Raman and Infrared Studies of Hexa-, Tetra-, and Dihydrates of Crystalline Magnesium Nitrate

Abstract

Raman and infrared spectra of Mg(NO3)2•6H2O, Mg(NO3)2•6D2O and partially dehydrated products have been obtained and assigned. As the water content is reduced a different set of lines appears and maximizes at the composition Mg(NO3)2 4H2O On further dehydration a third set of lines characteristic of Mg(NO3)2•2H2O appears. The existence of the metastable tetrahydrate had not been confirmed since it was reported in 1932. The spectra suggest that four equatorial sites aroung Mg2+ in the tetrahydrate are occupied by four water molecules and two axial sites by nitrate ions, oriented in monodentate fashion. The spectra suggest that in the dihydrate approximately octahedral coordination is maintained by having two nitrate ions oriented in bidentate fashion and two water molecules trans to each other on the remaining sites.