ELECTROSYNTHESIS AND ELECTRODOPING OF C-60(N-) (N = 0, 1, 2, OR 3) FILMS - ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE STUDY IN ACETONITRILE SOLUTIONS OF ALKALI-METAL, ALKALINE-EARTH-METAL, AND TETRA-N-BUTYLAMMONIUM CATIONS

The electrosynthesis, electrodoping/undoping, and electrodissolution of thin films of C60 and its salts were studied in acetonitrile solutions at a Au/quartz electrode by simultaneous electrochemistry and microgravimetry with an electrochemical quartz crystal microbalance. The C-60(0) films were deposited either by electrooxidation of C-60(2-) in solutions containing CsAsF6, KPF6, or Ca(PF6)2, or by electrooxidation of C-60(3-) in solutions containing tetra-n-butylammonium perchlorate, (TBA)ClO4. The initial C-60(2-) or C-60(3-) anions were prepared by controlled-potential bulk electroreduction of a C-66(0) suspension. The C-60(0) films electrodeposited from a C-60(2-) solution containing Cs+, K+, or Ca2+ cations could not be electrodoped with these cations but a conductive (Cs+)3(C60(3-)) film could be quantitatively electrosynthesized by electroreduction of C60(2-) in a solution containing Cs+. Attempts to electrodeposit (K+)3(C60(3-)) or (Ca2+)3(C60(3-))2 films were unsuccessful but a (Ca2+)(C60-)2 film could be prepared. The composition of a given C-60(0) film electrodeposited by constant potential electrooxidation of C-60(3-) in an acetonitrile solution containing (TBA)ClO4 was controlled by the initial C-60(3-) concentration and/or the electrodeposition potential. These C-60(0) films could be electrodoped with TBA+ cations from solution upon electroreduction at appropriate potentials and both (TBA+)(C60-) and (TBA+)2(C60(2-)) films were obtained. Films of the same composition could also be obtained by electrooxidation of concentrated C-60(3-) solutions containing (TBA)ClO4 at a suitably selected potential.