engleski

CW-EPR study on a heterometallic (Ni2+ and Cr3+) complex

A powder sample and a single crystal of the heterometallic complex [Ni(bpy)3]2[Cr(C2O4)3]NO3∙ 10H2O, where bpy stands for 2, 2'-bipyridine, have been studied by continuous wave electron paramagnetic resonance (CW-EPR) at the microwave frequency ν ≈ 9.6 GHz. The crystal was rotated round three arbitrary, mutually perpendicular axes and EPR spectra were recorded from room to low temperatures (300-5 K). In the complex investigated, two paramagnetic species are present: Ni2+ with the spin S = 1 and Cr3+ with S = 3/2. In the frequency range examined, there was no evidence for the Ni2+ species, through the whole investigated range of temperature. Only the transition for the Cr3+ species has been observed. By using Bruker XSophe software, a powder simulation has been obtained and from the single-crystal measurements, with the spin-Hamiltonian approach, the following parameters for Cr3+ have been deduced: , cm-1, cm-1 and , where ρ is the angle between the magnetic z axis and the crystallographic b axis. The obtained EPR parameters exhibit nearly the same values at room and low temperatures confirming the absence of significant antiferromagnetic or ferromagnetic coupling. Non-appearance of Ni2+ spectrum in this experiment could be explained by the high value of its zero-field splitting parameter D or by the relaxation phenomena.

Heterometallic complexes; Nickel complexes; Chromium complexes; EPR

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