Variable band filling in organic conductor with proton donor/acceptor HnTNBP(2−n)− (TNBP: 3,3′,5,5′-tetranitro-4,4′-biphenyldiol)

H2TNBP (3,3′,5,5′-tetranitro-4,4′-biphenyldiol) is known as a proton donor forming monoanion HTNBP1− and dianion TNBP2−. We have studied radical salts of TTF-series with TNBP2− as counter anion, and found two kinds of ET (BEDT-TTF) salts, namely 4:1 and 2:1. In the 2:1 salt, it is strongly suggested that the formula is represented as (ET0.5+)2(HTNBP1−) by the optical data and relatively high conductivity. The chemical species of anion part is determined by the chemical shift of 13C-CP/MAS NMR in the solid state. Coexistence of TNBP2− and HTNBP1− is observed in 3:1 BO salt and 2:1 TMTSF salt, though only TNBP2− exists in 4:1 ET salt. The 2:1 TMTSF salt exhibited optical transitions at ca. 2500 and 7500 cm−1 simultaneously in the reflection spectrum, however, the intensity ratio differs from crystal to crystal. It suggests that the charge of TMTSF varies between +0.5 and +1.0, and the formula is represented as (TMTSF(1−x/2)+)2(TNBP2−)1−x(HTNBP1−)x (0<x<1).