Synthesis of Two New Metallic Alkali Metal Silver Selenides, K2Ag12Se7.11and RbAg5Se3, from Supercritical Ethylenediamine

Two new compounds K2Ag12Se7.11, (I), and RbAg5Se3, (II), have been synthesized in supercritical ethylenediamine. Compound I crystallizes in the hexagonal space groupP63witha=18.955(2) ?,c=4.406(2) ?,V=1371.0(7) ?3,Z=3,R/Rw= 0.0396/0.0417. This compound has a columnar structure, similar to the previously reported K2Ag12Se7and Zr2Ni12P7. However, I contains two types of Ag–Se columns while Zr2Ni12P7has only one. In one type, ordered selenium atoms are located inside the columns, and in the other, disordered selenium atoms are found in the columns leading to a nonstoichiometric composition. As a result of this nonstoichiometry, the compound is metallic with a resistivity of 14.9 ohm · cm at 23°C. Compound II crystallizes in the tetragonal space groupP4/nbmwitha=6.0814(9) ?,c=11.112(1) ?,V=411.0(1) ?3,Z=2,R/Rw=0.0416/0.0490. This compound has a layered structure with Rb+cations located between silver selenide layers. There are numerous Ag–Ag interactions less than 3.041(1) ? and the compound is weakly metallic with a resistivity of 1.5 ohm · cm at 23°C.