Formation of nanoporous and non-porous organic-inorganic hybrid materials incorporating α-Keggin phosphotungstate anion: X-ray crystal structure of a 3D polymeric complex [{Na6(C9H5O6)3(H2O)15}{PW12O40}]∞ with a 'Ball-in-Bowl' type molecular structure

Two different synthetic approaches to prepare inclusion complexes of Keggin anion [PW12O40](3-) and [Cu-3(BTC)(2)(H2O)(3)](n) (also known as HKUST-1) have resulted in the formation of two different materials [Cu-3(C9H3O6)(2)(H2O)(3)](2)Na3PW12O40 center dot nH(2)O (1) and [Na-6(BTC-H-2)(3)(H2O)(15)][PW12O40](2). Compound I is a thermally stable, nanoporous material with a type I adsorption isotherm. it contains the well-known MOF material [Cu-3(BTC)(2)(H2O)(3)](n) with half of its pores occupied by the guest Keggin anion. The second product 2 is a crystalline, 3D coordination polymer with a composition of [Na-6(BTC-H-2)(3)(H2O)(15)] [PW12O40] (where BTC-H-3 stands for 1,3,5-benzene-tricarboxylic acid) and is a non-porous, highly water soluble and thermally unstable material. The compound I was prepared hydrothermally using precursors of HKUST-1 and Na-3[(PW12O40)] whereas 2 was obtained at room temperature from aqueous solutions containing [Cu-3(BTC)(2)(H2O)(3)](n) and Na-3[(PW12O40)] salts. The molecular structure of 2 is unique and features two distinct elements: an anionic Keggin ion [PW12O40](3-) and a bowl type hexameric [Na-6(C9H5O6)(3)(H2O)(15)](3+) macrocation which is formed by coordination of Na+ ions by (BTC-H-2)(-) anions and water molecules. The macrocation extends in three dimensions due to Y type (BTC-H-2)(-) to form a porous MOF offering triangular voids. In this framework the globular Keggin ions support themselves above these voids by coordinating to Na+ ions and render it completely nonporous. The complex has an unusual structure in the sense that the polyoxoanion is coordinated to [Na-6(C9H5O6)(3)(H2O)(15)](3+) ions by using the three terminal oxygen atoms in a single M3O13 triplet, when each one of them is also bridging between two Na+ ions. In the crystal structure the POM anion is encapsulated by six octahedrally disposed (BTC-H-2)(-) moieties. H-bonding interactions among water molecules produce supramolecular water hexamers and dimers. (C) 2009 Published by Elsevier Ltd.