Zirconium complexes oxygen ligands

Diantipyrinylmethane in 2M-HQ acts on a bidentate oxygen ligand towards forming an eight-membered chelate ring. No evidence could be obtained for N-co-ordination as previously suggested for the zirconium complex of this ligand. 

No zirconium(III) complexes with oxygen donor ligands have been isolated. However, the electronic absorption spectra of aqueous solutions of Zrl3 have been interpreted in terms of the formation of aqua complexes (equation 4).29 The spectrum of a freshly prepared solution of Zrl3 exhibits a band at 24 400 cm-1, which decays over a period of 40 minutes, and a shoulder at 22000 cm-1, which decays more rapidly. The 24400 cm-1 band has been assigned to [Zr(H20)6]3+, and the 22000 cm-1 shoulder has been attributed to an unstable intermediate iodo-aqua complex. If it is assumed that the absorption band of [Zr(H20)6]3+ is due to the 2T 2Ee ligand-field transition, the value of A is 24 400 cm. This corresponds to a A value of 20 300 cm-1 for [Ti(H20)6]3+ 30 and 17 400 cm-1 for the octahedral ZrCl6 chromophore in zirconium(III) chloride.25... 

Very little X-ray data is available for zirconium or hafnium complexes that contain oxo ligands. The only X-ray evidence for the existence of the zirconyl or hafnyl group, M=Oz+, comes from a structural study of K2Zr03.157 This compound contains chains of Zr05 square pyramids that share basal edges. The Zr—O distance to the apical oxygen atom (1.92 A) is appreciably shorter than the sum of ionic radii (2.20 A), the sum of the covalent radii (2.22 A)... 

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