Easy coordinate geometry indexes, τ4 and τ5 and HSA study for unsymmetrical Pd(II), Fe(II), Zn(II), Mn(II), Cu(II) and VO(IV) complexes of a tetradentate ligand: Synthesis, characterization, properties, and antioxidant activities

[Display omitted] •Six new monomeric Schiff base complexes of [M = Pd (1), Zn (2), Cu (3), Fe (4), Mn (6) and V(O) (7)] have been synthesized.•Coordinate geometry indexes, τ4 and τ5 were calculate. Interesting findings were highlighted.•The antioxidant of the complexes are also studied which show a good result.•Hirshfeld surfaces and fingerprint plots analysis were provided.•X-ray crystal structures were done and discussed. In this study, versatile multifunctional Schiff base derivative and its metal complexes were synthesized and characterized by 1H, 13C NMR, UV–vis, IR, CHN analysis, Mass spectra, m.p. and X-ray diffraction. The tetradentate Schiff base H2L was synthesized using a microwave-assisted method. Metal complexes [M = Pd (1), Zn (2), Cu (3), Fe (4), Ni (5) Mn (6) and V(O) (7)] were prepared using mild conditions. Their antioxidant activities were assessed by four different methods (DPPH, FTC, HRSA, and H2O2 SA). The antioxidant results revealed that these compounds have moderate to good activities against the BHA which was used as a standard or a positive control. The crystal and molecular structures of H2L, 1, 2 and 7 have been determined by X-ray diffraction on single crystals with Hirshfeld surfaces and fingerprint plots analysis facilitating a comparison of intermolecular interaction. H2L possesses intra-molecular hydrogen bonds. In the complexes, the tetra dentate Schiff base ligands (ONNO) forms a heterocyclic base plane of a distorted square-pyramidal coordination geometry in 1, 2 and 7. Interestingly, only the enol-imine tautomeric form was confirmed by various techniques as an EE isomer. Geometric parameter for four and five-coordinate complexes, τ4 and τ4 for quantitatively evaluating the geometry of the complexes are presented.