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)21H4–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.