MOLYBDOTUNGSTOVANADATES [V2MONW(4-N)O19](4-)

The complete series of hexametalate anions [V2MonW(4-n)O-19](4-), with the two vanadiums cis and n = 0-4, has been identified in aqueous sol ution by V-51 NMR spectroscopy. The vanadium shifts and the pK(a) valu es both increase with increasing substitution of Mo for W. They correl ate well with semiquantitative models, showing that somewhat greater c hanges arise from substitutions taking place in the V2O9 plane. A cons istent preference is also found for like metal atoms to lie mutually c is.