Ionothermal Synthesis of Cadmium Coordination Polymers: Ionic Liquid Effects on the Synthesis, Structural, and Thermal Characterization

Ionothermal synthesis is a little used method for the preparation of coordination polymers. By this method, two cadmium compounds were synthesized, 1, with formula Cd₃(ox)F₂(Ina)₂ (Ina = isonicotinate) and 2, Cd(NO₃)₂(4,4'-Bpy) (4,4'-Bpy = 4,4'-Bipyridine). The modification of the reaction conditions has allowed to obtain 2 as a pure phase. The structure of both compounds was determined by a single-crystal X-ray diffraction. Compound 1 is isostructural to the previously reported Cd₂Zn(ox)(OH)₂(Ina)₂. It crystallizes in the monoclinic space group P2₁/n and present a three-dimensional (3D) network, built-up from [Cd₃(ox)F₂]_n²ⁿ⁺ layers, linked by isonicotinate ligands. Crystals of 2 are formed by twins of two components which are rotated ca. 180° to each other. This compound crystallizes in the triclinic P-1 space group and its structure can be describe as a two-dimensional (2D) 4 connected 'sql' net. The layers are composed by [Cd(NO₃)₂]_n chains linked through 4,4'-Bpy ligands, and are pillared along the [011] direction. The thermal decomposition of 2 was studied by thermogravimetric and thermodiffractiometric techniques. The compound decomposes gradually starting from 160 °C, and due to heating, the structure suffers slight reversible changes in the bond distances and angles.