BaO2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and three equivalent O(2) atoms. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one O(4) atom to form a mixture of distorted corner and edge-sharing OBa4O square pyramids. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent Ba(2), three equivalent Ba(1), and one O(3) atom. In the third O site, O(3) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one O(2) atom to form a mixture of distorted corner and edge-sharing OBa4O square pyramids. In the fourth O site, O(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one O(1) atom to form a mixture of distorted corner and edge-sharing OBa4O trigonal bipyramids.
BaO2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and three equivalent O(2) atoms. There is one shorter (2.74 Å) and one longer (2.78 Å) Ba(1)-O(1) bond length. There is one shorter (2.74 Å) and one longer (2.78 Å) Ba(1)-O(3) bond length. There is one shorter (2.73 Å) and one longer (2.76 Å) Ba(1)-O(4) bond length. There are a spread of Ba(1)-O(2) bond distances ranging from 2.73-3.06 Å. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. There is one shorter (2.64 Å) and one longer (2.78 Å) Ba(2)-O(1) bond length. There is one shorter (2.73 Å) and one longer (2.90 Å) Ba(2)-O(2) bond length. There is one shorter (2.62 Å) and one longer (2.79 Å) Ba(2)-O(3) bond length. There is one shorter (2.68 Å) and one longer (2.80 Å) Ba(2)-O(4) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one O(4) atom to form a mixture of distorted corner and edge-sharing OBa4O square pyramids. The O(1)-O(4) bond length is 1.50 Å. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent Ba(2), three equivalent Ba(1), and one O(3) atom. The O(2)-O(3) bond length is 1.49 Å. In the third O site, O(3) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one O(2) atom to form a mixture of distorted corner and edge-sharing OBa4O square pyramids. In the fourth O site, O(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one O(1) atom to form a mixture of distorted corner and edge-sharing OBa4O trigonal bipyramids.