Naslov
ELECTROSTATIC ATTRACTION OF IONS VS HYDROGEN BONDING –CRYSTAL STRUCTURES OF SUBSTITUITED PYRIDINIUM PICRATES

Autori
Stilinović, Vladimir ; Kaitner, Branko

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

Izvornik
Nineteenth Slovenian-Croatian Crystallographic Meeting Book of Abstravts / Lah, Nina ; Leban, Ivan - Ljubljana : Fakulteta za kemijo in kemijsko tehnologijo Univerze v Ljubljani, 2010, 39'-39'

Skup
Nineteenth Slovenian-Croatian Crystallographic Meeting

Mjesto i datum
Strahinj, Slovenija, 16.06.2010. - 20.06.2010

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
pyridinium; picrate; hydrogen bonding; crystal structure

Sažetak
Among the first crystal structures a student is acquainted to, are those of ionic compounds. The basic rule such a student is supposed to learn at that point is that ions of opposite charges are placed next to each other, so that every ion is surrounded by neighbours having the opposite charge. However, when simple inorganic ions are replaced by organic ones, in particularly such which are capable of hydrogen bonding, this rule may no longer apply, since in such crystals there are interactions other then the electrostatic ones, and these codetermine the crystal structure. To study the interplay of electrostatic and other interactions (with emphasis on the hydrogen bond) we have selected picrates of various pyridine derivatives. 18 such compounds were synthesised, crystallised and their crystal structures determined. Since the picrate anion can only act as a hydrogen acceptor, the hydrogen bonding will be determined by hydrogen donor abilities of the substituents on the pyridinium cation. The supramolecular synthon (I) is to be expected in the majority of structures since it combines N—H∙∙∙O hydrogen bonding with electrostatic interactions bringing the positively charged pyridinium nitrogen in proximity to the negatively charged picrate oxygen. Synthon I was indeed encountered in the structures of such pyridine derivatives which posses no hydrogen donors other than the positively charged nitrogen. However, when other hydrogen donors are present, hydrogen bonding often changes drastically. These changes include bonding of cations directly to other cations, different protonation sites on the cation and formation of hydrates, which occurs when other hydrogen donors are present, but not in their absence. Generally, the alkoxide oxygen atom of the picrate anion, being the best hydrogen acceptor, will form hydrogen bonds with the best donor, even at the cost of increasing the distance between the positive and the negative charge. It therefore seems that hydrogen bonding plays a greater role in the determination of crystal structures of pyridinium picrates than electrostatic interactions do.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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