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Valence–Tautomeric Interconversion in a Bis(dioxolene)cobalt Complex with Iminopyridine Functionalized by a TEMPO Moiety. Phase Transition Coupled with Monocrystal Destruction

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journal contribution
posted on 29.11.2017, 12:45 by Alexey A. Zolotukhin, Michael P. Bubnov, Alla V. Arapova, Georgy K. Fukin, Roman V. Rumyantcev, Artem S. Bogomyakov, Alexander V. Knyazev, Vladimir K. Cherkasov
Iminopyridine modified by TEMPO nitroxide was utilized for the synthesis of an octahedral bis­(o-semiquinonato)cobalt complex. Variable-temperature magnetic susceptibility measurements detect a valence tautomeric transformation in the temperature range 200–300 K. A reproducible hysteresis loop of about 40 K width is observed on the magnetic moment temperature dependence in the transition region. Differential scanning calorimetry measurements confirm different temperatures of phase transitions accompanying a valence–tautomeric transformation upon heating and cooling. Attempts to study the structural changes associated with the valence–tautomeric transformation by single-crystal X-ray diffraction failed because of the crystal destruction taking place upon cooling from 220 K. The powder X-ray diffraction pattern indicated an essential change of the unit cell upon cooling from 240 K.