Li2Ni2Si2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded in a 3-coordinate geometry to one O(4), one O(5), and one O(7) atom. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(4), one O(5), and one O(6) atom. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms to form distorted NiO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Ni(2)O4 tetrahedra,  an edgeedge with one Ni(1)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. In the second Ni site, Ni(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form NiO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-72°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Ni(2)O4 tetrahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 59°. In the second Si site, Si(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Ni(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-56°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Li(2), one Ni(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Li(2), one Ni(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ni(2), two equivalent Ni(1), and one Si(1) atom. In the fourth O site, O(4) is bonded to one Li(1), one Li(2), one Ni(2), and one Si(2) atom to form distorted OLi2SiNi tetrahedra that share corners with two equivalent O(7)LiSiNi2 tetrahedra and corners with four equivalent O(5)Li2SiNi tetrahedra. In the fifth O site, O(5) is bonded to one Li(1), one Li(2), one Ni(2), and one Si(2) atom to form OLi2SiNi tetrahedra that share corners with two equivalent O(7)LiSiNi2 tetrahedra and corners with four equivalent O(4)Li2SiNi tetrahedra. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Li(2), one Ni(1), and one Si(2) atom. In the seventh O site, O(7) is bonded to one Li(1), one Ni(1), one Ni(2), and one Si(1) atom to form corner-sharing OLiSiNi2 tetrahedra.
Li2Ni2Si2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded in a 3-coordinate geometry to one O(4), one O(5), and one O(7) atom. The Li(1)-O(4) bond length is 2.10 Å. The Li(1)-O(5) bond length is 2.00 Å. The Li(1)-O(7) bond length is 2.05 Å. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(4), one O(5), and one O(6) atom. The Li(2)-O(1) bond length is 2.55 Å. The Li(2)-O(2) bond length is 2.04 Å. The Li(2)-O(4) bond length is 2.19 Å. The Li(2)-O(5) bond length is 2.10 Å. The Li(2)-O(6) bond length is 2.05 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms to form distorted NiO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Ni(2)O4 tetrahedra,  an edgeedge with one Ni(1)O6 octahedra, and edges with two equivalent Si(1)O4 tetrahedra. The Ni(1)-O(1) bond length is 2.32 Å. The Ni(1)-O(2) bond length is 1.98 Å. The Ni(1)-O(6) bond length is 1.97 Å. The Ni(1)-O(7) bond length is 2.14 Å. There is one shorter (2.10 Å) and one longer (2.20 Å) Ni(1)-O(3) bond length. In the second Ni site, Ni(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form NiO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-72°. The Ni(2)-O(3) bond length is 1.97 Å. The Ni(2)-O(4) bond length is 1.98 Å. The Ni(2)-O(5) bond length is 1.98 Å. The Ni(2)-O(7) bond length is 1.99 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Ni(2)O4 tetrahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 59°. The Si(1)-O(1) bond length is 1.67 Å. The Si(1)-O(2) bond length is 1.60 Å. The Si(1)-O(3) bond length is 1.66 Å. The Si(1)-O(7) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Ni(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-56°. The Si(2)-O(1) bond length is 1.69 Å. The Si(2)-O(4) bond length is 1.65 Å. The Si(2)-O(5) bond length is 1.65 Å. The Si(2)-O(6) bond length is 1.62 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Li(2), one Ni(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Li(2), one Ni(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ni(2), two equivalent Ni(1), and one Si(1) atom. In the fourth O site, O(4) is bonded to one Li(1), one Li(2), one Ni(2), and one Si(2) atom to form distorted OLi2SiNi tetrahedra that share corners with two equivalent O(7)LiSiNi2 tetrahedra and corners with four equivalent O(5)Li2SiNi tetrahedra. In the fifth O site, O(5) is bonded to one Li(1), one Li(2), one Ni(2), and one Si(2) atom to form OLi2SiNi tetrahedra that share corners with two equivalent O(7)LiSiNi2 tetrahedra and corners with four equivalent O(4)Li2SiNi tetrahedra. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Li(2), one Ni(1), and one Si(2) atom. In the seventh O site, O(7) is bonded to one Li(1), one Ni(1), one Ni(2), and one Si(1) atom to form corner-sharing OLiSiNi2 tetrahedra.