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- Title
Zinc Complexes of a Bioinspired Binucleating Ligand Platform - Equilibria in Solution and Structures in the Solid State.
- Authors
Wöckel, Simone; Gałęzowska, Joanna; Dechert, Sebastian; Meyer-Klaucke, Wolfram; Nordlander, Ebbe; Meyer, Franc
- Abstract
The zinc(II) coordination chemistry of the bioinspired bis(tetradentate) ligand 3,5-bis{bis[2-(1-methylimidazolyl)methyl]aminomethyl}pyrazole (L) was studied in detail both in solution and in the solid state. Six different species were determined in aqueous solution by means of potentiometry within the pH range 2-11, namely mononuclear [ZnH2L]4+, dinuclear [Zn2L]4+, [Zn2H-1L]3+ and [Zn2H-2L]2+, as well as tetranuclear [Zn4H-5L2]3+ and [Zn4H-6L2]2+. Complexes representing the protonation state of four of these species could be isolated and structurally characterized by X-ray diffraction, namely [ZnH2L(MeCN)](ClO4)4 ( 1), [Zn2H-1L](SO3CF3)3 ( 4), [Zn2H-1L(MeOHOMe)](ClO4)2 ( 5a), [Zn2H-1L(OMe)](ClO4)2 ( 5b), and [(Zn2H-1L)2(μ-O)(μ-OH)](ClO4)3 ( 6). In addition, a bis(pyrazolato)-bridged complex, [(ZnH-1L)2](ClO4)2 ( 2), was obtained and structurally characterized, and it was found to exhibit ligand dynamics in solution. Both 5a and 5b are likely present in solution, which requires significant plasticity of the Zn ···Zn distance (4.21 Å in 5a vs. 3.38 Å in 5b). Interconversion of 5a and 5b is proposed to be a facile process, supporting the idea that the Zn-O2H3-Zn moiety is a functionally relevant hydrolytic zinc-aqua structure in oligozinc metalloenzymes. The tetranuclear complex 6 that features two {Zn2H-1L} subunits connected by a central μ-oxido-μ-hydroxido moiety is unprecedented in zinc(II) chemistry. Combining X-ray crystallography with potentiometry, ESI mass spectrometry, as well as NMR and EXAFS spectroscopy has provided a comprehensive picture of the multitude of species present in this rather complex system.
- Subjects
ZINC ions; COORDINATE covalent bond; LIGANDS (Chemistry); PYRAZOLES; COMPLEX compounds; MOIETIES (Chemistry); METALLOENZYMES
- Publication
European Journal of Inorganic Chemistry, 2012, Vol 2012, Issue 29, p4728
- ISSN
1434-1948
- Publication type
Article
- DOI
10.1002/ejic.201200269