Synthesis and structures of tetrahedral zinc(II) complexes bearing indomethacin and nitrogen donor ligands

Abstract

The interaction between imidazole (imi) linker with the selected non-steroidal anti-inflammatory drug indomethacin (indo) [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid)], and Zinc(II) acetate dihydrate resulted in the formation of a polymeric complex {[Zn(indo-O)(µ-indo-O,O’)(imi)].2.5H2O}nZI-1, (indo-O is monodentate indomethacin, µ-indo-O,O’ is bridging bidentate indomethacin, imi is imidazole, and n = 2). Also, two mononuclear Zn(II) carboxylate complexes with the general formula [Zn(indo-O)2(L)], synthesized from N, N'-donor ligands denoted by L, namely 2,2′-bipyridine (bpy) (ZI-2), and 1,10-phenanthroline (phen) (ZI-3), with indomethacin are reported. In a bid to understand the indomethacin ligand's binding mode, the three synthesized complexes have been characterized using elemental analysis, FT-IR, UV–Visible, 1H, and 13C NMR spectroscopies, as well as TG analysis. The results from single-crystal X-ray diffraction studies showed that ZI-1 is polymeric and consists of Zn(II) units having trans- ZnNO3 chromophore, in which one of the indomethacin ligands is coordinated in a monodentate mode to each of the Zn(II) ion, while two indomethacin ligands with the use of their carboxylate oxygen atoms, act as bridges between two tetrahedral Zn(II) centers. Also, three lattice water molecules present in the coordination sphere formed an interaction with the imidazole and indomethacin ligands. Structural analysis of the mononuclear complexes ZI-2 and ZI-3 confirmed the bidentate coordination of the N, N'-donor ligands, and a tetrahedral geometry around the Zn(II). The crystal packing of ZI-2 and ZI-3 complexes were dominated by C-H···O, C-H···N, C-H···Cl, π···π, and C-H···π interactions. FT-IR analysis of the three complexes provided evidence of monodentate coordination of the indomethacin ligand. 1H NMR result of the complexes in DMSO-δ6 confirmed the presence of proton signals corresponding to the indomethacin ligand and the nitrogen donor ligands. ZI-1 had the least stability, as observed in TG studies.