A sandwich-type aluminium complex composed of tri-lacunary Keggin-type polyoxotungstate: synthesis and X-ray crystal structure of [(A-PW9O34)2{W(OH)(OH2)}{Al(OH)(OH2)}{Al(μ-OH)(OH2)2}2]7-

The synthesis and molecular structure of a dimeric aluminium complex composed of tri-lacunary alpha-Keggin polyoxometalate is described. The polyoxometalate, K6Na[(A-PW9O34)(2){W(OH)(OH2)} {Al(OH)(OH2)}{Al(mu-OH)(OH2)(2)}(2)]center dot 19H(2)O (KNa-1), afforded by the reaction in water of a tri-lacunary Keggin polyoxotungstate with excess aluminium nitrate, followed by crystallization from water, was obtained as analytically pure, homogeneous, colorless crystals. The compound KNa-1 was characterized by elemental analysis, TG/DTA, FT-IR, solution NMR (P-31, Al-27, and W-183), and X-ray crystallography. The single-crystal X-ray structure analysis revealed that two 6-coordinate aluminium ions linked with two bridging hydroxyl groups and four water molecules, i.e., [Al-2(III)(mu-OH)(2)(OH2)(4)](4+); a unit of a 6-coordinate tungsten ion linked with a hydroxyl group and a water molecule, i.e., [W(OH)(OH2)](5+); a unit of a 6-coordinate aluminium ion linked with a hydroxyl group and a water molecule, i.e., [Al(OH)(OH2)](2+), were sandwiched between two tri-lacunary alpha-Keggin polyoxotungstates, resulting in an overall C-s symmetry.