Thermal decomposition of ammonium hexachloroosmate

Area of Science:

• Materials Science
• Inorganic Chemistry
• Solid State Chemistry

Background:

• Ammonium hexachloroosmate ((NH4)2[OsCl6]) is a precursor for osmium metal synthesis.
• Understanding its thermal decomposition is crucial for controlling osmium production and properties.

Purpose of the Study:

• To investigate the structural changes of (NH4)2[OsCl6] during thermal decomposition in a reduction atmosphere.
• To identify any intermediate species formed during the process.
• To elucidate the local atomic structure of any revealed intermediates.

Main Methods:

• In situ combined energy-dispersive X-ray absorption spectroscopy (ED-XAFS).
• In situ powder X-ray diffraction (PXRD).
• Multivariate Curve Resolution (MCR) analysis of XANES and EXAFS data.

Main Results:

• PXRD indicated direct transformation to metallic osmium, bypassing crystalline intermediates.
• XANES and EXAFS data revealed an amorphous intermediate, {OsCl4}x, with a potential polymeric structure.
• This amorphous intermediate was identified for the first time, allowing for determination of its local atomic structure.

Conclusions:

• The thermal decomposition of (NH4)2[OsCl6] is a complex, multi-step process.
• An amorphous {OsCl4}x intermediate is formed, which was previously unobserved.
• The study provides new insights into the reaction pathway of hexachloroosmate decomposition.