Ca3UN4 crystallizes in the orthorhombic Fmm2 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent N(1) and four equivalent N(2) atoms to form CaN6 octahedra that share corners with six equivalent Ca(1)N6 octahedra, edges with four equivalent Ca(1)N6 octahedra, edges with four equivalent Ca(2)N6 octahedra, and edges with four equivalent U(1)N6 octahedra. The corner-sharing octahedral tilt angles range from 3-22°. In the second Ca site, Ca(2) is bonded to two equivalent N(2) and four equivalent N(1) atoms to form CaN6 octahedra that share corners with two equivalent U(1)N6 octahedra, corners with four equivalent Ca(2)N6 octahedra, edges with four equivalent U(1)N6 octahedra, and edges with eight equivalent Ca(1)N6 octahedra. The corner-sharing octahedral tilt angles range from 1-3°. U(1) is bonded to two equivalent N(2) and four equivalent N(1) atoms to form UN6 octahedra that share corners with two equivalent Ca(2)N6 octahedra, corners with four equivalent U(1)N6 octahedra, edges with four equivalent Ca(2)N6 octahedra, and edges with eight equivalent Ca(1)N6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. There are two inequivalent N sites. In the first N site, N(1) is bonded to two equivalent Ca(1), two equivalent Ca(2), and two equivalent U(1) atoms to form a mixture of corner and edge-sharing NCa4U2 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second N site, N(2) is bonded in a 6-coordinate geometry to one Ca(2), four equivalent Ca(1), and one U(1) atom.
Ca3UN4 crystallizes in the orthorhombic Fmm2 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent N(1) and four equivalent N(2) atoms to form CaN6 octahedra that share corners with six equivalent Ca(1)N6 octahedra, edges with four equivalent Ca(1)N6 octahedra, edges with four equivalent Ca(2)N6 octahedra, and edges with four equivalent U(1)N6 octahedra. The corner-sharing octahedral tilt angles range from 3-22°. Both Ca(1)-N(1) bond lengths are 2.50 Å. All Ca(1)-N(2) bond lengths are 2.49 Å. In the second Ca site, Ca(2) is bonded to two equivalent N(2) and four equivalent N(1) atoms to form CaN6 octahedra that share corners with two equivalent U(1)N6 octahedra, corners with four equivalent Ca(2)N6 octahedra, edges with four equivalent U(1)N6 octahedra, and edges with eight equivalent Ca(1)N6 octahedra. The corner-sharing octahedral tilt angles range from 1-3°. Both Ca(2)-N(2) bond lengths are 2.98 Å. There are two shorter (2.44 Å) and two longer (2.45 Å) Ca(2)-N(1) bond lengths. U(1) is bonded to two equivalent N(2) and four equivalent N(1) atoms to form UN6 octahedra that share corners with two equivalent Ca(2)N6 octahedra, corners with four equivalent U(1)N6 octahedra, edges with four equivalent Ca(2)N6 octahedra, and edges with eight equivalent Ca(1)N6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. Both U(1)-N(2) bond lengths are 2.02 Å. There are two shorter (2.37 Å) and two longer (2.53 Å) U(1)-N(1) bond lengths. There are two inequivalent N sites. In the first N site, N(1) is bonded to two equivalent Ca(1), two equivalent Ca(2), and two equivalent U(1) atoms to form a mixture of corner and edge-sharing NCa4U2 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second N site, N(2) is bonded in a 6-coordinate geometry to one Ca(2), four equivalent Ca(1), and one U(1) atom.