Abstract: This paper reports the formation thermodynamic properties of the vapor complex REAl₃Cl₁₂(RE= La—Lu except for Pm)investigated by quenching experiments in roughly the same temperature and pressure range( 604～851 Kand 0.02～0.20 MPa).The results of the investigation would be the first complete set of property values for vapor rare earth complexes.The relationship between Δ_rH⁰₂₉₈ and Δ_rS⁰₂₉₈ and the atomic numbers of the rare earth elements shows that the values of Δ_rH⁰₂₉₈ and Δ_rS⁰₂₉₈ decrease from La to Eu and then increase from Eu to Gd,and decrease from Gd to Er and then increase from Er to Lu, indicating a significant Gd break and two weak minimum points at Eu and Er. Here the Gd break is consistent with 1/2-filled 4f shell.

Key words: Vapor rare earth complex, Thermodynamic properties, Gadolinium break