Structural and fluorescent regulation of Cd(ii) coordination polymers with homoterephthalate by N-donor second ligands

Abstract

This work reports the synthesis and fluorescence of a series of five Cd(II) coordination polymers with a variety of structure topologies. Homoterephthalic acid (H2htpa) reacts with Cd(OAc)2 to produce the coordination polymer [Cd(htpa)(H2O)]n (1). If a kind of dipyridyl-type second linear ligand is introduced into the synthetic system, three interpenetrating complexes are isolated, namely, [Cd(htpa)(bpp)]n (2), [Cd(htpa)(bpe)]n (3), and [Cd3(htpa)2(bpa)2(OAc)2]n (4) (bpp = 1,3-di(4-pyridyl)propane, bpe = 1,2-di(4-pyridyl)ethylene, and bpa = 1,2-bi(4-pyridyl)ethane), whereas the use of a circular second ligand, 1,2,4-triazole (Htrz), leads to a porous 3D framework {[Cd3(htpa)(trz)3(OAc)(H2O)4]·4H2O}n (5). Complex 1 has parallel Cd–O inorganic chains linked further by the htpa ligands forming individual 2D Cd(II)–carboxylate layers, complex 2 features the parallel interpenetration of two coincident 44 net sheets producing an overall 2D → 2D entanglement topology, complex 3 displays the inclined interpenetration of two sets of parallel corrugated 44 net sheets giving an overall 2D → 3D entanglement topology, complex 4 displays the normal interpenetration of three pcu nets affording an overall 3D → 3D entanglement topology, and complex 5 is characterized as Cd–triazolate layers cohered further by carboxylate linkers affording a single (3,5)-connected 3D open-framework (gra topology) with H-bonding water chains encapsulated in the cavities. The five complexes display a wide range of fluorescent emission behaviors, which are tentatively related with the local ligand environments with the different degrees of inter-chromophore coupling.