Structure and stability of closo-BnHn−2(CO)2 (n = 5-12)

Closo-BnHn−2(CO)2 (n = 5-12), isolobal analogues of closo-C2Bn−2Hn, have been investigated at the B3LYP/6-311+G**density functional level of theory. The most stable isomers of closo-BnHn−2(CO)2 are similar to those of closo-C2Bn−2Hn in geometric patterns apart from closo-B6H4(CO)2, and closo-BnHn−2(CO)2 is much less strained than closo-C2Bn−2Hn. Energetic analysis identifies closo-B6H4(CO)2, closo-B12H10(CO)2 and closo-B10H8(CO)2 to be most stable, of which the latter two cages have been prepared experimentally. On the basis of the negative and rather large nucleus independent chemical shifts (NICS), closo-BnHn−2(CO)2 are aromatic. To aid further experimental study, the CO stretching frequencies have been computed.