Redox active Ni–Pd carbonyl alloy nanoclusters: syntheses, molecular structures and electrochemistry of [Ni22−xPd20+x(CO)48]6− (x = 0.62), [Ni29−xPd6+x(CO)42]6− (x = 0.09) and [Ni29+xPd6−x(CO)42]6− (x = 0.27)

Abstract

A redox active Ni–Pd alloy nanocluster [Ni_22−xPd_20+x(CO)₄₈]⁶⁻ (x = 0.62) ([1]⁶⁻) was obtained from the redox condensation of [NBu₄]₂[Ni₆(CO)₁₂] with 0.7–0.8 equivalents of Pd(Et₂S)₂Cl₂ in CH₂Cl₂. Conversely, [Ni_29−xPd_6+x(CO)₄₂]⁶⁻ (x = 0.09) ([2]⁶⁻) and [Ni_29+xPd_6−x(CO)₄₂]⁶⁻ (x = 0.27) ([3]⁶⁻) were obtained by employing [NEt₄]₂[Ni₆(CO)₁₂] and 0.6–0.7 equivalents of Pd(Et₂S)₂Cl₂ in CH₃CN. The molecular structures of these high nuclearity Ni–Pd carbonyl clusters were determined by single-crystal X-ray diffraction (SC-XRD). [1]⁶⁻ adopted an M₄₀ccp structure comprising five close-packed ABCAB layers capped by two additional Ni atoms. Conversely, [2]⁶⁻ and [3]⁶⁻ displayed an hcp M₃₅ metal core composed of three compact ABA layers. [1]⁶⁻, [2]⁶⁻ and [3]⁶⁻ showed nanometric sizes, with the maximum lengths of their metal cores being 1.3 nm ([1]⁶⁻) and 1.0 nm ([2]⁶⁻ and [3]⁶⁻), which increased up to 1.9 and 1.5 nm, after including also the CO ligands. Ni–Pd distribution within their metal cores was achieved by avoiding terminal Pd–CO bonding and minimizing Pd–CO coordination. As a consequence, site preference and partial metal segregation were observed, as well as some substitutional and compositional disorders. Electrochemical and spectroelectrochemical studies revealed that [1]⁶⁻ and [2]⁶⁻ were redox active and displayed four and three stable oxidation states, respectively. Even though several redox active high nuclearity metal carbonyl clusters have been previously reported, the nanoclusters described herein represent the first examples of redox active Ni–Pd carbonyl alloy nanoclusters.