Synthesis and characterization of soluble alkali metal, alkaline earth metal and related Keggin-type [PMo12O40]3− salts for heterogeneous catalysis reactions

Abstract

Abstract Soluble [PMo12O40]3− salts of the Group 1 (Li+ and Na+), Group 2 (Mg2+, Ca2+, Sr2+ and Ba2+) and Group 13 (Al3+) metals have been synthesized and thoroughly characterized by chemical analysis, TGA/DTA, IR spectroscopy, X-ray powder diffraction (XRD), and by both solid-state and solution 31 P NMR spectroscopy. The structure of Ba3[PMo12O40]2·(55.3)D2O at 150 K has also been determined by neutron powder diffraction. The compounds may be prepared by combination of H3[PMo12O40] and the carbonates or hydroxide/carbonates in the appropriate stoichiometry or, in the case of Al3+, by addition of Al2(SO4)3 and subsequent removal of the SO42− as insoluble BaSO4 through the addition of BaCO3. All soluble (Mn+)3/n[PMo12O40] compounds, where Mn+ is a cation of a Group 1, 2 or 13 element, crystallize from solution with about 27–31 water molecules per [PMo12O40]3− ion. The crystallized solids are cubic (all with a ≈ 23.3 A), space group Fd3m, and are isostructural with H3[PMo12O40]·(29–30)H2O. Neutron and X-ray powder diffraction show that the cations and water molecules of crystallization are effectively disordered in the interanionic voids (channels) in the unit cell, and cannot be located. There is no evidence for any co-crystallization of hydrolysed species, based on examination of the crystallized solids by IR spectroscopy and both solid-state and solution 31 P NMR spectroscopy.