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Spanish researchers used an unusual synthetic route to make the first compound containing a zinc-zinc bond and confirmed its existence with chemical, spectroscopic and X-ray methods. This unprecedented compound and unusual synthesis could provide new ways of making reactive and interesting compounds containing a Zn-Zn bond. Irene Resa and Ernesto Carmona of the University of Seville and Enrique Gutierrez-Puebla and Angeles Monge of the Madrid Institute of Materials Science, Spain, point out that chemists rarely see a +1 oxidation state for the Group 12 metals of the periodic table, which includes zinc, cadmium, and mercury, with the exception that a formal oxidation state of +1 is important only for mercury. Indeed, the Hg22+ cation is well known and although the Cd-Cd2+ unit is also well established it is less common than the mercury equivalent. It, therefore, came as something of a surprise to the team to crystallize a product that appeared to contain a Zn-Zn unit. This, would essentially be a Zn22+ unit analogous to the mercury cation with the zincs in the +1 state. The team were investigating putative sandwich compounds of zinc when they stumbled on the Zn-Zn bond. They reacted Zn(C5Me5)2 and Zn(C2H5)2 in diethyl ether at -10 Celsius and obtained decamethyldizincocene, Zn2(eta5-C5Me5)2), which they describe as an organometallic compound of Zn(I) formally derived from the dimetallic {Zn-Zn}2+. The team then used X-ray studies to show that this compound contains two eclipsed Zn(eta5-C5Me5) fragments in which the distance between the two zinc atoms is just 2.305(+/-3) angstroms. This is "indicative of a metal-metal bonding interaction," confirms Carmona. "The bond is appreciably shorter than the Zn...Zn separation found in a recently described hydride-bridged complex of Zn(II)," he told X-Factors, "there is only one structurally characterized hydride-bridged Zn(II) compound, made by Herbert Roesky {University of Gottingen} and co-workers in 2001". Writing in the same issue of Science, Gerard Parkin of Columbia University, New York, suggests that the finding shows how molecular chemistry can "still yield surprises". He adds that, "The next frontier for zinc chemistry will be the isolation of a simple molecular compound that features a bona fide zinc-zinc centre with a "+1" charge." Carmona and colleagues suggest that their structure bodes well for such endeavours, they also hint that it might be possible to make cadmium and mercury analogues. "It is difficult to predict applications for the Zn-Zn compound," Carmona confesses, "These studies are fundamental, for zinc it is mostly the interest of discovering a new oxidation state for this common metal, whose chemistry has been intensively explored for many years." He hopes that further work will help them elucidate the chemistry of Zn(I). "It is actually very exciting to be able to explore it," he adds. Related Links: |
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