Targeting Vacancies in Nitridosilicates: Aliovalent Substitution of M 2+ (M=Ca, Sr) by Sc 3+ and U 3+

Based on the known linking options of their fundamental building unit, that is the SiN 4 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 2+ for trivalent M 3+ using the ion exchange approach is reported. As proof of concept, the first Sc and U nitridosilicates were prepared from α‐Ca 2 Si 5 N 8 and Sr 2 Si 5 N 8 . Powder X‐ray diffraction (XRD) and synchrotron single‐crystal XRD showed random vacancy distribution in Sc 0.2 Ca 1.7 Si 5 N 8 , and partial vacancy ordering in U 0.5 x Sr 2−0.75 x Si 5 N 8 with x ≈1.05. The high chemical stability of U nitridosilicates makes them interesting candidates for immobilization of actinides.