E-Mail In a number of biological processes, iron-sulfur clusters play a vital role, where they act as cofactors to enzymes. Research published in Angewandte Chemie now shows that cubic clusters can support unusual bonding states. This study shows that the cluster copes well with a multiple bond between iron and nitrogen--a structural motif that may be involved in biological nitrogen fixation. Clusters made of iron and sulfur atoms are essential cofactors for a number of enzymes, especially in biological processes involving electron transfer. As an example, nitrogen-fixing bacteria use iron-sulfur clusters to convert nitrogen from the air into useful nitrogen compounds. To understand this important biological process, scientists dig deep into the bonding relationships possible between nitrogen and iron atoms in such clusters.