engleski

Solid state study of three pseudopolymorphic forms of flexible tripodal host for complex oxoanions

The field of anion binding chemistry has roots in the early 1970’ s, but, unlikely the coordination chemistry of cations, this field expresses very slow development, which is credited to the anions properties. The importance of anionic species in natural processes is today well-known, and the field has experienced veritable growth in the last ten years, but the design of hosts is still a challenging task. Many variables must be taken in account to build effective receptor[1], such as anions charge, geometry and volume, the choice of receptors binding groups (charged or neutral receptor), solvent (protic solvents can be very competitive) and receptor geometry.[2] One of the main approaches in receptor tailoring is synthesis of fairly simple, flexible host capable to adapt to anion demands. They do not display high affinity constants for target anion, but the conformational freedom and adaptations of each host provide a library of architectures valuable in the art. Flexible hosts derived from dehydroacetic acid and polyamine are known from literature and they express both high affinity and amazing anion-dependent behavior[3]. In case of (dha)3tren, L, a tripodal host with affinity for nitrate anion[4], the structure of ligand itself was not known. The structural study of (dha)3tren reveals considerable conformational changes and binding abilities of this ligand in presence of different guests, such as methanol, ethanol and propanol molecules. In all three cases L displays one up, two down conformation of side legs. The main host-guest contact is provided over O– H• • • O hydrogen bond between the hydroxyl-group of the alcohol and oxo-group of the pyrone moiety. Depending on guest properties, the ligand takes variable spatial arrangements and different oxo-groups are responsible for bonding. The structures are further stabilized through network of weak noncovalent interactions thus resulting in variety of architectural motifs. These guest-induced adaptations denote this ligand as potential host for C3-anions other than nitrate and the further studies are leading in that way. [1] P. D. Beer, P. A. Gale, Angew. Chem. Int. Ed., 40, (2001), 486– 516. [2] J. W. Steed, Chem. Commun. (2006), 2637– 2649. [3] K. Užarević, I. Đilović, D. Matković-Čalogović, D. Šišak, M. Cindrić, Angew. Chem. Int. Ed., 47 (2008), 37, 7022-7025. [4] L.-W. Yang, S. Liu, S. J. Rettig, C. Orvig, Inorg. Chem., 34, (1995), 4921-4925.

host-guest chemistry; solid-state study; flexible receptors; tripodal host

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