title: Varying spin state composition by the choice of capping ligand in a family of molecular chains: detailed analysis of magnetic properties of chromium(III) horseshoes.
abstract: We report a detailed physical analysis on a family of isolated, antiferro-magnetically (AF) coupled, chromium(III) finite chains, of general formula (Cr(RCO(2))(2)F)(n) where the chain length n = 6 or 7. Additionally, the chains are capped with a selection of possible terminating ligands, including hfac (= l,l,l,5,5,5-hexafluoropentane-2,4-dionate(l-)), acac (= pentane-2,4-dionate(l-)) or (F)(3). Measurements by inelastic neutron scattering (INS), magnetometery and electron paramagnetic resonance (EPR) spectroscopy have been used to study how the electronic properties are affected by n and capping ligand type. These comparisons allowed the subtle electronic effects the choice of capping ligand makes for odd member spin 3/2 ground state and even membered spin 0 ground state chains to be investigated. For this investigation full characterisation of physical properties have been performed with spin Hamiltonian parameterisation, including the determination of Heisenberg exchange coupling constants and single ion axial and rhombic anisotropy. We reveal how the quantum spin energy levels of odd or even membered chains can be modified by the type of capping ligand terminating the chain. Choice of capping ligands enables Cr-Cr exchange coupling to be adjusted by 0, 4 or 24%, relative to Cr-Cr exchange coupling within the body of the chain, by the substitution of hfac, acac or (F)(3) capping ligands to the ends of the chain, respectively. The manipulation of quantum spin levels via ligands which play no role in super-exchange, is of general interest to the practise of spin Hamilton modelling, where such second order effects are generally not considered of relevance to magnetic properties.
authors.affiliation: School of Chemistry, The University of Manchester, Oxford Road, Manchester, UK M13 9PL. baker@ill.fr
authors.forename: Michael L
authors.initials: ML
authors.lastname: Baker
authors.forename: Alberto
authors.initials: A
authors.lastname: Bianchi
authors.forename: Stefano
authors.initials: S
authors.lastname: Carretta
authors.forename: David
authors.initials: D
authors.lastname: Collison
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Docherty
authors.forename: Eric J L
authors.initials: EJ
authors.lastname: McLnnes
authors.forename: Andrew
authors.initials: A
authors.lastname: McRobbie
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Muryn
authors.forename: Hannu
authors.initials: H
authors.lastname: Mutka
authors.forename: Stergios
authors.initials: S
authors.lastname: Piligkos
authors.forename: Marzio
authors.initials: M
authors.lastname: Rancan
authors.forename: Paolo
authors.initials: P
authors.lastname: Santini
authors.forename: Grigore A
authors.initials: GA
authors.lastname: Timco
authors.forename: Philip L W
authors.initials: PL
authors.lastname: Tregenna-Piggott
authors.forename: Floriana
authors.initials: F
authors.lastname: Tuna
authors.forename: Hans U
authors.initials: HU
authors.lastname: Güdel
authors.forename: Richard E P
authors.initials: RE
authors.lastname: Winpenny