engleski

Transferability of selected supramolecular synthons from organic to metalorganic systems

Directed supramolecular interactions (such as hydrogen and halogen bonds) have proven to be invaluable tools in the field of crystal engineering. In simple systems, it is possible to predict the formation of supramolecular synthons when using these types of interactions. Problems concerning synthon prediction arise in more complicated systems where multiple competing donor and acceptor sites are present. If we want to harness specific interactions in such systems, without relying on chance, a means of predicting the interaction motifs needs to be developed. One approach is using the relative strengths of donors and acceptors to predict the interactions between them and a general rule was proposed that the best donors will interact with the best acceptors. This method of prediction has shown merit but measuring the “strength” of donors and acceptors still remained a problem. Electrostatic potential maps mapped on total density surfaces obtained via quantum-mechanical calculations offered an elegant solution for donor/acceptor strength assessment. It was shown that in purely organic systems the molecules tend to interact so that the best hydrogen bond donor (ESP maxima) pairs up with the best acceptor (ESP minima). Here we opted to test transferability of selected supramolecular synthons form organic systems to metal-organic environment, where additional competing acceptor sites are necessarily present. We focus our attention to those synthons that have already proven to be robust and reliable in purely organic systems. For this purpose, we prepared a series of β-diketonato complexes of Co2+, Ni2+ and Cu2+ with simple and rigid heterocyclic ligands bearing functionalities capable of forming self-complementary and directional interactions with HB donors and acceptors being directly attached to the heterocyclic systems. Complexes were synthesized by solution methods and solvent assisted grinding. Single crystals were obtained either by slow evaporation from mother liquor or by liquid diffusion methods. Crystal structures were determined by single crystal X-ray diffraction experiments and DFT calculations were performed to assess the capacity of acceptors and donors present in them.

supramolecular synthons ; metal-organic systems ; hydrogen bond

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