Charge transfer complexes of fullerenes containing C60˙− and C70˙− radical anions with paramagnetic CoII(dppe)2Cl+ cations (dppe: 1,2-bis(diphenylphosphino)ethane)†
Abstract
The reduction of CoII(dppe)Cl2 with sodium fluorenone ketyl produces a red solution containing the CoI species. The dissolution of C60 in the obtained solution followed by the precipitation of crystals with hexane yields a salt {CoI(dppe)2+}(C60˙−)·2C6H4Cl2 and a novel complex {Co(dppe)2Cl}(C60) (1). With C70, only the crystals of {Co(dppe)2Cl}(C70)·0.5C6H4Cl2 (2) are formed. Complex 1 contains zig-zag fullerene chains whereas closely packed double chains are formed from fullerenes in 2. According to the optical spectra and magnetic data charge transfer occurs in both 1 and 2 with the formation of the CoII(dppe)2Cl+ cations and the C60˙− or C70˙− radical anions. In spite of the close packing in crystals, C60˙− or C70˙− retain their monomeric form at least down to 100 K. The effective magnetic moments of 1 and 2 of 1.98 and 2.27μB at 300 K, respectively, do not attain the value of 2.45μB expected for the system with two non-interacting S = 1/2 spins at full charge transfer to fullerenes. Most probably diamagnetic {CoI(dppe)2Cl}0 and neutral fullerenes are partially preserved in the samples which can explain the weak magnetic coupling of spins and the absence of fullerene dimerization in both complexes. The EPR spectra of 1 and 2 show asymmetric signals approximated by several lines with g-factors ranging from 2.0009 to 2.3325. These signals originate from the exchange interaction between the paramagnetic CoII(dppe)2Cl+ cations and the fullerene˙− radical anions.