ESR Studies on C₆₀.O_X and C₆₀.HMTTEF

Abstract

The electron spin resonance (esr) of C₆₀.O_x and C₆₀.HMTTEF (hexamethylentetratellurafulvalene) has been investigated at 9.36 GHz as a function of temperature. T (298 T 4 K). C₆₀.O_x shows an esr absorption of equal ‘g’ value to that of C₆₀ exposed to O₂ and light but is more intense. The C₆₀ in its pure form is in a singlet state. The impurity sites introduced by O₂ produce the esr absorption. The Curie - Weiss plots of inverse esr absorption intensity versus temperature indicate an antiferromagnetic TH = 50 for air exposed C₆₀ and 90K for C₆₀O_x. From the esr intensity at room temperature, the calculated number of free spins (S = 1/2) is =1/3 per mole of C_60-O_x. In case of C₆₀.HMTTEF, there is a very weak esr absorption at room temperature suggesting that the room temperature form is diamagnetic with very small charge transfer between C₆₀ and HMTTEF. This conclusion is consistent with the structure and magnetic susceptibility of this cocrystal. As the temperature is lowered, the equilibrium: AD <=> A∗⁻ + D∗⁺ is displaced towards the formation of free radical species, A∗⁻ and D∗⁺.