Crystal structures of two decavanadates(V) with pentaaquamanganese(II) pendant groups: (NMe4)2[V10O28{Mn(H2O)5}2]·5H2O and [NH3C(CH2OH)3]2[V10O28{Mn(H2O)5}2]·2H2O

Two heterometallic decavanadate(V) compounds, bis(tetramethylammonium) decaaquadi-μ4-oxido-tetra-μ3-oxido-hexadeca-μ2-oxido-hexaoxidodimanganese(II)decavanadate(V) pentahydrate, (Me4N)2[V10O28{Mn(H2O)5}2]·5H2O, A, and bis{[tris(hydroxymethyl)methyl]ammonium} decaaquadi-μ4-oxido-tetra-μ3-oxido-hexadeca-μ2-oxido-hexaoxidodimanganese(II)decavanadate(V) dihydrate, [NH3C(CH2OH)3]2[V10O28{Mn(H2O)5}2]·2H2O, B, have been synthesized under mild reaction conditions in an aqueous medium. Both polyanions present two [Mn(OH2)5]2+ complex units bound to the decavanadate cluster through oxide bridges. In A, the decavanadate unit has 2/m symmetry, whereas in B it has twofold symmetry. Apart from this, the main differences between A and B rest on the organic cations, tetramethylammonium and [tris(hydroxymethyl)methyl]ammonium, respectively, and on the number and arrangement of the water molecules of crystallization. In both compounds, the H atoms from the coordinating water molecules participate in extensive three-dimensional hydrogen-bonding networks, which link the cluster units both directly and through solvent molecules and, in B, through the `tris' cation hydroxyl groups. The cation in B also participates in N—H...O hydrogen bonds. A number of C—H...O interactions are also observed in both structures