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) Å. 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.