title: Synthesis and characterizations of cyclic octanuclear mixed-valence vanadium(IV,V) clusters with polyoxometalate counterions.
abstract: Hydrothermal reaction of Na2WO4, VOSO4, 2,2'-bpy and H3PO4 has afforded in high yield the compound [V(IV)2V(V)6O14(bpy)8(PO4)2][PW11V(V)O40](bpy).12H2O (1). Compound 1 contains a novel octanuclear mixed valence V(IV,V) cluster, [V(IV)2V(V)6O14(bpy)8(PO4)2]4+, with [PW11V(V)O40]4- as counterion. In the vanadium cluster, four V(V) centers are localized and the remaining two V(IV) and two V(V) ions are disordered over four crystallographically equivalent positions. The isostructural compound [V(IV)2V(V)6O14(bpy)8(PO4)2][PMo11V(V)O40](bpy).3H2O (2) has also been synthesized. Thermodiffractometry experiments indicate that 2 is stable up to 360 degrees C. Redox activities for both the vanadium and molybdenum centers have been observed by solid-state electrochemical measurements performed on mechanically attached microparticles of 2. Magnetic measurements performed on have shown the occurrence of weak ferromagnetic interactions between the V(IV) centres (J = +0.34 cm(-1), H(ex) = -JS1 x S2), and combined with DFT calculations, have allowed to propose a localization of the two V(IV) centers on two of the four equivalent crystallographic sites. Finally high field electron paramagnetic resonance has evidenced the magnetic axial anisotropy of the paramagnetic centers (g(x) = g(y) = 1.975(3); g(z) = 1.939(4)).
authors.affiliation: Institut Lavoisier, UMR 8180, Université de Versailles Saint-Quentin, 45 Avenue des Etats-Unis, 78035, Versailles Cedex, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Lisnard
authors.forename: Anne
authors.initials: A
authors.lastname: Dolbecq
authors.forename: Pierre
authors.initials: P
authors.lastname: Mialane
authors.forename: Jérôme
authors.initials: J
authors.lastname: Marrot
authors.forename: Eric
authors.initials: E
authors.lastname: Rivière
authors.forename: Serguei A
authors.initials: SA
authors.lastname: Borshch
authors.forename: Sébastien
authors.initials: S
authors.lastname: Petit
authors.forename: Vincent
authors.initials: V
authors.lastname: Robert
authors.forename: Carole
authors.initials: C
authors.lastname: Duboc
authors.forename: Timothy
authors.initials: T
authors.lastname: McCormac
authors.forename: Francis
authors.initials: F
authors.lastname: Sécheresse
mesh_terms: D018360:Crystallography, X-Ray; D004563:Electrochemistry; D008280:Magnetics; D008956:Models, Chemical; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D013696:Temperature; D017973:Tungsten Compounds / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D017973:Tungsten Compounds; D014639:Vanadium