X-Ray crystallographic and tungsten-183 nuclear magnetic resonance structural studies of the [M 4 (H 2 O) 2 (XW 9 O 34 ) 2 ] 10– heteropolyanions (M = CO II or Zn, X = P or As)

The crystal structures of K10[Co4(H2O)2(PW9O34)2]·22H2O (1) and isomorphous K10[Zn4(H2O)2(AsW9O34)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 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.