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Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 21: Bio- und molekularer Magnetismus

MA 21.6: Talk

Thursday, March 11, 2004, 11:30–11:45, H22

ESR analysis of the cyclic cluster [Na@Fe6(tea)6]·ClO4·2MeOH — •Ilka Keilhauer1, Bernd Pilawa1, Danira Marinov2, Arthur Grupp3, and Stefan Knorr31Physikalisches Institut, Universität Karlsruhe (TH), D-76128 — 2Anorganische Chemie, LMU, D-81377 München — 32. Physikalisches Institut, Universität Stuttgart,D-70550 Stuttgart

The six FeIII-ions of Na@Fe6(tea)6 (1) are antiferromagnetically coupled. The magnetic anisotropy can be analysed by ESR measurements. The crystal structure of (1) is triclinic with two magnetically nonequivalent Fe6 clusters per unit cell. This gives rise to complicated spectra composed of the resonances of the two clusters X and Y. It will be shown that the splittings of the first excited states S=1,2 and 3 and the orientation of the molecular symmetry axes can be determined for both clusters by the analysis of the ESR spectra taken at 7 K and 20 K. The parameters of the single ion on-site anisotropy are d/kB=−0.2875±0.0023 K and d/kB=−0.2921±0.0035 K, respectively.
The relative angle between the cluster axes of 69.7±1 determined at low temperature deviates considerably from the room temperature value of 54. This might indicate a structural phase transition which can be caused by the temperature dependent motion of the ClO4 tetraeders.

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