β-K₂Se₂ and K₂Se₄. Missing links in the binary system K-Se

Two missing compounds within the binary K-Se system have been synthesized and structurally characterized by means of single-crystal diffraction. β-K₂Se₂ comprises cell parameters that are in line with predictions made from the series α/β-A₂Ch_x. K₂Se₄, in contrast, incorporates ''Se₅^2-'' chains with 50% occupation of the terminal selenium atoms, and has been synthesized on a rather unconventional solvothermal pathway employing successively mercury and ethylene dithiol as solvents.