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Homoleptic versus Heteroleptic Formation of Mononuclear Fe(II) Complexes with Tris-Imine Ligands

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posted on 13.04.2016, 11:34 by Leoní A. Barrios, Carlos Bartual-Murgui, Eugènia Peyrecave-Lleixà, Boris Le Guennic, Simon J. Teat, Olivier Roubeau, Guillem Aromí
We show a marked tendency of Fe­(II) to form heteroleptic [Fe­(L)­(L′)]­(ClO4)2 complexes from pairs of chelating tris-imine 3bpp, tpy, or 2bbp ligands. New synthetic avenues for spin crossover research become thus available, here illustrated with three new heteroleptic compounds with differing magnetic behaviors: [Fe­(H4L1)­(Cl-tpy)]­(ClO4)2·C3H6O (1), [Fe­(H2L3)­(Me3bpp)]­(ClO4)2·C3H6O (2), [Fe­(H4L1)­(2bbp)]­(ClO4)2·3C3H6O (3). Structural studies demonstrate that 1 is in the low-spin (LS) state up to 350 K, while complexes 2 and 3 are, by contrast, in the high-spin (HS) state down to 2 K, as corroborated through magnetic susceptibility measurements. Upon exposure to the atmosphere, the latter exhibits the release of three molecules of acetone per complex, turning into the solvent-free analogue [Fe­(H4L1)­(2bbp)]­(ClO4)2 (3a), through a single-crystal-to-single-crystal transformation. This guest extrusion process is accompanied by a spin switch, from HS to LS.

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