Bonding behaviour

The first zinc-zinc bonded complex shown to be stable.

Future editions of undergraduate text books might have to be rewritten following the discovery of a complex containing an unsupported single bond between two zinc atoms. The discovery of a new oxidation state of any element has always been met with much enthusiasm. However, the first synthesis of an isolated compound containing a zinc-zinc bond has been of particular interest because it was presumed that such a compound would be too unstable. Furthermore, the chemistry of zinc is well understood, employed widely in organometallic chemistry and well studied during undergraduate classes. This latest find by Spanish researchers will add to our understanding.

The zinc-zinc bonded compound (Cp*2Zn2) was synthesised initially as an unanticipated product by graduate student Irene Resa who works for Ernesto Carmona, professor of inorganic chemistry at the University of Seville. Analogous compounds containing metal-metal bonds with similar elements - mercury-mercury and cadmium-cadmium - were already known. However, until now, only Zn2+ compounds had been identified and previous attempts to isolate compounds containing Zn1+ had proved elusive. Antonio Laguna, professor of inorganic chemistry at the University of Zaragoza believes this is a very important step forward. ’This work can open the door to the synthesis of new complexes with new metal-metal bonds,’ he told Chemistry World.

The understandably delighted Spanish team has now devised a more direct route to the product and is also working on similar compounds and theoretical studies. Carmona is not prepared to disclose any synthetic details just yet but hopes to publish new work in the near future adding cautiously that ’the chemistry is difficult, at this early stage it appears mostly due to the tendency of Zn2Cp*2 to disproportionate, but we will pursue it and I am convinced that we will make additional progress very soon.’

Proving the structure of the new compound to show this fundamental interaction was also challenging. The team gathered evidence to support their work including an x-ray structure which shows a very short zinc-zinc bond length (2.31?) which discounts the possibility of any bridging ligands that are normally seen in complexes containing more than one zinc atom.

Vikki Allen