PREPARATION AND CHARACTERIZATION OF THE C-60 CHARGE-TRANSFER COMPLEX METHYL-DELTA-2,2'-BI(IMIDAZOLIDINE)](-DOT)(CENTER)

Ferromagnetism in the C-60 charge transfer salt C-60(-.) ,3'-tetrameth yl-Delta(2,2')-bi(imidazolidine)](+.) (C-60[TMBI]) with Curie temperat ures T-c above 140 K and coercive forces H-c of about 1000 Oe were rep orted by Wang and Zhu (J. Phys. Chem. Solids 55 (1994) 437). This dram atic increase of T-c and H-c by a small variation of the counterion co mpared to the first C-60 ferromagnet C-60(-.)[tetrakis(dimethylamino)e thylene](+.) (Allemand et al., Science 253 (1991) 301) triggered us to elucidate the charge transfer from TMBI to C-60 by absorption measure ments in the VIS/NIR. We found that the reaction kinetics is much more complex than in C-60[TDAE]. Solid state investigations of C-60[TMBI] with EPR and microwave conductivity are in dear disagreement with the results published by Wang and Zhu. We found instead strong evidence th at C-60[TMBI] is rather a diamagnetic C-60 CT complex with a lot of st ructural defects than a high temperature molecular ferromagnet.