Magnetic properties of the mononuclear iron (III) complexes with biphenyl-disubstituted Schiff base ligand: EPR and SQUID study

The magnetic features of the mononuclear iron (III) complexes [Fe(L)(2)]X-+(-) with tridentate Schiff base ligands [where L is 4-(4-diphenylcarboxy)-2 '-oxysalicylidene-N '-ethylene-N-ethylene-2 '-amine-(carboxy-4-diphenyl) and X- = Cl- (1), PF6- (2) and NO3- (3) counter-ions] have been studied by electron paramagnetic resonance (EPR) spectroscopy, SQUID (superconducting quantum interference device) magnetometry (solid), and Evans H-1 nuclear magnetic resonance method (solution). EPR established that compounds (1) and (2) consist of two types high-spin (HS, S = 5/2) centers with weak distorted and strong low-symmetry octahedral crystal fields. The signals from low-spin centers (LS, S = 1/2) of Fe (III) are observed in the spectra of compounds 2 and 3. SQUID revealed permanent HS behavior in (1) and mixed LS + HS in (2), (3) in wide temperature range, while solution method-only HS. Magnetic measurements allowed to estimate part of HS and LS fractions and detected antiferromagnetic exchange interactions between the neighboring Fe (III) ions in complexes."