engleski

Robustness of the dimeric R2 2(6) hydrogen bond motif in the crystal structures of β-diketonato cobalt(II) and nickel(II) complexes with pyridine-based oximes

The β-diketonates are promising class of chelating ligands that exclude a need for involvement of additional ions in building of supramolecular assemblies. The supramolecular moieties are not under the influence of disruptive effect of counter ions and are expected to interact with each other in the same manner as in organic systems. Some supramolecular synthons, like an R2 2(6) motif, proved to be useful and reliable tools in crystal engineering of organic substances e. g. oximes. The oxime moiety is a supramolecular connector that can generate infinite low-dimensional networks by involving a dimeric oxime-oxime O‒H···N hydrogen-bonded R2 2(6) motif. By combining the oxime moiety with a coordination site for a metal ion, supramolecular assemblies of metal complexes can be obtained. By introducing the oxime moieties into the β-diketonato Co(II) and Ni(II) complexes, we wanted to examine the robustness of the R2 2(6) motif in metal-organic systems and to explore factors responsible for its persistence or disruption e.g. the position of the oxime moiety on the pyridine ring, the type of the substituent in oxime moiety (‒C(R)=NOH ; R = H, CH3, NH2). We have prepared a series of 1, 3-diphenyl-1, 3-propanedionato Co(II) and Ni(II) complexes with selected pyridine-based oximes, containing the oxime moiety in the position -3 or -4. The oxime ligands are bound to metal ions via their pyridine N atoms, leaving the oxime moieties available for supramolecular interactions. The R2 2(6) motif was preserved only in one case (the oxime moiety in m-position), while the β-diketonato O atom acts as an acceptor of oxime H atom in all other cases. The position of oxime moiety seems to be a decisive factor, responsible for preservation of the R2 2(6) motif in the studied metal-organic systems.

hydrogen bond motif; β-diketonato; cobalt; nickel; oxime

nije evidentirano