Theoretical Studies of Inorganic Compounds. 36 1) Structures and Bonding Analyses of Beryllium Chloro Complexes with Nitrogen Donors

Quantum chemical calculations at various levels of theory (BP86, B3LYP, MP2, CCSD(T), CBS‐QB3) of the beryllium complexes [BeCl 2 (NHPH 3 )], [BeCl 2 (NHPH 3 ) 2 ], [BeCl 3 (py)] − , [BeCl 2 (NH 3 )], [BeCl 2 (NH 3 ) 2 ], [BeCl 3 (py)] − and [BeCl 3 (NH 3 )] − as well as the boron compounds [BCl 3 (py)] and [BCl 3 (NH 3 )] show that BeCl 2 is a very strong Lewis acid. The theoretically predicted bond dissociation energy at CBS‐QB3 of Cl 2 Be‐NH 3 (D e = 32.5 kcal/mol)is even higher than that of Cl 3 B‐NH 3 (D e = 28.6 kcal/mol). Even the second ammonia molecule in [BeCl 2 (NH 3 ) 2 ] still has a strong bond with D e = 24.2 kcal/mol. The theoretically predicted bond strengths for the phosphaneimine ligands in [BeCl 2 (NHPH 3 ) 2 ] are D e = 46.7 kcal/mol for the first ligand and D e = 29.8 kcal/mol for the second. The anion BeCl 3 − is a moderately strong Lewis acid which has bond energies of D e = 14.1 kcal/mol in [BeCl 3 (py)] − and D e = 14.2 kcal/mol in [BeCl 3 (NH 3 )] − . The higher bond energy of [BeCl 2 (NH 3 )] compared with [BCl 3 (NH 3 )] comes from less deformation energy for BeCl 2 than for BCl 3 . The intrinsic attraction between BeCl 2 and NH 3 calculated with frozen geometries of the complex geometry is ∼5 kcal/mol less than the attraction between BCl 3 and NH 3 . The bonding analysis with the EDA method shows that the attractive energy of the beryllium complexes comes manly from electrostatic attraction. The larger contribution of the electrostatic term is the most significant difference between the nature of the donor‐acceptor bonds of the beryllium and boron complexes.