A new Ni²⁺, Pd²⁺, and Pt²⁺ coordination compounds of carbothiohydrazide based chelating agent: Synthesis, characterization, crystal structure, DFT-TDFT calculations, antioxidant, and antimircrobial activities

The new (Z)-N’-(1-methyl-2-oxoindolin-3-ylidene)morpholine-4-carbothiohydrazide chelating agent (HL) and its [Ni(L)₂] (1), [Pd(L)Cl] (2), and [Pt(L)₂] (3) chelates were prepared. Different spectroscopic and analytical tools, including elemental analyses, conductivity measurements, ¹H- and ¹³C NMR, FT-IR, UV–Vis, FAB-MS, XRD, SEM, and thermal analysis (TG/DTG), were employed to elucidate structures and mode of bonding in the investigated compounds. The results informed that the metal:ligand ratio in Pd²⁺ chelate is 1:1, whereas in Ni²⁺ and Pt²⁺ chelates, it is 1:2. Moreover, all the examined complexes are neutral species. The chelating agent acted as a tridentate mono-negatively charged ion (in its thiolate form) in Ni²⁺ and Pd²⁺ chelates bind via thiolate sulfur, imine nitrogen, and carbonyl oxygen atoms. Using X-ray single crystal diffraction, the molecular structure of Pt²⁺ chelate (3) has been identified. With a, b, and c equal to 14.3478 (4), 17.9373 (5), and 14.2769(4) Å, respectively, it crystallizes in the monoclinic P 21/c space group, with angles α = β = 90° and γ = 111.7310(10)°. Based on the geometrical parameter τ₄ of 0.048, the Pt²⁺ chelate has a slightly distorted square planer arrangement with two chelating agent anions (in their thiolate forms) acting as a bidentate NS chelating agents, bonded to the central Pt²⁺ ion via thiolate sulfur and imine nitrogen atoms leading to two five-membered chelate rings. Magnetic and UV–Vis measurements suggested that Pd²⁺ and Pt²⁺ chelates have a square-planar geometry. Meanwhile, the Ni²⁺ ion in 1 existed in the octahedron coordination sphere. XRD diffractograms of all investigated compounds showed high-intensity diffraction peaks due to their crystalline nature. The lack of hydrated and coordinated water molecules in compound formulae was verified through thermal pyrolysis investigations of the chelating agent and its metal chelates. Experimental data of the chelating agent and its metal(II) chelate compounds were compared with predicted ones measured at the B3LYP/LanL2DZ of theory. Theoretical data revealed that the Z form of chelating agent HL is steadier than the E form by a relative energy of 6.5 kcal mol⁻¹. The interconnects in [Pt(L)₂] were identified through the Hirshfeld surface analysis. The antioxidant activity tests disclose that the Pt²⁺ chelate has a potent antioxidant ability compared to the Ni²⁺ and Pd²⁺ chelates. The Pd²⁺ chelate displayed the highest antifungal effects against A. fumigatus, with activity even higher than that demonstrated by the Ketoconazole drug standard.