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.
Single functional molecules are regarded as future components of nanoscale spintronic devices. Supramolecular coordination chemistry provides unlimited resources to implement multiple functions to individual molecules. A novel coordination [Fe ] helicate exhibiting spin-crossover is demonstrated to be ideally suited to encapsulate a [Cr(ox) ] complex anion (ox=oxalate), unveiling for the first-time single ion slow relaxation of the magnetization for this metal. A possibility of tuning the dynamics of this relaxation as well as the performance of the Cr center as qubit arises from the observation that metastable high spin Fe centers from the host can be generated by irradiation with green light at low temperature.
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