Distinct CdII and CoII thiocyanate coordination complexes with 2,5-bis(pyrazinyl)-1,3,4-oxadiazole: Metal-directed assembly of a 1-D polymeric chain and a 3-D supramolecular network

The reactions of 2,5-bis(pyrazinyl)-1,3,4-oxadiazole (bpzo) with CdII or CoII salt in the presence of thiocyanate afford two distinct complexes, a 1-D coordination array [Cd(bpzo)2(SCN)2]n (1) and a 3-D hydrogen-bonded supramolecular network [Co(bpzo)2(SCN)2(H2O)2](CH3CN)2(H2O)2 (2). X-ray single-crystal structural determination reveals that the extended networks of complexes 1 and 2 are manipulated via different directional propagating forces. In 1, the adjacent CdII centers are bridged by a pair of μ1,3-SCN− anions to form a 1-D array, whereas in 2, the monomeric CoII coordination entities are hydrogen-bonded into a novel 3-D architecture in which the thiocyanate ions take the only N-binding mode. In both cases, bpzo behaves as monodentate terminals. These results indicate that the choice of metal ions does play a critical role in the supramolecular assembly. The structural and binding features of bpzo in all related compounds have also been discussed.

Graphical abstractAssemblies of CdII or CoII thiocyanate with a multidentate organic ligand 2,5-bis(pyrazinyl)-1,3,4-oxadiazole (bpzo) generate a 1-D coordinated chain [Cd(bpzo)2(SCN)2]n (1) and a monomeric complex [Co(bpzo)2(SCN)2(H2O)2](CH3CN)2(H2O)2 (2). In both structures, bpzo is monodentate coordination, whereas the thiocyanate ions take the bridging or terminal modes, respectively. The neutral CoII complex units and lattice water molecules in 2 are interlinked to result in a novel 3-D hydrogen-bonded network with 1-D channels, in which the acetonitrile guests are included. This work reveals that the metal ions do play a critical role in tuning the network structures.Figure optionsDownload full-size imageDownload as PowerPoint slide