Triel-Bonded Complexes between TrR3 (Tr=B, Al, Ga; R=H, F, Cl, Br, CH3 ) and Pyrazine

Abstract

Complexes between TrR₃ (Tr=B, Al, Ga; R=H, F, Cl, Br, CH₃ ) molecules and pyrazine have been characterized at the MP2 and CCSD(T) levels of theory. The adducts can be grouped according to the type of molecular arrangement. The first situation places the Tr atom in the plane of the pyrazine ring and contains a triel bond to the N lone pair. For the boron complexes the orbital interaction energy is almost equal to the electrostatic component, while the former is only half the latter for Tr=Al and Ga. The two monomers are stacked above one another in the second configuration, which depends to a greater degree upon orbital interaction and dispersion. The former complexes are more strongly bonded than the latter. Interaction energies (E_int ) for the stronger complexes vary between -50 and -20 kcal/mol for BBr₃ and Ga(CH₃ )₃ paired respectively with pyrazine. E_int is much smaller for the stacked configurations, ranging from -8 for GaF₃ to -1.4 kcal/mol for BF₃ . The value of the maximum of the electrostatic potential correlates poorly with E_int , attributed in part to monomer distortions upon complexation.

Keywords: ab initio calculations; complexes; molecular modelling; π-holes, pyrazine.