Naslov
Halogen Bonding in Halogenopyridinium Hexacyanoferrates

Autori
Jakupec, Nikola ; Stilinović, Vladimir

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

Izvornik
The Twenty-Sixth Croatian-Slovenian Crystallographic Meeting - Book of abstracts and Programme / Matković-Čalogović, Dubravka ; Popović, Stanko ; Skoko, Željko - Zagreb : Hrvatska akademija znanosti i umjetnosti (HAZU) ; Hrvatska Kristalografska Zajednica, 2018, 28-28

Skup
26th Croatian-Slovenian Crystallographic Meeting (CSCM26)

Mjesto i datum
Poreč, Hrvatska, 13.06.2018. - 17.06.2018

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
halogen bonding, hexacyanoferrates, halogenpyridines

Sažetak
Hexacyanoferrates (hcf) are well known to form metal-organic frameworks, (Prussian blue analogues) by coordination to metal atoms or acting as hydrogen bond acceptors. Recently, however it has been demonstrated that a new class of hcf-based materials by using partly protonated hcf anions which assemble via direct hydrogen bonding of the anions into chains, 2D or 3D networks of the protonated hcf species, with 2D networks of hydrogen bonded H2hcf2– anions being the most common motif.[1] It has been shown that the exact mode of the assembly of hcf species can be tuned by the strength (pKa value), steric properties, or the amount of the base.[1] However, in principle this should also be achievable through modification of the ability of the base to form additional interactions with the hcf anions. In order to examine this, we have ventured to study hcf-s of halogenpyridines, which can act as halogen bond donors (with hcf cyano groups as halogen acceptors [2]). Comparing the structures within a series of halogenpyridines –meta- (3- chloropyridine, 3-Clpy ; 3- brompyridine, 3- Brpy ; 3-iodopyridine, 3-Ipy) or ortho- (2- chloropyridine, 2-Clpy ; 3- brompyridine, 2- Brpy ; 2-iodopyridine, 2-Ipy), allowed us to isolate the effect of halogen bond on the structure of the formed, as the pKa values as well as molecular shapes within a series is almost identical, and the only significant difference is the ability of the pyridine to form halogen bond (increasing with the size of the halogen). Crystallisation of the meta- halogenpyridines with hexacyanoferric(II) acid (H4hcf) yielded structures containing H2hcf2– anions. The two stronger halogen donors, 3-Brpy and 3-Ipy, yielded isostructural compounds with hydrogen bonded chains of anions bridged by water molecules and cations bridging between the chains by forming a hydrogen bond with one chain and halogen bond with the other. Weak halogen donor, 3-Clpy yielded a 2D network of hydrogen bonded H2hcf2– anions with 3-ClpyH+ cations bonded to the networks through hydrogen bonds only. Ortho- halogenpyridines on the other hand formed three different structures, with 2- Clpy and 2-Brpy forming hydrogen bonded 3D netwotks (latter of directly bonded H3hcf– anions, and former of hcf4– anions bridged by H3O+ cations), pyridinium cations and neutral pyridine molecules filling the space within the network without participating in either hydrogen or halogen bonding with the hcf network. Conversely, 2-Ipy, being the strongest halogen bond donor, binds to the anions both through hydrogen and halogen bonds, thus disrupting the 3D network and forming 2D networks of H2hcf2–, heavily distorted by the halogen bond. For comparison, when 4-Ipy was used 2D networks of H2hcf2– also formed, however now they were regular in spite of 4-Ipy being a halogen bond donor, as the halogen bonding in this case did not bend a hydrogen bonded network, but rather interconnect neighbouring networks.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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