Three 3D Supramolecular Organic Salts Assembled from Melamine and Aliphatic Carboxylic Acids: Preparation, Crystallographic Characterization, and Hirshfeld Surface Analysis

Three crystalline organic salts (melamine)₂: (itaconic acid): 3H₂O [(Hmem)₂²⁺·(itca²⁻)·(H₂O)₃, itca²⁻ = itaconate] (1), (melamine)₂:(2-bromo-but-2-enedioic acid):DMF:2H₂O [(Hmem⁺)₂·(bbda²⁻)·DMF·(H₂O)₂, bbda²⁻ = 2-bromo-but-2-enedioate] (2) and (melamine):(α-ketoglutaric acid) [(Hmem⁺)·(Hketglua⁻), Hketglua⁻ = hydrogen α-ketoglutarate] (3) were featured by X-ray diffraction analysis, IR, mp, and elemental analysis. Significant non-covalent interactions were calculated by means of the Hirshfeld surface analysis. All salts involve extensive N–H···OH-bonds as well as other non-covalent associations. The melamine polymers/dimers were set up at 1–2/3 by the pair of complmentary N–H···NH-bonds. The role of these non-covalent interactions in the crystal packing is ascertained. These weak interactions combined, all salts exhibited 3D framework motifs.

The crystal structures of the salts from melamine, itaconic acid, 2-bromo-but-2-enedioic acid and α-ketoglutaric acid are predominantly stabilized by the classical hydrogen bonds as well as CH2···O, CH3···O, Br···Br, C···C, O···C, and π···π interactions.