The crystal structure of rubidium–7,7,8,8-tetracyanoquinodimethane, Rb–TCNQ, at –160°C

Abstract

Crystals of Rb-TCNQ have monoclinic symmetry; the space group is P2t/c, a = 7-187 (1), b = 12.347 (2), c= 13.081 (3) A, fl=98"88 (2) °, Z=4. Rb + and TCNQ-are both at general positions. The intensities were collected at -160°C on an automatic Nonius diffractometer. Approximate values for the atomic coordinates were obtained from Patterson and difference Fourier maps. Anisotropic least-squares refinement decreased the residual R to 0.066 for 5512 independent reflexions. The bond lengths in the TCNQ-ion show that the ion has quinoid character; the group is not planar but has the shape of a shallow boat. The TCNQ-radical-ions form charge-resonance bounded rows along the a axis. The interaction between the rows is small. Within a row interplanar spacings of 3" 159 and 3"484/~, alternate. The distance of 3"159 ~ is the shortest distance found so far between successive TCNQ planes. The Rb + ions also form rows along the a axis with alternating distances of 3-483 and 3.726 A between the ions. These distances are appreciably longer than twice the radius of Rb ÷ (3.0 A). Rb + is octahedrally surrounded by eight negatively charged TCNQ nitrogen atoms at distances of 2. 982, 2.996, 3.004, 3.009, 3.025, 3.055, 3.057 and 3.108 ~.

Structure and packing arrangement of molecular compounds. VII. 7,7,8,8-Tetracyanoquinodimethane–naphthalene (1:1)

“…Bond distances in the TCNQ molecule [Fig. 6,Table 4(b)] agree remarkably well with those found in the structure of TCNQ (Long, Sparks & Trueblood, 1965), and when compared to the compilation by Hoekstra, Spoelder & Vos (1972) they are indicative of a neutral ground state of the molecule. The quinonoid bond length is also very close to those found in the essentially neutral TCNQ compounds with phenazine and dibenzo-pdioxin (Goldberg & Shmueli, 1973a, b).…”

The crystal structure of the 1:2 complex of N-methyl-N-ethylmorpholinium and 7,7,8,8-tetracyanoquinodimethane, MEM(TCNQ)2, at –160°C

“…Fig. 3 shows that both molecules have a slight boat form which resembles the situation found in Rb-TCNQ-I (Hoekstra, Spoelder & Vos, 1972;Fig. 6).…”

“…Hoekstra, Spoelder & Vos (1972) noticed that bond c has a relatively large increase in length with increasing charge. It is therefore noteworthy that in this study it is bond c for which the possibly significant difference has been found, as this may indicate that the charge on (A) is slightly larger than on (B).…”

Magnetic susceptibility of alkali-tetracyanoquinodimethane salts and extended Hubbard models with bond order and charge density wave phases

“…We also consider χ(T ) of dimerized stacks for T < T d without, however, treating the transition. There are two Rb salts: Rb-TCNQ(I) is strongly dimerized [15] at 300 K while Rb-TCNQ(II) has regular stacks [16,17] with A − at inversion centers at both 100 and 295 K. The recent 100 K structure [17] rules out a dimerization transition around 220 K that was inferred from magnetic susceptibility [18] and infrared [19] data. We reinterpret these observations.…”