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MA: Magnetismus
MA 21: Bio- und molekularer Magnetismus
MA 21.6: Vortrag
Donnerstag, 11. März 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 Knorr3 — 1Physikalisches 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.