A study of the phase transition in semiconducting 1:2 tetracyanoquinodimethane charge transfer complexes with dipropylamine derivatives: X-ray structure and polarized reflection spectra

Abstract

Chem. 69, 1804 (1991).The donors dipropylamine (DPA), methyldipropylamine (MDPA), and ethyldipropylamine (EDPA) from 1:2 charge transfer complexes with the acceptor tetracyanoquinodimethane (TCNQ). All crystals in the above series are semiconductors and undergo a first-order phase transition at the temperature around 210 K as obtained from conductivity measurements. The X-ray structure of DPA-(TCNQ)? was obtained as a function of temperature, and shows a distinct order-disorder transition in the hydrogen-bond network between donors and acceptors. Polarized reflection spectra on single crystals of these compounds were measured as a function of temperature in the frequency range from 400 to 4000 crn-'. A detailed study of the e N modes of TCNQ indicates this mode is strongly influenced by the transition due to it being hydrogen bonded to the donors. The reflection coefficients of the IR active Ag modes of TCNQ also undergo a sharp discontinuity at the transition temperature. These results are interpreted as due to a cooperative order-disorder and electronic spin -Peierls transition.Key words: organic semiconductors, X-ray structure, polarized reflection spectra, phase transition, cooperative orderdisorder transition, spin-Peierls transition. La dipropylamine (DPA), la mCthyldipropylamine (MDPA) et l'ithyldipropylamine (EDPA) agissent comme donneurs pour former des complexes de transfert de charge 1 : 2 avec le titracyanoquinornithane (TCNQ) qui agit comme accepteur. Tous les cristaux des series sus-mentionnies sont des semi-conducteurs et, d'aprks les mesures de conductiviti, ils subissent une transition de phase du premier ordre B une tempirature d'environ 210 K. Faisant appel B la diffraction des rayons-X, on a dCterminC la structure du complexe DPA-(TCNQ)? en fonction de la tempirature; on observe une transition distincte ordreldCsordre dans le riseau des liaisons hydrogknes entre donneurs et accepteurs. On a mesuri le spectre de riflexion polarisie de cristaux uniques en fonction de la tempirature entre 400 et 4000 cm-' . Une Ctude dttaillCe des modes C=N du TCNQ indique que ce mode est fortement influencC par la transition; cet effet est dfi au fait que cette liaison est impliquie dans une liaison hydrogkne avec les donneurs. Les coefficients de riflexion des modes Ag du TCNQ actifs en infrarouge subissent aussi une discontinuiti importante au niveau de la temperature de transition. On interprkte ces risultats en fonction d'une transition coopirative ordreldksordre et spin ClectroniquelPeierls.

Thermochemical Hole Burning on DPA(TCNQ)2and MEM(TCNQ)2Charge Transfer Complexes Using a Scanning Tunneling Microscope

“…Figure 1a is the highresolution image of the DPA(TCNQ) 2 crystal, which exhibiting periodic rows of bright spots. The repeating distances within each row and between the rows are 6.3 and 7.9 Å, respectively, in agreement with the crystallographic constants a and b of the DPA-disordered phase, 15 for which the lattice constant a is half that of the DPA-ordered phase due to a phase transition at 210 K. The arrangement of TCNQ groups for the DPA-disordered phase is shown in Figure 1b, which is in agreement with the specific features of Figure 1a. 16 The hole burning experiment is done on the ab plane by turning off real-time scan and applying voltage pulses to the tunneling gap at selected region of the surface using a computer-controlled program.…”

Preparation and Characterization of {[M(dmb)2]TCNQ·xTCNQ°}n Polymers (M = Cu,Ag; dmb = 1,8-Diisocyano-p-menthane; x = 0, 0.5, 1.0, 1.5; TCNQ = 7,7,8,8-Tetracyano-p-quinodimethane) and Design of New Semi- and Photoconducting Organometallic Materials

“…There is no obvious chain of the type (TCNQ) 3 2- ···toluene··· etc., in this case. The interplanar distances within the (TCNQ) 3 2- species are 3.32(4) Å, and compare favorably to that of other literature examples as listed above. −

2 X-ray structure of {[Ag(dmb) 2 ]TCNQ·0.5TCNQ°· 0.5 toluene} n . Green = {[Ag(dmb) 2 + } n chains; red and blue = TCNQ; yellow = toluene.

…”

“…In direct relevance to this work, the solid-state structure for {[Ag(dmb) 2 ]TCNQ‚2THF} n also reveals the presence of dimeric TCNQ 2 2species, consistent with our previous observations for other polymers. 12 In this case the interplanar TCNQ -‚‚‚TCNQseparation (3.24(4) Å) is somewhat shorter than that of the sum of the van der Waals radii for C (2 × 1.70 Å), the values found in the {[Ag(dmb) 2 ]TCNQ‚solvate} n polymeric isomers (3.346, 3.436, and 3.312 Å), 12 and the data reported for other dimer or trimer species (see for instance data for [Pd(CNCH 3 ) 4 ](TCNQ) 4 (3.29 and 3.36 Å), 22 [Fe 2 (η 5 -C 5 H 5 ) 2 -(µ-CO) 2 ((C 6 H 5 ) 2 PN(C 2 H 5 )P(C 6 H 5 ) 2 )](TCNQ) 3 (3.24 and 3.39 Å), 23 ((H 7 C 3 ) 2 NH)(TCNQ) 2 (3.20 and 3.30 Å), 24 and [C(C 6 Me 6 )-Fe(η 5 -C 5 H 5 )](TCNQ) 2 (3.35 and 3.37 Å) 25 ). In the TCNQ°c rystal, this distance is also shorter (3.45 Å).…”

“…The interplanar distances within the (TCNQ) 3 2species are 3.32(4) Å, and compare favorably to that of other literature examples as listed above. [22][23][24][25] The role of toluene seems unclear at first, with respect to the π-stacked TCNQ xchain. The Ag‚‚‚Ag separation is 4.8816(4) Å and is the shortest distance ever measured for such polymeric systems.…”

Thermodynamic Phase Transition Triggered by Distinct Distortion and Ordering of Dipropylammonium Picrate

“…Therefore, there are great opportunities to obtain phase transition materials with the DPA cation 9d. 13 In the present work, we have utilized the flexible dipropylamine to react with organic picric acid and successfully constructed a new reversible solid‐state phase transition compound, dipropylammonium picrate (compound 1 ). Variable‐temperature structure determinations, differential scanning calorimetry (DSC), and specific heat capacity and dielectric measurements have been used to confirm its phase transition behaviors.…”