Nickel poly-acetylidecarbonyl clusters: structural features, bonding and electrochemical behaviour

Abstract

The reactions of [NEt₄]₂[Ni₆(CO)₁₂] with miscellaneous carbon halides (e.g. CCl₄, C₄Cl₆) in CH₂Cl₂ have been extensively investigated particularly focusing on the stoichiometric ratio of the reagents and reaction temperature. This allowed the preparation of the previously known acetylide clusters [Ni₁₆(C₂)₂(CO)₂₃]⁴⁻, [HNi₂₅(C₂)₄(CO)₃₂]³⁻ and [Ni₂₂(C₂)₄(CO)₂₈Cl]³⁻, as well as isolation and full characterisation of the closely related [Ni₁₇(C₂)₂(CO)₂₄]⁴⁻ and [Ni₂₅(C₂)₄(CO)₃₂]⁴⁻ tetraanions. From a structural point of view, all these clusters are based on a Ni₁₆ square orthobicupola which contain interstitial C₂, Ni(η²-C₂)₄ or Ni₂(μ-η²-C₂)₄ moieties, displaying rather short C–C bonds. Electrochemical studies reveal that all these species undergo different redox processes, even if their stability is rather limited. This is corroborated by an extensive analysis of the interaction between interstitial C₂ acetylide units and the metal cluster cage by Extended Huckel Molecular Orbital (EHMO) calculations, which indicates that tightly bonded C–C units are less effective than isolated C-atoms in stabilising the cluster cage.