Hydrothermal syntheses, crystal structures and luminescent properties of zinc(II) coordination polymers constructed by bifunctional tetrazolate-5-carboxylate ligands

Two bifunctional 1H-tetrazolate-5-carboxylate ligands with different flexibilities, H(2)tza (1H-tetrazolate-5-acetic acid) and H(2)tzf (1H-tetrazolate-5-formic acid), were employed in the construction of zinc(II) complexes in the presence/absence of secondary ligands such as 2,2'-bipy and 4,4'-bipy. Three tza coordination polymers and two tzf dinuclear complexes, namely [Zn(tza)(H2O)](n) (1), [Zn-3(tza)(2)Cl-2(2,2'-bipy)(2)(H2O)(2)](n) (2), [Zn-2(tza)(2)(4,4'-bipy)](n) (3), [Zn(tzf)(H2O)(3)](2) center dot 2H(2)O (4) and [Zn(tzf)(2,2'-bipy)(H2O)](2) center dot H2O (5), were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Polymer 1 is a 3-D two-fold interpenetrating diamond-like network with tetranuclear [Zn(COO)](4) clusters as tertiary building units (TBUs) and mu(3)-kappa N-3:kappa O-2:kappa O1,N1 bridging tza as linkers. Polymer 2 presents a 2-D structure formed by the linkage of 1-D Zn-carboxylate [Zn(COO)](n) helical chains and mu(3)-kappa N-4:kappa O-2:kappa O-1,N-1 bridging tza. In 3, 2-D (4,4) nets are built up with dinuclear [Zn(COO)](2) clusters and mu(3)-kappa N-4:kappa O-2:kappa O-1,N-1 bridging tza, which are pillared through 4,4'-bipy to gain a 3-D self-penetrating LB-1 (4(4)6(10)8) topology. In dinuclear complexes 4 and 5, two Zn(II) atoms are bridged by a tzf ligand in a mu 2-kappa N2:kappa O1,N1 fashion. The results denote that tetrazolate-5-carboxylate ligands can adopt variable coordination modes in the formation of the complexes, and different Zn-carboxylate aggregates can serve as tertiary building units (TBUs). The effects of the nature of tetrazolate-5-carboxylate ligands and secondary ligands, and hydrothermal reaction conditions on the structural topologies of the obtained complexes have been investigated. The photoluminescent properties and thermal stabilities of 1-5 have also been discussed.