Studies on π-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

Abstract

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˙^–)₂8. The X-ray crystal structure of complexe 8 reveals stacks of TMTTF molecules along the xdirection in the sequence A ‥ B ‥ A ‥ A ‥ B ‥ A ‥etc.. The A ‥ A and A ‥ B interplanar separation distances are 3.51 Å and 3.44 Å, respectively. The DCNQ radical anions form dinners, with a remarkably short interplanar separation of 3.02 Å, which are orthogonal to the TMTTF stacks. The complex is diamagnetic. Other π-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 1and 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.