Vibronic Model for Charge Transfer Iinduced by Ax2YAZF

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									         Vibronic Model for Charge Transfer Iinduced
                       Spin-Transitions
         in Pentanuclear {[Os(CN)6]2[Fe(tmphen)2]3}
                      Cluster Compound

      Sergey Ostrovsky1, Andrew Palii1, Sophia Klokishner1, Kim Dunbar2, Boris Tsukerblat3

        1 - Institute of Applied Physics, Academy of Sciences of Moldova, Kishinev, Moldova
         2 - Department of Chemistry, Texas A&M University, College Station, Texas, USA
        3 - Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva, Israel



We present a theoretical microscopic approach to the problem of the charge transfer induced spin
transition in crystals containing cyano-bridged pentanuclear clusters {[Os(CN) 6]2[Fe(tmphen)2]3}
with a trigonal bipyramidal structure. A reversible transition between ls FeII-N≡C-ls OsIII and hs
FeIII-N≡C-ls OsII redox pairs was observed with the change of temperature (ls = low spin, hs =
high spin). The magnetization of those photomagnetic Prussian blue analogues, very low before
irradiation, strongly increases under irradiation by visible light at low temperature. When the light
is switched off, their magnetization remains very high. The compounds are trapped in a metastable
state of long lifetime at low temperature. The low-spin Fe(II)  high-spin Fe(III) transition is
considered as a cooperative phenomenon (phase transition) that is driven by the interaction of the
electronic shells of Fe ions with the full symmetric deformation of the local surronding that is
extended over the crystal lattice via the acoustic phonon field. Due to the proximity of Fe ions in
the clusters, the short-range intracluster interactions between these ions via the optic phonon field
is included as well. The model also takes into consideration the exchange interaction between the
hs-FeIII and ls-OsIII ions. The proposed model explains the temperature dependence of the static
magnetic susceptibility and the Mössbauer spectra of the title compound. The approach described
in this paper represents a theoretical tool for the study of charge transfer induced spin transitions
in systems based on metal clusters.

Financial support of STCU (project N5062) is highly appreciated. B.T. and K.D. gratefully
acknowledge financial support from BSF (grant 2006498). B.T. thanks ISF (grant 168/09) for the
financial support




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