Naslov
Modelling the position of halogen atoms in the crystals containing halonium ions

Autori
Eraković, Mihael ; Stilinović, Vladimir ; Cinčić, Dominik

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
25th Slovenian – Croatian Crystallographic Meeting - Book of abstracts / - , 2017, 40-40

Skup
25th Slovenian – Croatian Crystallographic Meeting

Mjesto i datum
Ljubljana, Slovenija, 15.06.2017. - 17.06.2017

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
computational chemistry ; halonium compound ; CSD

Sažetak
Halonium ions of the formula [R−X−R]+ (R = substituted pyridine) present an interesting system for testing different models used to describe halogen bonding. Halogen atoms in these compounds are placed between two nitrogen atoms at distances significantly shorter (~40%) than the sum of van der Waals radii. Therefore, they can be viewed upon as N-halogenated pyridinium ion which forms strong halogen bond with the nitrogen atom of the other pyridine. Up to date, there have been 43 compounds of that type in the Cambridge Structural Database, all of which contain one type of substituted pyridine. As a part of this research, three new halonium compounds have been prepared: bis(2- methylpyridyl)iodonium perchlorate (b2MePyl), bis(3-methylpyridyl)bromonium perchlorate (b3MePyBr) and bis(3, 5- dimethylpyridyl)bromonium tribromide (b35DiMePyBr). Prepared compounds have been characterized by single crystal XRD, in order to determine distances between halogen atom and nitrogen atoms, and attenuated total reflectance IR spectroscopy (ATR), which has been used to determine the frequency of vibrations which include movement of the halogen atom. In the crystal of b2MePyI the iodine atom is placed on the twofold rotation axis and is equidistant between the two pyridine nitrogen atoms. On the other hand, in the crystal of b3MePyBr, the halonium ion is placed on a general position and, as a result, forms bonds of different lengths. Therefore, these compounds are ideal for studying the effects of the crystal structure on halogen bonding. Because of the many atoms in the general position in the crystal structure of b35DiMePyBr, this compound has been too complex for theoretical description and was not investigated. In order to describe the bonding theoretically, structures of both ions have been optimized both in vacuo and with several layers of surrounding molecules using ONIOM calculations. Theoretically obtained geometries were then compared to the experimental ones. Furthermore, in order to describe vibrations of the halogen atom, vibrational frequencies have been obtained within harmonic approximation using Gaussian 09 program and with the exact potential using Fourier grid Hamiltonian method. Both calculations have been performed for the ions in vacuo and ions surrounded with several layers of neighbouring molecules and the results have been compared with the experimental ATR spectra.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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