Tetra-ammonium bis-(metforminium) di-μ 6 -oxido-tetra-μ 3 -oxido-tetra-deca-μ 2 -oxido-octa-oxidodeca-vanadium(V) hexa-hydrate.

The title compound, (NH 4 ) 4 (C 4 H 12 N 5 ) 2 [V 10 O 28 ]·6H 2 O, crystallizes with the deca-vanadate anion placed on an inversion centre in space group P . This anion is surrounded by a first shell of ammonium cations and water mol-ecules, forming efficient N-H⋯O and O-H⋯O hydrogen bonds. A second shell includes metforminium monocations with a twisted geometry, also forming numerous inter-molecular hydrogen bonds. The complex three-dimensional network of non-covalent inter-actions affords a crystal structure in which the cations and anions are densely packed.