Synthesis, Crystal Structure and Properties of a new Hydrate of Manganese Thiocyanate with the Composition Mn(NCS)2(H2O)2

The reaction of Mn(NCS)2 with 3‐cyanopyridine in water accidentally leads to the formation of single crystals of Mn(NCS)2(H2O)2 (1). If the synthesis is performed without 3‐cyanopyridine, the known tetrahydrate Mn(NCS)2(H2O)4 is formed. In the crystal structure of the new hydrate, the Mn2+ cations are linked by pairs of μ‐1,3‐bridging anionic ligands to chains, which are further connected via Mn(NCS)2(H2O)4 units into layers, that are additionally stabilized by intralayer hydrogen bonding. These layers are linked by interlayer hydrogen bonding into a 3D network. The structure of 1 shows strong similarities to that of both the tetrahydrate and of Mn(NCS)2. The synthesis from water always leads to the tetrahydrate, which is also obtained, when Mn(NCS)2 is stored in a humid atmosphere. Thermoanalytical measurements on the tetrahydrate show a more complicated behavior, which includes melting at about 46 °C and on cooling sometimes the dihydrate is observed. If the tetrahydrate is stored in vacuum at room temperature, the dihydrate forms before the transformation to the anhydrate is observed. Isothermic water sorption measurements prove, that at low humidity the dihydrate is obtained, which transforms into the tetrahydrate at higher humidities.