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−

Abstract

The synthesis and molecular structure of a dimeric aluminium complex composed of tri-lacunary α-Keggin polyoxometalate is described. The polyoxometalate, K₆Na[(A-PW₉O₃₄)₂{W(OH)(OH₂)}{Al(OH)(OH₂)}{Al(μ-OH)(OH₂)₂}₂]·19H₂O (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 (³¹P, ²⁷Al, and ¹⁸³W), 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^III₂(μ-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 α-Keggin polyoxotungstates, resulting in an overall C_s symmetry.