Binding energies of Co(H2)n+ (n = 1-3) and CrN2+ computed using the modified coupled-pair functional approach agree well with measured values. The calculations show that both H-2 and N2 bond much more strongly to Co+ than to Cr+. Theoretical studies also show that despite the similar polarizabilities of N2 and Ar, the CrN2+ binding energy is twice as large as that of CrAr+ due to the charge-quadrupole contribution. Finally, the bonding of H-2 and N2 with Na+ and Mg+ is contrasted with that for Cr+ and Co+.
