Photoreactive Polymorphic Cocrystals Utilizing a Molecular Template with Dual Halogen and Hydrogen Bonding Capabilities

Abstract

The ability of 1,2,4,5-tetrachloro-3-iodobenzene to act as a template to form a pair of polymorphic cocrystals with trans-1,2-bis(4-pyridyl)ethylene is reported. After exposure to ultraviolet light, a nearly quantitative yield for the [2 + 2] cycloaddition reaction was observed for both concomitant cocrystals. These crystalline solids engage in both I•••N halogen bonds along with nontraditional C−H•••N hydrogen bond which results in a one-dimensional chain. In addition, the components homogeneous π−π stack which positions the carbon−carbon double bond on the reactant molecule in a suitable orientation to undergo a photoinduced cyclization reaction.

Preference of halogen bonds over hydrogen bonds within a discrete three-component co-crystal that undergo a [2+2] cycloaddition reaction

“…4 Recently, we reported the ability of 1,2,4,5-tetrachloro-3-iodobenzene ( C 6 HICl 4 ) to act as a molecular template to achieve a [2+2] cycloaddition reaction when combined with trans -1,2-bis(4-pyridyl)ethylene ( BPE ). 5 The ability of C 6 HICl 4 to form both I⋯N halogen bonds along with C-H⋯N hydrogen bonds produced a pair of concomitant polymorphs each comprised of a one-dimensional chain with a formula of ( C 6 HICl 4 )·( BPE ) with alternating halogen and hydrogen bonds. Molecules of C 6 HICl 4 formed homogenous and face-to-face π-stacks thereby positioning the carbon–carbon double bond (CC) within BPE in a similar photoreactive position.…”

“…A similar yield for the photoreaction was observed for the stoichiometric co-crystals ( C 6 HICl 4 )·( BPE ). 5…”

“…These solids are all discrete 2 : 1 stoichiometric co-crystals rather than the 1 : 1 co-crystal (C 6 HICl 4 )Á(BPE) featuring the one-dimensional chain with both halogen and hydrogen bonds. 5 Doubling the initial stoichiometric amount of C 6 HICl 4 lead to the change in structure that reflects the preference of the IÁ Á ÁN halogen bond over the C-HÁ Á ÁN hydrogen bond in these solids.…”

“…A similar yield for the photoreaction was observed for the stoichiometric co-crystals (C 6 HICl 4 )Á(BPE). 5 A pair of additional isostructural co-crystals were realized when C 6 HICl 4 was combined with two other isosteric halogenbond acceptor molecules, namely BPA and AP. In particular, 2(C 6 HICl 4 )Á(BPA) and 2(C 6 HICl 4 )Á(AP) were also discrete solids held together by IÁ Á ÁN halogen bonds [IÁ Á ÁN (Å): BPA 2.937(3) and AP 2.959( 8); normalised contact .83 for BPA and .84 for AP; C-IÁ Á ÁN (1): BPA 174.41 (12) and AP 175.8(3)] to yield a similar three-component structure (Fig.…”

“…S5, ESI †). 5 Even though the solid containing BPE was prepared with a 2 : 1 stoichiometric ratio the 1 : 1 co-crystal was also observed in the bulk solid.…”