title: A family of ferro- and antiferromagnetically coupled decametallic chromium(III) wheels.
abstract: The synthesis and crystal structures of a family of decametallic Cr(III) "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 CrCr 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 Cr(III) 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.
authors.affiliation: School of Chemistry, The University of Manchester, Manchester M13 9PL, UK.
authors.forename: David M
authors.initials: DM
authors.lastname: Low
authors.forename: Gopalan
authors.initials: G
authors.lastname: Rajaraman
authors.forename: Madeleine
authors.initials: M
authors.lastname: Helliwell
authors.forename: Grigore
authors.initials: G
authors.lastname: Timco
authors.forename: Joris
authors.initials: J
authors.lastname: van Slageren
authors.forename: Roberta
authors.initials: R
authors.lastname: Sessoli
authors.forename: Stefan T
authors.initials: ST
authors.lastname: Ochsenbein
authors.forename: Roland
authors.initials: R
authors.lastname: Bircher
authors.forename: Christopher
authors.initials: C
authors.lastname: Dobe
authors.forename: Oliver
authors.initials: O
authors.lastname: Waldmann
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Güdel
authors.forename: Mark A
authors.initials: MA
authors.lastname: Adams
authors.forename: Eliseo
authors.initials: E
authors.lastname: Ruiz
authors.forename: Santiago
authors.initials: S
authors.lastname: Alvarez
authors.forename: Eric J L
authors.initials: EJ
authors.lastname: McInnes