Thermodynamic properties of bis-(η6-cumene)chromium fulleride [(η6-PhCH(CH3)2)2Cr]+[C60]− over the range from Т → (0 to 310) K

In the present research, the temperature dependence of heat capacity Cp,m∘=f(T) of crystalline bis-(η6-cumene)chromium fulleride [(η6-PhCH(CH3)2)2Cr]+[C60]− has been measured between Т = (6 and 310) K in the precision adiabatic vacuum calorimeter and reported for the first time. Also, for the first time, the temperature dependence of EPR signal parameters of bis-(η6-cumene)chromium fulleride over the range from T = (120 to 290) K was investigated by electron paramagnetic resonance. In the interval from T = (196 to 240) K the reversible endothermic transformation was detected and its thermodynamic characteristics were estimated. This transformation was caused by dissociation of dimer (C60-)2 and formation of fulleride [(η6-PhCH(CH3)2)2Cr]+[C60]− during heating. The experimental results have been used to calculate the standard (р° = 0.1 MPa) thermodynamic functions Cp,m∘/R, ΔT1T2Hm∘/RT, ΔT1T2Sm∘/R, and Φm∘/R=ΔT1T2Sm∘/R-ΔT1T2Hm∘/RT (where R is the universal gas constant) for dimeric fulleride over the range from T → (0 to 196) K and for monomeric complex [(η6-PhCH(CH3)2)2Cr]+[C60]− between Т = (240 and 310) K.

► Heat capacity and thermodynamic properties of crystalline bis-(η6-cumene)chromium fulleride between Т = (6 and 310) K.
► Temperature dependence of EPR signal parameters of bis-(η6-cumene)chromium fulleride over the range from T = (120 to 290) K.
► The reversible dimerization of fullerene fragments and thermodynamic characteristics of the transformation..
► The stability of dimeric dianions (C60-)2 depends significantly on the nature of substituent.