Dynamic disorder in the crystal structure of an organic semiconductor: an unusual phase transition involving the heat capacity.

(E,E)-1-[2-(4-Nitrophenyl)ethenyl]-4-[2-(2,4-dimethoxyphenyl)ethenyl]benzene was characterised by X-ray diffraction and shown to be dynamically disordered at room temperature. The structure was re-determined over a range of temperatures to infer the thermodynamic parameters related to this disorder. A phase transition of third order according to the Ehrenfest classification scheme was discovered. To the best of our knowledge, this is the first experimentally observed phase transition of formal third order. It can be explained by the involvement of long-range lattice vibrations.

Synthesis and structures of substituted triphenyl(phenylimino)phosphoranes.

Three substituted triphenyl(phenylimino)phosphoranes, namely (4-cyanophenylimino)triphenylphosphorane, C(25)H(19)N(2)P, (I), (4-nitrophenylimino)triphenylphosphorane, C(24)H(19)N(2)O(2)P, (II), and (3-nitrophenylimino)triphenylphosphorane, C(24)H(19)N(2)O(2)P, (III), were synthesized as precursors for the preparation of substituted diphenylcarbodiimides. All three compounds display a supramolecular arrangement in which the substituted benzene rings are organized in an antiparallel fashion. The nitro group on the ring participates in C-H...O and O...pi interactions, forming intermolecular dimers. Compound (III) shows disorder which involves the rotation of one of the phenyl rings of the triphenylphosphine group.

4-[(E)-2-(2,4,6-Trinitro-phenyl)ethyl-idene]benzonitrile.

In the crystal of the title compound, C(15)H(8)N(4)O(6), the mol-ecules are organized in layers due to their linkage by weak C-H⋯N hydrogen bonds. The layers are themselves inter-connected by weak C-H⋯O hydrogen bonds and π-π inter-actions [centroid-centroid distances = 3.8690 (15) and 3.9017 (16) Å]. The dihedral angle between the rings is 31.9 (1)°.