Three novel complexes Co(II), Ni(II) and Zn(II) containing p-hydroxybenzoates and caffeine ligands were
synthesized and characterized by elemental analysis, FT-IR and UVevis Spectroscopy, molar conductivity
and single crystal X-ray diffraction methods. The thermal properties of the synthesized complexes were
investigated by TGA/DTA. The general formula of the complexes is [M(HOC6H4COO)2(H2O)4]$
2(C8H10N4O2)$8H2O (where: M: Co, Ni and Zn). The IR studies showed that carboxylate groups of phydroxybenzoate
ligands have monodentate coordination mode. The M2þ ions are octahedrally coordinated
by two p-hydroxybenzoate ligands, four water molecules leading to an overall MO6 coordination
environment. The medium-strength hydrogen bondings involving the uncoordinated caffeine ligands
and water molecules, coordinated and uncoordinated water molecules and p-hydroxybenzoate ligands
lead to three-dimensional supramolecular networks in the crystal structures.