Mechanochemical Synthesis and Co‐Former–Controlled Assembly of Azobenzene Polycarboxylate Organic Salts: From Framework Node to Passive Guest in HOF‐Like Architectures

ABSTRACT Hydrogen‐bonded organic salts are versatile supramolecular materials whose architecture can be tuned through co‐former selection. Here, we report two multicomponent crystals of the azobenzene polycarboxylic acid 4,4′‐(diazene‐1,2‐diyl)bis(3,5‐dicarboxybenzoic acid) ( DADIA ): one with imidazole ( DADIA:IMD2 ) and one with N ‐methylimidazole ( DADIA:MeIMD ). Both were prepared by mechanochemical grinding followed by recrystallization from methanol. In each case, proton transfer from the carboxylic acid groups to the imidazole nitrogen gives charge‐assisted N + –H···O − hydrogen bonds, so the materials are best described as organic salts. Single‐crystal x‐ray diffraction shows that DADIA:IMD2 crystallizes in a monoclinic ( C2/c ) and DADIA:MeIMD in a triclinic ( P‐1 ), both forming two‐dimensional HOF‐like architectures. In DADIA:IMD2 , protonated imidazole acts as an active network node, generating channels occupied by disordered solvent. In DADIA:MeIMD , the 2D sheet is stabilized by O–H···O bonding between DADIA host molecules, with protonated N ‐methylimidazole housed in the pores as a passive guest. The compounds were further characterized by 1 H NMR, FT‐IR, PXRD, and TGA. These results show how a single N ‐methyl substituent switches the co‐former between the network node and the guest, with implications for gas storage, separation, and drug delivery.