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 Zn+ in a sealed container at 120-180 degrees C for several hours leads to cation exchange and the formation of [ZP5W30O110](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 occurred for Z = Cd2+, Sn2+, Tl3+, Ce3+, Pr3+, or Th4+ at temperatures up to 180 degrees C. The lanthanide selectivity appears to be determined by ionic radius. The new complexes, which are hydrolytically stable from pH 0 to pH 9--10, are characterized by cyclic voltammetry, IR spectra, and 31P NMR spectra (single line in all cases except when Z = Y3+ which shows 2J(31P-O-89Y) = 1.6 Hz); δ = -68.1 to +17.6 ppM. The lanthanide-induced shifts of the 31P nucleus are predominantly pseudocontact in origin. The 183W NMR spectrum of the Eu3+ derivative has four doublets at +62.5, -201.7, -209.5, and -297.5 ppM (1:2:1:1) consistent with the C5v structure found for the Na derivative. The emission spectrum of the Eu derivative and the ESR spectrum of the Gd derivative are reported. The low proton relaxivity of the latter complex (ca. 1.0 mM s-1 at 300 MHz) is consistent with the presumed structure in which Gd3+ is inaccessible to solvent water. 25 refs., 7 figs., 3 tabs