Neutron diffraction investigation of the crystal structure of ammonium molybdate tetrahydrate

In this study, the hydrogen-bonding network in the crystal structure of ammonium molybdate tetrahydrate, (NH₄)₆[Mo₇O₂₄]·4H₂O, was investigated using single-crystal time-of-flight neutron diffraction. The H-atom positions were determined and refined using anisotropic displacement parameters. Three of the six ammonium ions exhibit hydrogen-site disorder, which is attributable to the availability of multiple hydrogen-bonding configurations around each disordered ion. Ammonium ions are connected to a heptamolybdate polyanion and water molecules through N-H...O hydrogen bonds. Water molecules form O-H...O hydrogen bonds with the heptamolybdate polyanion. The extensive N-H...O and O-H...O hydrogen bonds form a three-dimensional supramolecular structure.