Preparation and magnetism of the binuclear iron(II) complexes [{Fe(C9H21N3)X2}2](X = NCS, NCO, or N3) and their reaction with NO. Crystal structures of [{Fe(C9H21N3)(NCS)2}2] and [Fe(C9H21N3)(NO)(N3)2

Abstract

Reaction of Fe(ClO4)2·6H2O with N,N′,N′-trimethyl-1,4,7-triazacyclononane (L) in methanol and addition of solid NaSCN, NaOCN, or NaN3 gave yellow compounds of the type [{FeLX2}2](X = NCS, NCO, or N3). [{FeL(NCS)2}2] is a binuclear, neutral complex in the solid state containing two bridging and two terminal thiocyanato ligands as has been shown by X-ray crystallography. Variable-temperature magnetic susceptibility measurements indicate negligible intramolecular spin coupling in [{FeL(NCS)2}2] and [{FeL(NCO)2}2][µeff.(298 K)= 5.4 and 5.35 µB per FeII, respectively]. In [{FeL(N3)2}2] intramolecular antiferromagnetic exchange coupling of high-spin configurated FeII centres is observed (J=–11 cm–1, g= 2.2). [{FeL(NCS)2}2]and [{FeL(N3)2}2}] reacted with NO to yield [FeL(NO)(NCS)2] and [FeL( NO)(N3)2], respectively. [FeL(NO)(N3)2] is a six-co-ordinate neutral complex with a bent Fe–NO group [155.5(10)°]. The structure for [FeL(NO)(N3)2] has been determined. [FeL(NO)(NCS)2] and [FeL(NO)(N3)2] are paramagnetic with magnetic moments of 4.20 and 4.06 µB, between 100 and 293 K indicating three unpaired electrons, respectively. Reaction of [ FeL′Cl3](L′= 1,4,7-triazacyclononane) with NaNO2 in 0.1 dm–3 mol HCl and addition of NaClO4 afforded yellow-brown [FeL′(NO)(NO2)2][ClO4]·2H2O. The cyclic voltammogram of [FeL′(NO)(NO2)2][ClO4]·2H2O in acetonitrile revealed a reversible one-electron transfer (E½=–0.29 V vs. ferrocenium–ferrocene) corresponding to the couple ′{Fe–NO}6–{Fe–NO}7′ and an irreversible reduction wave (E=–1.18 V vs. ferrocenium–ferrocene).