Synthesis, structural and physicochemical characterization of a titanium(IV) compound with the hydroxamate ligand N,2-dihydroxybenzamide

Passadis, S. S., Hadjithoma, S., Siafarika, P., Kalampounias, A. G., Keramidas, A. D., Miras, H. N. and Kabanos, T. A. (2021) Synthesis, structural and physicochemical characterization of a titanium(IV) compound with the hydroxamate ligand N,2-dihydroxybenzamide. Molecules, 26(18), 5588. (doi: 10.3390/molecules26185588)

Abstract

The siderophore organic ligand N,2-dihydroxybenzamide (H2dihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of H2dihybe with TiCl4 in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [TiIV4(μ-O)2(HOCH3)4(μ-Hdihybe)4(Hdihybe)4]Cl4∙10H2O∙12CH3OH (1). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, 13C, and 1H NMR spectroscopy, solid-state and solution UV–Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti4(μ-O)2 of 1 constitutes a rare structural motif for discrete TiIV4 oxo-clusters. High-resolution ESI-MS studies of 1 in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti4(μ-O)2}. Solid-state IR spectroscopy of 1 showed the presence of an intense band at ~800 cm−1 which is absent in the spectrum of the H2dihybe and was attributed to the high-energy ν(Ti2–μ-O) stretching mode. The ν(C=O) in 1 is red-shifted by ~10 cm−1, while the ν(N-O) is blue-shifted by ~20 cm−1 in comparison to H2dihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. 1H and 13C NMR solution (CD3OD) studies of 1 reveal that it retains its integrity in CD3OD. The observed NMR changes upon addition of base to a CD3OD solution of 1, are due to an acid–base equilibrium and not a change in the TiIV coordination environment while the decrease in the complex’s lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of 1 in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC 1 exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations.

• Item Type: Articles
• Additional Information: The research work was supported by the Hellenic Foundation for Research and Innovation (HFRI) under the HFRI PhD Fellowship grant (Fellowship Number: 1553). This work was co-funded by the European Regional Development Fund and the Republic of Cyprus through the Research and Innovation Foundation (Project: EXCELLENCE/1216/0515). The APC was funded by EPSRC. We would like to thank EPSRC (EP/S017046/1) and the University of Glasgow for supporting this work.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Moiras, Professor Haralampos

Creator Roles

Miras, H. N.: Writing – original draft, Writing – review and editing, Supervision

• Authors: Passadis, S. S., Hadjithoma, S., Siafarika, P., Kalampounias, A. G., Keramidas, A. D., Miras, H. N., and Kabanos, T. A.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Molecules
• Publisher: MDPI
• ISSN: 1420-3049
• ISSN (Online): 1420-3049
• Published Online: 15 September 2021
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in Molecules 26(18): 5588
• Publisher Policy: Reproduced under a Creative Commons License

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
302667		3DSynth: Design and fabrication of cartridges for digital chemical synthesis	Leroy Cronin	Engineering and Physical Sciences Research Council (EPSRC)	EP/S017046/1	Chemistry