Sandwich-type HfIV and ZrIVcomplexes composed of tri-lacunary Keggin polyoxometalates: structure of [M3(μ-OH)3(A-α-PW9O34)2]9? (M = Hf and Zr)?

Dalton Transactions Pub Date: 2008-12-04 DOI: 10.1039/B813710M

Abstract

The syntheses and structures of hafnium(IV) and zirconium(IV) complexes with Keggin tri-lacunary polyoxometalates (POM) [A-α-PW9O34]9?, i.e., (Et2NH2)7H2[Hf3(μ-OH)3(A-α-PW9O34)2]·11H2O (Et2NH2-1) and (Et2NH2)7H2[Zr3(μ-OH)3(A-α-PW9O34)2]·12H2O (Et2NH2-2) are described. The two POMs, Et2NH2-1 and Et2NH2-2, were obtained as analytically pure, colorless crystals in 30.0 and 40.9% yields, respectively, by 1:3-molar ratio reactions of [A-PW9O34]9? with Hf(SO4)2 and Zr(SO4)2, respectively, in aqueous solutions at 80–90 °C, followed by refluxing. The two POMs were characterized by elemental analysis, TG/DTA, FTIR, solution (31P and 183W) NMR and X-ray crystallography. X-Ray structure analysis of Et2NH2-1 revealed that in polyoxoanion 1, the three 6-coordinate prismatic HfIV ions linked with the three bridging OH groups, i.e., the [Hf3(μ-OH)3]9+ cluster cation was sandwiched between two α-Keggin tri-lacunary POMs. The molecular structure of 1 was isostructural with that of polyoxoanion 2 in Et2NH2-2. X-Ray crystallography also showed that the crude crystals of Et2NH2-1 and Et2NH2-2, which were first formed without refluxing, contained the two isomeric crystalline species in a 7:3 ratio with the α,α- and α,β-junctions of the two Keggin tri-lacunary POMs. These facts were also confirmed by 31P NMR in D2O. By refluxing the solutions containing the crude crystals, only the α,α-isomers of Et2NH2-1 and Et2NH2-2 were finally isolated.

Graphical abstract: Sandwich-type HfIV and ZrIVcomplexes composed of tri-lacunary Keggin polyoxometalates: structure of [M3(μ-OH)3(A-α-PW9O34)2]9? (M = Hf and Zr)
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