Dinitrosyl iron complexes of the type R2Fe(NO)2 play an important role in the storage and transport of nitric oxide, NO, which is a key signaling molecule involved in vasodilation, inflammation, neuron transmission, and immune system response. Researchers in Taiwan have discovered a version of the iron complex that defies conventional wisdom in that it contains NO ligands in two different oxidation states (Inorg. Chem., DOI: 10.1021/ic3018437). When a team led by Wen-Feng Liaw of National Tsing Hua University and Jen-Shiang K. Yu of National Chiao Tung University treated the dithiolate dinitrosyl complex [S(CH2)3S]Fe(NO)2 with NO gas, the researchers observed that two NO molecules replaced the dithiolate ligand. In the product complex, [Fe(NO)4]–, the X-ray crystal structure distinctly shows that two of the NO ligands have significantly longer bonds. With support from computational studies, the team attributes the difference in bond lengths to one pair of NO ligands serving as nitrosyl groups (•NO, nitrogen formally 2+) and one pair serving as nitroxyl groups (NO–, nitrogen formally 1+). The finding could help scientists better understand NO’s physiological actions and lead to advanced medical treatments.