Rational syntheses, characterization, crystal structure, and replacement reactions of coordinated water molecules of [As2W18M4(H2O)(2)O-68](10-) (M =Cd, Co, Cu, Fe, Mn, Ni or Zn)

Rational, high-yield, and isomerically pure syntheses of [As2W18M4(H2O)(2)O -68](10-) (M = Cd, Co, Cu, Fe, Mn, Ni or Zn) have been achieved. The produc ts were well characterized by means of IR, UV-vis, CV, W-183 NMR, TG-DSC, a nd elemental analyses. The properties have been studied. The results allow a number of conclusions to be drawn. (i) The B-type tri(tungsten)vacant for m of B-[AsW9O34](9-) is a key structural requirement for formation of the d imetal(2+)-substituted dimers [As2W18M4(H2O)(2)O-68](10-). (ii) The structu res of the compounds K-10[Mn-4(H2O)(2)(AsW9O34)(2)]. 18H(2)O and K8Na2[Cu-4 (H2O)(2)(AsW9O34)(2)]. 32H(2)O have been solved, and are similar to that of the zinc derivative, comprising a rhomb-like M4O16 group encapsulated betw een two fragments of the trivacant Keggin polyanion [AsW9O34](9-). (iii) Th e crystal structures of the arsenic series have been compared with those of the phosphorus-series. Jahn-Teller distortions of the CuO6 groups and the absence of Jahn-Teller distortions in the MO6 octahedra for M = Mn and Zn a re predicted. (iv) Two water molecules are coordinated to two metal atoms. [Fe(CN)(6)](4-), [Fe(CN)(6)](3-), SO32-, SCN-, etc. can replace the coordin ated water giving characteristic colors in aqueous solutions, while in orga nic solvents the coordinated water molecules are lost, leaving unshared coo rdination positions that can be occupied by organic ligands such as pyridin e, lactic acid, and acetone to restore the octahedral coordination of M-II. (v) The crystal morphologies of [Co-4(H2O)(2)(AsW9O34)(2)](10-) anion are dependent on different organic ligands, which substitute the two coordinate d waters after phase transfer.