title: Guest-, Light- and Thermally-Modulated Spin Crossover in [Fe(II) 2 ] Supramolecular Helicates.
abstract: A new bis(pyrazolylpyridine) ligand (H2 L) has been prepared to form functional [Fe2 (H2 L)3 ](4+) metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅xCH3 OH (1, x=5.7 and X=Cl; 2, x=4 and X=Br), X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅yCH3 OH⋅H2 O (1 a, y=3 and X=Cl; 2 a, y=1 and X=Br) and X@[Fe2 (H2 L)3 ](I3 )2 ⋅3 Et2 O (1 b, X=Cl; 2 b, X=Br). Their structure and functional properties are described in detail by single-crystal X-ray diffraction experiments at several temperatures. Helicates 1 a and 2 a are obtained from 1 and 2, respectively, by a single-crystal-to-single-crystal mechanism. The three possible magnetic states, [LS-LS], [LS-HS], and [HS-HS] can be accessed over large temperature ranges as a result of the structural nonequivalence of the Fe(II) centers. The nature of the guest (Cl(-) vs. Br(-) ) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS-HS] or [HS-HS] states are generated through irradiation. All helicates (X@[Fe2 (H2 L)3 ])(3+) persist in solution.
authors.affiliation: Departement de Inorgánica, Universitat de Barcelona, Diagonal 645, 08028, Barcelona, Spain.
authors.forename: Mohanad
authors.initials: M
authors.lastname: Darawsheh
authors.affiliation: Departement de Inorgánica, Universitat de Barcelona, Diagonal 645, 08028, Barcelona, Spain.
authors.forename: Leoni A
authors.initials: LA
authors.lastname: Barrios
authors.affiliation: Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC and Universidad de Zaragoza, Plaza San Francisco s/n, 50009, Zaragoza, Spain. roubeau@unizar.es.
authors.forename: Olivier
authors.initials: O
authors.lastname: Roubeau
authors.affiliation: Advanced Light Source, Berkeley Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Teat
authors.affiliation: Departement de Inorgánica, Universitat de Barcelona, Diagonal 645, 08028, Barcelona, Spain. guillem.aromi@qi.ub.es.
authors.forename: Guillem
authors.initials: G
authors.lastname: Aromí
keywords: coordination chemistry; crystallography; iron(II) helicates; spin crossover; supramolecular chemistry