Non-classical covalent bonds

The possibility of multiple bond formation between Periodic Table Group 13–15 elements is considered. The ways of triple bond formation between these elements are discussed; particular attention is paid to the $B \equiv B$ triple bonds. New non-linear compounds with triple bonds and their molecular structures are considered. The causes are given for the formation of compounds with unusually short distances between chemically non-bonded atoms. The grounds of the theory of two-centre three-electron bonds are presented and conditions of existence of isolated square planar carbon clusters are analyzed. The bibliography includes 181 references.