Theoretical studies of transition-metal hydrides. 4. Comparison of the transition-metal dihydride ions CrH₂⁺ and MoH₂⁺

The electronic and geometric structure of two transition-metal dihydride cations, CrH₂⁺ and MoH₂⁺, has been studied theoretically by using generalized valence bond and configuration interaction methods. MoH₂⁺ is found to have two equally favorable geometries: R_e = 1.705 Å, θ_e = 64.6°; R_e = 1.722 Å, θ_e, = 112.3°. These lead to bond energies of D_e(HMo⁺-H) of 35.1 and 34.7 kcal/mol, respectively, compared with D_e(Mo⁺-H) = 33.8 kcal/mol. CrH₂⁺ leads to an open geometry with R_e = 1.635 Å and θ_e = 107.5°. The bond energy is D_e(HCr⁺-H) = 19.4 kcal/mol compared with D_e(Cr⁺-H) = 26.9 kcal/mol.