Evidence of Back Charge Transfer in DMBP-TCNQ3

The single crystal conductivity of (N,N'-dimethyl-4,4'-bipyridinium)2+(7,7,8,8-tetracyanop- quinodimethanide)3 2-, DMBP-TCNQ3, exhibits an anomaly at 170 K which may be attributed to a phase transition and, also, a change in activation energy at 135 K which may be attributed to the onset of extrinsic behaviour. Above 135 K the conductivity varies as σ = σ0 exp(-E2/kT) where σ300K. = 1 S cm-1 and Ea = 0.18 eV. In the high temperature region the thermoelectric e.m.f. saturates to a temperature independent value of S = - 20 μVK-1 whereas for the related monoquaternised salt, [N-phenyl-4-(4'-pyridyl)-pyridinium]+(TCNQ)2 -, ØBP-TCNQ2, S = - 55 μVK-1. The thermoelectric data may be interpreted in…