Charged nitronyl nitroxide biradicals as building blocks for molecular ferrimagnetics

A crystal-engineering approach to organic ferrimagnetics is reported. Coulo mbic energy between cationic biradical with S=1 and anionic radical with S= 1/2 is a promising driving force of co-crystallizing the hetero-molecular a ssemblage in a controllable manner. As a cationic component of "organic sal t ferrimagnetics", two kinds of nitronyl nitroxide biradicals, 2,6- and 3,5 -substituted pyridine derivatives, were examined. It was predicted from sem i-empirical molecular orbital calculations that both the 2,6- and 3,5-deriv atives have the triplet ground states both in the neutral and cationic stat es. The molecular ground state of the 2,6-biradical in the neutral state wa s found to be triplet from magnetic susceptibility measurements, while the susceptibility and ESR measurements suggested a singlet ground state for th e 3,5-biradical.