THE 1ST KEGGIN-ANION WITH TETRAHEDRAL COORDINATION OF COPPER(II)-OXYGEN - [ALPHA-CU0.4(H2)0.6O4W12O36]6-

The solution of the Cu(II)-containing heteropolyanion was prepared sta rting from an aqueous solution of Na2WO4, adjusting to pH 5-6 by addin g slowly a solution of Cu(NO3)2 in HNO3. The addition of the correspon ding amount of N(CH3)4Br to the concentrated solution led to the cryst allization of the greenish-yellow mixed crystals (TMA)6[alpha-Cu0.4(H2 )0.6O4W12O36] . 9H2O. After repeated recrystallization it has been inv estigated by chemical, spectroscopic (IR/Raman, UV, W-183/H-1-NMR, ESR ) and X-ray diffraction methods (monoclinic; space group P2(1); a = 13 .117(4), b = 21.466(4), c = 13.223(3) angstrom, beta = 91.60-degrees; 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 t o 1.93 angstrom. The alternative occupation of the central KEGGIN posi tion with copper(II) and two protons, respectively, accounts for the d ifferent distances. The prepared solid solution represents the first e xample for the tetrahedral copper(II)-oxygen coordination in any heter opolyanion compound.