Magnetic properties of phenol-substituted nitronyl nitroxide biradicals asbuilding blocks of organic salt ferrimagnets

A practical difficulty in constructing organic molecule-based ferrimagnetic s is co-crystallization of two distinct molecules with different spin quant um numbers. Coulombic energy between cationic and anionic molecules in orga nic salts is a promising driving force for co-crystallization. We investiga ted magnetic properties of four kinds of phenoxide-substituted nitronyl nit roxide biradical salts; a potassium and a sodium salt of 2,4-bis(1-oxyl-3-o xido-4,4,5,5-tetramethyl-2-imidazolin-2-yl)-phenol (1a and 1b), and a potas sium and a sodium salt of 4-methyl-2,6-bis(1-oxyl-3-oxido-4,4,5,5-tetrameth yl-2-imidazolin-2-yl)-phenol (2a and 2b). For la and 2a, it was found from the analysis of magnetic susceptibility in the solid state and ESR spectra in diluted frozen solutions that the ground-state spin multiplicities chang ed from triplet (S = 1) into singlet (S = 0) on ionization. For Ib and 2b, magnetic susceptibility in the solid state suggested the weakening of their intramolecular ferromagnetic interaction or the conversion of the ground-s tate spin multiplicities into singlet. (C) 2001 Elsevier Science Ltd. All r ights reserved.