期刊
CANADIAN JOURNAL OF CHEMISTRY
卷 100, 期 4, 页码 245-251出版社
CANADIAN SCIENCE PUBLISHING
DOI: 10.1139/cjc-2021-0245
关键词
solid-state NMR; X-ray diffraction; halogen bond; cocrystal; polymorphism; stoichiometry; stoichiomorphism
资金
- Natural Sciences and Engineering Research Council
This study explores the concept of variable stoichiometry cocrystallization in halogen-bonded systems and synthesizes three novel cocrystals. Single-crystal X-ray diffraction analysis reveals key differences between these cocrystals. Powder X-ray diffraction and NMR experiments are carried out to investigate the chemical shifts and halogen bond formation in the cocrystals.
The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Single-crystal X-ray diffraction analysis reveals key differences between each of the nominally similar cocrystals. For instance, the 1:1 cocrystal crystallizes in the P2(1)/n space group and features a single chemically and crystallographically unique halogen bond between iodine and the pyridyl nitrogen. The 2:1 cocrystal crystallizes in the PT space group and features a halogen bond between iodine and one of the nitro oxygens in addition to an iodine-nitrogen halogen bond. The 1:2 cocrystal crystallizes with a large unit cell (V = 9896 angstrom(3)) in the Cc space group and features 10 crystallographically distinct iodine-nitrogen halogen bonds. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. H-1 -> C-13 and F-19 -> C-13 cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. Carbon-13 chemical shifts in the cocrystals are shown to change only very subtly relative to pure solid 1,4-diiodotetrafluorobenzene, but the shift of the carbon directly bonded to iodine nevertheless increases, consistent with halogen bond formation (e.g., a shift of +1.6 ppm for the 2:1 cocrystal). This work contributes new examples to the field of variable stoichiometry cocrystal engineering with halogen bonds.
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