Gaseous vanadium molybdate and tungstates: thermodynamic properties and structures
Anastasia O Gunina1, Sergey I Lopatin, Sergey M Shugurov
1Laboratory of High Temperature Chemistry, Faculty of Chemistry, St. Petersburg State University, St. Petersburg, Russia.
Inorganic Chemistry
|April 14, 2012
Summary
This study confirms the stability of gaseous vanadium molybdate and tungstate compounds using high-temperature mass spectrometry. New standard formation enthalpies were determined for these molecules, providing crucial thermodynamic data.
Area of Science:
- Inorganic Chemistry
- Physical Chemistry
- Computational Chemistry
Background:
- Vanadium-based compounds are crucial in catalysis and materials science.
- Accurate thermodynamic data for gaseous metal oxides are essential for understanding reaction mechanisms and chemical stability.
- Previous data on gaseous vanadium oxides and their complexes were limited or uncertain.
Purpose of the Study:
- To determine the thermodynamic stability and standard formation enthalpies of gaseous vanadium molybdate (VMoO4) and vanadium tungstates (VWO3, VWO4).
- To investigate the molecular structures and spin states of these gaseous species.
- To re-evaluate literature data for gaseous vanadium monoxide (VO) and vanadium dioxide (VO2) to improve overall accuracy.
Main Methods:
- High-temperature mass spectrometry was employed to study the gas-phase reactions and confirm the stability of the target compounds.
- Equilibrium constants derived from mass spectrometry data were used to calculate standard formation enthalpies.
- Theoretical calculations were performed to determine the lowest-lying isomers and their spin states.
Main Results:
- Standard formation enthalpies at 298 K were determined for gaseous VMoO4 (-676 ± 27 kJ/mol), VWO3 (-331 ± 29 kJ/mol), and VWO4 (-706 ± 23 kJ/mol).
- Theoretical studies identified the most stable isomer structures, featuring bidentate vanadium cation binding, with specific quartet and sextet spin states for VMoO4, VWO4, and VWO3, respectively.
- Revised standard formation enthalpies for VO(g) (135 ± 10 kJ/mol) and VO2(g) (-185 ± 15.0 kJ/mol) were established, leading to an estimated enthalpy for VMoO3 of -318 kJ/mol.
Conclusions:
- The stability of gaseous vanadium molybdate and tungstates has been experimentally confirmed.
- The study provides critical thermodynamic data and structural insights into these important inorganic compounds.
- The revised thermochemical data for VO and VO2 enhance the reliability of calculations involving vanadium-oxygen systems.
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