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Magnetic Anisotropy of Cr(III) Ions in Polymeric Oxalate Complexes as Revealed by HF-ESR Spectroscopy

Research paper by Dijana Žilić, Lidija Androš, Yulia Krupskaya, Vladislav Kataev, Bernd Büchner

Indexed on: 13 Jan '15Published on: 13 Jan '15Published in: Applied Magnetic Resonance



Abstract

Two new Cr(III) paramagnetic polymeric complexes: {[CaCr2(phen)2(C2O4)4]·0.33H2O}n (CrPhen) and {[CaCr2(bpy)2(C2O4)4]·0.83H2O}n (CrBpy), where phen = 1,10-phenanthroline and bpy = 2,2\('\)-bipyridine, have been studied by high-field high-frequency electron spin resonance (HF-ESR) spectroscopy. From the oriented powder spectra, recorded in the frequency range 83–332 GHz in magnetic fields up to 16 T, the spin-Hamiltonian parameters, \(g\), \(D\) and \(E\), have been obtained. Both chromium complexes have a small negative (easy axis) magnetic anisotropy \(|D|<1\) K. CrPhen complex is biaxial, i.e., besides axial \(D\), there is also significant rhombic zero-field splitting (ZFS) parameter, \(E\). Contrary to CrPhen, CrBpy complex is uniaxial, but described by two sets of axial ZFS parameters. Despite very similar crystallographic structures of both complexes, HF-ESR spectroscopy resolved the existence of two magnetically inequivalent Cr(III) ions in CrBpy complex. The results fully support the earlier X-ray, SQUID magnetization and powder X-band ESR studies.