Laboratory of High Temperature Chemistry, Faculty of Chemistry, St. Petersburg State University, St. Petersburg, Russia.
Inorg Chem. 2012 May 7;51(9):4918-24. doi: 10.1021/ic201644f. Epub 2012 Apr 12.
The stability of gaseous vanadium molybdate and vanadium tungstates was confirmed by high-temperature mass spectrometry. A number of gas-phase reactions involving vanadium-containing salts were studied. On the basis of equilibrium constants, the standard formation enthalpies of gaseous VMoO(4) (-676 ± 27 kJ/mol), VWO(3) (-331 ± 29 kJ/mol), and VWO(4) (-706 ± 23 kJ/mol) at 298 K were determined. A theoretical study of these salts revealed the structure with bidentate binding of the vanadium cation to the anion part to be the lowest-lying isomer, with a quartet spin state for VMoO(4) and VWO(4) molecules as well as a sextet spin state for the VWO(3) molecule. On the basis of critical analysis of the literature data concerning standard formation enthalpies of gaseous VO and VO(2), we adopted new values of Δ(f)H°(298) = 135 ± 10 kJ/mol for VO(g) and -185 ± 15.0 kJ/mol for VO(2)(g). Overall, the results obtained allowed us to estimate the standard formation enthalpy of VMoO(3) to be -318 kJ/mol with an accuracy near 40 kJ/mol.
气态钒钼酸盐和钒钨酸盐的稳定性通过高温质谱法得到了证实。研究了许多涉及含钒盐的气相反应。基于平衡常数，在 298 K 下确定了气态 VMoO(4)(-676 ± 27 kJ/mol)、VWO(3)(-331 ± 29 kJ/mol)和 VWO(4)(-706 ± 23 kJ/mol)的标准生成焓。这些盐的理论研究表明，钒阳离子与阴离子部分的双齿键合结构是最低能量异构体，VMoO(4)和 VWO(4)分子具有四重态自旋态，而 VWO(3)分子具有六重态自旋态。基于对气态 VO 和 VO(2)标准生成焓的文献数据的批判性分析，我们采用了新的 VO(g)的 Δ(f)H°(298) = 135 ± 10 kJ/mol 和 VO(2)(g)的-185 ± 15.0 kJ/mol 值。总的来说，这些结果使我们能够估计 VMoO(3)的标准生成焓为-318 kJ/mol，准确度接近 40 kJ/mol。
