Naslov
Interrelationship of Proton Transfer and Hydrogen Bonding Patterns in Salts and Co-crystals of Gentisic Acid with Pyridine Derivatives

Autori
Stilinović, Vladimir ; Kaitner, Branko

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

Izvornik
XXI Slovenian-Croatian Crystallographic Meeting, Book of Abstracts / Lah, Nina ; Trdin, Miha ; Leban, Ivan - Ljubljana : Univerza v Ljubljani, 2012, 55-55

Skup
XXI Slovenian-Croatian Crystallographic Meeting

Mjesto i datum
Pokljuka, Slovenija, 13.06.2012. - 17.06.2012

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
proton transfer crystal structure; hydrogen bonding

Sažetak
Since the mid 1960-es, the question of intermolecular proton transfer i.e. whether a given combination of substances will crystallize as a salt or as a co-crystal is among the most commonly reoccurring topics within the study of multicomponent solids. Unlike in solutions, the assessment of (Brønsted) acid-base behaviour in the crystalline state based on pKa values is only partly possible, since the behaviour of hydrogen donors and acceptors in the crystalline state is greatly affected by the characteristics of their specific environments in the crystal structure. If proton transfer leads to considerable changes in the electronic properties of molecules, most noticeably, by rendering them positively or negatively charged. Therefore the interrelationship between hydrogen bonding and proton transfer is twofold – on one hand hydrogen bonding affects the proton transfer, while on the other proton transfer alters the hydrogen bonding potential of a molecule. Our study covered 22 (new) crystal structures of dicomponent compounds of gensitic (2, 5-dihydroxybenzoic) acid and pyridine derivatives. In 16 of these, proton transfer from the acid to the pyridine has occurred (and can be classified as salts), while in 6 it was found to be absent (co-crystals). The structures of the majority of salts comprise ion pairs, further connected either in chains or into (pseudo)centrosymmetric dimers, while co-crystals have much more variable structures. There is some correlation between the solution pKa values of pyridines and the proton transfer, as it was found that proton transfer to the pyridine always occurred when pyridines with pKa values over ca 5 were employed. The O—H∙∙∙N hydrogen bonds between the carboxylic group and pyridine nitrogen in co-crystals were found to be somewhat shorter than the O−∙∙∙H—N+ bonds in salts indicating that the increased hydrogen bond strength might be the cause of the absence of proton transfer in these structures, even though the pyridine derivatives employed are sufficiently strong bases to deprotonate gensitic acid (in solution). Additionally, in some cases the proton transfer appears to be facilitated by the participation of gensitic acid carboxyl functionality in additional hydrogen bonding with hydroxyl groups of neighbouring gensitic acid molecules.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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