Pyridyl-Substituted Nitronyl Nitroxides: Comprehensive Magnetochemical and Quantum Chemical Study.

A series of pyridyl-substituted nitronyl nitroxides was synthesized and structurally characterized. A comprehensive magnetochemical and quantum chemical study of extended raw of the nitroxides with different substituents R in the pyridine fragment was performed. It was shown, that temperature-dependent magnetic properties are determined by the short contacts between nitroxide groups of adjacent molecules as well as between nitroxide group and methyl substituents in the pseudo axial positions of imidazoline fragments. Quantum chemistry allows to select the appropriate model of exchange cluster for analysis of experimental magnetic data and evaluation of the exchange interaction parameters. For NN-Py the "order-disorder" transition was detected by means of low temperature XRD. The difference in the experimental and calculated exchange interaction energies may serve as an indicator of temperature-induced structural rearrangements. For instance, for methyl substituted nitronyl nitroxide NN-Py structural transformations and significant changes in exchange interaction energies were observed.