Temperature-Controlled Assembly/Reassembly of Two Dicarboxylate-Based Three-Dimensional Co(II) Coordination Polymers with an Antiferromagnetic Metallic Layer and a Ferromagnetic Metallic Chain

Two new dicarboxylate-based three-dimensional cobalt coordination polymers, [Co(Me₂mal)(bpe)_0.5(H₂O)]_n (1) and [Co(Me₂mal)(bpe)_0.5]_n (2), were synthesized from dimethylmalonic acid (H₂-Me₂mal) in temperature-controlled solvothermal reactions. Lower temperatures (6080 °C) favored the formation of 1, while higher temperatures (120 °C) favored the production of 2. Compound 1 is comprised of Co(II) corrugated layers linked by syn-anti carboxylate bridges from the Me₂mal^2- ligands and pillared through bis-monodentate bpe groups. Compound 2 is comprised of a three-dimensional network involving one-dimensional Co-carboxylate chains bonded by antisymmetric µ₄-Me₂mal^2- ligands and aligned parallel to the [001] direction. The solvothermal retreatment of crystalline samples of 1 in a DMF/H₂O solvent at 120 °C allowed the structural reassembly, with complete conversion within 2 over 48 h. Magnetic analyses revealed that compound 1 exhibits both spin-orbital coupling and antiferromagnetic interactions through a syn-anti carboxylate (Me₂mal^2-) bridge exchange pathway [Co-Co separation of 5.478 Å] and compound 2 showed a ferromagnetic interaction resulting from the short Co-Co separation (3.150 Å) and the small Co-O-Co bridging angles (98.5° and 95.3°) exchange pathway which was provided by µ₄-Me₂mal^2- bridging ligand.