Dioxo- and aminooxopyrimidotetrathiafulvalenes: π-electron donors for design of conducting materials containing intramolecular hydrogen bonds of nucleic acid base pair type

Dimethyl[2,4‐dioxo(1 H,3 H)pyrimido]tetrathiafulvalene (1) and dimethyl‐[2‐amino‐4‐oxo(3 H)pyrimido]tetrathiafulvalene (4) form unusual inner salts by oxidation in the presence of bases. The insoluble black‐green betaines 2 and 5 react with acids to form cation radical salts. Betaine 2 in the presence of acid and bis‐(ethylenedithio)tetrathiafulvalene forms the unexpected double salt 8. In order to synthesise the cation radical salts of 1 and 4, it is necessary to use the ultrasonic method owing to the insolubility of the starting compounds. Electrical measurements of the betaines and cation radical salts in pressed samples show an unexpectedly low resistivity with semiconducting character: for betaine 2 ρ(RT) = 840 O cm, for betaine 5 ρ(RT) = 10 O cm, for salt 7 ρ(RT) = 40 O cm, but for double salt 8 ρ(RT) = 50 O cm. In the case of salt 8, very low values of activation energy of electrical conductivity of the order of kT were observed. The synthesis and purification of tetrathiafulvalene 4 from 5‐amino‐7‐oxo(6 H)‐1,3‐dithiolo[4,5‐d]pyrimidineselone‐2 are described. © 1997 John Wiley & Sons, Ltd.