From molecular salt to pseudo CAB cocrystal: Expanding solid-state landscape of carboxylic acids based on charge-assisted COOH⋯COO− hydrogen bonds

Using three carboxylic acids, we show that the COOH⋯COO− synthon is robust for directing the cocrystallization between a carboxylic acid and a carboxylate of either the same or a chemically different molecule to form a CAB or pseudo CAB cocrystal, respectively. For a given carboxylic acid and a counterion, only one salt could be prepared. However, additional one CAB cocrystals and two pseudo CAB cocrystals could be prepared based on the COOH⋯COO− synthon. The same synthon has the potential to enable the preparation of additional molecular pseudo CAB cocrystals using other chemically distinct carboxylic acids. This significantly increased number of solid forms highlights the values of charge-assisted synthons, such as COOH⋯COO−, in crystal engineering for expanding the range of material properties of a given molecule for optimum performance in product design.