Novel supramolecular isomerism in coordination polymer synthesis from unsymmetrical bridging ligands: Solvent influence on the ligand placement orientation and final network structure

The assembly of Co(NCS)(2) with 1-methyl-1'-(3-pyridyl)-2-(4-pyridyl)ethene (L-1) exhibits a novel supramolecular isomerism of [Co(L-1)(2)(NCS)(2)](infinity) caused by different placement orientation of L-1 around metal centers. The reaction in MeOH/ H2O and EtOH/H2O resulted in a double chain structure of 1, and that in EtOH/CH3NO2 led to an open framework structure of 2. The reaction in MeOH/CH3NO2 solvent system concomitantly afforded 1 and 2. The assemblies of 1-(3-pyridyl)-2-(4-pyrimidyl)ethene (L-2) with Co(NCS)(2) created the water-coordinated complexes of Co(L-2)(2)(H2O)(2)(NCS)(2) (3 and 4), an MeOH coordinated complex of Co(L-2)(2)(H2O)(2)(NCS)(2) (5), and an open framework coordination polymer of [Co(L-1)(2)(NCS)(2)](infinity) (6) depending on the reaction solvent system. From these observations, it is suggested that in the formation of 1, the solvent-coordinated intermediate species would be generated first and its trans coordination configuration should define the placement orientation of L-1 in the resulting polymer of 1. On the other hand, it is presumed that the solvent-coordinated intermediate would not be produced during the formation of 2 due to the weaker coordination ability of EtOH and CH3NO2 molecules. The open framework coordination polymers of 2 and 6 are converted in the solid state into the isomeric coordination polymer of 1 and hydrogen bonded network structure of 3, respectively.