Sublimation enthalpies of gadolinium and thulium triiodides and formation enthalpies of the molecules LnI3, Ln2I6, and Ln3I9 (Ln = Gd, Tm)

•Sublimation of GdI3 and TmI3 was studied by Knudsen effusion mass spectrometry.•Monomer, dimer, and trimer molecules were registered in vapor.•Partial vapor pressures of the molecules were determined.•Sublimation and formation enthalpies were evaluated.

The sublimation of solid gadolinium and thulium triiodides was studied by Knudsen effusion mass spectrometry. The partial vapor pressures [atm] of the monomer and dimer molecules were determined as: lnp(GdI3) = −(32.31 ± 0.18) × 103/T + (21.38 ± 0.21) for 777-946 K; lnp(Gd2I6) = −(38.07 ± 0.42) × 103/T + (24.49 ± 0.47) for 843-946 K; lnp(TmI3) = −(31.84 ± 0.25) × 103/T + (21.88 ± 0.29) for 760-965 K; and lnp(Tm2I6) = −(38.23 ± 0.27) × 103/T + (25.71 ± 0.43) for 799-965 K. In addition, the trimers Gd3I9 and Tm3I9 were detected in very small fractions. On the basis of a joint analysis of all available data in literature, the sublimation enthalpies [kJ mol−1] at 298.15 K are recommended as 283 ± 9 (GdI3), 336 ± 16 (Gd2I6), 366 ± 50 (Gd3I9), 276 ± 3 (TmI3), 330 ± 6 (Tm2I6), and 354 ± 50 (Tm3I9). The standard formation enthalpies [kJ mol−1] of the gaseous species at 298.15 K are −341 ± 9 (GdI3), −912 ± 16 (Gd2I6), −1506 ± 50 (Gd3I9), −344 ± 5 (TmI3), −909 ± 7 (Tm2I6), and −1506 ± 50 (Tm3I9).

Graphical abstractDownload high-res image (191KB)Download full-size image