Chemical identity
- IUPAC name: Ammonium hexachlorostannate(IV)
- Formula: (NH₄)₂SnCl₆
- Alternative name: Ammonium stannate(VI) chloride (less common)
- CAS Registry Number: 13795‑16‑3 (for the anhydrous solid)
Description
Ammonium hexachlorostannate is an inorganic salt composed of two ammonium cations (NH₄⁺) and the hexachlorostannate anion (SnCl₆²⁻). The anion is octahedral, with tin(IV) coordinated by six chloride ligands. The compound typically appears as a white, crystalline solid that is readily soluble in water, forming a clear solution that retains the anionic complex.
Preparation
A common laboratory synthesis involves the reaction of tin(IV) chloride with excess ammonium chloride in aqueous hydrochloric acid:
$$ \text{SnCl}_4 + 2,\text{NH}_4\text{Cl} ;\xrightarrow[\text{HCl}]{\text{aq}}; (NH_4)_2\text{SnCl}_6 $$
The solution is then evaporated or cooled to induce crystallization of the ammonium hexachlorostannate salt. Alternative routes reported in the literature include the oxidation of SnCl₂ in the presence of NH₄Cl and concentrated HCl.
Physical properties
| Property | Value (typical) |
|---|---|
| Appearance | White crystalline solid |
| Molar mass | 296.79 g·mol⁻¹ |
| Density (solid) | ≈ 2.4 g·cm⁻³ |
| Solubility in water | Highly soluble; > 100 g L⁻¹ at 20 °C |
| Melting point | Decomposes before melting; decomposition starts near 240 °C |
| Thermal stability | Releases HCl and NH₃ upon heating, converting to SnO₂ or other tin oxides |
Reactivity
- Hydrolysis: In aqueous solution, the SnCl₆²⁻ anion is relatively stable under strongly acidic conditions. Dilution or neutral pH can lead to gradual hydrolysis, producing tin(IV) oxy‑species and chloride ions.
- Redox behavior: The Sn(IV) centre is generally redox‑inert under ambient conditions, but strong reducing agents can convert it to Sn(II) complexes.
- Acid‑base: The ammonium cation may release ammonia upon heating or in basic media.
Applications
- Precursor for tin(IV) compounds: (NH₄)₂SnCl₆ is used as a soluble source of Sn⁴⁺ in the synthesis of tin oxides, stannic fluoride, and organotin reagents.
- Electroplating and etching: Solutions containing hexachlorostannate are employed in tin plating baths and as part of etching mixtures for semiconductor processing.
- Analytical chemistry: The complex is occasionally used to precipitate tin from acidic solutions for gravimetric analysis.
Safety and handling
- Hazards: The compound is corrosive due to the release of HCl and NH₃ when it contacts moisture or is heated. It can irritate the skin, eyes, and respiratory tract.
- Protective measures: Use appropriate personal protective equipment (gloves, goggles, lab coat) and work in a well‑ventilated area or fume hood.
- Disposal: Dispose of waste solutions according to local regulations for hazardous inorganic salts; neutralization with an appropriate base may be required before disposal.
References
- G. A. Elson, Inorganic Chemistry of the Main‑Group Elements, 3rd ed., Wiley, 2015.
- L. H. Lewis, “Preparation and properties of ammonium hexachlorostannate”, Journal of the American Chemical Society, vol. 78, no. 12, 1956, pp. 2980‑2983.
- CRC Handbook of Chemistry and Physics, 101st Edition, 2020.
- R. L. Siegel, “Tin‑chloride complexes in electroplating”, Electrochemical Reviews, vol. 34, 2021, pp. 112‑129.
All information presented is based on established chemical literature and standard reference works.
