Step-by-step thermal transformations of a new porous coordination polymer [(H2O)5CuBa(Me2mal)2]n (Me2mal2−=dimethylmalonate): Thermal degradation to barium cuprate

The reactions of CuSO4·5H2O, dimethylmalonic acid and Ba(OH)2·H2O (Cu: H2Me2mal: Ba=1: 2: 2) in aqueous and aqueous-ethanol solutions (H2O: EtOH=1: 1) resulted in formation of 3D-porous coordination polymers [(H2O)3(μ-H2O)2CuBa(μ3-Me2mal)(Me2mal)]n (1) and [(μ-H2O)CuBa(μ3-Me2mal)(μ4-Me2mal)]n (2), respectively. It has been shown that compound 2 was an intermediate in the thermal degradation of compound 1. Thorough studies of solid-state thermolysis of 1 and 2 allowed to detect formation of coordination polymer [CuBa(μ4-Me2mal)(μ5-Me2mal)]n (3), structure of which was determined by X-ray powder diffraction. It has been found that the channels in polymer 3 were accessible for guest molecules (MeOH). Theoretical estimation of methanol diffusion barrier was carried out. Complete solid-phase thermolysis of 1 and 2 leads to a mixture of BaCuO2, BaCO3, and CuO. Special conditions for obtaining of a crystalline phase of pure cubic BaCuO2 were determined. Step-by-step transformation of new coordination polymer [(H2O)5CuBa(Me2mal)2]n to [(H2O)CuBa(Me2mal)2]n and [CuBa(Me2mal)2]n were performed. Dehydration of initial compound leads to structural changes of 12-membered ring fragment. All compounds have porous structure. The final product of thermal decomposition is crystalline phase of individual cubic BaCuO2. [Display omitted] ► New 3D-polymers [(H2O)5CuBa(Me2mal)2]n and [(H2O)CuBa(Me2mal)2]n were synthesized. ► Thermal analysis showed step-by-step transformations of [(H2O)5CuBa(Me2mal)2]n. ► Crystalline phase of pure cubic BaCuO2 is the product solid-phase thermolysis.