We designed a series of metal–organic solids using ligands with similar molecular structures that were expected to afford coordination complexes with similar solid-state structures. The metal component is silver­(I) p-toluenesulfonate, and the ligands differ in their ability to undergo dynamic molecular motion. Although the ligands are similar in their molecular structure, the metal complexes exhibit different solid-state structures because of differences in π-stacking arrangements and the presence or lack of Ag···Ag interactions. The coordination units (ligand-Ag-ligand) in each complex respond differently to temperature changes, which results in thermal expansion behaviors ranging from negative to zero to positive within the series. Two unique complexes were obtained with the azo-containing ligand, and preparation of each complex in bulk was controlled by synthetic conditions. Two polymorphs were obtained with the olefin-containing ligand, and both complexes undergo dynamic molecular motion, although the supramolecular structures differed dramatically. Overall, we show that simple modifications to the ligand structure can significantly affect solid-state structure, crystal form, and subsequent thermal expansion behavior.

The impact of intermolecular interactions and molecular motion on solid-state properties is an active field of interest for chemists and materials scientists. For example, cocrystallization has been shown to modify and/or enhance the solid-state behaviors of a molecule when compared to the single-component solid. Here, we describe a series of cocrystals containing bis(pyridin-4-ylmethylene)benzene-1,4-diamine (BPDI) and ditopic or tritopic hydrogen-bond-donor molecules that are conformationally flexible. The components in all the cocrystals self-assemble through hydroxyl-pyridine heterosynthons to afford one-dimensional chains due to the conformations of the donor molecules. BPDI is torsionally flexible, and in cocrystals with ditopic hydrogen-bond donors, the molecule is almost planar, whereas in cocrystals with tritopic hydrogen-bond donors, BPDI is significantly twisted. This twisting in BPDI affects crystal packing and affords higher thermal expansion coefficients. Cocrystallization of BPDI with resveratrol, another torsionally flexible molecule, induces molecular pedal motion in BPDI and results in larger expansion behavior in the cocrystal.

A strategy for modifying thermal expansion properties in dichroic, charge-transfer cocrystals is described. A solid-state Diels-Alder reaction is used to covalently connect adjacent molecules in the cocrystal, and thermal expansion...