The mixed anion oxonitridosilicate La 16[Si 8N 22][SiON 3] 2 has been synthesized by the reaction of LaN, finely ground SiO 2 and silicon diimide (Si(NH) 2) at 1600 °C in a radiofrequency furnace. The structure has been determined by single-crystal X-ray diffraction (La 16[Si 8N 22][SiON 3] 2, P 1 ¯ , a = 5.718(2), b = 11.391(2), c = 13.435(3) Å, α = 112.02(3), β = 90.19(3), γ = 90.58(3)°, V = 811.1(3) Å 3, Z = 2, R 1 = 0.027, 4460 independent reflections, 258 refined parameters). Besides La 3+ and non-condensed [SiON 3] 7− tetrahedra, there are chains of both corner-sharing and edge-sharing SiN 4 tetrahedra with additional Q 1-type SiN 4 groups attached to all non-edge-sharing SiN 4 units of the chain. The resulting infinite chains are alternately built up of pairs of edge-sharing [Si 2N 6] 10− units that are linked by a common nitrogen atom to two corner-sharing single branched Q 3-type SiN 4 tetrahedra. According to its low degree of condensation, La 16[Si 8N 22][SiON 3] 2 is moisture sensitive and undergoes rapid hydrolysis on exposure to air. Rietveld refinement of X-ray powder diffraction data is in accordance with the results of the single-crystal X-ray structure determination.