Quantum chemical calculations at the MP2 level using large bases is C(NH 2 ) 2 Ͼ NH 3 Ͼ CO, but the ordering of Lewis acid strength of EX 3 depends on the coordinated Lewis base. valence basis sets up to TZ+2P quality have been carried out in order to predict the geometries and bond energies of the TiF 4 and TiCl 4 have similar Lewis acidities as BF 3 , but the titanium tetrahalides may bind one or two donor molecules title compounds. The nature of the donor-acceptor bond has also been investigated. The calculations show clearly that with almost the same bond strength. The investigated donoracceptor bonds have a high degree of ionic character. The diaminocarbenes are much stronger Lewis bases than amines. The complexation energies of C(NH 2 ) 2 have been largest covalent contributions are found for the diaminocarbene complexes. The covalent character of the calculated to be 14-27 kcal/mol higher than those of NH 3 . The most strongly bonded complex is Cl 3 Al-C(NH 2 ) 2 , which X 3 E-CO bond increases on going from E = boron to the heavier Group 13 elements, while the opposite order is found has a theoretically predicted Al-C bond energy D o = 59.1 kcal/mol. In all the complexes, the strength of the Lewis for the X 3 E-NH 3 and X 3 E-C(NH 2 ) 2 bonds.
from BF 3 to BI 3 , depending on whether the donorϪac-