A new bistriazine hydrazone ligand (H2L; H2BDTB) is derived from 5,6‐diphenyl‐1,2,4‐triazine‐3‐ylhydrazine (DTH) with o‐phthalaldehyde in ratio (2:1). The Fe(III), Co(II), Ni(II), Cu(II), and Th(IV) complexes (1–5), as well as the Co(II) complex (6) (prepared in the presence of cetyltrimethylammonium bromide [CTAB]), are synthesized. They are characterized by elemental analyses, spectral (ultraviolet–visible [UV–Vis], infrared [IR], mass, 1H NMR, and electron spin resonance [ESR]), magnetic susceptibility, molar conductivity, and thermal gravimetric analysis (TGA) measurements; and morphological structures are scanned by electron microscopy (SEM) that showed rod shape, irregular bulk sheets, and fused aggregated clusters for free ligand, Co(II) complexes (2 and 6), respectively. Moreover, cobalt(II) complex (6) exhibited an octahedral geometry; however, cobalt(II) complex (2) showed square planar geometry as deduced from magnetic moment and UV–Vis measurements. Fluorescence spectra for ligand and its Fe(III) and Th(IV) complexes have been measured in different solvents to investigate their solvatochromic behavior that used to estimate dipole moments either in ground and excited states. The antimicrobial and antitumor activities of free ligand and its complexes were investigated, in addition to molecular docking studies using MOE 2014.0901 software (PDB. I.D.3ce3). The data showed that Co(II) complex (6) can be nominated as one of the most powerful antitumor. The theoretical calculation for bistriazine ligand and its complexes were performed using DFT and PM3, and the data are correlated with the experimental results.
