Effect of Methyl Substitution on Conformation and Molecular Arrangement of BEDT-TTF Derivatives in the Crystalline Environment

Abstract

Two methylated bis(ethylenedithio)tetrathiafulvalene (ET) derivatives, Me2ET and Me4ET were stereoselectively synthesized to examine the effect of methylation on conformations of dihydrodithiin rings and molecular arrangements in the crystalline state. Since the donating ability of Me2ET and Me4ET are similar to that of ET, the methylated ET derivatives are considered to be appropriate to investigate the “lattice pressure” effect on ET radical salts by changing the volume of donor molecules. The upper limit of an activation energy for the ring inversion of the dimethylated dihydrodithiin in solution was estimated to be 32 kJ mol−1 by 13C NMR spectroscopy. The X-ray structure analyses revealed that orientations of methyl groups are fixed to axial in Me2ET and to equatorial in Me4ET, accompanied by the change of molecular stacking. The “volume of a methyl group” was evaluated by comparing the molecular volumes of Me2ET and Me4ET with that of ET, and the effective volume for the axial methyl group turns out to be 15% larger than that of the equatorial. The solid state 13C NMR (CP/MAS) spectra of ET and its derivatives showed that the chemical shifts of resonance lines reflect the conformations of dihydrodithiin rings in crystals.

Enantiopure Radical Cation Salt Based on Tetramethyl-Bis(ethylenedithio)-Tetrathiafulvalene and Hexanuclear Rhenium Cluster

“…Contrary to what was observed so far in the literature (see above), here the donors adopt all-ax conformations which certainly hamper closer axial S¨¨¨S intermolecular contacts. The methine carbon atoms show opposite displacements with respect to the planar S-C=C-S motif of the dithiine rings (Table 1), thus leading to sofa-type conformations of the six membered rings [3]. One can hypothesize that the occurrence of this unusual all-ax conformation which only allows lateral S¨¨¨S intermolecular interactions, and not the classical axial σ-type interactions between open-shell species, is strongly favoured by the peculiar nature of the anion which can engage in hydrogen, halogen and chalcogen bonding, as detailed above.…”

“…Tetramethyl-bis(ethylenedithio)-tetrathiafulvalene 1 (TM-BEDT-TTF) has in principle several possible stereoisomers, yet the only ones which have been properly described are the (S,S,S,S) ( Figure 1) and (R,R,R,R) enantiomers [1][2][3], henceforth abbreviated (S)-1 and (R)-1, respectively.…”

“…Tetramethyl-bis(ethylenedithio)-tetrathiafulvalene 1 (TM-BEDT-TTF) has in principle several possible stereoisomers, yet the only ones which have been properly described are the (S,S,S,S) ( Figure 1) and (R,R,R,R) enantiomers [1][2][3], henceforth abbreviated (S)-1 and (R)-1, respectively. (S)-1 represents the first example of a chiral TTF derivative [4], and its synthesis allowed the preparation of several TTF based chiral conducting radical cation salts by electrocrystallization [1,5], including the ferromagnetic metal [TM-BEDT-TTF]x[MnCr(ox)3] (ox = oxalate) [6] or the paramagnetic semiconductor [TM-BEDT-TTF]3(PPh4)[K I Fe III (Cl2An)3] (Cl2An = dichloroanilate) [7].…”

Chemical Modifications of BDH-TTP [2,5-Bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene]: Control of Electron Correlation

“…The syntheses of the corresponding dimethyl-substituted derivatives of BEDT-TTF, for which three kinds of stereoisomers, that is, a meso (or cis)-form ( Figure 25) and an enantiomeric pair of (R,R)-and (S,S)-forms are possible, have been previously reported [48,49] …”

Substituted BEDT‐TTF Derivatives: Synthesis, Chirality, Properties and Potential Applications

“…29,30 A reported crystal structure on the "racemic" donor TMET (prepared from racemic 51) almost certainly contains a disordered mixture of racemic 52 and the meso isomer 53. 31 Keller electrocrystallised an unspecified mixture of TMET isomers: a metallic 2:1 salt with PF 6 -appears to contain the isomer 54, and a chlorobenzene solvate of a 1:1 PF 6 -salt appears to contains both isomers 54 and 55 in a pseudosymmetrical arrangement. 32 In both cases the relation between adjacent methyl groups is cis and one methyl group will lie in an axial position for an envelope conformation of the outer ring.…”