Abstract: | In the tetramethylarsonium salt of 2,5‐dichloro‐7,7,8,8‐tetracyanoquinodimethanide systematic name: tetramethylarsonium 2,2′‐(2,5‐dichlorocyclohexa‐2,5‐diene‐1,4‐diylidene)bis(propanedinitrile)], C4H12As+·C12H2Cl2N4? or As(CH3)4](C12H2Cl2N4), the cation lies disordered about a twofold axis and the radical ion lies about an inversion center forming a uniform interplanar distance 3.35 (2) Å] and one‐dimensional stacking without any slip. The electrical conductivity of the single crystal at room temperature was less than 10?9 S cm?1, and the temperature dependence of paramagnetic susceptibility obeyed a one‐dimensional antiferromagnetic Heisenberg model with a spin‐exchange integral of 83 K in the temperature range 1.8–320.0 K. |