Pyridinedicarboxylic acids have been widely used as organic ligands for the construction of organic–inorganic hybrid materials and combine the advantages of both organic multicarboxylic acid and hetero aromatic compound [1, 2]. The introduction of oxime-containing auxiliary ligand, such as 4-pyridine-aldoxime into the reaction systems, was expected to induce the evolution of novel metal–organic frameworks. So the rigid pyridinedicarboxylic acids as well as 4-pyridine-aldoxime were applied as mixed- ligand systems to coordinate with Zn(II) metal center, and the mononuclear complexes have emerged. Herein we present two new mononuclear compounds, [Zn(2,5-pdc)2(H2O)2](4-pyaoH)2 (1) and [Zn(2,6-pdc)2(4-pyao)2] (2), where 2,5pdcH2 = pyridine-2,5-dicarboxylic acid; 2,6-pdcH2 = pyridine-2,6-dicarboxylic acid; 4-pyao = 4pyridine-aldoxime, which were obtained in very similar synthetic conditions. The crystal structure of 1 consists of one complex anion [Zn(2,5-pdc)2(H2O)2]2- and two protonated 4pyridiniumaldoxime cations. The Zn(II) ion has a distorted octahedral configuration coordinated by two bidentate 2,5-pdc and two aqua ligands. The 2,5-pdc ligand is coordinated to the Zn(II) ion by a nitrogen atom and carboxylate oxygen atoms, creating a chelate ring, while the protonated 4-pyaoH cation behaves as counter ion (Fig. 1a). The coordination polyhedron of Zn(II) in 2 comprises two monodentate 4-pyao ligands and one tridentate pyridinedicarboxylate dianion and two 4-pyridine-aldoxime molecules.