Two nickel(II) and cobalt(II) complexes with phenanthroline, [Ni(Phen)(H2O)(3)Br]Br (1) and [Co(Phen)(2)(H2O)(2)](Hba)(2)center dot 2H(2)O (2), Phen = 1,10-phenanthroline and Hba = barbiturate anion, were synthesized and characterized by powder XRD, TGA and FT-IR. Their structures were determined by single crystal X-ray diffraction techniques. The Ni2+ ion is coordinated by two N atoms of Phen molecule, Br- ion and three H2O molecules forming an octahedron. Uncoordinated and coordinated Br- ions are connected with water molecules by O-H center dot center dot Br intermolecular hydrogen bonds with the formation of a 2D plane network which is extended into a 3D network by pi-pi stacking interactions. The [Co(Phen)(2)(H2O)(2)](2+) cation contains a six-coordinated cobalt atom chelated by two Phen ligands and two aqua ligands in the cis arrangement. N-H center dot center dot center dot O, O-H center dot center dot center dot O and C-H center dot center dot center dot O intermolecular hydrogen bonds form a 3D net. N-H center dot center dot center dot O hydrogen bonds form the infinite chains of Hba(-). In addition, coordinated Phen molecules and lattice water molecules are linked via C-H center dot center dot center dot OW hydrogen bonds to form infinite zigzag chains. These different chains are connected by OW-H center dot center dot center dot O hydrogen bonds. pi-pi interaction plays an important role in the stabilization of structures 1-2. FT-IR, TGA, the diffuse reflectance, and UV-Vis spectra were also used to characterize these compounds. (C) 2018 Elsevier B.V. All rights reserved.