Synthesis and Catalysis of Di- and Tetranuclear Metal Sandwich-Type Silicotungstates [(γ-SiW10O36)2M2(μ-OH)2]10−and [(γ-SiW10O36)2M4(μ4-O)(μ-OH)6]8−(M = Zr or Hf)
- 28 March 2008
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 130 (16), 5472-5478
- https://doi.org/10.1021/ja078313i
Abstract
The di- and tetranuclear metal sandwich-type silicotungstates of Cs10[(γ-SiW10O36)2{Zr(H2O)}2(μ-OH)2]·18H2O (Zr2, monoclinic, C2/c (No. 15), a = 25.3315(8) Å, b = 22.6699(7) Å, c = 18.5533(6) Å, β = 123.9000(12)°, V = 8843.3(5) Å3, Z = 4), Cs10[(γ-SiW10O36)2{Hf(H2O)}2(μ-OH)2]·17H2O (Hf2, monoclinic, space group C2/c (No. 15), a = 25.3847(16) Å, b = 22.6121(14) Å, c = 18.8703(11) Å, β = 124.046(3)°, V = 8974.9(9) Å3, Z = 4), Cs8[(γ-SiW10O36)2{Zr(H2O)}4(μ4-O)(μ-OH)6]·26H2O (Zr4, tetragonal, P41212 (No. 92), a = 12.67370(10) Å, c = 61.6213(8) Å, V = 9897.78(17) Å3, Z = 4), and Cs8[(γ-SiW10O36)2{Hf(H2O)}4(μ4-O)(μ-OH)6]·23H2O (Hf4, tetragonal, P41212 (No. 92), a = 12.68130(10) Å, c = 61.5483(9) Å, V = 9897.91(18) Å3, Z = 4) were obtained as single crystals suitable for X-ray crystallographic analyses by the reaction of a dilacunary γ-Keggin silicotungstate K8[γ-SiW10O36] with ZrOCl2·8H2O or HfOCl2·8H2O. These dimeric polyoxometalates consisted of two [γ-SiW10O36]8− units sandwiching metal–oxygen clusters such as [M2(μ-OH)2]6+ and [M4(μ4-O)(μ-OH)6]8+ (M = Zr or Hf). The dinuclear zirconium and hafnium complexes Zr2 and Hf2 were isostructural. The equatorially placed two metal atoms in Zr2 and Hf2 were linked by two μ-OH ligands and each metal was bound to four oxygen atoms of two [γ-SiW10O36]8− units. The tertanuclear zirconium and hafnium complexes Zr4 and Hf4 were isostructural and consisted of the adamantanoid cages with a tetracoordinated oxygen atom in the middle, [M4(μ4-O)(μ-OH)6]8+ (M = Zr or Hf). Each metal atom in Zr4 and Hf4 was linked by three μ-OH ligands and bound to two oxygen atoms of the [γ-SiW10O36]8− unit. The tetra-nuclear zirconium and hafnium complexes showed catalytic activity for the intramolecular cyclization of (+)-citronellal to isopulegols without formation of byproducts resulting from etherification and dehydration. A lacunary silicotungstate [γ-SiW10O34(H2O)2]4− was inactive, and the isomer ratio of isopulegols in the presence of MOCl2·8H2O (M = Zr or Hf) were much different from that in the presence of tetranuclear complexes, suggesting that the [M4(μ4-O)(μ-OH)6]8+ core incorporated into the POM frameworks acts as an active site for the present cyclization. On the other hand, the reaction hardly proceeded in the presence of dinuclear zirconium and hafnium complexes under the same conditions. The much less activity is possibly explained by the steric repulsion from the POM frameworks in the dinuclear complexes.Keywords
This publication has 67 references indexed in Scilit:
- Synthesis and Structural Characterization of a γ-Keggin-Type Dimeric Silicotungstate with a Bis(μ-hydroxo) Dizirconium Core [(γ-SiW10O36)2Zr2(μ-OH)2]10-Inorganic Chemistry, 2007
- ZrIV-Monosubstituted Keggin-Type Dimeric Polyoxometalates: Synthesis, Characterization, Catalysis of H2O2-Based Oxidations, and Theoretical StudyInorganic Chemistry, 2006
- Synthesis and Structure of Asymmetric Zirconium-Substituted Silicotungstates, [Zr6O2(OH)4(H2O)3(β-SiW10O37)3]14- and [Zr4O2(OH)2(H2O)4(β-SiW10O37)2]10-Inorganic Chemistry, 2006
- Zirconium-Substituted Isopolytungstates: Structural Models for Zirconia-Supported Tungsten CatalystsInorganic Chemistry, 2006
- Synthesis, Structural Characterization, and Catalytic Performance of Dititanium-Substituted γ-Keggin SilicotungstateInorganic Chemistry, 2006
- Stereoisomerism in polyoxometalates: structural and spectroscopic studies of bis(malate)-functionalized cluster systemsChemical Communications, 2005
- Atomic-scale structure of nanocrystallineprepared by high-energy ball millingPhysical Review B, 2005
- A Novel Zirconium Polyoxometalate Complex That Contains Both a Coordinated Saturated Anion, [PMo12O40]3-, and a Coordinated Unsaturated Anion, [PMo11O39]7-Inorganic Chemistry, 2003
- [20] Processing of X-ray diffraction data collected in oscillation modeMethods in Enzymology, 1997
- Polyoxoanions derived from tungstosilicate, A-.beta.-SiW9O3410-: synthesis and crystallographic and tungsten-183 NMR characterization of Si2W18Zr3O71H311-, including its organic solvent soluble Bu4N+ saltInorganic Chemistry, 1989