Correlating Boron-Hydrogen Stretching Frequencies with Boron-Hydrogen Bond Lengths in Closoboranes: An Approach Using DFT Calculations

Using harmonic and anharmonic DFT calculations, we have established a general correlation between B-H stretching frequencies and B-H bond lengths valid for the closoboranes BxHx2- (x = 6 -12), substituted closoboranes B12H12 (-) X-n(n)2- (with X = F, Cl, Br and n = 1 - 3 and 9 - 12) and the carboranes CB9H10- and CB11H12-, suggesting that this correlation is also applicable to other similar species. It appears that the average B-H stretching frequency observed around 2500 cm(-1) shift by about -100 cm(-1) if the average B-H bond length increases by 1 pm. In contrast to BH4-, the B-H bond in closoboranes is practically covalent and the correlation evidenced between its stretching frequency and its length proves to be similar to the one observed for the C-H bond.