Unexpected formation of the cobalt-formate coordination polymer [Co3(HCO2)6]·dmf from Co(NO3)2 and 2,2'-bipyridine-5,5'-dicarboxylic acid in dmf-EtOH-H2O

Abstract

Under hydro(solvo)thermal conditions, the cobalt-formate coordination polymer [Co3(HCO2)6]·dmf (1·dmf) was formed from Co(NO3)2 and 2,2'-bipyridine-5,5'-dicarboxylic acid (bpdcH2) in a mixed solvent of dmf, EtOH, and H2O. Polymer 1·dmf contains a formate ligand (HCO2-), which may have been formed by decarboxylation of bpdcH2 or hydrolysis of dmf. Heating up 1·dmf at 150 oC removed the dmf guests to give crystalline [Co3(HCO2)6] (1), a guest-free form of 1·dmf. By immersing polymer 1 into several solvents (guests), we could obtain the corresponding guest-containing crystals of the formula of 1·guest (guest = CH3CN, acetone, or thf). The dimensions of the unit-cell volumes of these crystals depended on the contained guests in increasing order of 1·CH3CN < 1 < 1·thf < 1·acetone < 1·dmf.