engleski

Flexible supramolecular host for trigonal and pyramidal anion guests

Natural anions receptors use convergent and rigid display of hydrogen bond donors to bind small anion species. Development of synthetic receptors is a rapidly growing area of interest in supramolecular chemistry. Anions have relatively low charge to radius ratio, can be pH sensitive (by lower pH values can become protonated and lose their negative charge, and complex anions can have different geometries which can be studied from transition-metal ions coordination point of view). Therefore, anion receptors must function in active pH range of anions. They should satisfy sterical, hydrophobical and other demands in order to capture guest species with high affinity and selectivitiy. In our work, we have prepared a supramolecular host for a two anions of fairly different geometries: ClO3- and NO3-. The crystals are unstable upon exposure to air so the diffraction experiments were carried in loop (mother liquid/glicerol mixture) at 100 K. When the nitrate is guest (from methanol), 1, it occupies the center of the supramolecular ring (formed by three host molecules) since the hydrophilic parts of the host molecules are pointed inwards. It is the first known example where the nitrate forms 12 hydrogen bonds in natural or sinthetic hosts. Disordered methanol and water molecules occupy large channels. On the other hand, when nitrate (2) (from acetonitrile) and chlorate (3) anion are guests, the supramolecular host exibit different „ ZC like“ folding where anions occupy voids in the crystal structure together with solvent molecules.

anion receptor; supramolecular chemistry; hydrogen bonds; crystal and molecular structures

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