Acid/base responsive assembly/dis-assembly of a family of zirconium(iv) clusters with a cyclic imide-dioxime ligand

Passadis, S. S., Hadjithoma, S., Papanikolaou, M. G., Keramidas, A. D., Miras, H. N. and Kabanos, T. A. (2022) Acid/base responsive assembly/dis-assembly of a family of zirconium(iv) clusters with a cyclic imide-dioxime ligand. Dalton Transactions, 51(5), pp. 1806-1818. (doi: 10.1039/d1dt03641f) (PMID:35018917)

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Abstract

The hydrolytically stable dioxime ligand (2Z-6Z)-piperidine-2,6-dione (H3pidiox) acts as a strong chelator mainly with hard metals in high oxidation states, a pre-requisite for potential applications in metal sequestering processes from aqueous solutions. Reaction of ZrCl4 with H3pidiox in methanol gives the mononuclear compound [ZrIV(η1,η1,η2-H2pidiox-O,N,O′)2(OH2)2]Cl2·H2O·CH3OH (1), while the same reaction mixture in the presence of KOH gave the pentanuclear ZrOC [ZrIV5(μ2-OH)4(OH2)4(μ2–η1,η1,η2-Hpidiox-O,N,O′)4(η1,η1,η1-HpidioxO,N,O′)4]·5KCl·3CH3OH·8H2O (2). Compound 1 is formed at very acidic pH = 0, and the pentanuclear ZrOC 2 at higher pH values (pH = 2). Compounds 1 and 2 were characterized by single crystal X-ray structure analysis, multi-nuclear NMR spectroscopy and ESI-MS spectrometry. The single crystal X-ray structure analysis of 1 revealed a mononuclear zirconium(IV) compound containing an eight-coordinate zirconium atom bound to two singly deprotonated H2pidiox− ligands and two water molecules in a severely distorted bicapped octahedral geometry. The pentanuclear ZrOC 2 constitutes the second example of a Zr5 cluster to be reported and the first one in which the four zirconium atoms are arranged in a tetrahedral arrangement with the fifth occupying the center of the tetrahedron. 1D and 2D NMR spectroscopies of the acidic CD3OD solutions of complex 1 reveal a fast equilibrium between 1 and 2. Addition of KOH into a CH3OH solution of 2 results in the controlled fast transformation of 2 to an asymmetric hexanuclear ZrOC 3 as evidenced by the NMR and real-time ESI-MS solution studies. Further addition of KOH to the solution of 3 leads to the ZrOC 4, and on the basis of NMR and ESI-MS data and in comparison with the known hexanuclear titanium(IV)/H3pidiox cluster, it is concluded that the cluster 4 should have a hexanuclear structure. Electrospray ionization mass spectrometry (ESI-MS) demonstrated not only the structural stability 1 and 2 in solution, but also revealed the reversible pH driven dis-assembly/re-assembly process between the monomeric 1 and the pentanuclear ZrOC 2.

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). We would like to thank EPSRC (EP/R01308X/1) and the University of Glasgow for supporting this work.
Keywords:Inorganic Chemistry
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Moiras, Dr Haralampos
Authors: Passadis, S. S., Hadjithoma, S., Papanikolaou, M. G., Keramidas, A. D., Miras, H. N., and Kabanos, T. A.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Dalton Transactions
Publisher:Royal Society of Chemistry (RSC)
ISSN:1477-9226
ISSN (Online):1477-9234
Published Online:24 December 2021
Copyright Holders:Copyright © The Royal Society of Chemistry 2022
First Published:First published in Dalton Transactions 51(5): 1806-1818
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
300591Programmable Molecular Metal Oxides (PMMOs) - From Fundamentals to ApplicationLeroy CroninEngineering and Physical Sciences Research Council (EPSRC)EP/R01308X/1Chemistry