Structure and bonding of the remarkable donor-acceptor complexes XBeO (X = NH_3, NMe_3, CO, N_2, C_2H_2, C_2H_4, H_2, H_2CO, O_2)

摘要

Quantum mechanical calculations at the MP4/6-311G(2df,2pd)//MP2/6-31G(d,p) level of theory are reported for the compounds XBeO with X = NH_3, NMe_3, CO, N_2, C_2H_2, C_2H_4, H_2, H_2CO and O_2. The calculations show that BeO is a very strong Lewis acid. The X-BeO bond strength is between D_e = 69.5 kcal mol~(-1) for Me_3NBeO and D_e = 11.2 kcal mol~(-1) for π-bonded N_2BeO. The calculated bond strength for the yet unknown donor-acceptor complex Me_3NBeO is significantly higher than the strongest experimentally known main-group donor-acceptor complex Me_3NAlCl_3 (D_o = 47.5 kcal mol~(-1)). Even the weak donor H_2 is bonded with D_e = 18.5 kcal mol~(-1). The compounds O_2BeO and its isomer berylliumozonide BeO_3 should not be considered as donor-acceptor complexes. The results of the CDA method show that the donor-acceptor interactions in terms of orbital mixing are mainly described by the mixing of occupied orbitals of X with vacant orbitals of BeO, while the mixing of occupied orbitals of BeO with vacant orbitals of X is negligible. The topological analysis of the electronic charge distribution and the NBO partitioning scheme demonstrate that the X-BeO bonds have little or no covalent character; the bonds are caused by electrostatic attraction. The charge concentration at the donor atoms in the stronger bonded compounds is significantly deformed towards the beryllium atom.