Structural and dynamical disorder in carbamazepine-oxalic acid cocrystal

Abstract

This study explores the structural and dynamic disorder in the nanoporous organic cocrystal carbamazepine-oxalic acid, synthesized via liquid-assisted grinding, using a combination of broadband dielectric spectroscopy and molecular dynamics simulations. Notably, the oxalic acid molecules within the channel-like cocrystalline structure exhibit both translational and rotational dynamic disorder. These oxalic acid molecules are arranged as one-dimensional, interrupted single files within the channels. Their translational motion occurs through small hops, characterized as single-file diffusion at short timescales, transitioning to classical Fickian diffusion over longer times. Rotational dynamics involve jumps between preferred orientations, altering the molecular dipole moments, which are detectable through dielectric relaxation spectroscopy. Despite this disorder, it appears only partial due to hydrogen bonding between the oxalic acid and carbamazepine molecules, which imparts some degree of order within the channels. These findings underscore the value of disordered channel-like cocrystals as model systems for studying dynamics in nanoconfined environments.