Ammonium heptamolybdate

Ammonium heptamolybdate
Names
	IUPAC name Ammonium docosaoxoheptamolybdate(6–)
	Other names Ammonium molybdate; Ammonium paramolybdate; (see text)
Identifiers
CAS Number	12027-67-7 ; 12054-85-2 (tetrahydrate) ;
3D model (JSmol)	Interactive image; Interactive image;
ChemSpider	23786 ;
ECHA InfoCard	100.031.553
EC Number	234-320-9;
PubChem CID	71306766;
UNII	21Y68J178E ; OGI154X474 (tetrahydrate) ;
CompTox Dashboard (EPA)	DTXSID5036896 ;
	InChI InChI=1S/7Mo.6H3N.24H2O/h;;;;;;;61H3;241H2 Key: QGAVSDVURUSLQK-UHFFFAOYSA-N ; InChI=1/7Mo.6H3N.24H2O/h;;;;;;;61H3;241H2 Key: QGAVSDVURUSLQK-UHFFFAOYAC;
	SMILES [NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[O-][Mo](=O)(=O)[O-].[O-][Mo](=O)(=O)[O-].[O-][Mo](=O)(=O)[O-]; [NH4+].[NH4+].[NH4+].[Mo]3479%12[O+]1[Mo]25([O-])([O-])O[Mo]1%10([O-])([O-])O[Mo]%11([O-])([O-])(O[Mo]8([O-])([O-])(O[Mo]6([O-])([O-])(O[Mo]([O-])([O-])(O2)(O3)[O++]456)[O+]78)[O++]9%10%11)O%12.[NH4+].[NH4+].[NH4+];
Properties
Chemical formula	(NH4)6Mo7O24
Molar mass	1163.9 g/mol; 1235.86 g/mol (tetrahydrate)
Appearance	white solid
Density	2.498 g/cm3
Melting point	~90 ˚C (loses water molecule) ; 190 °C (decomp.)
Solubility in water	65.3 g / 100 ml (tetrahydrate)
Hazards
Main hazards	Irritant
Safety data sheet	External MSDS
NFPA 704 (fire diamond)	0 2 0
Flash point	Non-flammable
Related compounds
Other anions	Ammonium orthomolybdate; Ammonium dimolybdate
Other cations	Potassium paramolybdate
Related compounds	Molybdenum(VI) oxide; Molybdic acid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Ammonium heptamolybdate is the inorganic compound whose chemical formula is (NH₄)₆Mo₇O₂₄, normally encountered as the tetrahydrate. A dihydrate is also known. It is a colorless solid, often referred to as ammonium paramolybdate or simply as ammonium molybdate, although "ammonium molybdate" can also refer to ammonium orthomolybdate, (NH₄)₂MoO₄, and several other compounds. It is one of the more common molybdenum compounds.[1]

Synthesis

Ammonium heptamolybdate is easily prepared by dissolving molybdenum trioxide in an excess of aqueous ammonia and evaporating the solution at room temperature. While the solution evaporates, the excess of ammonia escapes. This method results in the formation of six-sided transparent prisms of the tetrahydrate of ammonium heptamolybdate.[2]

Solutions of ammonium paramolybdate react with acids to form molybdic acid and an ammonium salt. The pH value of a concentrated solution will lie between 5 and 6.

Structure

The compound was first analyzed crystallographically by Lindqvist, but has been reanalyzed.[3] All Mo centers are octahedral. Some oxide ligands are terminal, some doubly bridging, and a few are triply bridging ligands.

The salt contains the heptamolybdate hexaanion.

Uses

as an analytical reagent to measure the amount of phosphates, silicates, arsenates and lead in aqueous solution (e.g. pigments, river water, sea water etc.)[4]
in the production of molybdenum metal and ceramics
in the preparation of dehydrogenation and desulfurization catalysts
in the fixing of metals
in electroplating
in fertilizers for crops.
as a negative stain in biological electron microscopy, typically in the 3–5% (vol/vol) concentration range and in the presence of trehalose;[5] or at saturated concentration to perform cryo-negative staining.[6][7]
For the detection of recreational drugs as a component of the Froehde reagent

Related compounds

Potassium heptamolybdate, also obtained as the tetrahydrate, is very similar to the ammonium salt.[3]

Safety

Molybdates are typically of low toxicity, so much so that few reports of incidents have ever been reported.[1]

References

Sebenik, Roger F.; et al. (2000). "Molybdenum and Molybdenum Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.
L. Svanberg & H. Struve, J. pr. Ch. 44 [1848], p. 282; cited in Gmelin's Handbuch für Anorganische Chemie, 53, p. 255.
Evans, H.T., Jr.; Gatehouse, B. M.; Leverett, P. "Crystal Structure of the Heptamolybdate(VI) (paramolybdate) ion, (Mo₇O₂₄)⁶⁻, in the ammonium and potassium tetrahydrate salts" Journal of the Chemical Society. Dalton Transactions, Inorganic Chemistry1975, p.505-p514.
Parsons, T.; Maita, V. & Lalli, C. (1984). A manual of chemical and biological methods for seawater analysis. Oxford: Pergamon.
Harris, J. R. and Horne, R. W. 1991. "Negative staining", in Harris J. R. (Ed.), Electron Microscopy in Biology, Oxford University Press, Oxford.
Adrian, Marc; Dubochet, Jacques; Fuller, Stephen D.; Harris, J. Robin (1998). "Cryo-negative staining". Micron. 29 (2–3): 145–160. doi:10.1016/S0968-4328(97)00068-1. PMID 9684350.
De Carlo, S.; El-Bez, C.; Alvarez-Rúa, C.; Borge, J.; Dubochet, J. (2002). "Cryo-negative staining reduces electron-beam sensitivity of vitrified biological particles". Journal of Structural Biology. 138 (3): 216–226. doi:10.1016/S1047-8477(02)00035-7. PMID 12217660.