Synthesis, Structures, Spectroscopic and Electrochemical Properties of Dinitrosyl Iron Complexes with Bipyridine, Terpyridine, and 1,10-Phenathroline

Three new dinitrosyl iron complexes LFe(NO)2 (L = 2,2′-bipyridine (bipy) (1), 2,2′,2′′-terpyridine (terpy) (2) and 1,10-phenathroline (phen) (3)) were synthesized by the reaction of Fe(NO)2(CO)2 with corresponding ligands in tetrahydrofuran. Complexes 1−3 were studied using IR, UV−vis, MS, NMR, and electrochemical techniques. Complexes 1 and 2 were also characterized using single crystal X-ray diffraction analysis. IR spectra of complexes 1−3 display two strong characteristic NO stretching frequencies (νNO) in the region reflecting donor properties of the ligands. Cyclic voltammetry studies show two quasi-reversible one-electron reductions for all complexes. Electrochemical investigations using different concentrations show that an irreversible one-electron reduction at −1.85 V for complex 2 and −1.80 V for complex 3 are from solvated species. Single-crystal X-ray structural analysis reveals that complex 1 crystallizes in the triclinic P1̅ space group and the asymmetric unit consists of one Fe(NO)2(bipy) molecule with the two NO groups located on two sides of Fe(bipy) plane. Complex 2 crystallizes in monoclinic P21/n space group, and the asymmetric unit contains one Fe(NO)2(terpy) molecule, in which the NO groups are located on two sides of the plane consisted of Fe and two coordinated pyridyl rings, but almost parallel to the uncoordinated pyridyl ring. The crystal packings of both complexes 1 and 2 show intermolecular H-bonding and strong π−π stacking interactions.