Nitric oxide (NO) reactivity studies on mononuclear iron(ii) complexes supported by a tetradentate Schiff base ligand

Abstract

Mononuclear high-spin [Fe^II(Gimpy)(Cl)₂], (1) and low-spin [Fe^II(Gimpy)(CN)₂]·3H₂O, (2·3H₂O) complexes, where; Gimpy: (1,2-bis(2-phenyl-2-(pyridin-2-yl)hydrazono)ethane), were synthesized and characterized by various analytical and spectral techniques. The NO reactivity of complex 2·3H₂O via acidified nitrite solution gave rise to a mixture of two different complexes; a ligand nitrated unsymmetrical complex [Fe(Gimpy-NO₂)(CN)₂]·CH₂Cl₂, (3·CH₂Cl₂) via electrophilic route as well as nitrosylation at the metal centre, formation of unstable complex [Fe(Gimpy)(NO)(CN)]²⁺, (4). Formation of unstable complex 4 was monitored via visual colour change from purple to brownish-red and evidence of this complex has been established by means of in situ IR, ESI-MS and UV-visible spectral studies. In addition, the structures of complexes 2·3H₂O and 3·CH₂Cl₂ have been established unambiguously through single crystal X-ray diffraction analysis. Interestingly, after nitration of imine proton twisting of one phenyl ring (near to –NO₂ group) in complex 3 was obtained, leading to an unsymmetrical complex 3 (nitration of one imine proton only is supported by theoretical studies), possibly due to steric hindrance of –NO₂ group and results of electrochemical studies of all complexes (1–3) were also examined.