1. Acid/base responsive assembly/dis-assembly of a family of zirconium(IV) clusters with a cyclic imide-dioxime ligand.
- Author
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Passadis, Stamatis S., Hadjithoma, Sofia, Papanikolaou, Michael G., Keramidas, Anastasios D., Miras, Haralampos N., and Kabanos, Themistoklis A.
- Subjects
ELECTROSPRAY ionization mass spectrometry ,ZIRCONIUM ,CHELATING agents ,NUCLEAR magnetic resonance spectroscopy ,ATOMS ,HYDROGEN bonding ,DERACEMIZATION ,BRITANNIA metal - Abstract
The hydrolytically stable dioxime ligand (2Z-6Z)-piperidine-2,6-dione (H
3 pidiox) 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 H3 pidiox in methanol gives the mononuclear compound [ZrIV (η1 ,η1 ,η2 -H2 pidiox-O,N,O′)2 (OH2 )2 ]Cl2 ·H2 O·CH3 OH (1), while the same reaction mixture in the presence of KOH gave the pentanuclear ZrOC [ZrIV 5 (μ2 -OH)4 (OH2 )4 (μ2 –η1 ,η1 ,η2 -Hpidiox-O,N,O′)4 (η1 ,η1 ,η1 -HpidioxO,N,O′)4 ]·5KCl·3CH3 OH·8H2 O (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 H2 pidiox− 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 CD3 OD solutions of complex 1 reveal a fast equilibrium between 1 and 2. Addition of KOH into a CH3 OH 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)/H3 pidiox 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. [ABSTRACT FROM AUTHOR]- Published
- 2022
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