Scientists from Australia and the UK have made an iron complex in which a diazene ligand is bound to the metal side-on, something never seen before.

'This is the first ever member of this class of compounds,' said Leslie Field of the University of New South Wales in Sydney, Australia. His synthesis of the iron-diazene complex by reacting an iron complex with hydrazine was a lucky break. 'We had been trying to make diazene complexes for some time by a number of routes, but without success,' said Field. Ironically, in this reaction diazene complexes weren't the intended target. 'We were expecting hydrazine-containing compounds,' said Field.

Diazene (HN=NH) is an unstable and very reactive molecule at room temperature, and Field hopes that the new complex may provide a surrogate source of the compound for studying its chemistry. He said it is particularly interesting as the side-on binding of diazene is a previously unknown binding mode for this molecule. 

In the bigger picture, Field said that the complex is a possible intermediate in the reduction of nitrogen to ammonia. Studying the chemistry of the complex may shed light on the role of iron as a catalyst in this process. According to Field, better understanding of the mechanisms of nitrogen reduction could lead to improved strategies for the reaction.

Ammonia is one of the world's most highly produced chemicals, with worldwide production in 2006 totalling 122 megatonnes, according to the US Geological Survey. Field said that the industrial process of reducing nitrogen to ammonia requires high temperatures and pressures. 'If we get a better handle on understanding the reduction of dinitrogen and the key intermediates involved, this may lead to development of better catalysts and milder reaction conditions than are currently used,' he said.

Danièle Gibney