New aspects in the chemistry of low-coordinated inter-element compounds of heavier Group 15 elements

Recent results obtained in the studies of the author and co-workers on the synthesis and properties of doubly bonded systems between heavier Group 15 elements are described together with a brief historical survey on the chemistry of low-coordinated heavier Group 15 elements. The first stable distibene and dibismuthene were successfully synthesized by taking an advantage of kinetic stabilization using new bulky substituents and the spectroscopic studies and crystallographic analysis of them led to the systematic comparison of structural parameters and physical properties for all doubly bonded systems between heavier Group 15 elements from phosphorus to bismuth. In addition to these experimental data, theoretical calculations also revealed the intrinsic character of low-coordinated inter-element compounds containing heavier Group 15 elements, especially that of dibismuthene, i.e. the heaviest double-bond compounds of non-radioactive elements. Furthermore, a unique intermolecular crystalline-state reaction was observed in the oxidation of the overcrowded distibene and dibismuthene, the reaction process of which was successfully monitored by repeated measurements of the cell dimensions using an imaging-plate X-ray diffraction technique.