MAGNETISM IN ORGANIC MATERIALS

Tailoring magnetic interactions of organic solids is currently an area of intense research activity. We show that the quasi-one dimensional antiferromagnetic exchange coupling of the well-known organic free radical triphenylverdazyl (TPV) can be increased by a factor of 3 by systematic molecular modifications (i.e. J(1d)/k(B) = -16 K for 1,3,5,6-tetraphenylverdazyl). 1,3,5-tri-6'-(1,3,5-triphenylverdazyl)-benzene as a representative of covalently bound multiradical molecules was analyzed as solid and in solution. The energetic spin-doublet-quartet separation and intermolecular exchange interaction were estimated. Cooperative magnetic behaviour with ordering temperature of about 40K and well-defined hysteresis loops (H-c(5 K) approximate to 40 Oe) has been achieved by the chelation of transition metals (e.g. Mn) in appropriate organic materials. NMR, ESR, static magnetic susceptibility, in part also a.c. susceptibility, specific heat and x-ray structural analysis were used to characterize these new organic magnetic materials.