Das erste KEGGIN-Anion mit tetraedrischer. Kupfer(II)—Sauerstoff-Koordination: [α-Cu0,4(H2)0,6O4W12O36]6−

The First KEGGIN-Anion with Tetrahedral Coordination of Copper(II)-Oxygen: α-Cu_0,4(H₂)_0.6O₄W₁₂O₃₆]^6? The solution of the Cu^II-containing heteropolyanion was prepared starting from an aqueous solution of Na₂WO₄, adjusting to pH 5–6 by adding slowly a solution of Cu(NO₃)₂ in HNO₃. The addition of the corresponding amount of N(CH₃)₄Br to the concentrated solution led to the crystallization of the greenish-yellow mixed crystals (TMA)₆α-Cu_0.4(H₂)_0.6O₄W₁₂O₃₆] · 9 H₂O. After repeated recrystallization it has been investigated by chemical, spectroscopic (IR/Raman, UV, ¹⁸³W/¹H-NMR, ESR) and X-ray diffraction methods (monoclinic; space group P2₁; a = 13.117(4), b = 21.466(4), c = 13.223(3) Å, β = 91.60°; Z = 2; D_c = 3.041 g · cm^?3; R = 8.0%). The distances of the four “tetrahedral” oxygen atoms to the position (0, 0, 0) range from 1.67 to 1.93 Å. The alternative occupation of the central KEGGIN position with copper(II) and two protons, respectively, accounts for the different distances. The prepared solid solution represents the first example for the tetrahedral copper(II)-oxygen coordination in any heteropolyanion compound.