The thermal expansion for a series of aliphatic diacids, HOOC­(CH2) n−2­COOH (n = 2–10), has been studied. Even (n = even) acids exhibit higher melting points and corresponding lower volumetric thermal expansions compared to the odd (n = odd) acids. This behavior seems to be in accordance to the Lindemann’s correlation of melting point with volumetric thermal expansion. The trend of alternation is also reflected in the linear thermal expansion behavior of the series. A trend of higher thermal expansion anisotropy is observed for the odd members in the series compared to the even members.

The order of thermal expansion of the interhalogen interactions is I⋯I < Br⋯Br < Cl⋯Cl, indicating that the order of interhalogen interaction strength is I⋯I > Br⋯Br > Cl⋯Cl.

Crystal structures and thermal expansion properties have been studied for hexamethylbenzene (HMB), picric acid (PIC), tetracyanobenzene (TCB), HMB–PIC complex, and HMB–TCB complex. HMB–PIC and HMB–TCB form charge transfer complexes in the solid state as well as in solution. From the UV–vis spectroscopy study, it has been found that HMB–TCB forms a stronger π···π complex than HMB–PIC. On the other hand, HMB, in its crystal structure, forms a very weak π···π stacking interaction. A thermal expansion study shows that thermal expansion along the stacking direction is highest in HMB, which is followed by HMB–PIC and then by HMB–TCB complexes. Therefore, this study shows that stronger π···π stacking interaction leads to a weaker thermal expansion in the materials.

A higher dimensional (1-D) hydrogen bonded form shows smaller thermal expansion than a lower dimensional (0-D) hydrogen bonded form of 2-butynoic acid.