Ionic metal-fullerene adducts C60M ( M = Li+, Mg2+, Ca2+, Sr2+, Ba2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, A13+ Ag+, Ce3+ ) are synthesized by reaction of watersoluble C60Lin with metal salt. 13C NMR of C60Li in D20 gives a sharp peak at 171.44 ppm which is much higher than the chemical shift of C60 in benzene ( 142.98 ppm ). Elemental analysis suggests the state of C60 in the adducts is C60
5-. ESR spectra of the adducts show a strong narrow peak at 9=2.001. UV-Vis and IR spectra of those adducts are completely different from those of C60. Magnetic measurement indicates that C60Li, C60Ce are antiferromagnetism and C60Fe adducts is ferromagnetism in the range of 150–300 K. But C60Fe adduct becomes paramagnetism when temperature is lower than 150 K. Mossbauer spectroscopy indicates Fe3+ in C60Fe adduct is Fe3+ (I.S.=0.30 mm/s, Q.S.=0.67 mm/s). The experimental results strongly suggest that C60
5- is a stable single free radical polyanion of fullerene which is a weak acid radical and possesses the similar properties with general inorganic anion. This is the first report on the synthesis and properties of air-stable and water-soluble polyanion of fullerene( C60
5-). A method for preparing metal-fullerene adducts has been developed, and many unusual properties of the adducts are found.