Evolution des tenseurs de dilatation thermique en fonction de la temperature. II. Etude calorimetrique et cristallographique de la transition de phase ordre-desordre du thiophene chrome tricarbonyle C 4H 4SCr(CO) 3

Benzenechromium tricarbonyl C ₆H ₆Cr(CO) ₃ and thiophenechromium tricarbonyl C ₄H ₄SCr(CO) ₃ are isomorphous at room temperature. We have measured, in the range 77-295°K, the variations of specific heat and of the tensor of thermal expansion for these two molecular compounds. The first one exhibits quite normal behavior; on the other hand, the second one exhibits a first order phase transition, monoclinic ⇆ triclinic at T = 185°K, associated with an order-disorder phase transition. Structural evolution of thiophene-chromium tricarbonyl, during phase transition, has been explained from the variation of its tensor of thermal expansion.