(NH4)3CrO8: A new S = 1/2 system exhibiting no magnetic transition down to 0.3 K

Recent studies related to quantum computation suggest a need for developing a well-characterized low-spin, e.g., S = 1/2, metal complex with limited or no significant hyperfine interactions. To this end, we here report the synthesis, crystal structure and magnetic and thermodynamic characterization of ammonium peroxychromate, (NH4)3CrO8, a new compound of Cr(5+), with a 3dx2-y23dx2-y2, S = 1/2 ground state, with about 92% molecules devoid of any metal hyperfine interaction. It is the first Cr(5+) compound exhibiting a structural phase transition (at 137.5 K) tentatively assigned to the order–disorder motion of the NH4+ ions, but it remains paramagnetic down to 0.3 K. The compound is stable for years if stored in a refrigerator, but it could explode if crushed or subjected to high pressure, or heated to well above room temperature.

Graphical abstractWe here report the synthesis, crystal structure, and magnetic and thermodynamic characterization of ammonium peroxychromate, (NH4)3CrO8, a new compound of Cr(5+), with a 3dx2-y23dx2-y2, S = 1/2 ground state, with about 92% molecules devoid of any metal hyperfine interaction. It is the first Cr(5+) compound exhibiting a structural phase transition (at 137.5 K) tentatively assigned to the order–disorder motion of the NH4+ ions, but it remains paramagnetic down to 0.3 K. The compound is stable for years if stored in a refrigerator, but it could explode if crushed or subjected to high pressure, or heated to well above room temperature.Figure optionsDownload full-size imageDownload as PowerPoint slide