Abstracts 2001

Abstract of Publication No. 386

Ralph Schenker, Stephan Heer, Hans U. Güdel and Høgni Weihe
Optical Dimer Excitations and Exchange Parameters in (Et4N)3Cr2F9: First Observation of the 4A2 2A1 Transition
Inorg. Chem. 40, 1482-1488 (2001)      Full Text (PDF)      DOI-Link     

Abstract: The synthesis, crystal growth, and polarized optical absorption spectra in the visible and near-UV of (Et4N)3Cr2F9 are reported. In the energy range 25800-27700 cm–1 the 4A2 2A1 (O notation) ligand field transition can be resolved in detail for the first time in any Cr3+ compound. This allows the determination of the antiferromagnetic ground-state exchange splitting with great accuracy: J = 25.9 cm–1 and j = 0.27 cm–1 using the Hamiltonian H = J(SA·SB) - j(SA·SB)2, where j leads to deviations from the regular Landé pattern. The temperature dependence of the magnetic susceptibility is nicely reproduced by these parameters. A comparison with Cs3Cr2Cl9 and Cs3Cr2Br9 reveals an exponential dependence of the ground-state splitting upon the Cr-Cr distance in the [Cr2X9]3- dimers. This is the result of a dominant s-type orbital exchange pathway along the Cr-Cr axis.

Last modified: 13.12.11 by Gabriela Frei