Formation and thermochemical properties of oxychlorides of niobium (Nb) and tantalum (Ta): Towards the gas-phase investigation of dubnium (Db) oxychloride

摘要

The formation of NbOCl3 and TaOCl3 and their adsorption behavior on quartz surfaces was explored by applying an isothermal gas-chromatographic method. Trace amounts of short-lived Nb and Ta isotopes were used. Adsorption enthalpy values (Delta H-ads) at zero surface coverage of -Delta H-ads(NbOCl3) = 102 +/- 4 kJ/mol and -Delta H-ads (TaOCl3) = 128 +/- 5 kJ/mol were determined by analyzing the chromatographic behavior of the Nb and Ta complexes with a Monte-Carlo simulation method based on an adsorption-desorption kinetic model. By applying an empirical correlation, the experimental Delta H-ads values were successively related to the macroscopic standard sublimation enthalpy, Delta H-subl degrees, as a measure of the volatility of each substance. The inferred sublimation enthalpies are in agreement with tabulated thermochemical values. Thus, the linear empirical correlation between Delta H-ads and Delta H-ads and Delta H-subl degrees for metal-oxychlorides was updated with the inclusion of the present data. According to the predicted Delta H-subl degrees (DbOCl(3)), a Delta H-ads, (DbOCl(3)) value of 135 +/- 2 kJ/mol was extrapolated. The future accomplishment of comparative studies with DbOCl(3) under the same experimental conditions will provide valuable information on the volatility trend in Group-5 elements, together with an indication on the magnitude of relativistic effects on the electronic structure of dubnium.