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

摘要

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 Me2mal²⁻ 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-Me2mal²⁻ 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 (Me2mal²⁻) 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-Me2mal²⁻ bridging ligand.