A theoretical study on structures, stabilities, and potential energy surfaces of planar BnP2 (n = 1-7)

The geometries, stabilities, and potential energy surfaces of possible isomers of BnP2 (n = 1-7) are explored and investigated at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level. Many planar structures for the possible isomers of BnP2 (n = 1-7) and transition states are located. The lowest-energy structures (1a-7a) of BnP2 exhibit belt-like growth feature with two phosphorus atoms capped to two terminal B-B edges of Bn unit. The lowest-energy structures B2P2(2a), B4P2(4a), and B6P2(6a) are more stable than their neighbors. Especially, the lowest-energy isomer (4a) of B4P2 has exceptional stability. Results from molecular orbital analysis suggest that the formation of the delocalized π, the σ-radial, and σ-tangential MOs is favorable to stabilizing the structures of lowest-energy isomers (1a-7a) of BnP2. In addition, results from molecular orbital and nucleus independent chemical shift demonstrate that BP2 and B7P2 may have aromaticity. Importantly and interestingly, the lowest-energy isomers (2a, 3a, 4a, 5a, and 6a) of BnP2 (n = 2-6) are stable both thermodynamically and kinetically at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level and may be observable in laboratory, which is helpful for further experimental studies of BnP2.