Crystal structures of two decavanadates(V) with pentaaquamanganese(II) pendant groups: (NMe 4 ) 2 [V 10 O 28 {Mn(H 2 O) 5 } 2 ]·5H 2 O and [NH 3 C(CH 2 OH) 3 ] 2 [V 10 O 28 {Mn(H 2 O) 5 } 2 ]·2H 2 O

Two heterometallic decavanadate(V) compounds, bis(tetramethylammonium) decaaquadi-μ 4 -oxido-tetra-μ 3 -oxido-hexadeca-μ 2 -oxido-hexaoxidodimanganese(II)decavanadate(V) pentahydrate, (Me 4 N) 2 [V 10 O 28 {Mn(H 2 O) 5 } 2 ]·5H 2 O, A , and bis{[tris(hydroxymethyl)methyl]ammonium} decaaquadi-μ 4 -oxido-tetra-μ 3 -oxido-hexadeca-μ 2 -oxido-hexaoxidodimanganese(II)decavanadate(V) dihydrate, [NH 3 C(CH 2 OH) 3 ] 2 [V 10 O 28 {Mn(H 2 O) 5 } 2 ]·2H 2 O, B , have been synthesized under mild reaction conditions in an aqueous medium. Both polyanions present two [Mn(OH 2 ) 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.