Three Co(II) and Cu(II)-pyridine-2,5-dicarboxylate (pydc) proton transfer compounds with 1,4-butanediamine (ben) and 2,2-dimethylpropane-1,3-diamine (dmpen), trans-(H(2)ben)[Co(pydc)(2)(H2O)(2)]center dot 4H(2)O (1), trans-(H(2)dmpen)[Co(pydc)(2)(H2O)(2)]center dot 2H(2)O (2) and (H(2)ben)(2)[Cu-2(mu-Pydc)(4)(H2O)(2)] (3) have been synthesized and characterized by the methods of elemental, spectroscopic (IR and UV-Vis), thermal (TG/DTG. DTA) analysis, magnetic measurement and single crystal X-ray diffraction. The crystallographic analysis revealed that the complexes consist of [Co(pydc)(2)(H2O)(2)](2-) anion, bis(protonated) diamine cation (H(2)ben for 1 and H(2)dmpen for 2) and four and two crystal water molecules, respectively. The Co(II) ions are coordinated by two pydc and two aqua ligands. The bis(deprotonated) pydc ligands coordinate to the Co(II) ions through the nitrogen atom of pyridine ring and the oxygen atom of carboxylate group, creating a chelate ring. The distorted octahedral geometries are completed by two trans aqua ligands at axial positions. The molecular structure of the complex 3 consists of dinuclear [Cu-2(mu-Pydc)(4)(H2O)(2)](4-) units and bis(protonated) 1,4-butanediammonium cation. In the structure, each Cu(II) ion is coordinated by two nitrogen and two oxygen atoms from two pydc ligands and one oxygen atom from aqua ligand, forming a distorted square pyramidal geometry. (C) 2011 Elsevier Ltd. All rights reserved.