Retro-Crystal Engineering Analysis of Two <i>N</i>-Methylethylenediammonium Cadmium Halide Salts Obtained by Dimensional Reduction and Recombination of the Hexagonal CdX₂ Lattice

The reaction of the N-methylethylenediammonium dication (MEDA2+) with cadmium halides in acid solutions leads to the formation of the compounds (MEDA·H2O)2Cd4Cl12·2H2O and (MEDA·H2O)Cd3Br8·xH2O. Crystal structure determinations were carried out on both salts, and retro-crystal engineering analyses were made on the structures. The inorganic framework in both structures contain networks of edge-shared octahedra. The chloride complex has the appearance of slices cut from the hexagonal CdCl2 lattice by the MEDA2+ dications. The dications sheath the ribbons with one set of cations lying on the faces of the ribbons and with the second set capping the edges. N−H···Cl, O−H···Cl, N−H···O as well as C−H···Cl hydrogen bonds provide three-dimensional stability to the lattice. The bromide salt contains a microporous, stepped layer structure. This structure is derived from the parent hexagonal CdBr2 lattice by dimensional reduction to serrated (Cd3Br93-)∞ ribbons of edge-shared CdBr6 octahedra. Recombination via formation of edge-shared linkages between these ribbons leads to the development of a stepped layer structure. These layers are perforated due to the excision of Cd2Br22+ units at the step-edges in the layers. The MEDA2+ dications sit above and below these holes, providing charge compensation for the excised fragments. Thermal analyses of both compounds show the loss of water molecules in the temperature range of 80−120 °C with subsequent decomposition of the organic cations occurring above 300° C. Structural phase transitions were observed near 230 °C in both compounds.