Calcium caught in an inverse sandwich

Chemists in Germany and Switzerland have discovered the first stable complex of calcium(I) - a highly unusual structure for a metal whose chemistry is normally dominated by the +2 oxidation state.

Matthias Westerhausen and colleagues at the Friedrich Schiller University in Jena have found that two calcium(I) ions can be stabilised by inserting an arene group between them, forming a stable structure the team have termed an 'inverse sandwich' complex. This kind of complex has been seen before with group three metals such as gallium and indium, but not with group two metals.