Descriptive analysis of the crystal structure of the 1-D semiconducting TCNQ salt : TEA(TCNQ)2, as a function of temperature. - II. Charge distribution on the conducting TCNQ columns

Abstract

By reconsidering recent X-ray results, evidence is presented for a noticeable temperature dependence of the charge distribution on the two non-equivalent sites TCNQ A and TCNQ B in a conducting column of TEA(TCNQ)2. In particular, a simple law of the form : qA = (1/2 + T o/T) e and qB = (1/2 - To/T) e, with To = 24 K, well accounts for this dependence, giving the remarkable limit : qA = qB = e/2 when T → oo. These findings are considered in a brief theoretical analysis of the dimer unit in the TCNQ column, and their possible implications to the electronic properties of the semiconductor are also discussed

X-ray method for the structural investigation of thin organic films

“…It should be mentioned that some dimerization of the TCNQ has been observed [2] which has only a weak influence on the lateral stacking of TCNQ. This dimerization related to the 4-unit periodicity has been also evidenced in a similar compound (TMA-TCNQ salt) [8].…”

“…As the a parameter corresponds exactly to 4 times the standard distance (3.2 A) between TCNQ planes [8], it is obvious that the lateral stacking of the TCNQ lies along the a-axis. It should be mentioned that some dimerization of the TCNQ has been observed [2] which has only a weak influence on the lateral stacking of TCNQ.…”

Pattern of charge ordering in quasi-one-dimensional organic charge-transfer solids

“…This work clearly established the SW ′ SW bond distortion pattern associated with the ...1100... BCDW for T < T SP in MEM(TCNQ) 2 . Similarly, the charge and bond modulation pattern for TEA(TCNQ) 2 have been investigated by X-ray 45,46,47,48 and neutron 49 measurements. Below the structural transition at 210K, the amplitude of the SW ′ SW distortion increases rapidly, and ...1100... CO was found 45,47 .…”

Dipolar glass and magneto-electric coupling within a π-stacked organic system

“…a singlet state is formed) between the BAA 0 B 0 dimers. 13,16,17 One interesting feature of the TCNQ dimer is that the single electronic charge is split across the molecular unit unevenly over the temperature range from 395 to 110 K. 10,18 As the temperature increases (T 4 345 K) one may expect this charge distribution to become equal. However, at 295 K it is split at q A /e = 0.58 and q B /e = 0.42 (q A and q B denote the charge on the A and B TCNQ molecule respectively and e is the elementary charge) and is most pronounced at 110 K where q A /e = 0.72 and q B /e = 0.28.…”