X-ray diffuse scattering and conductivity studies of the N-methylphenazinium-tetracyanoquinodimethanide IA form

The x-ray diffuse scattering study of the highly conducting form (IA) of N-methylphenazinium-tetracyanoquinodimethanide [(NMP)(TCNQ)] shows that the methyl groups, although less ordered than in the less highly conducting form (IB), still display substantial local order of the same type along the stacking a direction. In addition, it shows two types of one-dimensional (1-D) scattering bearing resemblance to the Kohn anomalies earlier observed in (TTF)(TCNQ). A first 1-D scattering is observed at room temperature at the wave vector 0.33a*; it couples three-dimensionally below approximately 200 K. Further diffuse scattering is observed below 70 K at half the previous wave vector (0.165a*). As expected in an intrinsically disordered system (as potassium cyanoplatinate [K₂Pt(CN)₄{Br}0.30·3{H}₂$O (KCP)] no long-range 3-D ordering is observed down to 20 K. Our results cannot ascribe unambiguously the $0.33{a}*$ and a $0.165{a}*$ scattering to $4{k}F$ and $2{k}F$ anomalies (as was done for tetrathiafulvalenium-tetracyano-$p$-quinodimenthanide [(TTF)(TCNQ)], but strongly suggests that the charge transfer in (NMP)(TCNQ) is $2/3$ electron, and is quite far from unity as previously deduced from other work. Temperature-dependent dc conductivity measurements after x-ray study unequivalocally associate the highly conducting form with these properties.