NaCa3 crystallizes in the tetragonal I4/mmm space group. Na(1) is bonded to four equivalent Ca(2) and eight equivalent Ca(1) atoms to form NaCa12 cuboctahedra that share corners with four equivalent Na(1)Ca12 cuboctahedra, corners with eight equivalent Ca(2)Na4Ca8 cuboctahedra, edges with eight equivalent Na(1)Ca12 cuboctahedra, edges with sixteen equivalent Ca(1)Na4Ca8 cuboctahedra, faces with four equivalent Na(1)Ca12 cuboctahedra, faces with six equivalent Ca(2)Na4Ca8 cuboctahedra, and faces with eight equivalent Ca(1)Na4Ca8 cuboctahedra. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to four equivalent Na(1), four equivalent Ca(1), and four equivalent Ca(2) atoms to form CaNa4Ca8 cuboctahedra that share corners with twelve equivalent Ca(1)Na4Ca8 cuboctahedra, edges with eight equivalent Na(1)Ca12 cuboctahedra, edges with eight equivalent Ca(1)Na4Ca8 cuboctahedra, edges with eight equivalent Ca(2)Na4Ca8 cuboctahedra, faces with four equivalent Na(1)Ca12 cuboctahedra, faces with four equivalent Ca(2)Na4Ca8 cuboctahedra, and faces with ten equivalent Ca(1)Na4Ca8 cuboctahedra. In the second Ca site, Ca(2) is bonded to four equivalent Na(1) and eight equivalent Ca(1) atoms to form CaNa4Ca8 cuboctahedra that share corners with four equivalent Ca(2)Na4Ca8 cuboctahedra, corners with eight equivalent Na(1)Ca12 cuboctahedra, edges with eight equivalent Ca(2)Na4Ca8 cuboctahedra, edges with sixteen equivalent Ca(1)Na4Ca8 cuboctahedra, faces with four equivalent Ca(2)Na4Ca8 cuboctahedra, faces with six equivalent Na(1)Ca12 cuboctahedra, and faces with eight equivalent Ca(1)Na4Ca8 cuboctahedra.
NaCa3 crystallizes in the tetragonal I4/mmm space group. Na(1) is bonded to four equivalent Ca(2) and eight equivalent Ca(1) atoms to form NaCa12 cuboctahedra that share corners with four equivalent Na(1)Ca12 cuboctahedra, corners with eight equivalent Ca(2)Na4Ca8 cuboctahedra, edges with eight equivalent Na(1)Ca12 cuboctahedra, edges with sixteen equivalent Ca(1)Na4Ca8 cuboctahedra, faces with four equivalent Na(1)Ca12 cuboctahedra, faces with six equivalent Ca(2)Na4Ca8 cuboctahedra, and faces with eight equivalent Ca(1)Na4Ca8 cuboctahedra. All Na(1)-Ca(2) bond lengths are 3.84 Å. All Na(1)-Ca(1) bond lengths are 3.95 Å. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to four equivalent Na(1), four equivalent Ca(1), and four equivalent Ca(2) atoms to form CaNa4Ca8 cuboctahedra that share corners with twelve equivalent Ca(1)Na4Ca8 cuboctahedra, edges with eight equivalent Na(1)Ca12 cuboctahedra, edges with eight equivalent Ca(1)Na4Ca8 cuboctahedra, edges with eight equivalent Ca(2)Na4Ca8 cuboctahedra, faces with four equivalent Na(1)Ca12 cuboctahedra, faces with four equivalent Ca(2)Na4Ca8 cuboctahedra, and faces with ten equivalent Ca(1)Na4Ca8 cuboctahedra. All Ca(1)-Ca(1) bond lengths are 3.84 Å. All Ca(1)-Ca(2) bond lengths are 3.95 Å. In the second Ca site, Ca(2) is bonded to four equivalent Na(1) and eight equivalent Ca(1) atoms to form CaNa4Ca8 cuboctahedra that share corners with four equivalent Ca(2)Na4Ca8 cuboctahedra, corners with eight equivalent Na(1)Ca12 cuboctahedra, edges with eight equivalent Ca(2)Na4Ca8 cuboctahedra, edges with sixteen equivalent Ca(1)Na4Ca8 cuboctahedra, faces with four equivalent Ca(2)Na4Ca8 cuboctahedra, faces with six equivalent Na(1)Ca12 cuboctahedra, and faces with eight equivalent Ca(1)Na4Ca8 cuboctahedra.