Molecular reorientation in pyrene hexafluoroarsenate salts

Electron Spin Resonance: A Major Probe for Molecular Conductors

“…In the cases of perylene or fluoroanthene salts, Peierls phase transitions have been observed upon cooling, inducing a large modification of the spin relaxation. Moreover, because of the extremely narrow lines in the metallic phase, pulsed EPR was successfully applied to deduce the longitudinal and transverse relaxation times. − In particular, a decay of the correlation function as exp(−( t /τ) 3/2 ), characteristic of one-dimensional systems was observed . Accurate low field magnetometers were built with these materials taking advantage of the very small line width. , Unfortunately, this application has been limited by the instability of these materials at room temperature.…”

“…Moreover, because of the extremely narrow lines in the metallic phase, pulsed EPR was successfully applied to deduce the longitudinal and transverse relaxation times. [290][291][292][293][294][295][296][297][298][299][300] In particular, a decay of the correlation function as exp(-(t/τ) 3/2 ), characteristic of one-dimensional systems was observed. 301 Accurate low field magnetometers were built with these materials taking advantage of the very small line width.…”

Intrastack rotation in pyrene hexafluoroarsenate

“…The stacks are separated by the counterions, four neutral pyrene molecules and the solvent molecules (not shown in figure 1). Four of the seven stack molecules define the 0 • orientation, two are oriented at 60 • and the PY2 position is disordered, with about 50%-70% [2] of the PY2 molecules oriented at 60 • and the remaining ones at 0 • .…”

“…While most of the arenes show only one unique packing scheme [1], namely parallel for perylene, antiparallel for flouranthene and 90 • for naphthalene, pyrene (C 16 H 10 ) shows an unusual degree of freedom: (Py) 7 (Py) 4 (AsF 6 ) 4 •4CH 2 Cl 2 shows both parallel as well as 60 • oriented molecules in its stacks (figure 1). Since for one of the seven stacked molecules both orientations are possible, the system crystallizes in two different modifications: I and II [2]. Modification I shows a first-order structural phase transition (T C ) due to the reorientation of this molecule by 60 • when the crystal is cooled and thus the intrastack distance is reduced.…”

“…The evaporation of the solvent may also be the reason for the non-negligible ageing of the crystals. It was suggested [2] that in mod. I crystals there exist domains with slightly different Peierls transition temperature T P , caused by a differing degree of disorder as the reorientation of the stacked molecules mentioned above occurs in only 50%-70% of the unit cells.…”