Synthesis, characterization and properties of a family of lead(ii)–organic frameworks based on a multi-functional ligand 2-amino-4-sulfobenzoic acid exhibiting auxiliary ligand-dependent dehydration–rehydration behaviours

Abstract

A systematic investigation is reported of the use of the multi-functional ligand 2-amino-4-sulfobenzoate (asba(2-)) to construct lead(II)-organic frameworks in the presence and absence of N-donor auxiliary ligands phen, bipy and bix [phen = 1,10-phenanthroline, bipy = 2,2'-bipyridine and bix = 1,4-(methylene-benzene)bisimidazole]. Under ambient, aqueous conditions the assembly of asba(2-) with Pb(II) and phen or bipy leads to two iso-structural 2D double-layer frameworks, {[Pb2(asba)2(phen)2(H2O)]·2H2O}n (1) and {[Pb2(asba)2(bipy)2(H2O)]·2H2O}n (2). [Pb2(asba)2(bix)2(H2O)2]n (3) is obtained in the presence of the auxiliary ligand bix and possesses a 3D network built up from 2D Pb(II)-asba(2-)-bridged double-layer pillared by bix. A 2D (4,4) topological network [Pb(asba)(H2O)]n (4) is obtained in the absence of any second ligand or presence of some bistriazole bridging spacers. The coordination modes of the ligand asba(2-) in 1-4 are greatly dependent on the type of auxiliary ligand and the compounds exhibit auxiliary ligand-dependent dehydration-rehydration behaviours; 1 shows in situ rapid and reversible dehydration-rehydration behaviour in air, while the iso-structural compound 2 loses crystallinity in air and transforms into {[Pb2(asba)2(bipy)2(H2O)]·H2O}n (2A) verified by TGA, elemental analysis and powder X-ray diffraction analysis (PXRD). 3 also shows reversible dehydration-rehydration behaviour, but it takes around one week to rehydrate even after exposure to water vapor, while the dehydrated phase of 4 rehydrates to a new crystalline material. 1 and 3 fall within the category of the "recoverable collapsing" and "guest-induced re-formation" frameworks. The water molecules in 1 and 3 have some influence on their solid state fluorescent emission intensity.

An Ultrastable Luminescent Metal–Organic Framework for Selective Sensing of Nitroaromatic Compounds and Nitroimidazole-Based Drug Molecules

“…Metal–organic frameworks (MOFs), as an outstanding subclass of organic–inorganic hybrid solids with infinite, uniform, and porous framework structures, have emerged as promising materials for molecular recognition, − gas storage, − heterogeneous catalysis, electrocatalysis, − photoluminescence, − adsorption of volatile organic compounds, − and drug delivery owing to their designable and adjustable structures and properties. Among the various potential applications of MOFs, the fluorescence sensing of chemicals is a recently emerging research area, which is of great promise due to their operability, rapid response, high selectivity, sensitivity, and long-term stability. − Highly sensitive and efficient sensory materials for the sensing of trace amounts of nitroaromatic compounds (NACs), especially for TNP (2,4,6-trinitrophenol) and 4-NA (4-nitroaniline), are in high demand because of their explosive nature and high toxicity. − In this subject, MOF materials are of considerable interest and have been widely explored by researchers.…”

A new route for the syntheses of coordination polymers using magnetic influence: syntheses, crystal structures and fluorescence properties

“…The observed emissions in compounds 1-5 are probably caused by -* intra-ligand transitions of the Na 2 absa ligand (Cheng et al, 2012). The observed red and blue shifts of the emissions maximum between compounds 1-5 and the Na 2 absa ligand were mainly attributed to the coordination of ligands with metal ions (Zhang et al, 2014). However, it is found that the emission intensity of compound 3 is much higher than those of compounds 1, 2, 4 and 5.…”

Synthesis, structure and characterization of two copper(II) supramolecular coordination polymers based on a multifunctional ligand 2-amino-4-sulfobenzoic acid

“…The characteristic stretching vibrations for the sulfonate groups in (1) and (2) are located at 1180 and 1220 cm À1 , respectively. The broad bands centred on 3467 and 3288 cm À1 correspond to the mixed vibrations of both the -OH group of H 2 O and the -NH 2 group in (1) and (2), respectively (Zhang et al, 2014).…”

“…The multifunctional sulfosalicylic acid ligand has been used previously as an efficient 'building block' for the construction of novel Cu II supramolecular CPs (Marzotto et al, 2001;Fan & Zhu, 2007). To the best of our knowledge, there are no reported Cu II coordination complexes with multifunctional amino-substituted sulfobenzoate ligands and only four novel main group CPs based on 2-amino-4-sulfobenzoic acid (H 2 asba) have been synthesized and characterized in detail (Zhang et al, 2014). 1,10-Phenanthroline (phen) has been used to build supramolecular architectures due to its great potential to formstacking interactions.…”