Syntheses, structures and properties of silver–organic frameworks constructed with 1,2,3,4-benzenetetracarboxylic acid

Abstract

The reactions of 1,2,3,4-benzenetetracarboxylic acid (H₄mpda) and different silver(I) salts under hydrothermal or solvent evaporation conditions yielded four unusual coordination complexes with interesting frameworks: [Ag₄(mpda)]_n (1), {[Ag_2.5(mpda)(bpy)₂]·[Ag(bpy)]·[Ag(bpy)(H₂O)]·(NO₃)_0.5·(H₂O)₉}_n (2), {[Ag₅(mpda)₂(bpy)₄]·[Ag(bpy)]·[Ag(bpy)(H₂O)]·[Ag(bpy)(H₂O)]·(H₂O)₁₆}_n (3), {[Ag₂(mpda)(H₂O)]·[Ag(bpy)]·[Ag(bpy)]}_n (4) (bpy = 4,4′-bipyridine). Complex 1 displays a novel (3,4,7)-connected {4.6²}{4.6⁵}{4².6¹³.8⁵.10} topology, in which the carboxylic groups of the mpda⁴⁻ ligand adopt variable coordination modes. In 1, besides Ag–O coordination bonding, Ag⋯Ag and Ag⋯aromatic intermolecular interactions also make their appearance. In complexes 2–4, rare architectures comprising three or four isolated coordination polymers within the same crystalline structure have been obtained, respectively. In 2 and 3, neighboring layers are linked together through water tapes into a three-dimensional supramolecular architecture, which is also consolidated by π⋯π stacking, while independent infinite rod-like polymer chains fill the void space between layers. Interestingly, an anionic (H₂O–NO₃⁻)_n layer, built from water tapes and nitrate anions as well as consolidated by the mpda⁴⁻ ligands, has been structurally identified in compound 2. A new water tape constructed from alternating tetramers and decamers has been obtained in compound 3. In compound 4, a right-handed helical chain and two rod-like polymeric chains are interconnected through host–guest molecular recognition to generate a three-dimensional chiral supramolecular architecture. Bulk materials for 1 and 4 have second-harmonic generation activity, being approximately 0.6 and 0.4 times that of urea. The IR spectra, thermogravimetric analysis and luminescent properties of all compounds were also investigated.