Intrastack rotation in pyrene hexafluoroarsenate

The specific heat of the quasi-one-dimensional organic conductor pyrene hexafluoroarsenate ((Py)7(Py)4(AsF6)4·4CH2Cl2) was measured between 10 and 250 K using the method of continuous heating. The contribution of the lattice to the specific heat was modelled using the Debye model and Einstein terms. The variation of the specific heat at the structural phase transition that is accompanied by 60 deg. rotation of one of the stacked pyrene molecules could be reproduced well using a cooperation model including the formation of domains, and the surprisingly high transition entropy was explained qualitatively