A variable temperature single crystal X-ray diffraction study revealed an unusual thermal expansion property of an organic salt, imidazolium 4-hydroxybenzene carboxylate, which exhibits colossal negative and positive axial thermal expansion along the crystallographic b axis and approximately along the a axis, respectively. The hydrogen bonded, two-dimensional square grid type of the flexible network in the crystal structure of the salt resembles a fencing structure that undergoes scissor-like motion resulting the abnormal thermal behavior. Thermal expansion induced by a scissor motion of the hydrogen bonded network in a multicomponent crystalline organic compound has not been reported before, although this mechanism is mentioned to elucidate colossal thermal expansion in some inorganic framework materials.

Switching from positive to negative axial thermal expansion in pure organic materials is reported for the first time. This rare phenomenon has been rationalized based on the packing of molecules in crystal structures and transverse thermal vibrations of atoms in the molecule. Unique packing of the molecules in the crystal structure contributes to the restricted movement of molecules along the c axis. Subsequently, contraction of molecular dimensions with increasing temperature, due to transverse vibrations of some atoms, assists with the switch from Positive Thermal Expansion (PTE) to Negative Thermal Expansion (NTE).

Rare area negative thermal expansion of a new mixed metal mixed organic MOF has been described using an “elevator-platform” analogy induced by O–H⋯O hydrogen bonding.

Thermal expansion of a new mixed-metal mixed-linker metal organic framework (MOF) has been studied by variable temperature single crystal X-ray diffraction. Origin of axial positive, negative, and zero thermal expansion in the MOF has been elucidated by analyzing the crystal structures. Flexibility in coordination of ligands around the metal ions induces axial NTE and PTE in the 2D layers of the MOF. On the other hand, thickness of the 2D layers in the crystal structure remains unchanged along one of the principal axes resulting in rare ZTE. O···O Distances of O–H···O hydrogen bonding between the 2D layers in the crystal structure remain almost unaffected with increasing temperature.

The structural alteration of semiconducting polymer backbones can improve the optoelectronic properties of organic semiconductors and enhance field-effect mobilities. In our efforts towards improving the performance of organic field-effect transistors (OFETs), we are reporting a donor–acceptor polymer containing thieno[3,2-b]pyrrole (TP) donor and a furan-flanked diketopyrrolopyrrole (DPP) electron acceptor, which yielded an asymmetric poly(methylthienopyrrolo)furanyl)diketopyrrolopyrrol) P(FDPP-TP) organic semiconducting polymer. The introduction of a furan spacer improved thermally induced crystallinity and molecular packing, as confirmed by grazing incidence X-ray diffraction (XRD) and tapping-mode atomic force microscopy (TMAFM). The tested OFET devices gave maximum hole mobility of 0.42 cm2 V−1 s−1 with threshold voltages around 0 V for bottom-gate bottom-contact device configuration.

Thermal expansion of a 2-fold interpenetrated MOF has been studied by variable temperature single crystal X-ray diffraction within a broad range of temperature. The change of unit cell parameters with increasing temperature shows colossal linear PTE and NTE exhibited by the MOF. The anomalous thermal expansion in MOF has been explained by hinge-like motion of the 2D rectangular grids in the crystal structure of the MOF with the change of temperature. Generally, large NTE is not anticipated in interpenetrated MOF due to strong repulsion between the atoms in close proximity that may prevent transverse vibration. Thermal expansion property of the MOF in this study is reversible in nature within the temperature between 100 and 450 K.

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