Preparation and Tungsten-183 NMR Characterization of [α-1-P2W17O61]10-, [α-1-Zn(H2O)P2W17O61]8-, and [α-2-Zn(H2O)P2W17O61]8-

The preparation of the α-1 and α-2 isomers of the Wells−Dawson 17 tungsto derivatives by standard methods is accompanied by a significant proportion of the other isomer present as an impurity. In this study, the α-1 and α-2 isomers of [Zn(H2O)P2W17O61]8- have been prepared in >98% purity by reacting isomerically pure K9Li[α-1-P2W17O61] and K10[α-2-P2W17O61], respectively, with ZnCl2, while rigorously controlling the pH at 4.7. The molecules were isolated as potassium salts. For 183W NMR and 31P NMR characterization, both molecules were ion exchanged by cation-exchange chromatography, maintaining the pH at 4.7, to obtain the lithium salts. Removal of water and isolation of a solid sample of [α-1-Zn(H2O)P2W17O61]8- was achieved by lyophilization at −40 °C. The chemical shift data from 31P and 183W NMR spectroscopy of the isolated [α-1-Zn(H2O)P2W17O61]8- and [α-2-Zn(H2O)P2W17O61]8- isomers are consistent with a mixture of the α-1 and α-2 isomers reported previously;1 the molecules have the expected C1 and Cs...