Formation and thermochemical properties of oxychlorides of niobium (Nb) and tantalum (Ta); Towards the gas-phase investigation of dubnium (Db) oxychloride
Chiera, N. M.; Sato, Tetsuya
; Tomitsuka, Tomohiro; Asai, Masato
; Suzuki, Hayato*; Tokoi, Katsuyuki; Toyoshima, Atsushi; Tsukada, Kazuaki
; Nagame, Yuichiro 
The formation of NbOCl
and TaOCl
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 (
) at zero surface coverage of -
(NbOCl
) = 102
4 kJ/mol and -
(TaOCl
) = 128
5 kJ/mol were determined by analyzing the chromatographic behavior of the Nb andTa complexes with a Monte-Carlo simulation method based on an adsorption-desorption kinetic model.By applying an empirical correlation, the experimental
values were successively related to the macroscopic standard sublimation enthalpy,
, 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
and
for metal-oxychlorides was updated with the inclusion of the present data. According to the predicted
(DbOCl
), a
(DbOCl
) value of 135
2 kJ/mol was extrapolated. The future accomplishment of comparative studies with DbOCl
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.