Microwave and Conventional Hydro(solvo)thermal Syntheses of Three Co(II) Coordination Polymers: Supramolecular Isomerism and Structural Transformations Accompanied by Tunable Magnetic Properties

Two genuine supramolecular isomers [Co(1,4-NDC)-(5,5'-dmbpy)](n) (1 alpha and 1 beta) and compound {[Co(1,4-NDC)(5,5'-dmbpy)(H2O)(2)](2)}(n) (2) (1,4-NDCH2 = 1,4-naphthalenedicarboxylic acid, 5,5'-dmbpy = 5,5'-dimethy1-2,2'-dipyridyl) have been synthesized under conventional hydro(solvo)thermal reactions. The highly crystalline single-phases of 1 beta and 2 with a well-defined morphology could also be quickly prepared through microwave-assisted syntheses within 5 min. Compared with 2, which possesses a one-dimensional (1D) single-chain-like structure, 1 alpha and 1 beta feature the structures of 1D ladder-like chain and two-dimensional (2D) layer, respectively, constructed from the ring-like [Co-2(OOCR)(2)] dimeric units interlinked by the 1,4-NDC ligands. The drastic structural transformation from 1 alpha to 2, as well as the interconversion between 1 beta and 2, was observed, which involved the reversible destruction and reconstruction of the Co-2(OOCR)(2) unit during the transformation and was associated with remarkable changes in magnetic properties. Remarkably, microwave heating as an external driving force was adopted to achieve structure transformation from 2 to 1 beta within 5 min. This work demonstrates that the microwave technique can be used as a quick and efficient synthetic method to investigate the structural conversion between compounds and further bring about property modulation.