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

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Computational Chemistry

Background:

• Nickel hydride complexes are important in catalysis and coordination chemistry.
• Understanding metal-metal bonding and electronic states is crucial for predicting reactivity.

Purpose of the Study:

• To investigate the structural and electronic properties of the nickel hydride complex [Cp'Ni(μ-H)]2.
• To elucidate the origin of its unusual magnetic behavior.

Main Methods:

• X-ray crystallography to determine the Ni-Ni bond distance.
• Variable temperature and field magnetic susceptibility measurements.
• Density Functional Theory (DFT) and Complete Active Space Self-Consistent Field/Second-Order Perturbation Theory (CASSCF/CASPT2) calculations.

Main Results:

• A remarkably short Ni-Ni bond distance of 2.28638(3) Å was observed.
• The complex displays an unexpected triplet ground state with a large zero-field splitting of +90 K.
• Electronic structure calculations confirmed the triplet ground state is due to half-occupied degenerate Ni-Ni π* orbitals.

Conclusions:

• The short Ni-Ni bond and triplet ground state are intrinsically linked.
• The electronic structure provides a clear explanation for the observed magnetic properties.
• This study offers new insights into bonding in dinickel complexes.