The Electronic Structures of an Isostructural Series of Octahedral Nitrosyliron Complexes {Fe−NO}6,7,8 Elucidated by Mössbauer Spectroscopy

From the reaction of cis-[(cyclam)FeIII(Cl)2]Cl (cyclam = 1,4,8,11-tetraazacyclotetradecane) with hydroxylamine in water the octahedral nitrosyliron complexes trans-[(cyclam)Fe(NO)Cl](ClO4) (1) and cis-[(cyclam)Fe(NO)I]I (2) have been isolated as crystalline solids. EPR spectroscopy and variable-temperature susceptibility measurements established that 1 possesses an S = 1/2 and 2 an S = 3/2 ground state; both species are of the {Fe−NO}7 type. Electrochemically, 1 can be reversibly one-electron oxidized yielding trans-[(cyclam)Fe(NO)Cl]2+, an {Fe−NO}6 species, and one-electron reduced yielding trans-[(cyclam)Fe(NO)Cl]0, an {Fe−NO}8 species. These complexes have been characterized in CH3CN solutions by UV−vis and EPR spectroscopy; both possess a singlet ground state. All of these nitrosyliron complexes, including [LFe(NO)(N3)2] (S = 3/2; L = 1,4,7-trimethyl-1,4,7-triazacyclononane) and [L‘Fe(NO)(ONO)(NO2)](ClO4) (S = 0; L‘ = 1,4,7-triazacyclononane), have been studied by variable-temperature Mossbauer spect...