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

A series of new metal-organic frameworks (MOFs), [Zn(1,2-pda)(bipy)(H2O)(2)](n) (1), [Zn(1,3-pda)(bipy)(H2O)](n)center dot nH(2)O (2), [Zn(1,4-pda)(bipy)](n)center dot nCH(3)OH (3), [Zn(1,2-pda)(dpe)](n)center dot 3nH(2)O (4), and [Zn(1,3-pda)(bpa)](n)center dot 2nH(2)O (5) [H(2)pda = 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 Schlafli symbol (4(2),6(7),8)(4(2),6). Complex 4 features a rare 3D three-fold interpenetrated diamondoid framework (dia, 6(6) 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 Schlafli symbol (4(4),6(2)), 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.