Hydrothermal syntheses, structures and luminescent properties of d10 metal–organic frameworks based on rigid 3,3′,5,5′-azobenzenetetracarboxylic acid

Abstract

Four novel d¹⁰ metal–organic frameworks based on rigid 3,3′,5,5′- azobenzenetetracarboxylic acid (H₄abtc) in the presence of auxiliary 2,2′-biimidazole (biim), 1,10-phenanthroline (phen) and pyridine (py) have been synthesized under hydrothermal conditions and structurally characterized. Their formulae are [Cd₂(abtc)(biim)₂]_n (1), {[Cd(abtc)_0.5(phen)]₄·4H₂O}_n (2), {[Zn(abtc)_0.5(phen)]₄·2H₂O}_n (3) and [Zn₃(abtc)(py)₄(OH)₂]_n (4). Complex 1 possesses a one-dimensional (1D) infinite tubular structure by using biim as auxiliary ligand. The structures of complexes 2 and 3 exhibit three-dimensional (3D) (4,4)-connected frameworks with (4²8⁴) topologys by employing phen as auxiliary ligands. By utilizing py as auxiliary ligand, complex 4 is a (2,3,4)-connected framework with a (10)(8³)₂(8,10⁵) topology in which there exists -{Zn-O-Zn}- zigzag chains and 46-member macrocycles which are linked by multicarboxylate ligands to form a 3D supramolecular structure. The structural differences among 1–4 indicate the importance of the auxiliary ligands for the framework formation of the coordination polymers. In addition, the thermal stabilities and photoluminescence properties of 1–4 are also investigated.