Structures and aromaticity of Cationic closo-BnHn-3(CO)3+ (n = 5-12).

Structures and stabilities of tricarbonyl closo-boranes cation, BnHn-3(CO)3+ (n = 5-12), isolobal with cationic closo-carboranes C3Bn-3Hn+, have been investigated at the B3LYP/6-311+G** level of theory. The most stable positional isomers of individual cluster are in agreement with those of closo-C3Bn-3Hn+ clusters except for n = 8 and 10. Energetic analysis identifies closo-B6H3(CO)3+, closo-B10H7(CO)3+ and closo-B12H9(CO)3+ as the most stable cages. It is also found that closo-BnHn-3(CO)3+ is much less strained than closo-C3Bn-3Hn+. The negative nucleus independent chemical shifts (NICS) at the cage center reveal three-dimensional aromaticity of the closo-BnHn-3(CO)3+ cages. The CO stretching frequencies have been computed in advance to aid experimental study.