Materials Data on Na2O9 by Materials Project

Na2O9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Na sites. In the first Na site, Na is bonded in a 8-coordinate geometry to nine O atoms. There are a spread of Na–O bond distances ranging from 2.34–2.91 Å. In the second Na site, Na is bonded in a 7-coordinate geometry to seven O atoms. There are a spread of Na–O bond distances ranging from 2.39–2.89 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a 3-coordinate geometry to two Na and one O atom. The O–O bond length is 1.31 Å. In the second O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.25 Å. In the third O site, O is bonded in a 4-coordinate geometry to three Na and one O atom. The O–O bond length is 1.30 Å. In the fourth O site, O is bonded in a 2-coordinate geometry to two Na and two O atoms. There is one shorter (1.28 Å) and one longer (1.99 Å) O–O bond length. In the fifth O site, O is bonded in a 1-coordinate geometry to two Na and two O atoms. In the sixth O site, O is bonded in a 3-coordinate geometry to two Na and one O atom. In the seventh O site, O is bonded in a 3-coordinate geometry to two equivalent Na and one O atom. In the eighth O site, O is bonded in a bent 120 degrees geometry to one Na and one O atom. The O–O bond length is 1.29 Å. In the ninth O site, O is bonded in a 3-coordinate geometry to two Na and one O atom.