Synthesis and Characterization of the New Manganese Hydroxide Chloride γ‐Mn(OH)Cl

A new modification of Mn(OH)Cl was obtained under high‐pressure/high‐temperature conditions in a Walker‐type multianvil device. The pale pink, hygroscopic compound crystallizes in the orthorhombic space group Pnma (no. 62) with a = 602.90(4), b = 350.98(2), c = 1077.69(7) pm, and V = 228 × 10 6 pm 3 . The layered centrosymmetric structure consists of edge‐sharing Mn(OH) 3 Cl 3 octahedra arranged in sheets parallel to the (001) plane. The comparatively long H ··· Cl distance of 275 pm suggests only weak hydrogen bonds between neighboring layers. Spin‐polarized scalar‐relativistic DFT+ U calculations predict a non‐conducting magnetically ordered ground state with a band gap of at least 3.2 eV and an effective magnetic moment of 4.65 µ B /f. u. The experimentally determined magnetic response of Mn(OH)Cl is paramagnetic in the range of 10–300 K. The estimated moment of 5.6 µ B /f. u. indicates the high‐spin d 5 configuration of manganese(II). We find hints for a long‐range magnetic ordering below 10 K.