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.