Structure and stability of molecular and ionic complexes of AlCl ₃ with pyrazine and 4,4′-bipyridyl

Structural and thermodynamic characteristics of molecular and ionic complexes of aluminum trichloride with pyrazine (pyz) and 4,4′-bipyridyl (bipy) are calculated at the RI-BP86/def2-SVP level. It is found that for molecular 2AlCl₃·3L and 4AlCl₃·3L complexes an energy difference between isomers does not exceed 4 kJ/mol, and the rotation barrier of the AlCl₃ moiety relative to the N-Al-N bond does not exceed 24 kJ/mol. A comparison of the stability of molecular and ionic complexes of aluminum in the gas phase shows that the maximum energy difference is ∼60 kJ/mol. For L = pyz the molecular complex is more stable whereas for L = bipy it is the ionic one.