engleski

The amide oxygen vs. metal-bound halides as competitors in hydrogen bonding: Preferably heterogeneous or still self-complementary?

The main challenge within supramolecular chemistry still remains the full understanding and controlling the assembly of molecular building blocks into extended networks. In this context, the self-complementary amide bonding has already been accepted as the effective and reliable supramolecular tool in constructing the supramolecular architectures of organic, but recently, also of metal-organic solids. Besides, the metal-bound halides are generally recognized as excellent hydrogen bond acceptors, only slightly weaker than the halide ions themselves. Consequently, there arouse the question, which of the following scenarios is more probable one if these two interactions are met together: (i) the coexistence, or (ii) the total exclusiveness of one in presence of the other, and if so, which interaction is the prevailing one? One of the avenues for illumination of that issue could be facing the two interactions by slight modification of various structural factors. With this idea in mind, we report three halide complexes of cadmium(II) with picolinamide (pia), namely [CdCl2(pia)]n (1), [CdBr2(pia)]n (2) and [CdI2(pia)]n (3). In all three structures the same covalent pattern is found, but only for the bromide (2) and iodide (3) the non-covalent organization was achieved via self-complementary amide interactions. In 1, employing chloride as much stronger hydrogen bonding acceptor, the head-to-head amide bonds do not occur as the most robust supramolecular glue, but the hydrogen bonding interaction to the cadmium-bound chloride prevails.

cadmium(ii) complexes; picolinamide; hydrogen bonding

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