A case study of the Zn-II-BDC/bpt mixed-ligand system: positional isomeric effect, structural diversification and luminescent properties

To systematically investigate the influence of the positional isomeric ligands on the structures and properties of transition metal complexes, we synthesized eight Zn(II) complexes with three positional isomeric carboxylate ligands (p-BDC, m-BDC and o-BDC) and three positional isomeric dipyridyl bridging ligands (4,4'-bpt, 3,4'-bpt and 3,3'-bpt). {[Zn-2(p-BDC)(2)(4,4'-bpt)(2)]center dot H2O center dot(C2H5OH)}(n) (1), {[Zn(p-BDC)(3,4'-bpt)(2)(H2O)(2)]center dot 2H(2)O}(n) (2), {[Zn(p-BDC)(3,3'-bpt)(2)(H2O)(2)]center dot 3H(2)O}(n) (3), {[Zn-2(m-BDC)(2)(4,4'-bpt)(H2O)(3)]center dot H2O}(n) (4), [Zn(m-BDC)(3,4'-bpt)](n) (5), {[Zn(m-BDC) (3,3'-bpt)]center dot H2O}(n) (6), [Zn(o-BDC)(4,4'-bpt)](n) (7) and [Zn-2(o-BDC)(2)(3,4'-bpt)](n) (8) (p-BDC = 1,4-benzenedicarboxylate anion, m-BDC = 1,3-benzenedicarboxylate anion, o-BDC = 1,2-benzenedicarboxylate anion, 4,4'-bpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole, 3,4'-bpt = 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole and 3,30-bpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole). Structural analysis reveals that the benzenedicarboxylate isomers display versatile coordination modes to manage the Zn(II) ions to form 1D chains (for 2-5, 7 and 8) or 2D layers (for 1 and 6), which are further extended via the isomeric bpt connectors in different directions to give rise to a variety of coordination polymers, such as 1D decorated chain, 1D ladder-like chain, 2D sql layer, 2D bilayer with 8(2).10 topology, 2D wave-like layer, 3D 2-fold interpenetrating porous pcu net and 3D CsCl net. These results indicate that the nature of isomeric benzenedicarboxylates and bpt ligands has an important effect on the structural topologies of such Zn(II) complexes. Moreover, the luminescent properties of the complexes have been briefly investigated.