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

Abstract

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, ther- mal analysis, Hirshfeld surfaces and Fourier transform infrared spectroscopy of the compounds are pre- sented. 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 re- lated to the molecular sizes of the co-crystal formers thus allowing for the design of specific supramolec- ular 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.