Solvent Effect on the Spin State of an Iron(II)‐Triazole Trimer

Abstract

We report a triazole‐based trinuclear iron(II) compound with bridging 4‐(p‐methylphenyl)‐1,2,4‐triazole ligands with solvatochromic spin crossover (SC) behavior. The magnetic properties of this trimer depend on crystallization solvent molecules. Pink crystals (color suggesting low spin state), showing a triclinic structure can be obtained by slow diffusion of diethyl ether in acetonitrile solution. As in other SC materials, immersion of these crystals in different solvents promote color change. In this case, we have been able to define the microscopic effect of the solvent substitution following the single crystal to single crystal transformation by UV/Vis absorption spectroscopy and X‐ray diffraction. Furthermore, the solvent‐induced switching can be explained by weak intermolecular interactions provoking a variation in the relative orientations of the two aromatic rings in the ligands, which, in turn, determines the ligand field on the central Fe(II), and its SCO behavior. This study brings important details to the origin of solvatochromism in SCO materials, offering alternatives for better control of this switching and, potentially, for their application as colorimetric sensors.

Unlocking room-temperature bistable spin transition at the nanoscale: the synthesis of core@shell [Fe(NH2trz)3(NO3)2]@SiO2 nanoparticles

“…This effect has already been explored in Fe-trz metal complexes and other coordination polymers. 31,32 Unfortunately, this effect could not be properly observed in the SCO@SiO 2 -2, as the compound degraded more…”

Cooperative Spin-State Switching and Vapochromism of Mononuclear Ni(II) Complexes by Pyridine Coordination/Decoordination

“…The development of solid-state systems with magnetic properties dependent on reactions with volatile organic compounds (VOCs) is attracting a lot of attention due to their potential applications as chemical sensors . Spin crossover (SCO) complexes that change due to the interaction between organic solvents or gas molecules and the central metal ion in the complex have been well studied as magnetic sensors, among which Fe­(II)-MOFs (metal–organic frameworks) are attractive because they can be detected both magnetically and visually by causing spin transition between high spin (HS) ( S = 2) and low spin (LS) ( S = 0) . Guest molecules are typically trapped within crystals by weak supramolecular interactions, which are usually unstable and limit the range of operating temperatures as sensors.…”