Multicomponent crystals of p-coumaric acid and trans-ferulic acid: structures and physicochemical properties

Abstract

• P -coumaric and trans-ferulic acids co-crystallised with 4,4’-bipyridine and dioxane. • Only p -coumaric acid co-crystallised with pyridine. • Persistence of carboxylic acid homosynthon for dioxane and pyridine compounds. • Formation of heterosynthons for 4,4’-bipyridine co-crystals. • Greater thermal stability of trans-ferulic acid compounds. p -coumaric acid ( p CA) and trans -ferulic acid (TFA) formed multicomponent crystals with 4,4’-bipyridine (BIPY) and 1,4-dioxane (DX). p CA also co-crystallised with pyridine (PYR). The crystal structures, thermal analysis, Hirshfeld surfaces and Fourier transform infrared spectroscopy of the compounds are presented. Both ( p CA)·(BIPY) and (TFA)·(BIPY) displayed the supramolecular heterosynthons, COOH···N pyr and OH···N pyr . The ( p CA)·(DX), (TFA)·(DX) and ( p CA)·(PYR) crystal structures featured the carboxylic acid homosynthon and the (phenol)OH···O/N heterosynthon. The observed supramolecular synthons can be related to the molecular sizes of the co-crystal formers thus allowing for the design of specific supramolecular motifs. Differential scanning calorimetry (DSC) results showed that (TFA)·(BIPY) has a higher thermal stability than ( p CA)·(BIPY) . The thermal stability of the dioxane and pyridine compounds followed the trend, (TFA)·(DX) > ( p CA)·(DX) > ( p CA)·(PYR) . The greater thermal stability of the TFA co-crystals can be related to the presence of the methoxy group which formed an intramolecular hydrogen bond with the hydroxyl group.