A series of Zn(ii) coordination complexes derived from isomeric phenylenediacetic acid and dipyridyl ligands: syntheses, crystal structures, and characterizations

Abstract

A series of new metal–organic frameworks (MOFs), [Zn(1,2-pda)(bipy)(H₂O)₂]_n (1), [Zn(1,3-pda) (bipy)(H₂O)]_n·nH₂O (2), [Zn(1,4-pda)(bipy)]_n·nCH₃OH (3), [Zn(1,2-pda)(dpe)]_n·3nH₂O (4), and [Zn(1,3-pda)(bpa)]_n·2nH₂O (5) [H₂pda = phenylenediacetic acid, bipy = 4,4′-bipyridine, dpe = 1,2-di(4-pyridyl)ethylene, bpa = 1,2-bis(4-pyridyl)ethane] have been synthesized and structurally characterized. The structure determination reveals that complex 1 is a 2D layered network and exhibits a typical (4,4) topological net, which further assembles into a 3D two-fold interpenetrated pcu topology when hydrogen bonding interactions are considered. Complex 2 shows a 2D (5,2)-connected topological network via hydrogen bonding interactions based on the 1D double-chains. For complex 3, when the 1,4-pda ligands act as a three-connected node, the 2D double-layered structure displays a unique (5,3)-connected topology with a Schläfli symbol (4²,6⁷,8)(4²,6). Complex 4 features a rare 3D three-fold interpenetrated diamondoid framework (dia, 6⁶ topology) with (2.2.1) Hopf links and (6.3.3) Torus links, and the helical water chains are encased in the 1D neighboring channels. Complex 5 is a 2D corrugated net with a Schläfli symbol (4⁴,6²), and the puckered nature of the layers assembles them to interpenetrate in an unusual 2D → 3D parallel fashion. Particularly, a discrete tetramer water cluster, (H₂O)₄, is located in the crystal lattice of 5. The structural differences demonstrate that the backbones of the phenylenediacetic acids are a key point to form the final metal–ligand coordination polymers. Moreover, the fluorescent properties of complexes 1–5 were studied in the solid state at room temperature.