The hydrogen bond system of Mn-leonite: neutron diffraction results in comparison with IR spectroscopic data

Abstract

Abstract Single-crystal Time-Of-Flight (TOF) neutron diffraction data of Mn-leonite, K2Mn(SO4)2·4 H2O, were obtained at 110, 185 and 295 K. Two reversible phase transitions at low temperatures have been previously confirmed by optical, calorimetric, and X-ray data. The cause for the phase transitions of Mn-leonite is a dynamic disorder of sulphate groups at room temperature (C2/m), that freeze to an ordered structure (I2/a) at 205(1) K. At 169(1) K the crystal structure switches to another ordered phase (P21/a).In general, the investigation by neutron diffraction confirms the structures of the three phases and, in addition, reveals the changes of the hydrogen bond configurations which influence the cooperative arrangement of the tetrahedra during the two successive phase transitions observed in Mn-leonite. IR spectroscopic measurements in the range of the O—H stretching frequencies yield a broad absorption band at ~3200 cm–1 that can only be resolved at low temperatures. A distance-frequency plot, calculated from the experimental data of low temperature neutron diffraction and IR spectroscopy is in agreement with correlation data from literature.