THEORETICAL-STUDY OF THE BONDING OF NB2+ TO CH2, C2H2, AND C2H4

The bonding of Nb2+ with CH2, C2H2, and C2H4 is studied by using electronic structure calculations that include high levels of electron correlation. The binding energy for NbCH2(2+) is in good agreement with the lower bound determined from the reaction with CH4 but is significantly smaller than the value determined from the binding energy and ionization potential of NbCH2+. The calculations and a new interpretation of the experiment indicate that the larger value is in error primarily because the ionization potential of NbCH2+ determined from bracketing charge-exchange reactions is too small. The computed binding energy of NbC2H2(2+) is in good agreement with experiment. The calculations show that the bonding is predominantly covalent in character for both NbCH2(2+) and NbC2H2(2+), whereas for NbC2H4(2+) the electronic states that are predominantly ionic and covalent are nearly degenerate. The trend in binding energies, CH2 > C2H2 > C2H4, is consistent with the energy required to prepare the ligands for bonding.