Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.33: Poster

Samstag, 5. März 2005, 11:00–16:30, Poster TU C

Structural and magnetic investigations on new molecular quantum rings — •Volodymyr Pashchenko¹, Michael Lang¹, Bernd Wolf¹, Larisa Zherlitsina², Norbert Auner², Olga Shchegolikhina³, and Yulia Pozdniakova³ — ¹Physikalisches Institut, J.W. Goethe-Universität, FOR 412, 60054 Frankfurt(M), Germany — ²Institut für Anorganische Chemie, J.W. Goethe-Universität, 60439 Frankfurt(M), Germany — ³A.N. Nesmeyanov Institute of Organoelement Compounds (INEOS), 28 Vavilov Str., 117813 Moscow, Russia

Three oxygen-bridged polynuclear Cu(II) (N=6,8,10) cyclosiloxanolate complexes, [Cu₆(MeSiO₂)₁₂]·6DMF, {[Cu₈(MeSiO₂)₁₆]·8DMF}·EtOH and {[Cu₁₀(MeSiO₂)₂₀]·10DMF}·6DMF, have been synthesized and characterized structurally and magnetically. All three molecule-based complexes exhibit a similar structure consisting of rings of N=6, 8 or 10 Cu(II) atoms sandwiched by two N-membered cyclomethylsiloxanolate ligands. Within the rings, adjacent Cu²⁺ ions are linked by pairs of siloxanolate oxygen atoms which provide the magnetic exchange path for the Cu(II) S=1/2 spins. A detailed analysis of the magnetic properties reveals a strong ferromagnetic Cu-Cu exchange interaction (J/k_B=−62 K) for the N=6 compound with an S=3 high-spin ground state, a moderately strong ferromagnetic interaction (J/k_B=−27.6 K) for N=8 and an antiferromagnetic interaction (J/k_B=+17.2 K) with a nonmagnetic S=0 ground state for N=10. These results together with structural investigations enable to correlate structural parameters such as the Cu-O-Cu bridging angle with the sign and strength of the magnetic exchange coupling J.