Abstract Reaction of a Ni(II) complex of ligand L (L = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) (1) in methanol with NO2 has been studied. Addition of equivalent amount of NO2 resulted in the reduction of Ni(II) to Ni(I). The reduction was monitored by UV-visible, EPR spectroscopy. The Ni(I) intermediate reacted with further equivalent of NO2 to form Ni(II)-O-nitrito complex, [NiII(L)(η1-ONO)2] (2). Structural characterization confirmed the formation of 2. Subsequent equivalent of NO2 resulted in the oxo transfer from NO2 to the metal bound nitrito group leading to the formation of O-nitrato complex, [NiII(L)(η1-ONO2)]+ (3) with simultaneous release of NO. The release of NO in the reaction was evidenced by spin trapping experiment. Complex 3 was isolated and characterized structurally.