Guest-, light- and thermally-modulated spin crossover in [FeII2] supramolecular helicates

A new bis(pyrazolylpyridine) ligand (HL) has been prepared to form functional [Fe(HL)]metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe(HL)]X(PF)⋅xCHOH (1, x=5.7 and X=Cl; 2, x=4 and X=Br), X@[Fe(HL)]X(PF)⋅yCHOH⋅HO (1 a, y=3 and X=Cl; 2 a, y=1 and X=Br) and X@[Fe(HL)](I)⋅3 EtO (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 Fecenters. The nature of the guest (Clvs. 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@[Fe(HL)])persist in solution.G.A. thanks the Generalitat de Catalunya for the prize ICREA Academia 2008 and 2013 for excellence in research and the ERC for a Starting Grant (258060 FuncMolQIP). The authors thank the Spanish MICINN for funding through CTQ2012-32247 (G.A.,L.A.B.) and MAT2014-53961-R (O.R.). M.D. thanks the Avempace II Erasmus Mundus Action 2 program for a PhD scholarship. The Advanced Light Source is supported by the Directors of the Office of Science and the Office of Basic Energy Sciences of the U. S. Department of Energy under contract no. DE-AC02 -05CH11231.Peer Reviewe