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?

Dalton Transactions Pub Date: 2014-05-28 DOI: 10.1039/C4DT00659C

Abstract

A systematic investigation is reported of the use of the multi-functional ligand 2-amino-4-sulfobenzoate (asba2?) 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 asba2? 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)-asba2?-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 asba2? 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.

Graphical abstract: 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
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