Sr4Ni3O9 crystallizes in the trigonal P321 space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(5), and four equivalent O(3) atoms. In the third Sr site, Sr(3) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(5), and four equivalent O(4) atoms. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to three equivalent O(4) and three equivalent O(5) atoms to form face-sharing NiO6 octahedra. In the second Ni site, Ni(2) is bonded to three equivalent O(3) and three equivalent O(5) atoms to form face-sharing NiO6 octahedra. In the third Ni site, Ni(3) is bonded in a 6-coordinate geometry to six equivalent O(2) atoms. In the fourth Ni site, Ni(4) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form face-sharing NiO6 octahedra. In the fifth Ni site, Ni(5) is bonded in a 6-coordinate geometry to three equivalent O(3) and three equivalent O(4) atoms. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1), two equivalent Sr(3), and two equivalent Ni(4) atoms to form a mixture of distorted edge, face, and corner-sharing OSr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 30-54°. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Sr(2), one Sr(3), two equivalent Sr(1), one Ni(3), and one Ni(4) atom. In the third O site, O(3) is bonded to two equivalent Sr(1), two equivalent Sr(2), one Ni(2), and one Ni(5) atom to form a mixture of distorted edge, face, and corner-sharing OSr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 4-62°. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(3), one Ni(1), and one Ni(5) atom. In the fifth O site, O(5) is bonded to one Sr(2), one Sr(3), two equivalent Sr(1), one Ni(1), and one Ni(2) atom to form a mixture of distorted edge, face, and corner-sharing OSr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 4-62°.
Sr4Ni3O9 crystallizes in the trigonal P321 space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. The Sr(1)-O(1) bond length is 2.55 Å. There is one shorter (2.68 Å) and one longer (2.70 Å) Sr(1)-O(2) bond length. There is one shorter (2.52 Å) and one longer (2.77 Å) Sr(1)-O(3) bond length. There is one shorter (2.43 Å) and one longer (2.91 Å) Sr(1)-O(4) bond length. There is one shorter (2.66 Å) and one longer (2.67 Å) Sr(1)-O(5) bond length. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(5), and four equivalent O(3) atoms. Both Sr(2)-O(2) bond lengths are 2.47 Å. Both Sr(2)-O(5) bond lengths are 2.58 Å. There are two shorter (2.64 Å) and two longer (2.71 Å) Sr(2)-O(3) bond lengths. In the third Sr site, Sr(3) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(5), and four equivalent O(4) atoms. Both Sr(3)-O(1) bond lengths are 2.75 Å. Both Sr(3)-O(2) bond lengths are 2.88 Å. Both Sr(3)-O(5) bond lengths are 2.56 Å. There are two shorter (2.75 Å) and two longer (2.85 Å) Sr(3)-O(4) bond lengths. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to three equivalent O(4) and three equivalent O(5) atoms to form face-sharing NiO6 octahedra. All Ni(1)-O(4) bond lengths are 1.84 Å. All Ni(1)-O(5) bond lengths are 1.94 Å. In the second Ni site, Ni(2) is bonded to three equivalent O(3) and three equivalent O(5) atoms to form face-sharing NiO6 octahedra. All Ni(2)-O(3) bond lengths are 1.87 Å. All Ni(2)-O(5) bond lengths are 1.92 Å. In the third Ni site, Ni(3) is bonded in a 6-coordinate geometry to six equivalent O(2) atoms. All Ni(3)-O(2) bond lengths are 2.18 Å. In the fourth Ni site, Ni(4) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form face-sharing NiO6 octahedra. All Ni(4)-O(1) bond lengths are 1.90 Å. All Ni(4)-O(2) bond lengths are 1.88 Å. In the fifth Ni site, Ni(5) is bonded in a 6-coordinate geometry to three equivalent O(3) and three equivalent O(4) atoms. All Ni(5)-O(3) bond lengths are 2.17 Å. All Ni(5)-O(4) bond lengths are 2.15 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1), two equivalent Sr(3), and two equivalent Ni(4) atoms to form a mixture of distorted edge, face, and corner-sharing OSr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 30-54°. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Sr(2), one Sr(3), two equivalent Sr(1), one Ni(3), and one Ni(4) atom. In the third O site, O(3) is bonded to two equivalent Sr(1), two equivalent Sr(2), one Ni(2), and one Ni(5) atom to form a mixture of distorted edge, face, and corner-sharing OSr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 4-62°. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(3), one Ni(1), and one Ni(5) atom. In the fifth O site, O(5) is bonded to one Sr(2), one Sr(3), two equivalent Sr(1), one Ni(1), and one Ni(2) atom to form a mixture of distorted edge, face, and corner-sharing OSr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 4-62°.