Indole core-based Copper(II), Cobalt(II), Nickel(II) and Zinc(II) complexes: Synthesis, spectral and biological study

•Synthesis of indole core-based Copper(II), Cobalt(II), Nickel(II) and Zinc(II) complexes.•Thermal analysis studies for Copper(II), Cobalt(II), complexes indicated the presence of coordinated water molecules.•Structural properties are investigated by FT-IR, 1H NMR, ESI-mass, electronic spectra, thermal, magnetic measurements and powder-XRD data.•Mass fragmentation pattern is consistent with the proposed structures of the metal complexes.•The newly synthesized complexes are found to be biologically active. In search of biologically active compounds, we have synthesized new Copper(II), Cobalt(II), Nickel(II) and Zinc(II) metal complexes by the reaction of N'-(4-(diethylamino)-2-hydroxybenzylid-ene)-5-methyl-3-phenyl-1H-indole-2-carbohydrazide (L) with the corresponding metal salts. The synthesized metal complexes are thoroughly characterized by various spectral techniques. The spectral data reveal the octahedral geometry for Copper(II), Cobalt(II) and Nickel(II) complexes and tetrahedral geometry for Zinc(II) complex. All the compounds have been screened for their antibacterial, antifungal, anti-tuberculosis and antioxidant activity. The complexes [Cu(L)(Cl)(H2O)2] and [Co(L)(Cl)(H2O)2] exhibited excellent activity against bacteria E. coli and B. subtilis with MIC-12.50 µg/mL and fungi A. flavus and A. niger with MIC-12.50 µg/mL. Among the screened compounds for anti-tuberculosis activity, the complexes [Cu(L)(Cl)(H2O)2], [Co(L)(Cl)(H2O)2] and [Zn(L)(Cl)] was found to be the most active against M. tuberculosis with a MIC of 3.125 µg/mL. Further, the ligand (L) and its [Cu(L)Cl(H2O)2] and [Co(L)Cl(H2O)2] complexes have shown good scavenging activity. [Display omitted]