Polarization Switching from Valence Trapping in an Oxo-Bridged Trinuclear Iron Complex.

Switching electric polarization by external stimuli constitutes a technical foundation for various applications. Here, we reported the observation of polarization-switching behavior in an oxo-bridged mixed-valence complex [Fe3O(piv)6(py)3] (piv = pivalate, py = pyridine). Detailed variable-temperature Mössbauer spectral analyses unambiguously confirm the occurrence of an electron localization-delocalization transition between two inequivalent Fe sites. Given that the compound crystallizes in a polar space group, the change in the molecular dipole moments leads to a pyroelectric effect observed during this transition, indicating thermally induced polarization switching behavior. As the complex exhibits asymmetry in the valence-active sites and antiferromagnetic interaction between them, the possibility of magnetoelectric coupling in this compound is also discussed on the basis of the recent prediction of polarization switching through modulating the degree of electron delocalization by magnetic fields in the mixed-valence systems.