A new tetramolybdenumcobaltdi­phospho­nate, Na8[CoMo4O12{MeC(O)(PO3)2}2]·18H2O

A new tetramolybdate-diphosphate compound with the formula Na8[CoMo4O12{MeC(O)(PO3)2}2]·18H2O, octa­sodium(I) cobalt(II) tetramolybdenum(VI) bis(1-hydroxy­ethyl­idene­diphosphate) octadecahydrate, has been synthesized under weakly acidic conditions (pH = 5.5–6.0). The [CoMo4O12{MeC(O)(PO3)2}2]8− anion comprises two [Mo2O6{MeC(O)(PO3)2}]5− fragments linked by one six-coordinate CoII atom. 1–Hydro­xy­ethyl­idenedi­phospho­nate as a pentadentate ligand bonds to two pairs of face-sharing MoO6 octahedra. The Co atom in the anion is situated on a centre of inversion.