RIGID NONLABILE POLYOXOMETALATE CRYPTATES [ZP5W30O110](15-N)- THAT EXHIBIT UNPRECEDENTED SELECTIVITY FOR CERTAIN LANTHANIDE AND OTHER MULTIVALENT CATIONS

Reaction of aqueous solutions of the heteropolytungstate [NaP5W30O110] 14- with various cations Z(n+) in a sealed container at 120-180-degree s-C for several hours leads to cation exchange and the formation of [Z P5W30O110](15-n-) when Z = Ca2+, trivalent Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, or Bi, or tetravalent Ce or U. No exchange occurre d for Z = Cd2+, Sn2+, Hg2+, Tl3+, Ce3+, Pr3+, or Th4+ at temperatures up to 180-degrees-C. The lanthanide selectivity appears to be determin ed by ionic radius. The new complexes, which are hydrolytically stable from pH 0 to pH 9-10, are characterized by cyclic voltammetry, IR spe ctra, and P-31 NMR spectra (single line in all cases except when Z = Y 3+ which shows 2J(P-31-O-Y-89) = 1.6 Hz); delta = -68.1 to +17.6 ppm. The lanthanide-induced shifts of the P-31 nucleus are predominantly ps eudocontact in origin. The W-183 NMR spectrum of the Eu3+ derivative h as four doublets at +62.5, -201.7, -209.5, and -297.5 ppm (1:2:1:1) co nsistent with the C5v structure found for the Na derivative. The emiss ion spectrum of the Eu derivative and the ESR spectrum of the Gd deriv ative are reported. The low proton relaxivity of the latter complex (c a. 1.0 mM s-1 at 300 MHz) is consistent with the presumed structure in which Gd3+ is inaccessible to solvent water.