STUDIES ON PI-ACCEPTOR MOLECULES CONTAINING THE DICYANOMETHYLENE GROUP - X-RAY CRYSTAL-STRUCTURE OF THE CHARGE-TRANSFER COMPLEX OF TETRAMETHYLTETRATHIAFULVALENE AND 2,3-DICYANO-1,4-NAPHTHOQUINONE - (TMTTF)3-(DCNQ)2

The reaction of tetramethyltetrathiafulvalene (TMTTF, 7) with 2-dicyanomethyleneindane-1,3-dione (DCID, 1) leads to isomerisation of DCID to 2,3-dicyanonaphthoquinone (DCNQ, 3) to yield the charge-transfer complex [(TMTTF)3]2.+-(DCNQ.-)2 8. The X-ray crystal structure of complex 8 reveals stacks of TMTTF molecules along the x direction in the sequence A..B..A..A..B..A.. etc. The A..A and A..B interplanar separation distances are 3.51 angstrom and 3.44 angstrom, respectively. The DCNQ radical anions form dimers, with a remarkably short interplanar separation of 3.02 angstrom, which are orthogonal to the TMTTF stacks. The complex is diamagnetic. Other pi-acceptor molecules containing the dicyanomethylene group, viz. compounds 2 and 10-12, have been prepared and their redox properties studied by cyclic voltammetry. Compound 2 rearranges to compound 4 on complexation with TTF 6. DCID derivatives 1 and 2 react with a range of amines, by displacement of one cyano group, to yield enamines 15-19; the amphiphilic compound 18 forms Langmuir-Blodgett films which exhibit weak second harmonic generation.