Abstrakt
In the system Gly - Mn(NO3)2 - H2O at 10 °C and equilibrium conditions, crystallization of two new compounds was established: 2Gly.Mn(NO3)2 with a wide field of crystallization and 6Gly.2Mn(NO3)2.3H2O with a narrow field of crystallization. The crystal structures of both compounds are made up of chain-linked octahedra differing in composition.
In both compounds, glycine acts as a bidentate ligand. Water molecules are not involved in the coordination environment of the Mn(2+) ion, which is to be expected according to Pearson's softness-hardness concept.
In the compound 2Gly.Mn(NO3)2 (triclinic system, P-1 space group) the octahedra [MnO4(4/2Gly)O2(2NO3)]0 are composed of two types of ligands and are electroneutral, while in the compound 6Gly.2Mn (NO3)2.3H2O (monoclinic system, P21/n space group) positively charged octahedra [MnO6(6/2Gly)](2+) are built of glycine ligands only. For steric and electrostatic reasons, the structure of 2Gly.Mn(NO3)2 is more stable and provides a wider concentration interval of its crystallization.
The FTIR and Raman spectra, as well as the thermal behavior of both compounds are discussed.