Mechanochemical Synthesis of Alkaline Earth Mg – Ba Saccharinates. Connectivity in the Crystal Structures of Mg(sac)2∙7H2O, Ca(sac)2∙7H2O and Ba(sac)2∙4.5H2O (sac = saccharinate)

Abstract

Alkaline earth saccharinates Mg -Ba were synthesized by the known solution-based methods and also by mechanochemical synthesis. The compounds were characterized by TG/DSC, X-ray powder diffraction, and Mg, Ca and Ba saccharinates by single-crystal X-ray analysis. The structure of Mg(sac)2 •7H2O (sac = saccharinate), is known but the diffraction data were collected at 170 K in this study for comparison with other structures. Crystals of hydrates of Ca -Ba saccharinates are very thin needle-like. A 4 μm crystal of Ca(sac)2 •7H2O gave a low intensity diffraction pattern of sufficient quality to locate non-hydrogen atoms (triclinic crystal system, space group P-1, Z = 4). Crystals of strontium saccharinate were too thin for data collection, however the formula Sr(sac)2 •4H2O, proposed in a previous publication was confirmed by thermogravimetric analysis. Diffraction from a 12 μm thick crystal of Ba(sac)2 •4.5H2O resulted in a complete data set (monoclinic crystal system, space group P2/c, Z = 8). In the corresponding structures, the Mg ion is six-coordinated forming an octahedron, both Ca ions are irregularly eight-coordinated with the polyhedra bridged by saccharinate ions into chains, whereas both Ba ions are irregularly nine-coordinated with the polyhedra sharing edges and corners through bridging water molecules and bridging saccharinate ions into double chains. All water molecules are included into hydrogen bonding into layers with only van der Waals and weak C-H•••O bonds between the chains.