Moisture stable heteroleptic titanium (IV) complexes derived from 8-hydroxyquinoline: synthesis, antibacterial, and antifungal studies

Systematic efforts have been made for the synthesis of moisture stable derivatives of titanium (IV) with both nitrogen- and sulfur-based ligands. New heteroleptic titanium (IV) complexes derived from 8-hydroxyquinoline (HQ) of the types [(Q2)Ti{((OiPr)2-n(L1OR1)n-1)(L1OR)}] (3a–3c), [(Q2)Ti(OiPr)2-n(L2)] (3d,3g), [(Q2)Ti(L1OR)(L2)] (3e, 3f, 3h, 3i) were prepared by treating the precursor [(Q2)Ti(OiPr)2] (2) with different alkoxyalkanols, 2-hydroxypyridine (HPy), and 2-hetroaryl methyl ketone oxime in different mole ratios using anhydrous toluene as solvent (where, n = 1–2, HQ = 8-HQ, iPr = isopropyl, L1 = O–CH2–CH2–, R = CH3, C2H5, R1 = C2H5, and L2H = 2-HPy, HONC(Me)th-2). Stability study of all these complexes were performed by UV–Visible (UV–Vis) spectroscopy at room temperature and was interpreted on the basis of absorption band arose due to ligand-to-metal charge transfer. All these complexes have good stability against hydrolysis and the shift observed in the absorption band was negligible even after the duration of 72 h persistence in 9:1 mixture of dimethyl sulfoxide and water. All the derivatives were characterized by various physicochemical techniques such as NMR (1H, 13C), Elemental Analysis, Mass, Thermogravimetric Analysis (TGA), FT-IR, and UV–Vis spectroscopy. Monomeric nature of all these derivatives was confirmed by mass spectra. TGA describes the multistage decomposition of complexes at 900 °C. Elemental analyses results are in agreement with the theoretical values. Other spectral data (NMR, FTIR, and UV–Vis) propose the attachment of titanium and ligands in hexa-coordinated fashion. Further, these were subjected for antibacterial and antifungal evaluation against a panel of microorganisms. Complex 3i has shown better activity compared to all its analogs of this series and it was more potent than the standard drugs gentamicin and fluconazole with minimum inhibitory concentrations of 0.017 µM against the Escherichia coli and 0.035 µM for Aspergillus niger, respectively.