X-ray crystallographic and tungsten-183 nuclear magnetic resonance structural studies of the [M4(H2O)2(XW9O34) 2]10- heteropolyanions (M = COII or Zn, X = P or As)

Abstract

The crystal structures of K10[Co4(H2O)2(PW9O 34)2]·22H2O (1) and isomorphous K10[Zn4(H2O)2(AsW9O 34)2]·23H2O (2) have been determined {Mo-Kα radiation, space group P21/n, Z = 2; (1) a = 15.794(2), b = 21.360(2), c = 12.312(1) Å, β = 91.96°, R = 0.084 for 3 242 observed reflections [I ≥ 3σ(I)]; (2) a = 15.842(4), b = 21.327(5), c = 12.308(4) Å, β = 92.42(4)°, R = 0.066 for 4 675 observed reflections [F ≥ 3σ(F)]}. The anions have crystallographic symmetry 1 and non-crystallographic symmetry very close to 2/m (C2h). Each consists of two [XW9O34]9- moieties [α-B isomers; X = P (1) or As (2)] linked via four CoIIO6 or ZnO6 groups. Two Co or Zn atoms each carry a water ligand. The 183W n.m.r. spectra of the anions [Zn4(H2O)2(XW9O34) 2]10- (X = P or As) confirm that the anions retain 2/m symmetry in aqueous solution. Homonuclear coupling constants between 183W atoms are 5.8-9.0 Hz for adjacent WO6 octahedra sharing edges, and 19.6-25.0 Hz for octahedra sharing corners.