Abstracts 2006

Abstract of Publication No. 539

David M. Low, Gopalan Rajaraman, Madeleine Helliwell, Grigore Timco, Joris van Slageren, Roberta Sessoli, Stefan T. Ochsenbein, Roland Bircher, Christopher Dobe, Oliver Waldmann, Hans-Ulrich Güdel, Mark A. Adams, Eliseo Ruiz, Santiago Alvarez and Eric J. L. McInnes
A Family of Ferro- and Antiferromagnetically Coupled Decametallic Chromium(III) Wheels
Chem. Eur. J. 12, 1385-1396 (2006)      Full Text (PDF)      DOI-Link     

Abstract: The synthesis and crystal structures of a family of decametallic CrIII "molecular wheels" are reported, namely [Cr10(OR)20(O2CR’)10] [R’=Me, R=Me (1), Et (2); R’=Et, R=Me (3), Et (4); R’=CMe3, R=Me (5), Et (6)]. Magnetic studies on 1-6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R’) the nearest neighbour Cr···Cr magnetic exchange coupling is more antiferromagnetic for the ethoxide-bridged (R=Et) cluster than for the methoxide analogue. In complexes 2, 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S=0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high-spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D]1) by inelastic neutron scattering experiments, and these support the S=15 ground state expected for ferromagnetic coupling of ten CrIII ions, and they also indicate that a single J-value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1-6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2, and 5 and 6 are the result of relatively small changes in J that happen to cross J=0, hence changing the sign of J.

Last modified: 13.12.11 by Gabriela Frei