Electronic structure of tris(pyrazolyl)hydroborato [Tp] gallium complexes: density functional studies of monovalent Ga[Tp], terminal chalcogen complexes, Ga[Tp]E (E = O, S, Se or Te) and a GaI3 adduct, Ga2[Tp]I3

Abstract

Density functional theory calculations have been made on gallium complexes supported by the tris(pyrazolyl)hydroborato ligand [Tp], Ga[Tp] I, Ga[Tp]E II (E = O a, S b, Se c or Te d) and Ga₂[Tp]I₃ III aimed at modelling the bonding in the recently reported tris(3,5-di-tert-butylpyrazolylhydroborato ([Tp^But₂]) gallium complexes, Ga[Tp^But₂] 1, the terminal chalcogen complexes Ga[Tp^But₂]E 2 (E = S b, Se c or Te d), and the adduct Ga₂[Tp^But₂]I₃ 3. The calculated and observed structures are in good agreement. The gallium “lone pair” in Ga[Tp] has Ga–N antibonding character. The decrease in Ga–N bond lengths between Ga[Tp] and its adducts is associated with relief of this antibonding character. The bonding in Ga[Tp]E (E = O, S, Se or Te) is found to be almost entirely semipolar [[Tp]Ga⁺–E^–] irrespective of the nature of the chalcogen element although the polarisation of charge decreases on descending the group. The GaI₃ adduct is also best described by the resonance structure [Tp]Ga⁺–Ga^–I₃.