Water-soluble Cobalt(II) & Cobalt(III) complexes supported by new triazine Schiff base ligands: Synthesis, structure...

A new class of triazine ligands (E)-2-(2-(6-methyl-5-oxo-2,5-dihydro-1,2,4-triazin-3-yl)hydrazono)propanoic acid hydrate (HL1.H₂O) and (Z)-2-(((E)-4-amino-6-methyl-5-oxo-4,5-dihydro-1,2,4-triazin-3(2H)ylidene)hydrazono)propanoic acid (H₂L2) has been synthesized by the condensation reaction of pyruvic acid with diaminoguanidine and triaminoguanidine respectively. The corresponding Schiff base cobalt complexes [Co(L1)₂]_.2H₂O (1) and [Co(HL2)(L2)].H₂O (2) have also been synthesized and characterized by analytical, thermal, spectroscopic and diffraction studies. Strong field ligand results low spin Co(III) centre in 2, which was evidenced by the shorter bond length of Co(III) complex. In H₂L2 there is a choice of coordination modes based on distinct sets of donor atoms, both of which are seen in complex 2, involving either an -NH₂ group on position 4 of the triazine ring, or via a ring nitrogen of the triazine itself. The deprotonation of one version of L2 allows the formation of the ligand field stabilized low spin Co(III) in 2. In complex 1, each ligand binds to the metal via pyruvate oxygen, azomethine nitrogen and triazine nitrogen forming two five-membered stable chelate rings. In complex 2, the coordination sphere assembled by two types of coordinating atoms from the same ligand with different conformation. Their binding ability and mode of binding with CT-DNA and BSA was studied by UV- absorption, fluorescence and CD spectroscopy. Density Functional Theory (DFT) studies provide further insights into the mode of binding, structure and mechanism. The HOMO and LUMO energy gap values indicate that both the complexes are prone to interact with CT-DNA and BSA. We have also performed molecular docking calculations to understand the mode of binding and the corresponding results confirm our experimental findings.