Abstract The three new complexes, [Zn(picoH) 2·2H 2O] ( 1), [Mn(picoH) 2·2H 2O] ( 2) and [Cu(picoH) 2] ( 3) (HpicoH=3-hydroxypicolinic acid) were synthesized as single crystals by the hydrothermal reactions and characterized by single crystal X-ray diffraction, elemental analysis and thermal analysis. The complexes 1 and 2 are isomorphous and have rich hydrogen bonds formed by the coordinating water molecules with the carboxylate groups and the hydrogen atoms of the pyridine rings, respectively. The hydrogen bonds lead to the formation of supramolecules with three-dimensional network structures. In the crystal of the complex 3, the copper(II) ion is not only strongly coordinated by four atoms (N 2O 2) in a square-planar fashion, but also interacts weakly with other two oxygen atoms, forming a distorted octahedron. The coordination number of the copper(II) ion can be described as ‘4+2’. The weak Cu–O coordination bonds and hydrogen bonds in 3 bring the moieties into a supramolecule with three-dimensional network.