title: 1,2,3-triazolate-bridged tetradecametallic transition metal clusters [M14(L)6O6(OMe)18X6] (M=FeIII, CrIII and VIII/IV) and related compounds: ground-state spins ranging from S=0 to S=25 and spin-enhanced magnetocaloric effect.
abstract: We report the synthesis, by solvothermal methods, of the tetradecametallic cluster complexes [M14(L)6O6(OMe)18Cl6] (M=FeIII, CrIII) and [V14(L)6O6(OMe)18Cl6-xOx] (L=anion of 1,2,3-triazole or derivative). Crystal structure data are reported for the {M14} complexes [Fe14(C2H2N3)6O6(OMe)18Cl6], [Cr14(bta)6O6(OMe)18Cl6] (btaH=benzotriazole), [V14O6(Me2bta)6(OMe)18Cl6-xOx] [Me2btaH=5,6-Me2-benzotriazole; eight metal sites are VIII, the remainder are disordered between {VIII-Cl}2+ and {VIV=O}2+] and for the distorted [FeIII14O9(OH)(OMe)8(bta)7(MeOH)5(H2O)Cl8] structure that results from non-solvothermal synthetic methods, highlighting the importance of temperature regime in cluster synthesis. Magnetic studies reveal the {Fe14} complexes to have ground state electronic spins of S<or=25, among the highest known, while in contrast the {Cr14} complex has an S=0 ground state despite having a very similar structure and all complexes being dominated by intramolecular antiferromagnetic exchange interactions. The {Fe14} complexes undergo a magnetic phase transition to long-range ordering at relatively high temperatures for molecular species, which are governed by the steric bulk of the triazole (TN=1.8 and 3.4 K for L=bta- and H2C2N3-, respectively). The huge spins of the {Fe14} complexes lead to very large magnetocaloric effects (MCE)-the largest known for any material below 10 K-which is further enhanced by spin frustration within the molecules due to the competing antiferromagnetic interactions. The largest MCE is found for [Fe14(C2H2N3)6O6(OMe)18Cl6] with an isothermal magnetic entropy change -DeltaSm of 20.3 J kg-1 K-1 at 6 K for an applied magnetic field change of 0-7 T.
authors.affiliation: School of Chemistry, The University of Manchester, Manchester M13 9PL, UK.
authors.forename: Rachel
authors.initials: R
authors.lastname: Shaw
authors.forename: Rebecca H
authors.initials: RH
authors.lastname: Laye
authors.forename: Leigh F
authors.initials: LF
authors.lastname: Jones
authors.forename: David M
authors.initials: DM
authors.lastname: Low
authors.forename: Caytie
authors.initials: C
authors.lastname: Talbot-Eeckelaers
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wei
authors.forename: Constantinos J
authors.initials: CJ
authors.lastname: Milios
authors.forename: Simon
authors.initials: S
authors.lastname: Teat
authors.forename: Madeleine
authors.initials: M
authors.lastname: Helliwell
authors.forename: James
authors.initials: J
authors.lastname: Raftery
authors.forename: Marco
authors.initials: M
authors.lastname: Evangelisti
authors.forename: Marco
authors.initials: M
authors.lastname: Affronte
authors.forename: David
authors.initials: D
authors.lastname: Collison
authors.forename: Euan K
authors.initials: EK
authors.lastname: Brechin
authors.forename: Eric J L
authors.initials: EJ
authors.lastname: McInnes
mesh_terms: D002857:Chromium / Q000737:chemistry; D004583:Electrons; D007501:Iron / Q000737:chemistry; D008024:Ligands; D008280:Magnetics; D009942:Organometallic Compounds / Q000737:chemistry*; D013696:Temperature; D028561:Transition Elements / Q000737:chemistry*; D014230:Triazoles / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D028561:Transition Elements; D014230:Triazoles; D014639:Vanadium; D002857:Chromium; D007501:Iron