Molecular complexes of non-chelating polydentate Lewis bases with group 13 Lewis acids: crystal structure and computed energy of stepwise donor–acceptor bond formation

The crystal structures of five donor–acceptor (DA) complexes of 1:1 and 2:1 composition between E(C₆F₅)₃ (E = B, Al, Ga and In) and pyrazine (pyz) as a non-chelating bidentate nitrogen-containing donor, as well as the GaI₃ pyz GaI₃ complex have been established for the first time. A joint analysis of the experimental structural data and the results of computations at the M06-2X/def2-TZVP level of theory reveals that with an increase in the number of acceptor molecules in the DA complex, the DA bond distances increase, while the DA bond energies and Wiberg bond indexes decrease, indicating a weaker bonding. The previously reported ‘inverse’ relationship between the Lewis acidity and the capacity of a polydentate donor to complex with multiple Lewis acids is not confirmed.