engleski

Amide hydrogen bonding vs. coordination?

The amide moiety is well known as a robust and reliable supramolecular connector in organic systems. Even though there are a number of reports where amide hydrogen bonds were used in a deliberate strategy for connecting metal complexes into extended networks [1, 2], a predetermination of supramolecular architectures and topologies of metal-organic systems remains very challenging. Recently, we found for a series of picolinamide complexes of late 3d-block metal(II) ions that the self-complementary amide motif R22(8) is not the synthon of choice [3]. Instead, a motif involving other accessible hydrogen-bond acceptor atom(s), leading to an R24(8) assembly, is more readily formed, even though the difference in energy between the two motifs is rather small. Furthermore, the problems encountered during the optimization of geometries of Zn and Cu complexes suggested that the motif formation itself might be one of the coordination geometry determining factors. With this in mind, we wanted to give the system more freedom in realizing the optimal framework, and therefore decided to map out the structural landscape that would arise when different amide derivatives of pyridine and/or pyrazine ligands were employed as structure-directing connectors. As a result, we report here several complexes where the self-complementary R22(8) motif is again the synthon of choice due to introduced conformational flexibilities into the systems in hands.

self-assembly supramolecular chemistry ; amides ; hydrogen bonding of coordination compounds.

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