Tetraammonium diaquadiperoxidooctamolybdate(VI) tetrahydrate

The title compound (NH4)4[Mo8O24(O2)2(H2O)2]·4H2O, consists of an octamolybdate cluster with a crystallographic centre of symmetry. The clusters pack in a cubic close packing arrangement defining channels containing water molecules and ammonium cations, which exhibit hydrogen bonding with neighbouring clusters. Hydrogen bonding also exists between the coordinated water molecules of one cluster with one of the O atoms of the peroxido fragment in a neighbouring cluster.

The title compound (NH 4 ) 4 [Mo 8 O 24 (O 2 ) 2 (H 2 O) 2 ]Á4H 2 O, consists of an octamolybdate cluster with a crystallographic centre of symmetry. The clusters pack in a cubic close packing arrangement defining channels containing water molecules and ammonium cations, which exhibit hydrogen bonding with neighbouring clusters. Hydrogen bonding also exists between the coordinated water molecules of one cluster with one of the O atoms of the peroxido fragment in a neighbouring cluster.
The packing of the title complex ( Figure 2) shows the individual units to be stacked in a cubic close packing arrangement with water and ammonium ions distributed in the channels formed. Hydrogen bonding interactions exist between ammonium ions and the molybdenum cluster: H2B with O4, H1B with O10. In addition there exist hydrogen bonding interactions between the ammonium ions and the O atoms of neighbouring clusters: H2C with 011, H2D with O3, H1A with O9, and H1B with O10. The water molecules also hydrogen bond with the ammonium ions: O16 with H2A, O16 with H1C, and O17 with H1D. There is H-bonding between the H atoms of the water molecules with oxygen atoms of the molybdenum cluster: the strongest being that between O1 and H17A while 07 and H16A has a slightly longer hydrogen bond length.
There also exists hydrogen bonding with the protons of the coordinated water molecules (H12A) of one cluster with the O2 atom in a neighbouring cluster while the other proton (H12B) has a strong hydrogen bond to 017. The water molecules also exhibit weak interactions with neighbouring clusters whereby H16A and H16B interact with O3 and H17A and H17B interact with O10.

Experimental
Ammonium molybdate tetrahydrate (10 g, 8.1 mmol) was dissolved in a solution of hydrogen peroxide (30%, 50 ml) acidified to pH 2 with nitric acid (70%, 5 ml). Slow evaporation of the yellow solution afforded crystals of the title compound supplementary materials sup-2 (7.45 g, 93%). Crystals suitable for XRD studies were obtained from an aqueous solution of the complex that was kept at 288 K and 80% humidity in order to reduce the rate of evaporation.

Refinement
O-bound H atoms were located in the difference Fourier map and refined with bond length restraints of 0.95 (1) Å with U iso (H) 1.5 U eq (O). Fig. 1. The molecular structure of the title complex, with displacement ellipsoids drawn at 50% probability level. Water solvent and ammonnium ions omitted for clarity. Symmetry code used for generating equivalent atoms: 1 -x, -y, 1 -z.

Special details
Experimental. attached with Exxon Paratone N, to a short length of fibre supported on a thin piece of copper wire inserted in a copper mounting pin. The crystal was quenched in a cold nitrogen gas stream from an Oxford Cryosystems Cryostream.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.