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Using self-consistent field molecular-orbital theory, we show that the interaction of hydrogen molecules with a Ni+ ion is characteristically different from that with a neutral Ni atom. While hydrogen chemisorbs dissociatively on the neutral metal atom, it is bound to the cation in its molecular form. The atomic bonding is a consequence of the Pauli exclusion principle whereas the bonding of the molecular hydrogen results from an electrostatic interaction. We predict that a Ni+ ion can bind at least six hydrogen molecules.