NEW RESULTS ABOUT THE OXABORANE ANION OB11H12-

Improved synthesis of OB11H12- by oxydation of B11H14- with aqueous Na OH is described. Thus, [NEt4][OB11H12] is recovered with moderate yiel d (24%). Using NBu4Br (instead of NEt4Br) for the metathesis reaction results in a much lower yield. AM1 calculations were performed with th e 12-vertex 28-electron nido-oxaborane anion OB11H12-. A good agreemen t was obtained for the bond lengths and geometry of this OB11H12- anio n and of closely related isoelectronic clusters. From the calculated c harge densities performed on the anion the negative charge is not loca ted on the oxygen atom, but instead dissipated through the skeleton, t hus making the heteroatom more electropositive. Similar calculations w ere also performed with the unknown isoelectronic nido 12-vertex 28-el ectron XB11H12 species (X=CH2-, NH-, F) and with the icosahedra closo 12-vertex 26-electron species YB1lH11 (Y=NH, O, F+). In every case, th e oxygen-derivative is predicted to be the most stable, the close OB11 H11 being even more stable than the known NB11H12.