Optical and magnetic properties of ionic charge transfer complexes based on 1,2-dicyano[60]fullerene

Abstract

By using a stronger electron acceptor 1,2-dicyano[60]fullerene (C₆₀(CN)₂), a donor-acceptor type ionic complex (Bz₂Cr˙⁺)[C₆₀(CN)₂˙^¬] (1) (Bz₂Cr = bis(benzene)chromium), and two anionic salts, K⁺[C₆₀(CN)₂˙^¬](THF)_x (2) and [K⁺(DB18C6)(THF)_x]₂[C₆₀(CN)₂^2¬] (3) (DB18C6 = dibenzo-18-crown-6 ether), were prepared. The charge on the C₆₀(CN)₂ molecules in 1 was determined by comparison of the Raman spectrum with those of the potassium salts 2 and 3. An EPR spectrum of 2 showed a narrow Lorentzian-shaped signal with a slightly larger g factor (ΔH_pp = 2.8 Oe at g = 1.9997) than that of the C₆₀˙^¬ salt K⁺(C₆₀˙^¬)(THF) (ΔH_pp = 19 Oe at g = 1.9987), indicating the elimination of the low-lying excited state and thereby the reduction of spin–orbit coupling. For the solid 1, an EPR signal characteristic of Bz₂Cr˙⁺ spin was observed down to 4 K, while no signals arising from C₆₀(CN)₂˙^¬ spin were seen at any of the temperatures measured. Moreover, the static susceptibility of 1 can be explained in terms of only the paramagnetic spin on the Bz₂Cr˙⁺ cations. The formation of covalently linked [C₆₀(CN)₂]₂^2¬ dimers of 1 is proposed to account for this novel phenomena.