Département de chimie moléculaire

The manganese-nitronyl-nitroxide two-dimensional coordination polymer {\{}[Mn2(NITIm)3]ClO4{\}}n (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 temp., 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 NITRed2-). Upon cooling, the high-temp. species {\{}[MnII2(NITIm)3]ClO4{\}}n (1HT) turns into the low-temp. species {\{}[MnIII2(NITRed)2(NITIm)]ClO4{\}}n (1LT) around 274 K, while on heating the process is reversed at ∼287 K. This valence tautomeric phenomenon is supported by temp.-dependent magnetic susceptibility measurements, DSC, crystal structure detn., UV-visible absorption, x-ray absorption (XAS), and emission (XES) and EPR spectroscopies in the solid state. [on SciFinder(R)]