Temperature-dependent isomorphous phase transition studies in molecular crystals of 2,4,4′-trimethoxybenzophenone

The crystal structure analyses on 2,4,4′-trimethoxybenzophenone (I) for data collected at 297(2) K show that there is only one intermolecular C–H···O hydrogen bond whereas there are four intermolecular C–H···O hydrogen bonds and an C–H···Π interaction for data collected at the temperature 100.0(1) K. All these hydrogen bonds are found to be weak. However these weak hydrogen bond interactions are attributable to the reversible temperature-dependent isomorphous phase transition found for (I). Compound (I) undergoes a reversible temperature-dependent isomorphous phase transition from monoclinic P21 at temperatures higher than the critical temperature (TC) of 154.5 K to another monoclinic P21 at temperatures lower than TC. The phase transition is of first order, involving almost doubling of the c-axis at TC and is explained by Landau phenomenological theory. In the crystal structures at temperatures 297(2) and 100.0(1) K, the molecules are linked by the intermolecular C–H···O hydrogen bonds to form chains along the [1 0 0]-direction. At 100.0(1) K, another three intermolecular C–H···O hydrogen bonds and an C–H···Π interaction further interconnect these molecular chains into 2-dimensional sheets parallel to plane (0 0 1).