Two novel mixed-ligand Ni(II) and Co(II) complexes with 1,10-phenanthroline: Synthesis, structural characterization, and thermal stability

Two nickel(II) and cobalt(II) complexes with phenanthroline, [Ni(Phen)(H₂O)₃Br]Br (1) and [Co(Phen)₂(H₂O)₂](Hba)₂·2H₂O (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 OH⋯Br intermolecular hydrogen bonds with the formation of a 2D plane network which is extended into a 3D network by π−π 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. NH⋯O, OH⋯O and CH⋯O intermolecular hydrogen bonds form a 3D net. NH⋯O hydrogen bonds form the infinite chains of Hba^–. In addition, coordinated Phen molecules and lattice water molecules are linked via CH⋯OW hydrogen bonds to form infinite zigzag chains. These different chains are connected by OWH⋯O hydrogen bonds. π−π 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.