The synthesis and structural and physical characterization of a new family of rare-earth metal chalcoantimonates(III): K-2(RE)(2-x)Sb4+xSb4Se12, RE=La, Ce, Pr and Gd.

A family of rare-earth metal selenoantimonates(III) has been prepared by the reaction of the elements in alkali metal polyselenide fluxes or by the metathesis of rare-earth chlorides and alkali metal chalcoantimonates(III). The products are black, fine needles of K-2(RE)(2-x)Sb4+xSe12 where RE=La, Ce, Pr, and Gd and x similar to 0.33. The compounds were analyzed by single crystal and powder X-ray diffraction, and the praseodymium compound by diffuse reflectance spectroscopy, and magnetic susceptibility. The structure, optical spectrum, and susceptibility data of the praseodymium compound are reported.