title: Chromium(III) stars and butterflies: synthesis, structural and magnetic studies of tetrametallic clusters.
abstract: We report the synthesis, structures and magnetic properties of a series of chromium(III) metal-centered triangle (or "star") clusters, [Cr(4){RC(CH(2)O)(3)}(2)(4,4'-R'(2)-bipy)(3)Cl(6)] [R = Et, R' = H (2); R = HOCH(2), R' = H (3); R = Et, R' = (t)Bu (4)], prepared by two-step solvothermal reactions starting from [CrCl(3)(thf)(3)]. The product of the first stage of this reaction is the salt [Cr(bipy)(2)Cl(2)](2)[Cr(2)Cl(8)(MeCN)(2)] (1). In the absence of the diimine, a different family of tetrametallics is isolated: the butterfly complexes [Cr(4){EtC(CH(2)O)(3)}(2){NH(C(R)NH)(2)}(2)Cl(6)] (R = Me (5), Et (6), Ph (7)] where the chelating N-acetimidoylacetamidine NH(C(R)=NH)(2) ligands are formed in situ via condensation of the nitrile solvents (RCN) under solvothermal conditions. Magnetic measurements show the chromium stars to have an isolated S = 3 ground state, arising from antiferromagnetic coupling between the central and peripheral metal ions, analogous to the well-known Fe(III) stars. Bulk antiferromagnetic ordering is observed at 0.6 K. The butterfly complexes have a singlet ground state, with a low-lying S = 1 first excited state, due to dominant wing-body antiferromagnetic coupling.
authors.affiliation: School of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
authors.forename: Luke J
authors.initials: LJ
authors.lastname: Batchelor
authors.forename: Mario
authors.initials: M
authors.lastname: Sander
authors.forename: Floriana
authors.initials: F
authors.lastname: Tuna
authors.forename: Madeleine
authors.initials: M
authors.lastname: Helliwell
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Moro
authors.forename: Joris
authors.initials: J
authors.lastname: van Slageren
authors.forename: Enrique
authors.initials: E
authors.lastname: Burzurí
authors.forename: Oscar
authors.initials: O
authors.lastname: Montero
authors.forename: Marco
authors.initials: M
authors.lastname: Evangelisti
authors.forename: Fernando
authors.initials: F
authors.lastname: Luis
authors.forename: Eric J L
authors.initials: EJ
authors.lastname: McInnes