Complexation of different transition metals with 4-(4-carboxyphenyl)-1,2,4-triazole: Synthesis, crystal structure and hirshfeld surfaces

Four new complexes based on the 4-(4-carboxyphenyl)-1,2,4-triazole (Hcpt) ligand, {[Co(cpt)2(H2O)4]·H2O}(1), {[Cr(cpt)2(H2O)4]·10H2O}(2), {[Fe(cpt)2(H2O)4]·10H2O}(3), {[Zn(cpt)2 (H2O)2]}(4) have been synthesized and characterized by elemental analysis, single crystal X-ray diffraction and TGA. For complexes 1, 2, and 3, they almost have the same coordination mode that only one nitrogen atom of triazole are involved in the coordination, while in the complex 4, only the group COO− participates in the coordination. In the crystal structure of 1, each structural unit[Co(cpt)2(H2O)4] is linked to another by hydrogen bonding formed by the lattice water molecules, thus forming a one-dimensional chain structure; In the crystal structure of 2 or 3, each structural unit[Cr(cpt)2(H2O)4] or [Fe(cpt)2(H2O)4] forms a two-dimensional layered structure by intermolecular hydrogen bonds from the coordinated water molecule and the group COO−. The results of thermogravimetric analysis show that the loss of lattice water and coordinated water molecules in 1, 2 and 3 is below 120 °C, while the loss of coordinated water molecules in 4 is in the temperature range of 190-260 °C. Hirshfeld surface shows that the NH⋯O hydrogen bonding interaction plays a significant role towards the conformation of the basic structure of these complexes.