Douglass found **f to be trigonal, Laue symmetry **f, with **f, **f. X-ray and experimental density showed one formula unit in the unit cell, corresponding to a paramagnetic ion density of **f. The x-ray data did not permit Douglass to determine uniquely the space group, but a negative test for piezoelectricity led him to assume a center of symmetry. Under this assumption the space group must be **f and the following are the positions of the atoms in the unit cell. **f. This space group requires the hydrogen bond to be symmetric. Douglass found powder intensity calculations and measurements to agree best for **f. These data lead to a structure in which sheets of Cr atoms lie between two sheets of O atoms. The O atoms in each sheet are close packed and each Cr atom is surrounded by a distorted octahedron of O atoms. The **f layers are stacked normal to the [111] axis with the lower oxygens of one layer directly above the upper oxygens of the neighboring lower layer, in such a manner that the repeat is every three layers. The separate layers are joined together by hydrogen bonds. A drawing of the structure is to be found in reference 6.

The gross details of the structure appear reasonable. The structure appears to be unique among ROOH compounds, but is the same as that assumed by **f. The bond angles and distances are all within the expected limits and the volume per oxygen is about normal. However, the possible absence of a center of symmetry not only moves the hydrogen atom off **f, but also allows the oxygen atoms to become nonequivalent, with **f at **f and **f at **f (space group **f), where **f represents the oxygens on one side of the **f layers and **f those on the other side. However, any oxygen nonequivalence would shorten either the already extremely short **f interlayer distance of 2.55 A or the non hydrogen bonded **f interlayer interactions which are already quite short at 2.58 A. Hence it is difficult to conceive of a packing of the atoms in this material in which the oxygen atoms are far from geometrical equivalence. The only effect of lack of a center would then be to release the hydrogen atoms to occupy general, rather than special, positions along the [111] axis.