Stereochemistry of free boranes and heteroboranes from electron scattering and model chemistries.

The development of modern computational methods, linked to improved methods for analysis of experimental gas-phase structural data, has allowed the stereochemistry of many boranes and heteroboranes to be determined with great accuracy over the past two decades. Many of these compounds have been prepared in the Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic, and gas-phase electron diffraction (GED) data have been obtained mainly at the University of Edinburgh. Structural tools based on the concerted use of GED and computations of the geometries and "B chemical shifts (MOCED, SARACEN) have also been employed. The results of this extended programme of research are reviewed here. Many different closo-, nido-, arachno-, and hypho-geometrical shapes, as well as some that do not obey Wade's rules, are included. The outlook for the future of this type of structural chemistry research is assessed.