Naslov
Crystallographic, solution and computational study of strong halogen bonds in N-halosuccinimide-pyridine complexes

Autori
Stilinović, Vladimir ; Horvat, Gordan ; Hrenar, Tomica ; Nemec, Vinko ; Cinčić, Dominik

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

Izvornik
The Twenty-fourth Croatian-Slovenian Crystallographic Meeting - Book of Abstracts / Bijelić, Mirjana ; Cetina, Mario ; Čobić, Andrea ; Matković-Čalogović, Dubravka ; Popović, Stanko ; Štefanić, Zoran ; Tonejc, Antun ; Višnjevac Aleksandar - Zagreb : Hrvatska akademija znanosti i umjetnosti (HAZU) ; Hrvatska kristalografska zajednica HAZU, 2016, 84-84

Skup
The Twenty-fourth Croatian-Slovenian Crystallographic Meeting

Mjesto i datum
Bol, Hrvatska, 22.09.2016. - 24.09.2016

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
N-halogenosuccinimide ; cocrystals ; halogen bond ; pyridine derivatives

Sažetak
Over the past couple of decades, halogen bonds (XB) have transformed from an obscure intermolecular interactions known only to a handful of experts into an indispensable tool of crystal engineering rivalling even to hydrogen bond (HB). However, detailed studies of XB energetics are still quite scarcer than those for HB. In our study we have used commercially available N-iodo, N-bromo- and N-chlorosuccinimide (nis, nbs, ncs) as halogen bond donors, succinimide (s) as an equivalent HB donor, as well as seven p-substituted pyridines as halogen (or hydrogen) bond acceptors. The pyridines have been selected to cover as wide as possible range of Hammet coefficients (–0.88 to 0.66), while avoiding functionalities which could act as hydrogen (or halogen) bond donors. This has ensured a relatively large variability of XB acceptor qualities, while ensuring that the observed XB is the only strong intermolecular interaction. In order to provide a detailed description of the halogen bonding in these systems, N-halosuccinimides were crystallised with the pyridines in order to study the formed complexes in the solid state. Simultaneously, microcalorimetric measurements were made to study the formation of halogen bonded complexes in acetonitrile solution, and, extensive computations in order to study the deformation of electron density upon XB formation, as well as the effect of various geometric parameters on the energy of XB. Solid state studies have shown that nis and nbs form strong halogen bonds with all 7 pyridine derivatives. As expected, nis was found to be a better XB donor (N∙∙∙I distances in cocrystals with nis were 29-32% shorter than the sum of van der Waals radii, while N∙∙∙Br distances in cocrystals with nbs were ‘only’ 23-29% shorter than the sum of the respective van der Waals radii). In both cases the more nucleophilic pyridine nitrogen atoms were better XB acceptors forming shorter bonds. The scattering of the datapoints was larger in the case of nbs indicating wider and more shallow potential well for XB with nbs. This was also confirmed computationally. The differences in the measured bond lengths were mirrored in the stability of the NIS-pyridine complexes in the solution – the stability constants were found to vary by over three orders of magnitude from logK = 4.003(9) for the complex exhibiting the shortest XB to logK = 0.825(3) for the one with the longest bond. In comparisson, s was found to produce hydrogen-bonded cocrystals only with the two strongest nucleophiles used, and the corresponding stability constants were nearly four orders of magnitude lower than those for halogen bonded complexes with nis. In the case of ncs no measurements in solution were possible, and no single crystal samples of the cocrystals could be prepared, due to high reactivity of ncs as well as weakness of the corresponding N∙∙∙Cl halogen bond. However, grinding of ncs with stronger XB acceptors yielded materials shown by powder X-ray diffraction to be isostructural with the corresponding nbs cocrystals, indicating the formation of ncs-pyridine cocrystals in the solid state.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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