Thermal behavior of the saccharinates of K+, Na+, Rb+, Cs+ and NH4+: structural inferences

Four alkali saccharinates: K3(sac)3·2H2O (KSac, ‘sac’ denotes saccharinato ion, C7H4NO3S−), triclinic Na3(sac)3·2H2O (NaSac), Rb2(sac)2·H2O (RbSac), Cs(Hsac)(sac)·H2O (CsSac)) and ammonium saccharinate (AmmSac) were synthesized and their thermal decompositions were investigated in the temperature interval 293–873 K by means of thermogravimetric methods (TG, DTG, DTA) in static atmosphere of helium and by DSC in a flow of nitrogen. The thermal and the infrared spectroscopic data of NaSac and AmmSac were correlated with the corresponding structural data, whereas data for KSac, RbSac and CsSac were used to make inferences about their crystal structures. Excluding the anhydrous AmmSac, all compounds were dehydrated prior to the decomposition of the deprotonated saccharinato species. The decomposition temperature of the saccharinato ion is about 130 K higher than the one of pure saccharin. There are two types of water molecules in molar ratio 2:1 in KSac, the overall structure being similar to but not identical with that of NaSac. Coordination properties rather than the hydrogen bonding are responsible for the stronger bonding of the water in the former salt. The existence of molecular saccharin in CsSac is confirmed.