Synthesis, crystal structure, 57Fe Mossbauer spectroscopy and magnetic properties of high-spin iron(III) anionic complexes [Fe(azp)2]- (H2azp=2,2′- dihydroxyazobenzene) with organic cations

Two new iron(III) complexes, (TrBA)[Fe(azp)(2)] (1) and (TrPA)[Fe(azp)(2)] (2) (H(2)azp = 2,2' - dihydrox-yazobenzene, TrBA = tributylammonium and TrPA = tripropylammonium) were prepared by reaction of the azo dye H(2)azp, tributylamine (or tripropylamine) and FeCl3 in methanolic solution. The crystal structure of 1 was determined by single-crystal X-ray analysis. The asymmetric unit contains one tributylamonnium cation and one [Fe(azp)(2)](-) anion with an octahedrally coordinated Fe(III) ion with an FeN2O4 chromophore - the tridentate ligand azp(2-) is coordinated by two deprotonated phenolic oxygen atoms and one nitrogen atom from the azo group. The single-crystal X-ray analysis of 1 suggests that an N-H center dot center dot center dot O hydrogen bonding interaction between the TrBA cation and the [Fe(azp)(2)](-) anion may induce distortion of the coordination polyhedron resulting in a highspin complex. Magnetic investigation (DC magnetic data) revealed a high-spin state in the studied temperature range (2-300 K) for both 1 and 2. AC susceptibility measurements for 1 showed a field-induced slow relaxation of magnetization with an atypical temperature dependence of the relaxation time. Moreover, the cryogenic and room temperature Fe-57 Mossbauer spectroscopy parameters confirmed the high-spin state of 1. The study was also supported by theoretical calculations at the DFT level of theory.