Two new complexes [Co₂(L)(4,4´-bip)(H₂O)₃]_n (1) and [Co(L´)₂(phen)]·2H₂O)}_n (2) (H₄L = 1-(3,5-dicarboxybenzyl)-3,5-pyrazole dicarboxylic acid, H₃L´ = 1-(3,5-dicarboxybenzyl)-3-pyrazole carboxylic acid, 4,4´-bip = 4,4´-bis(1-imidazolyl)biphenyl, phen = 1,10-phenanthroline) were synthesized. Complexes 1 and 2 have been characterized by IR spectrography, X-ray single-crystal diffraction, elemental analysis and thermogravimetry. 1 crystallizes in monoclinic system, space group P2₁/c. Complex 2 crystallizes in monoclinic system, space group I2/a. It is remarkable that in situ hydrothermal decarboxylation was observed during preparing complex 2. In addition, magnetic analysis indicates that antiferromagnetic interaction exists among Co(II) ions in complexes 1 and 2.