N⋅⋅⋅Br Halogen Bonding: One‐Dimensional Infinite Chains through the Self‐Assembly of Dibromotetrafluorobenzenes with Dipyridyl Derivatives

Abstract

The N.Br halogen bonding drives the self-assembly of 1,4-dibromotetrafluorobenzene (1 a) and its 1,3 or 1,2 analogues (1 b,c, respectively) with dipyridyl derivatives 2 a,b. The isomeric supramolecular architectures 3 a-f are obtained as cocrystals that are stable in the air at room temperature. The solid-state features of these 1D infinite chains 3 have been fully characterized by single-crystal X-ray, Raman, and IR analyses. The occurrence of N.Br halogen bonding in solution has been detected with (19)F NMR spectroscopy. The N.Br halogen bonding is highly selective and directional and the geometry of the single strands of noncovalent copolymers 3 is programmed by the geometry of halogen-bonding donor and acceptor sites on the starting modules. The composition and topology of the instructed networks can be predicted with great accuracy. Experiments of competitive cocrystal formation established the strength of the N.Br interaction relative to other halogen bondings and the ability of different modules 1 to be involved in site-selective supramolecular syntheses.

C–halogen…O supramolecular synthons: in situ cryocrystallisation of 1,2-dihalotetrafluoroethane/HMPA adducts

“…on HB formation and metal coordination). It is at 1202 cm 21 in the pure and liquid HMPA, where weak HBs are present (18), and it is at 1192 cm 21 in the diiodide adduct 3a, at 1197 cm 21 in the monoiodides 3b and 3d and at 1199 cm 21 in the dibromide 3c. These values suggest that HMPA oxygen atoms in 3a -3d interact with stronger electron density acceptor sites than in pure HMPA, consistent with the presence of XBs in both solid and liquid 1:1 mixtures of starting tectons 1 and 2.…”

“…This hypothesis is confirmed by a comparison between the melting points of adducts 3 and the mean value of the melting points of the starting tectons 1 and 2. This type of comparison allowed for filing a ranking of different XBs which is similar to the rankings based on other approaches (21). The adduct 3a, wherein two strong CZI· · ·O XBs are expectedly present per starting tecton unit, melts 978C higher than the mean value of starting tectons (melting points: 3a, 908C; 1a, 2218C and 2, 78C; mean value, 278C) while 3c, wherein two weak CZBr· · ·O XBs are expectedly present, melts 658C higher than the mean value of starting tectons (melting points: 3c, 148C; 1c, 2110 8C and 2, 78C; mean value, 2518C).…”

“…Single point calculation on the crystal structure of 2 allows to establish that the binding energy of a dimer in the pure compound (1.08 kcal mol 21 ), which measures the strength of the HB network in pure 2, is smaller than binding energies of heteromeric co-crystals 3a and 3c. The higher stability of O· · ·X interactions over O· · ·H ones justifies the preferential growth of heteromeric and halogen bonded complexes 3 over the formation of the homomeric and hydrogen bonded crystal of pure 2.…”

Scalar Coupling Across [CH⋅⋅⋅FC] Interactions in (σ‐Aryl)‐Chelating Post‐Metallocenes

“…[39] Importantly, the close contacts between a methylene hydrogen atom on each benzyl group and the adjacent F atom (F(1)···HA C H T U N G T R E N N U N G (27 A) 2.48 , F(1)···HA C H T U N G T R E N N U N G (34B) 2.57 ) approaches those accurately determined for the Zr-[O,N,C] congener 6 (2.572(6) and 2.607(5) ) [24] and fall comfortably within the range of CÀH···FÀC hydrogen bonds previously reported in the literature. [17,18,22] The most noteworthy feature in 3 is a close Hf···F contact of 2.677(3) . This is in stark contrast to analogous Ti-and Zr-[O,N,C] structures bearing a CF 3 substituent, [23,24] in which the shortest M···F distances of around or above 3.0 exceed even the distance expected for a weak M···F À C interaction (M = Ti, Zr).…”

“…[12] Hence, although the living propagating species has been observed in solution by NMR spectroscopy, [13,14] verification of the proposed CÀ H···FÀC interactions remains elusive. More generally, notwithstanding the ongoing debate regarding the nature and significance of dispersion-dominated C À H···F À C hydrogen bonds, [15,16] interest in these interactions have proliferated in recent years and they are habitually invoked in such diverse fields as crystal engineering, [17] materials science, [18] rotational [19] and vibrational [20] spectroscopy, theoretical studies (including calculation and estimation of bond energies), [21] and biomolecular design and recognition. [22] Due to the emerging importance and functionality of fluorine substituents, it is desirable to develop additional spectroscopic techniques to probe fluorinated moieties and elucidate their surrounding environment and connectivity.…”