Supramolecular interactions and aromaticity in phenazine–hydroxybenzoic acid co-crystals

Abstract

This study presents a comparative structural and supramolecular analysis of two newly synthesised co-crystals of phenazine with hydroxybenzoic acid derivatives: 4-hydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid. The crystal structures were characterised via X-ray diffraction and analysed using Hirshfeld surface analysis and the Harmonic Oscillator Model of Aromaticity (HOMA). The experimental structures were compared with reference CSD entries (NUKXAT and XIPVAU) to elucidate how hydroxyl group positioning within the benzoic acid ring influences hydrogen bonding topology, molecular packing, and aromatic stabilisation. Importantly, the HOMA index is interpreted strictly as a geometry-based descriptor of aromaticity, reflecting bond length equalisation in π-conjugated systems. The study highlights the potential of supramolecular design as a tool to probe the relationship between molecular arrangement and material properties in aromatic systems.