title: From antiferromagnetic to ferromagnetic exchange in a family of oxime-based Mn(III) dimers: a magneto-structural study.
abstract: The reaction of Mn(ClO4)2·6H2O, a derivatised phenolic oxime (R-saoH2) and the ligand tris(2-pyridylmethyl)amine (tpa) in a basic alcoholic solution leads to the formation of a family of cluster compounds of general formula [Mn(III)2O(R-sao)(tpa)2](ClO4)2 (1, R = H; 2, R = Me; 3, R = Et; 4, R = Ph). The structure is that of a simple, albeit asymmetric, dimer of two Mn(III) ions bridged through one μ-O(2-) ion and the -N-O- moiety of the phenolic oxime. Magnetometry reveals that the exchange interaction between the two Mn(III) ions in complexes 1, 3 and 4 is antiferromagnetic, but that for complex 2 is ferromagnetic. A theoretically developed magneto-structural correlation reveals that the dominant structural parameter influencing the sign and magnitude of the pairwise interaction is the dihedral Mn-O-N-Mn (torsion) angle. A linear correlation is found, with the magnitude of J varying significantly as the dihedral angle is altered. As the torsion angle increases the AF exchange decreases, matching the experimentally determined data. DFT calculations reveal that the dyz|π*|dyz interaction decreases as the dihedral angle increases leading to ferromagnetic coupling at larger angles.
authors.affiliation: EaStCHEM School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK. ebrechin@staffmail.ed.ac.uk.
authors.forename: Wdeson P
authors.initials: WP
authors.lastname: Barros
authors.forename: Ross
authors.initials: R
authors.lastname: Inglis
authors.forename: Gary S
authors.initials: GS
authors.lastname: Nichol
authors.forename: Thayalan
authors.initials: T
authors.lastname: Rajeshkumar
authors.forename: Gopalan
authors.initials: G
authors.lastname: Rajaraman
authors.forename: Stergios
authors.initials: S
authors.lastname: Piligkos
authors.forename: Humberto O
authors.initials: HO
authors.lastname: Stumpf
authors.forename: Euan K
authors.initials: EK
authors.lastname: Brechin