Na3NiSiCO7 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms to form distorted NaO7 pentagonal bipyramids that share corners with two equivalent Na(2)O7 pentagonal bipyramids, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Na(2)O7 pentagonal bipyramid,  an edgeedge with one Si(1)O4 tetrahedra, and  a faceface with one Na(2)O7 pentagonal bipyramid. Ni(1) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms. Si(1) is bonded to one O(5), one O(6), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with four equivalent Na(2)O7 pentagonal bipyramids and edges with two equivalent Na(2)O7 pentagonal bipyramids. C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(3) atom. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Na(1), two equivalent Na(2), and one C(1) atom to form distorted corner-sharing ONa4C trigonal bipyramids. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(2), one Ni(1), and one C(1) atom. In the third O site, O(3) is bonded in a 1-coordinate geometry to one Na(1), two equivalent Na(2), one Ni(1), and one C(1) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(2), one Ni(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Na(2), one Ni(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(2), one Ni(1), and one Si(1) atom.
Na3NiSiCO7 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms. The Na(1)-O(2) bond length is 2.51 Å. The Na(1)-O(3) bond length is 2.50 Å. There is one shorter (2.60 Å) and one longer (2.63 Å) Na(1)-O(1) bond length. Both Na(1)-O(4) bond lengths are 2.43 Å. In the second Na site, Na(2) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms to form distorted NaO7 pentagonal bipyramids that share corners with two equivalent Na(2)O7 pentagonal bipyramids, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Na(2)O7 pentagonal bipyramid,  an edgeedge with one Si(1)O4 tetrahedra, and  a faceface with one Na(2)O7 pentagonal bipyramid. The Na(2)-O(1) bond length is 2.32 Å. The Na(2)-O(2) bond length is 2.72 Å. The Na(2)-O(3) bond length is 2.45 Å. The Na(2)-O(5) bond length is 2.47 Å. The Na(2)-O(6) bond length is 2.23 Å. There is one shorter (2.56 Å) and one longer (2.76 Å) Na(2)-O(4) bond length. Ni(1) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(5), one O(6), and two equivalent O(4) atoms. The Ni(1)-O(2) bond length is 2.03 Å. The Ni(1)-O(3) bond length is 2.46 Å. The Ni(1)-O(5) bond length is 1.91 Å. The Ni(1)-O(6) bond length is 2.01 Å. Both Ni(1)-O(4) bond lengths are 1.98 Å. Si(1) is bonded to one O(5), one O(6), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with four equivalent Na(2)O7 pentagonal bipyramids and edges with two equivalent Na(2)O7 pentagonal bipyramids. The Si(1)-O(5) bond length is 1.66 Å. The Si(1)-O(6) bond length is 1.61 Å. Both Si(1)-O(4) bond lengths are 1.66 Å. C(1) is bonded in a trigonal planar geometry to one O(1), one O(2), and one O(3) atom. The C(1)-O(1) bond length is 1.29 Å. The C(1)-O(2) bond length is 1.31 Å. The C(1)-O(3) bond length is 1.28 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Na(1), two equivalent Na(2), and one C(1) atom to form distorted corner-sharing ONa4C trigonal bipyramids. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(2), one Ni(1), and one C(1) atom. In the third O site, O(3) is bonded in a 1-coordinate geometry to one Na(1), two equivalent Na(2), one Ni(1), and one C(1) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(2), one Ni(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Na(2), one Ni(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(2), one Ni(1), and one Si(1) atom.