Cs3Sm2N9 crystallizes in the trigonal R-3c space group. Cs(1) is bonded to four equivalent N(1) and eight equivalent N(2) atoms to form distorted CsN12 cuboctahedra that share corners with six equivalent Cs(1)N12 cuboctahedra, corners with four equivalent Sm(1)N6 pentagonal pyramids, faces with eight equivalent Cs(1)N12 cuboctahedra, and faces with four equivalent Sm(1)N6 pentagonal pyramids. Sm(1) is bonded to three equivalent N(1) and three equivalent N(2) atoms to form distorted SmN6 pentagonal pyramids that share corners with six equivalent Cs(1)N12 cuboctahedra, faces with six equivalent Cs(1)N12 cuboctahedra, and  a faceface with one Sm(1)N6 pentagonal pyramid. There are two inequivalent N sites. In the first N site, N(2) is bonded in a 1-coordinate geometry to four equivalent Cs(1) and one Sm(1) atom. In the second N site, N(1) is bonded in a distorted L-shaped geometry to four equivalent Cs(1) and two equivalent Sm(1) atoms.
Cs3Sm2N9 crystallizes in the trigonal R-3c space group. Cs(1) is bonded to four equivalent N(1) and eight equivalent N(2) atoms to form distorted CsN12 cuboctahedra that share corners with six equivalent Cs(1)N12 cuboctahedra, corners with four equivalent Sm(1)N6 pentagonal pyramids, faces with eight equivalent Cs(1)N12 cuboctahedra, and faces with four equivalent Sm(1)N6 pentagonal pyramids. There are two shorter (3.64 Å) and two longer (3.69 Å) Cs(1)-N(1) bond lengths. There are a spread of Cs(1)-N(2) bond distances ranging from 3.23-3.76 Å. Sm(1) is bonded to three equivalent N(1) and three equivalent N(2) atoms to form distorted SmN6 pentagonal pyramids that share corners with six equivalent Cs(1)N12 cuboctahedra, faces with six equivalent Cs(1)N12 cuboctahedra, and  a faceface with one Sm(1)N6 pentagonal pyramid. All Sm(1)-N(1) bond lengths are 2.38 Å. All Sm(1)-N(2) bond lengths are 2.40 Å. There are two inequivalent N sites. In the first N site, N(2) is bonded in a 1-coordinate geometry to four equivalent Cs(1) and one Sm(1) atom. In the second N site, N(1) is bonded in a distorted L-shaped geometry to four equivalent Cs(1) and two equivalent Sm(1) atoms.