K2NpO4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. K(1) is bonded in a 9-coordinate geometry to four equivalent O(2) and five equivalent O(1) atoms. Np(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form corner-sharing NpO6 octahedra. The corner-sharing octahedra are not tilted. There are two inequivalent O sites. In the first O site, O(2) is bonded to four equivalent K(1) and two equivalent Np(1) atoms to form distorted OK4Np2 octahedra that share corners with two equivalent O(2)K4Np2 octahedra, corners with twelve equivalent O(1)K5Np octahedra, edges with two equivalent O(2)K4Np2 octahedra, faces with four equivalent O(2)K4Np2 octahedra, and faces with four equivalent O(1)K5Np octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second O site, O(1) is bonded to five equivalent K(1) and one Np(1) atom to form distorted OK5Np octahedra that share corners with five equivalent O(1)K5Np octahedra, corners with twelve equivalent O(2)K4Np2 octahedra, edges with eight equivalent O(1)K5Np octahedra, and faces with four equivalent O(2)K4Np2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°.
K2NpO4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. K(1) is bonded in a 9-coordinate geometry to four equivalent O(2) and five equivalent O(1) atoms. All K(1)-O(2) bond lengths are 2.93 Å. There is one shorter (2.68 Å) and four longer (3.04 Å) K(1)-O(1) bond lengths. Np(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form corner-sharing NpO6 octahedra. The corner-sharing octahedra are not tilted. Both Np(1)-O(1) bond lengths are 1.91 Å. All Np(1)-O(2) bond lengths are 2.15 Å. There are two inequivalent O sites. In the first O site, O(2) is bonded to four equivalent K(1) and two equivalent Np(1) atoms to form distorted OK4Np2 octahedra that share corners with two equivalent O(2)K4Np2 octahedra, corners with twelve equivalent O(1)K5Np octahedra, edges with two equivalent O(2)K4Np2 octahedra, faces with four equivalent O(2)K4Np2 octahedra, and faces with four equivalent O(1)K5Np octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second O site, O(1) is bonded to five equivalent K(1) and one Np(1) atom to form distorted OK5Np octahedra that share corners with five equivalent O(1)K5Np octahedra, corners with twelve equivalent O(2)K4Np2 octahedra, edges with eight equivalent O(1)K5Np octahedra, and faces with four equivalent O(2)K4Np2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°.