New Layered Germanide Halides RE₂GeX₂ (RE = Y, Gd; X = Br, I)

The title compounds were synthesized from RE, REX3, and Ge under an Ar atmosphere at 1200−1370 K. Y2GeI2 and Gd2GeI2 crystallize in space group R3̄m with lattice constants a = 4.2135(3) and 4.2527(1) Å and c = 31.480(2) and 31.657(1) Å, respectively. Gd2GeBr2 crystallizes in two modifications, the 1T-type (space group P3̄m1; a = 4.1668(2) Å, c = 9.8173(6) Å) and the 3R-type (space group R3̄m; a = 4.1442(9) Å, c = 29.487(7) Å). The structural motifs of RE2GeX2 compounds are Ge-centered slightly distorted RE6 octahedra connected via their common edges and extending in the a and b directions. The resulting close-packed double layers are separated by halogen atoms. The electrical resistivity measurements revealed semiconductor behavior for Y2GeI2 and Gd2GeI2 and a metal−semiconductor transition for 1T-Gd2GeBr2. Magnetic susceptibility and heat capacity measurements show long-range magnetic ordering for Gd2GeI2 and 1T-Gd2GeBr2 at ∼15 and ∼13 K, respectively.