First observation of hidden hysteresis in an Fe(III) spin crossover complex.

Abstract

Molecular magnetic switches are expected to form the functional components of future nanodevices. Herein we combine detailed (photo-) crystallography and magnetic studies to reveal the unusual switching properties of an iron(III) complex, between low (LS) and high (HS) spin states. On cooling, it exhibits a partial thermal conversion associated with a reconstructive phase transition from a [HS-HS] to a [LS-HS] phase with a hysteresis of 25 K. Photoexcitation at low temperature allows access to a [LS-LS] phase, never observed at thermal equilibrium. This work, reporting the first iron(III) spin crossover complex to exhibit reverse-LIESST (light-induced excited spin state trapping), also reveals a hidden hysteresis of 30 K between the hidden [LS-LS] and [HS-LS] phases. It also demonstrates that Fe(III) SCO complexes can be just as effective as Fe(II) systems, and with the advantage of being air-stable, makes them ideally suited for use in molecular electronics.