Iron complexes acting as nitric oxide carriers

A new strategy for NO-carrier synthesis depending on the strength of the ligand field, the configuration of the complex and the oxidation state of the metal is developed. The preparation of the trans- and cis-[Fe(1)(NO)(Cl)]Cl and trans-[Fe(2)(NO)(Cl)]Cl complexes, where 1 is 1,4,8,11-tetraaza-cyclotetradecane or cyclam and 2 is 6,6,13,13-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane, is reported. On the basis of spectroscopic data and PM3(tm) molecular modeling calculations, both species are characterized as complexes of the [FeNO]7 type possessing an S=1/2 and S=3/2 ground state for the trans- and cis-[Fe(1)(NO)(Cl)]Cl, respectively. The cis isomer can act as a NO carrier.