K4NpS2O10Cl crystallizes in the monoclinic P2/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded to one O(2), one O(4), two equivalent O(3), three equivalent O(1), and one Cl(1) atom to form distorted KClO7 hexagonal bipyramids that share  a cornercorner with one K(1)ClO7 hexagonal bipyramid,  a cornercorner with one S(1)O4 tetrahedra, edges with four equivalent K(1)ClO7 hexagonal bipyramids, and edges with two equivalent S(1)O4 tetrahedra. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(2), one O(3), three equivalent O(5), and two equivalent Cl(1) atoms. Np(1) is bonded in a distorted linear geometry to two equivalent O(3) atoms. S(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SO4 tetrahedra that share  a cornercorner with one K(1)ClO7 hexagonal bipyramid and edges with two equivalent K(1)ClO7 hexagonal bipyramids. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to three equivalent K(1) and one S(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one K(1), one K(2), and one S(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one K(2), two equivalent K(1), and one Np(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one K(1) and one S(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to three equivalent K(2) and one S(1) atom. Cl(1) is bonded to two equivalent K(1) and four equivalent K(2) atoms to form edge-sharing ClK6 octahedra.
K4NpS2O10Cl crystallizes in the monoclinic P2/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded to one O(2), one O(4), two equivalent O(3), three equivalent O(1), and one Cl(1) atom to form distorted KClO7 hexagonal bipyramids that share  a cornercorner with one K(1)ClO7 hexagonal bipyramid,  a cornercorner with one S(1)O4 tetrahedra, edges with four equivalent K(1)ClO7 hexagonal bipyramids, and edges with two equivalent S(1)O4 tetrahedra. The K(1)-O(2) bond length is 3.09 Å. The K(1)-O(4) bond length is 3.08 Å. There is one shorter (2.90 Å) and one longer (2.92 Å) K(1)-O(3) bond length. There are a spread of K(1)-O(1) bond distances ranging from 2.72-3.15 Å. The K(1)-Cl(1) bond length is 3.16 Å. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(2), one O(3), three equivalent O(5), and two equivalent Cl(1) atoms. The K(2)-O(2) bond length is 2.97 Å. The K(2)-O(3) bond length is 2.87 Å. There are a spread of K(2)-O(5) bond distances ranging from 2.79-2.95 Å. There is one shorter (3.20 Å) and one longer (3.23 Å) K(2)-Cl(1) bond length. Np(1) is bonded in a distorted linear geometry to two equivalent O(3) atoms. Both Np(1)-O(3) bond lengths are 1.85 Å. S(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SO4 tetrahedra that share  a cornercorner with one K(1)ClO7 hexagonal bipyramid and edges with two equivalent K(1)ClO7 hexagonal bipyramids. The S(1)-O(1) bond length is 1.48 Å. The S(1)-O(2) bond length is 1.51 Å. The S(1)-O(4) bond length is 1.53 Å. The S(1)-O(5) bond length is 1.47 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to three equivalent K(1) and one S(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one K(1), one K(2), and one S(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one K(2), two equivalent K(1), and one Np(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one K(1) and one S(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to three equivalent K(2) and one S(1) atom. Cl(1) is bonded to two equivalent K(1) and four equivalent K(2) atoms to form edge-sharing ClK6 octahedra.