Bonding and potential energy curves for NiH and NiH2

The MINDO/SR procedure does well in reproducing experimental observations and theoretical ab initio calculated properties of NiH and NiH2. The occupied Ni d orbitals are nonbonding and remain lower in energy than the bonding Ni s and p orbitals in both NiH and NiH2. In agreement with experiment the lowest state of NiH2 is calculated to be a triplet with σ and δ holes in the d orbitals. A number of bent metastable states of NiH2 have been found, with the geometry being influenced indirectly by the d‐orbital occupancy. One triplet state with a triangular geometry can be readily formed from H2 plus Ni and is stable by 9 kcal/mol with respect to dissociation into Ni plus H2. The H–H bond is stretched and reduced in energy but is not broken. This is a highly activated H2 molecule but there is still a large activation evergy, 42 kcal/mol, to completely break the H–H bond.

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