REVISITING B^sub 20^H^sub 16^ BY MEANS OF A JOINT COMPUTATIONAL/EXPERIMENTAL NMR APPROACH

摘要

A new synthesis of the fused macropolyhedral boron cluster B^sub 20^H^sub 16^ is described and its molecular structure in solution discussed, based on multi-nuclear NMR spectra, including COSY measurements, in relation to its previously elucidated solid-state structure. To verify the conclusions from the NMR study, experimentally determined chemical shifts are compared with calculated values at the GIAO-B3LYP level with a TZP basis set by Huzinaga. There is a very good agreement between the experimental and computed δ(^sup 11^B) values, suggesting that the MP2/6-31G* internal coordinates are a reasonable representation of the molecular geometry of this twenty-vertex cluster in solution that is essentially the same as its solid-state structure. A computational analysis of the FMO orbitals of B^sub 20^H^sub 16^, in particular of the LUMO, reveals that the four naked boron atoms, common for two shared icosahedral subclusters, are the reactive sites of this D^sub 2d^-symmetrical molecule. [PUBLICATION ABSTRACT]