Stoichiomorphic halogen-bonded cocrystals: a case study of 1,4-diiodotetrafluorobenzene and 3-nitropyridine

Abstract

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 P21/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 P1- 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 Å3) 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. 1H → 13C and 19F → 13C 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.

Anticooperativity and Competition in Some Cocrystals Featuring Iodine‐Nitrogen Halogen Bonds

“…Several reports have described the influence of halogen bonding on the NMR chemical shift response, particularly for 13 C and 19 F nuclides. [10,16,28,48,43,44,45,46,47,48,49,50] Shown in Figure 7 are the 13 C MAS NMR spectra of 3-aminopyridine and of cocrystal 1 b. The aromatic resonances of 3-aminopyridine are seen to generally become more shielded and broader upon halogenbond induced cocrystallization.…”

“…Several reports have described the influence of halogen bonding on the NMR chemical shift response, particularly for 13 C and 19 F nuclides [10,16,28,48,43,44,45,46,47,48,49,50] . Shown in Figure 7 are the 13 C MAS NMR spectra of 3‐aminopyridine and of cocrystal 1 b .…”

“…Its linearity and tuneability are well known and useful features which continue to propel and encourage new applications of the halogen bond in diverse disciplines. In the field of cocrystal engineering, the relationship between halogen bonds and the possibility of polymorphism and stoichiomorphism are of particular interest [4,5,6,7,8,9,10] . A related area of study is the role of halogen bonds, among other non‐covalent interactions, in generating ternary, quaternary, and higher‐order cocrystals with particular properties or applications [11,12,13,14,15] .…”

“…In the field of cocrystal engineering, the relationship between halogen bonds and the possibility of polymorphism and stoichiomorphism are of particular interest. [4,5,6,7,8,9,10] A related area of study is the role of halogen bonds, among other non-covalent interactions, in generating ternary, quaternary, and higher-order cocrystals with particular properties or applications. [11,12,13,14,15] Several routes exist towards exploring the polymorphic and stoichiomorphic landscapes of particular cocrystalline systems.…”

How the Position of Substitution Affects Intermolecular Bonding in Halogen Derivatives of Carboranes: Crystal Structures of 1,2,3- and 8,9,12-Triiodo- and 8,9,12-Tribromo ortho-Carboranes

“…The strength of the halogen bond is highly correlated with the degree of iodobenzene fluorination [ 17 ]. Therefore, it is not surprising that 1,4-diiodoperfluorobenzene and its analogs are widely used in the design of halogen-bonded supramolecular systems [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ], although arylacetylene iodides also play an important role [ 16 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. In the absence of other electron density donors, the iodine atoms in these compounds are also able to play this role, which leads to the formation of I⋯I dihalogen bonds [ 36 , 37 , 38 , 39 ], and the number of such bonds, as a rule, increases with the number of iodine atoms in the molecule [ 40 ].…”