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)

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) A, b = 22.6699(7) A, c = 18.5533(6) A, β = 123.9000(12)°, V = 8843.3(5) A3, 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) A, b = 22.6121(14) A, c = 18.8703(11) A, β = 124.046(3)°, V = 8974.9(9) A3, Z = 4), Cs8[(γ-SiW10O36)2{Zr(H2O)}4(μ4-O)(μ-OH)6]·26H2O (Zr4, tetragonal, P41212 (No. 92), a = 12.67370(10) A, c = 61.6213(8) A, V = 9897.78(17) A3, 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) A, c = 61.5483(9) A, V = 9897.91(18) A3, 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 ...