Key indicatorsSingle-crystal X-ray study T = 298 K Mean '(Ni±O) = 0.006 A Ê H-atom completeness 1% R factor = 0.053 wR factor = 0.137 Data-to-parameter ratio = 18.5For details of how these key indicators were automatically derived from the article, see The polyanion structure in (NH 4 ) 4 [H 6 NiMo 6 O 24 ]Á4H 2 O. H atoms are not shown. Displacement ellipsoids are shown at the 50% probability level.

The very stable title crystals, K3[H6CoMo6O24]·7H2O, that include the well known B‐type Anderson–Evans heteropolyoxometalate, were obtained by recrystallization of powder K3[H6CoMo6O24]·nH2O at pH 3.5. The unit cell consists of two different crystallographically discrete [H6CoMo6O24]3− polyanions. The two anions have the Co atoms at inversion centers and have close to m symmetry, with Co—O bond lengths in the range 1.898 (3)–1.912 (3) Å, Mo—O bond lengths in the ranges 1.700 (4)–1.726 (4), 1.895 (3)–1.960 (3) and 2.259 (3)–2.313 (3) Å.