Structural analysis of the sodium salt of ([(O3PCHN(CH3)(2)PO3)W2O6](4-))infinity revealed a novel polymeric heteropolyanion of tungsten which is composed of negatively-charged chains where [(O3PCHN(CH3)(2)PO3)W2O6](4-) (I) is the repeat unit. I comprises two corner-shared WO6 octahedra and one (dimethylamino)methylenediphosphonate hetero group. In the polymer, the monomeric units are linked to give an undulating chain in which the hetero groups alternate up and down. In each chain the tungsten atoms and their bridging oxygens can be viewed as the planar backbone describing a sine wave.