engleski

HF-ESR study of Cr(III) polymeric oxalate complexes

Commercial electron spin resonance ESR spectrometers (X-band) are not appropriate for investigation of the transition metal complexes with spin S > 1/2. In order to obtain the spin Hamiltonian parameters in these systems: g-tensor, D-tensor (zero-field splitting) and A-tensor (hyperfine splitting), it is necessary to have spectrometers that operate in high magnetic fields and at high frequencies (High Field-High Frequency ESR, HF-ESR). Among a large number of new compounds, oxalate complexes of transition metals are interesting because of high efficiency of oxalate bridge (C2O42–) in transmission of exchange interaction between metal ions. Two new polymeric oxalate complexes: {; ; ; ; [CaCr2(phen)2(C2O4)4]•0.33H2O}; ; ; ; n (CrPhen) and {; ; ; ; [CaCr2(bpy)2(C2O4)4]•0.83H2O}; ; ; ; n (CrBpy) are presented. [1, 2] Mononuclear [Cr(N-ligand)(C2O4)2]− anions are bridged by calcium ions, and altogether form infinite, neutral heterobimetallic (chromium and calcium) double zigzag chains. Magnetic susceptibility study showed that both polymeric complexes are paramagnetic i.e. no exchange interaction between chromium spins S = 3/2 were detected. At low temperatures (T < 20 K) the susceptibility deviates from the Curie law, due to existence of the small magnetic anisotropy of Cr(III) ion. Here, detailed HF-ESR investigation ( = 83–332 GHz, B = 0 –16 T) of the anisotropy and determination of spin-Hamiltonian parameters of CrPhen and CrBpy complexes are presented.[3] Despite very similar crystallographic structures, HF-ESR spectroscopy resolved remarkably different magnetic anisotropies of Cr(III) ions in the investigated complexes.[3] References: 1. L. Androš, M. Jurić, J. Popović, D. Pajić, K. Zadro, K. Molčanov, D. Žilić, P. Planinić, submitted in Inorg. Chem. (2014) 2. L. Androš, M. Jurić, K. Molčanov, P. Planinić, Dalton Trans. 41, 14611 (2012) 3. D. Žilić. L. Androš, Y. Krupskaya, V. Kataev, B. Büchner, manuscript in preparation (2014)

HF-ESR; Cr complexes; spin hamiltonian parameters

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