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Download fileSynthesis, 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
journal contribution
posted on 2020-12-08, 13:35 authored by Stamatis
S. Passadis, Michael G. Papanikolaou, Alexander Elliott, Constantinos G. Tsiafoulis, Athanassios C. Tsipis, Anastasios D. Keramidas, Haralampos N. Miras, Themistoklis A. KabanosThe
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.
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Keywords
CH 3 OHsingle-crystal X-ray diffractionligand H 3 dihybohexanuclear clusters 1ESI-MSOCHn Bu 4 NOHNICS zz scan curveszirconium compounds 1zirconium atomsUVZr 6 clustersring cores exhibitDFThexanuclear M 6trinuclear M 3KOHZr 6 Oxo Clusters BearingTiZr 6 core structurehexanuclear metal core13 C NMRH 3 dihyboMultinuclear NMR solution measurementsIVOON