Preparation of a Mott insulator based on a BEDT-TTF charge transfer complex of hydrogen cyananilate: α′-(BEDT-TTF)2HCNAL

BEDT-TTF (ET) and cyananilic acid (H2CNAL) afforded charge transfer crystals by a diffusion method. The chemical formula of the complex was deduced based on all the information concerning the elemental, structural, electric, magnetic and optical analyses. The ET molecules form one-dimensional columnar stacks composed of twisted dimers with a face-to-face overlap (α′-type stack). The acid works as an oxidant and is deprotonated to form the monoanion, HCNAL1−, which forms ribbon-like aggregation by means of hydrogen-bonds. The ribbons form anion layers that sandwich the ET layer. The crystal is semiconductive with a room temperature conductivity of 0.20–0.83 Scm−1 and activation energy of 0.15 eV along the stacking direction, though the band calculation by the extended Huckel method suggests a metallic nature, indicating strong electron-correlation in this system. The complex is a Mott insulator and its magnetic susceptibility is described by the one-dimensional S = 1//2 antiferromagnetic Heisenberg chain model with J/kB = −52 ± 3 K.