Hydrogen- and Halogen-Bonded Binary Cocrystals with Ditopic Components: Systematic Structural and Photoreactivity Properties That Provide Access to a Completed Series of Symmetrical Cyclobutanes

A series of binary cocrystals involving the ditopic hydrogen- and halogen-bond (H- and X-bond, respectively) donors resorcinol (res) and hydroquinone (hq), and 1,3- and 1,4-diiodotetrafluorobenzene (1,3- and 1,4-di-I-tFb), respectively, cocrystallized with one of the three symmetric bipyridines trans-1,2-bis­(n-pyridyl)­ethylene ( n , n ′-bpe, where n = n′ = 2, 3, 4) is reported. The structures of the six novel cocrystals, (1,3-di-I-tFb)·(3,3′-bpe), 4­(res)·3­(3,3′-bpe), (1,3-di-I-tFb)·(4,4′-bpe), 3­(hq)·2­(2,2′-bpe), (1,4-di-I-tFb)·(3,3′-bpe), and (hq)·(3,3′-bpe), are described. The cocrystals comprise components that assemble by either O–H···N and O–H···O H-bonds (res and hq) or N···I X-bonds (1,3- and 1,4-di-I-tFb). The work completes a series of 18 cocrystals involving either the three dihydroxybenzenes catechol (cat), res, and hq or the three diiodotetrafluorobenzenes (1,2-, 1,3-, and 1,4-di-I-tFb) as H- or X-bond donors, respectively, with each of the three structurally isomeric symmetric bipyridines n , n ′-bpe. Our study demonstrates the significant consequences that minimally subtle variations to molecular structure of coformers can have for stoichiometric formulations, molecular packing, and solid-state photoreactivity. The work also provides access to a completed series of symmetrically substituted rctt-tetrakis­(n-pyridyl)­cyclobutanes (where: n = 2, 3, or 4).