Carbon-13 nuclear magnetic resonance studies on nickel carbonyl clusters

Abstract

Carbon-13 n.m.r. spectra, over a range of temperature, are reported for [Ni₅(CO)₁₂]^2–, [Ni₆(CO)₁₂]^2–, [Ni₉(CO)₁₈]^2–, and [Ni₁₂(CO)₂₁H_4–x]^x–(x= 2 or 3). At –80 °C the spectra of [Ni₆(CO)₁₂]^2–, [Ni₉(CO)₁₈]^2–, and [Ni₁₂(CO)₂₁H₂]^2– are consistent with their solid-state structures; terminal–bridge carbonyl exchange is observed at higher temperatures with the lowest-energy process involving exchange on the outer metal triangles. Similar behaviour is found for [Ni₁₂(CO)₂₁H]^3– and in addition H migration may occur. Spectroscopic and chemical evidence is presented for the formation of a new cluster, [Ni₇(CO)₁₅]^2–, and its fluxional behaviour is reported. At 60 °C [Ni₁₂(CO)₂₁H₂]^2– is transformed cleanly into [Ni₉(CO)₁₈]^2– whereas [Ni₁₂(CO)₂₁H]^3– does not react under the same conditions.