Crystal Structure of (DPPP) (TCNQ)₅ (H₂O) and Electrical Properties of the Mixed Valence TCNQ Salts of Diquaternised 1,3-BiS (4-pyridyl) propane

Abstract

The conductivities and thermoelectric e.m.f.'s of an isostructural series of TCNQ salts are reported together with the crystal structure of (DPPP)(TCNQ)₅(H₂O), representative of the series. The 1:5 salt has a monoclinic subcell, space group P2₁/c, with a = 12.73(2), b = 3.87(2), c = 28.47(10) Å, β = 107.9(4)°. The TCNQs stack plane-to-plane in columns, parallel to b, with (i) an average interplanar spacing of ∼ 3.3Å and (ii) an exocyclic double bond to quinonoid ring overlap of adjacent molecules. The hydrated cation lattice shows no long-range order. (DPPP)(TCNQ)₅(H₂O) and its isostructural congeners, (DHPP)(TCNQ)₄(H₂O), (DMPP)(TCNQ)_4-1/2(H₂O) and (DEPP)(TCNQ)₅(H₂O), are small band gap semiconductors. The room temperature conductivities, determined parallel to b, are in the range 0.05 to 100 S cm⁻¹.