Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.5: Poster

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

S=1 ground state in a hexacopper(II) molecular complex — •Volodymyr Pashchenko¹, Michael Lang¹, Bernd Wolf¹, Bernhard Brendel¹, Norbert Auner², Olga Shchegolikhina³, and Yulia Molodtsova³ — 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

We report on an experimental determination by ESR of the molecular ground state in a hexacopper(II) siloxanolate compound. This system is distinct in that the six Cu²⁺ ions within the molecule are arranged in two almost parallel, linear trimers. According to magnetic measurements, the individual trimers couple antiferromagnetically with the dominant intratrimer exchange of J/k_B=85 K, yielding a spin-1/2 ground state at low temperatures. The weak intertrimer interactions of J′/k_B=−3 K appear to favor a ferromagnetic ground state for the molecules, with weak antiferromagnetic interactions between the molecules. Our low temperature single crystal ESR study clearly demonstrates that the molecular ground state of the complex is a triplet-singlet state, which is typical for an effective S=1 spin state. The data have been fitted by using the solutions of the spin Hamiltonian Ĥ=DS_z²+E(S_x²−S_y²)+µ_BĝBS with the parameters D=−0.30 cm⁻¹, E=−0.12 cm⁻¹, g_x=g_y=g_z=2.00±0.05. It was found that the progressive formation of the molecular S=1 ground state occurs only below 40 K when the excited doublet and quartet states of individual trimers become completely thermally depopulated.