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Zinc Complexes of a Bioinspired Binucleating Ligand Platform – Equilibria in Solution and Structures in the Solid State
Author(s) -
Wöckel Simone,
Gałęzowska Joanna,
Dechert Sebastian,
MeyerKlaucke Wolfram,
Nordlander Ebbe,
Meyer Franc
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201200269
Subject(s) - chemistry , zinc , protonation , ligand (biochemistry) , aqueous solution , moiety , crystallography , stereochemistry , solid state , x ray crystallography , inorganic chemistry , medicinal chemistry , diffraction , organic chemistry , ion , biochemistry , receptor , physics , optics
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 [ZnH 2 L] 4+ , dinuclear [Zn 2 L] 4+ , [Zn 2 H –1 L] 3+ and [Zn 2 H –2 L] 2+ , as well as tetranuclear [Zn 4 H –5 L 2 ] 3+ and [Zn 4 H –6 L 2 ] 2+ . Complexes representing the protonation state of four of these species could be isolated and structurally characterized by X‐ray diffraction, namely [ZnH 2 L(MeCN)](ClO 4 ) 4 ( 1 ), [Zn 2 H –1 L](SO 3 CF 3 ) 3 ( 4 ), [Zn 2 H –1 L(MeOHOMe)](ClO 4 ) 2 ( 5a ), [Zn 2 H –1 L(OMe)](ClO 4 ) 2 ( 5b ), and [(Zn 2 H –1 L) 2 (μ‐O)(μ‐OH)](ClO 4 ) 3 ( 6 ). In addition, a bis(pyrazolato)‐bridged complex, [(ZnH –1 L) 2 ](ClO 4 ) 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–O 2 H 3 –Zn moiety is a functionally relevant hydrolytic zinc–aqua structure in oligozinc metalloenzymes. The tetranuclear complex 6 that features two {Zn 2 H –1 L} 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.