Synthesis, structural, and physicochemical characterization of a Ti6 and a unique type of Zr6 oxo clusters bearing an electron-rich unsymmetrical {OON} catecholate/oxime ligand and exhibiting metalloaromaticity

Passadis, S. S., Papanikolaou, M. G., Elliott, A., Tsiafoulis, C. G., Tsipis, A. C., Keramidas, A. D., Miras, H. N. and Kabanos, T. A. (2020) Synthesis, structural, and physicochemical characterization of a Ti6 and a unique type of Zr6 oxo clusters bearing an electron-rich unsymmetrical {OON} catecholate/oxime ligand and exhibiting metalloaromaticity. Inorganic Chemistry, 59(24), pp. 18345-18357. (doi: 10.1021/acs.inorgchem.0c02959) (PMID:33289378)

Abstract

The chelating catechol/oxime ligand 2,3-dihydroxybenzaldehyde oxime (H3dihybo) has been used to synthesize one titanium(IV) and two zirconium(IV) compounds that have been characterized by single-crystal X-ray diffraction and 1H and 13C NMR, solid-state UV–vis, and ESI-MS spectroscopy. The reaction of TiCl4 with H3dihybo and KOH in methanol, at ambient temperature, yielded the hexanuclear titanium(IV) compound K2[TiIV6(μ3-O)2(μ-O)3(OCH3)4(CH3OH)2(μ-Hdihybo)6]·CH3OH (1), while the reaction of ZrCl4 with H3dihybo and either nBu4NOH or KOH also gave the hexanuclear zirconium(IV) compounds 2 and 3, respectively. Compounds 1–3 have the same structural motif [MIV6(μ3-Ο)2(μ-Ο)3] (M = Ti, Zr), which constitutes a unique example with a trigonal-prismatic arrangement of the six zirconium atoms, in marked contrast to the octahedral arrangement of the six zirconium atoms in all the Zr6 clusters reported thus far, and a unique Zr6 core structure. Multinuclear NMR solution measurements in methanol and water proved that the hexanuclear clusters 1 and 3 retain their integrity. The marriage of the catechol moiety with the oxime group in the ligand H3dihybo proved to be quite efficient in substantially reducing the band gaps of TiO2 and ZrO2 to 1.48 and 2.34 eV for the titanium and zirconium compounds 1 and 3, respectively. The application of 1 and 3 in photocurrent responses was investigated. ESI-MS measurements of the clusters 1 and 3 revealed the existence of the hexanuclear metal core and also the initial formation of trinuclear M3 (M = Ti, Zr) building blocks prior to their self-assembly into the hexanuclear M6 (M = Ti, Zr) species. Density functional theory (DFT) calculations of the NICSzz scan curves of these systems revealed that the triangular M3 (M = Ti, Zr) metallic ring cores exhibit pronounced metalloaromaticity. The latter depends upon the nature of the metallic center with NICSzz(1) values equal to −30 and −42 ppm for the Ti (compound 1) and Zr (compound 2) systems, respectively, comparable to the NICSzz(1) value of the benzene ring of −29.7 ppm calculated at the same level of theory.

• 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), and funded by the European Regional Development Fund and the Republic of Cyprus through the Research and Innovation Foundation (Project: EXCELLENCE/1216/0515). H.N.M. would like to thank the University of Glasgow for supporting this work and Prof. L. Cronin for providing access to the X-ray and ESI-MS facilities.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Elliott, Mr Alexander and Moiras, Professor Haralampos
• Authors: Passadis, S. S., Papanikolaou, M. G., Elliott, A., Tsiafoulis, C. G., Tsipis, A. C., Keramidas, A. D., Miras, H. N., and Kabanos, T. A.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Inorganic Chemistry
• Publisher: American Chemical Society
• ISSN: 0020-1669
• ISSN (Online): 1520-510X
• Published Online: 08 December 2020
• Copyright Holders: Copyright © 2020 American Chemical Society
• First Published: First published in Inorganic Chemistry 59(24):18345–18357
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher