Targeting Vacancies in Nitridosilicates: Aliovalent Substitution of M (M=Ca, Sr) by Sc and U.

Based on the known linking options of their fundamental building unit, that is the SiN tetrahedron, nitridosilicates belong to the inorganic compound classes with the greatest structural variability. Although facilitating the discovery of novel Si-N networks, this variability represents a challenge when targeting non-stoichometric compounds. Meeting this challenge, a strategy for targeted creation of vacancies in highly condensed nitridosilicates by exchanging divalent M for trivalent M using the ion exchange approach is reported. As proof of concept, the first Sc and U nitridosilicates were prepared from α-Ca Si N and Sr Si N . Powder X-ray diffraction (XRD) and synchrotron single-crystal XRD showed random vacancy distribution in Sc Ca Si N , and partial vacancy ordering in U Sr Si N with x≈1.05. The high chemical stability of U nitridosilicates makes them interesting candidates for immobilization of actinides.