The crystal structure of the 2:3 complex of rubidium and 7,7,8,8-tetracyanoquinodimethane, Rb2TCNQ3, at 113 K

Abstract

RbETCNQ3 [Rb2(Ct2H4N4) 3, C36H12N12Rb2] is isostructural with Cs2TCNQ3. The space group is P2~/c with a = 7.269 (2), b = 10.264 (3), c = 21.328 (6)/~, fl = 97.11 (2) ° , U = 1579.2 /~a and Z = 2. The intensities were collected at 113 K with Mo radiation on an automatic Nonius CAD-3 diffractometer. Anisotropic least-squares refinement decreased the weighted residual R e to 0.038 for 3631 observed reflexions. The TCNQ groups are stacked in columns along the b axis and lie either at inversion centers (groups c) or at general positions (groups nc) in the arrangement nc... c...nc...nc...c...nc.., etc. Comparison with the room-temperature structure shows that decreasing the temperature from 300 to 110 K gives the same percentage reduction in the nc...c and nc...nc distances. Rb ions also lie in linear arrays along b and are surrounded by edge-sharing cubes of eight N atoms. The cubes show an elongation in the stacking direction which is much more pronounced for the Rb than for the Cs salt. Within the TCNQ stack the shifts 'parallel' to the TCNQ planes do not depend on the temperature but quite strongly on the atomic radii, whereas the reverse is the case for the distances between the planes.