Stable iminonitroxide biradicals: Building blocks for organic heterospin, heteromolecular complexes

A stable cationic biradical has been designed and synthesized, and its magnetic property and crystal structure have been examined. An iminonitroxide derivative of 3,5-disubstituted pyridine (1) with a triplet ground state has been cationized by a reaction with methyl trifluoromethanesulfonate (MeTfO), which gave a salt of N-methylated pyridinium 2+, 2+ · TfO−. The ground state of the cation 2+ has been found to be triplet with 2J/kB = 7.5 K from magnetic susceptibility measurements for 2+ · TfO− in a magnetically diluted organic matrix. The magnetic susceptibility of neat crystalline solids of 2+ · TfO− has been explained by an exchange coupling model based on the X-ray crystal structure. It is well known that the energy preference for a high-spin ground state for a m-phenylene coupling unit is disturbed by heteroatomic substitution and an ionic charge. The present experimental results show that the high-spin preference in 1 is little affected by the ionic charge in 2+. The ground-state triplet biradical serves as building blocks for molecule-based magnets of S > 1/2 of molecular assemblages based on electrostatic interactions between molecular ions.

A salt of radical-substituted pyridinium triflate 2+ · TfO− has been synthesized. The cationic biradical 2+ has been found to have a triplet ground state from magnetic susceptibility measurements. The ground-state triplet biradical serves as a building block for molecule-based magnets of S > 1/2 based on intermolecular noncovalent bonding architecture.Figure optionsDownload as PowerPoint slide