Two new complexes involving 3,4-pyridinedicarboxylic acid (3,4-H 2 pdc), copper(II) and cobalt(II) complexes, {[Cu(3,4-Hpdc) 2 (H 2 O) 2 ]·2dmso} n (1) and {[Co(3,4-Hpdc) 2 (H 2 O) 2 ]·2H 2 O·2dmso} n (2) (dmso = dimethylsulfoxide), have been synthesized by the diffusion method and characterized by elemental analysis, IR spectroscopy, thermal analysis, powder and single-crystal X-ray diffraction analysis, and electron paramagnetic resonance (EPR). In both compounds, the metal coordination sphere is composed of a trans-MO 4 N 2 core and adopts a distorted octahedral geometry in accordance with X-ray diffraction and EPR results. 3,4-Hpdc − ligands bridge the metal centers giving two-dimensional (2-D) coordination polymers with four-connected uninodal nets of (4,4) topology.