands depending on the nature of complexing agent. The boron cluster anions form mononuclear, binuclear, and polymeric complexes in reactions with metals that act as Pearson’s soft acids (Cu(I), Ag(I), Pb(II), Hg(II)). Metals belonging to the intermediate group (Zn(II), Fe(II), Co(II), Ni(II), Cu(II), Mn(II)) form cationic complexes with boron cluster anions as counterions. In the presence of metals acting as hard acids (Fe(III), Co(III)), boron clusters usually participate as reducing agents decreasing the metal oxidation state. This review allows one to trace the effect of different geometry of boron polyhedra and substitutes introduced into the boron cage on coordination ability of boron clusters with a giving metal.