Na4NpH7O9 crystallizes in the triclinic P-1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(3), two equivalent O(4), and two equivalent O(5) atoms to form distorted NaO6 octahedra that share  a cornercorner with one Na(3)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, and edges with three equivalent Np(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. In the second Na site, Na(2) is bonded in a 7-coordinate geometry to one H(2), one O(1), one O(2), one O(3), one O(8), and two equivalent O(6) atoms. In the third Na site, Na(3) is bonded to one O(2), one O(3), one O(8), one O(9), and two equivalent O(6) atoms to form distorted NaO6 octahedra that share  a cornercorner with one Na(1)O6 octahedra,  an edgeedge with one Na(3)O6 octahedra, and edges with two equivalent Np(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. In the fourth Na site, Na(4) is bonded in a 8-coordinate geometry to one H(1), one H(3), one O(3), one O(4), one O(5), one O(9), and two equivalent O(7) atoms. Np(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form NpO6 octahedra that share edges with two equivalent Na(3)O6 octahedra and edges with three equivalent Na(1)O6 octahedra. There are seven inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one Na(4) and one O(5) atom. In the second H site, H(2) is bonded in a single-bond geometry to one Na(2) and one O(6) atom. In the third H site, H(3) is bonded in a single-bond geometry to one Na(4) and one O(7) atom. In the fourth H site, H(4) is bonded in a linear geometry to one O(7) and one O(8) atom. In the fifth H site, H(5) is bonded in a single-bond geometry to one O(8) atom. In the sixth H site, H(6) is bonded in a single-bond geometry to one O(9) atom. In the seventh H site, H(7) is bonded in a distorted single-bond geometry to one O(9) atom. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Np(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Na(2), one Na(3), and one Np(1) atom. In the third O site, O(3) is bonded in a distorted trigonal bipyramidal geometry to one Na(1), one Na(2), one Na(3), one Na(4), and one Np(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Na(4), two equivalent Na(1), and one Np(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Na(4), two equivalent Na(1), one Np(1), and one H(1) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to two equivalent Na(2), two equivalent Na(3), one Np(1), and one H(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to two equivalent Na(4), one H(3), and one H(4) atom. In the eighth O site, O(8) is bonded in a distorted water-like geometry to one Na(2), one Na(3), one H(4), and one H(5) atom. In the ninth O site, O(9) is bonded in a distorted water-like geometry to one Na(3), one Na(4), one H(6), and one H(7) atom.
Na4NpH7O9 crystallizes in the triclinic P-1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(3), two equivalent O(4), and two equivalent O(5) atoms to form distorted NaO6 octahedra that share  a cornercorner with one Na(3)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, and edges with three equivalent Np(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. The Na(1)-O(1) bond length is 2.38 Å. The Na(1)-O(3) bond length is 2.55 Å. There is one shorter (2.47 Å) and one longer (2.54 Å) Na(1)-O(4) bond length. There is one shorter (2.37 Å) and one longer (2.41 Å) Na(1)-O(5) bond length. In the second Na site, Na(2) is bonded in a 7-coordinate geometry to one H(2), one O(1), one O(2), one O(3), one O(8), and two equivalent O(6) atoms. The Na(2)-H(2) bond length is 2.53 Å. The Na(2)-O(1) bond length is 2.47 Å. The Na(2)-O(2) bond length is 2.45 Å. The Na(2)-O(3) bond length is 2.50 Å. The Na(2)-O(8) bond length is 2.36 Å. There is one shorter (2.55 Å) and one longer (2.58 Å) Na(2)-O(6) bond length. In the third Na site, Na(3) is bonded to one O(2), one O(3), one O(8), one O(9), and two equivalent O(6) atoms to form distorted NaO6 octahedra that share  a cornercorner with one Na(1)O6 octahedra,  an edgeedge with one Na(3)O6 octahedra, and edges with two equivalent Np(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. The Na(3)-O(2) bond length is 2.46 Å. The Na(3)-O(3) bond length is 2.52 Å. The Na(3)-O(8) bond length is 2.35 Å. The Na(3)-O(9) bond length is 2.38 Å. There is one shorter (2.51 Å) and one longer (2.52 Å) Na(3)-O(6) bond length. In the fourth Na site, Na(4) is bonded in a 8-coordinate geometry to one H(1), one H(3), one O(3), one O(4), one O(5), one O(9), and two equivalent O(7) atoms. The Na(4)-H(1) bond length is 2.39 Å. The Na(4)-H(3) bond length is 2.61 Å. The Na(4)-O(3) bond length is 2.46 Å. The Na(4)-O(4) bond length is 2.93 Å. The Na(4)-O(5) bond length is 2.64 Å. The Na(4)-O(9) bond length is 2.32 Å. There is one shorter (2.41 Å) and one longer (2.45 Å) Na(4)-O(7) bond length. Np(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form NpO6 octahedra that share edges with two equivalent Na(3)O6 octahedra and edges with three equivalent Na(1)O6 octahedra. The Np(1)-O(1) bond length is 1.93 Å. The Np(1)-O(2) bond length is 1.92 Å. The Np(1)-O(3) bond length is 1.94 Å. The Np(1)-O(4) bond length is 1.91 Å. The Np(1)-O(5) bond length is 2.31 Å. The Np(1)-O(6) bond length is 2.36 Å. There are seven inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one Na(4) and one O(5) atom. The H(1)-O(5) bond length is 0.98 Å. In the second H site, H(2) is bonded in a single-bond geometry to one Na(2) and one O(6) atom. The H(2)-O(6) bond length is 0.98 Å. In the third H site, H(3) is bonded in a single-bond geometry to one Na(4) and one O(7) atom. The H(3)-O(7) bond length is 0.98 Å. In the fourth H site, H(4) is bonded in a linear geometry to one O(7) and one O(8) atom. The H(4)-O(7) bond length is 1.57 Å. The H(4)-O(8) bond length is 1.03 Å. In the fifth H site, H(5) is bonded in a single-bond geometry to one O(8) atom. The H(5)-O(8) bond length is 0.99 Å. In the sixth H site, H(6) is bonded in a single-bond geometry to one O(9) atom. The H(6)-O(9) bond length is 0.99 Å. In the seventh H site, H(7) is bonded in a distorted single-bond geometry to one O(9) atom. The H(7)-O(9) bond length is 1.02 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Np(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Na(2), one Na(3), and one Np(1) atom. In the third O site, O(3) is bonded in a distorted trigonal bipyramidal geometry to one Na(1), one Na(2), one Na(3), one Na(4), and one Np(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Na(4), two equivalent Na(1), and one Np(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Na(4), two equivalent Na(1), one Np(1), and one H(1) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to two equivalent Na(2), two equivalent Na(3), one Np(1), and one H(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to two equivalent Na(4), one H(3), and one H(4) atom. In the eighth O site, O(8) is bonded in a distorted water-like geometry to one Na(2), one Na(3), one H(4), and one H(5) atom. In the ninth O site, O(9) is bonded in a distorted water-like geometry to one Na(3), one Na(4), one H(6), and one H(7) atom.