An "intermediate spin" nickel hydride complex stemming from delocalized Ni2(μ-H)2 bonding.

The nickel hydride complex [Cp′Ni(μ-H)]2 (1, Cp′ = 1,2,3,4-tetraisopropylcyclopentadienyl) is found to have a strikingly short Ni–Ni distance of 2.28638(3) A. Variable temperature and field magnetic measurements indicate an unexpected triplet ground state for 1 with a large zero-field splitting of +90 K (63 cm–1). Electronic structure calculations (DFT and CASSCF/CASPT2) explain this ground state as arising from half occupation of two nearly degenerate Ni–Ni π* orbitals.