The energy frameworks of aufbau synthon modules in 4-cyanopyridine co-crystals

摘要

The supramolecular arrangement of 4-cyanopyridine (4CN_(py)) in its native crystal form and its co-crystals with halogen bond (XB) donors is discussed in terms of long-range synthon aufbau modules (LSAMs) and energy frameworks. Dissociations of 2D zigzag chains of parent 4CN_(py) into 1D dimers observed in its cocrystals are in good agreement with the aufbau model. Its co-formers, XB donors 1,4-I2(CF2)4, C2I2, 1,3- and 1,4-I2C6F4 (m- and p-DITFB), provide equal energy of I···N XBs, but perfluorinated iodo-alkane 1,4- I2(CF2)4 and diiodoacetylene C2I2 cannot achieve the same strength of homomolecular aggregation as π-π stacking in columnar DITFB modules. As a result, DITFBs form I···N XBs with both N_(py) and N_(CN) nitrogen atoms of 4CN_(py), while 1,4-I2(CF2)4 and C2I2 only with the N_(py) atom. This is not a particular case of 4CN_(py) co-crystals, but in general, DITFB appears to be a more effective XB donor co-former than C2I2, 1,4- I2(CF2)n and other iodo-XB donors, which has similar potential to an iodine atom but lacks homomolecular aggregation. In supramolecular reactions of p-DITFB with (η~6-Ar)RuX2[(4CN_(py)) (Ar = p-cymene, X = Cl, I) bearing N_(py)-coordinated 4CN_(py), the former gives definite preference to the XBs with the halogen atoms, but not to the CN group of the 4CN_(py) ligand.