Dinuclear diazene iron and ruthenium complexes as models for studying nitrogenase activity.

The strength of hydrogen bonds has been investigated in various dinuclear diazene FeII, FeIII, and RuII complexes by use of the recently developed shared-electron number approach. Hydrogen bonding in these compounds plays an essential role in view of designing a model system for nitrogenase activity. The general conclusions for iron-sulfur complexes are: hydrogen bonds can stabilize diazene by at least 20% of the total coordination energy; the strength of the hydrogen bonds can be directly controlled through the hydrogen-sulfur bond length; reducing FeIII centers to FeII can double the hydrogen bond energy.