Room Temperature Magnetic Switchability Assisted by Hysteretic Valence Tautomerism in a Layered Two-Dimensional Manganese-Radical Coordination Framework.

The manganese-nitronyl-nitroxide two-dimensional coordination polymer {[Mn(NITIm)]ClO} (1) (NITImH = 2-(2-imidazolyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-3-oxide-1-oxyl) undergoes an unusual hysteretic thermo-induced valence tautomeric transition near room temperature, during which the manganese(II) ions are oxidized to manganese(III) and two of the three deprotonated radicals (NITIm) are reduced to their diamagnetic aminoxyl form (denoted NIT). Upon cooling, the high-temperature species {[Mn(NITIm)]ClO} (1) turns into the low-temperature species {[Mn(NIT)(NITIm)]ClO} (1) around 274 K, while on heating the process is reversed at about 287 K. This valence tautomeric phenomenon is supported by temperature-dependent magnetic susceptibility measurements, differential scanning calorimetry (DSC), crystal structure determination, UV-vis absorption, X-ray absorption (XAS), and emission (XES) and electron paramagnetic resonance (EPR) spectroscopies in the solid state.