PREPARATION AND W-183 NMR CHARACTERIZATION OF [ALPHA-1-P2W17O61](10-), [ALPHA-1-ZN(H2O)P2W17O61](8-), AND [ALPHA-2-ZN(H2O)P2W17O61](8-)

The preparation of the alpha-1 and alpha-2 isomers of the Wells-Dawson 17 tungsto derivatives by standard methods is accompanied by a signif icant proportion of the other isomer present as an impurity. In this s tudy, the alpha-1 and alpha-2 isomers of [Zn(H2O)P2W17O61](8-) have be en prepared in >98% purity by reacting isomerically pure K9Li-[alpha-1 -P2W17O61] and K-10[alpha-2-P2W17O61], respectively, with ZnCl2, while rigorously controlling the pH at 4.7. The molecules were isolated as potassium salts. For W-183 NMR and P-31 NMR characterization, both mol ecules were ion exchanged by cation-exchange chromatography, maintaini ng the pH at 4.7, to obtain the lithium salts. Removal of water and is olation of a solid sample of [alpha-1-Zn(H2O)P2W17O61](8-) was achieve d by lyophilization at -40 degrees C. The chemical shift data from P-3 1 and W-183 NMR spectroscopy of the isolated [alpha-1-Zn(H2O)P2W17O61] (8-) and [alpha-2-Zn(H2O)P2W17O61](8-) isomers are consistent with a m ixture of the alpha-1 and alpha-2 isomers reported previously;(1) the molecules have the expected C-1 and C-s symmetry, respectively. The [a lpha-1-Zn(H2O)P2W17O61](8-) isomer is stable in the pH range of 4.6-6 at temperatures <35 degrees C. Using the same ion exchange and lyophil ization techniques, the lacunary [alpha-1-P2W17O61](10-) isomer was is olated as the lithium salt; characterization by W-183 NMR spectroscopy confirms the C-1 symmetry.