Präreaktive Komplexe der Dihalogene XY mit Lewis-Basen B in der Gasphase: eine systematische Studie der Halogen-Analoga B⋅⋅⋅XY der Wasserstoffbrückenbindungen B⋅⋅⋅HX

It is well known [1] that carbon-bound halogen atoms (frequently iodine and bromine, but also chlorine and even fluorine) can act as electron acceptors and form short contacts with different species (both neutral and negatively charged) that possess an ability to act as an electron donor. [2] These noncovalent interactions can be strong enough to control the aggregation of organic molecules in solid, [3] liquid, [4] and gas [5, 6] phases and the term ªhalogen bondingº [2, 6] has been suggested in order to emphasize the similarity with hydrogen bonding. While metal-ion coordination [7] is frequently the key feature in inorganic supramolecular systems, hydrogen bonding [8] is by far the most frequently used tool to assemble organic molecules in solid, liquid, or gas phases, and it plays an important role in stabilizing supramolecular aggregates even in water.Here we show that when the recognition pattern controlling the self-assembly process can be based on either hydrogen or halogen bonding, the latter can dominate over the former and, under appropriate conditions, will single out the molecules that will be involved in the construction of supramolecular architectures. We have already described specific I´´´N intermolecular interactions occurring between a,w-diiodoperfluoroalkanes and dinitrogen hydrocarbons. [9±11] These interactions are strong enough to overcome the low affinity [12] that exists between perfluorocarbons and hydrocarbons to assemble them into oligomeric structures in the liquid phase [4] and into crystalline 1D networks in the solid phase. [9±11] methacrylate as a comonomer. The copolymer 1 was shown to have good film-forming properties on a solid substrate. The fluorescence of the polymer was effectively quenched by photochemically generated acid and afforded finely resolved fluorescent images on a solid substrate. Experimental Section4: Potassium carbonate (82.9 g, 0.60 mol) and benzyl bromide (136.8 g, 0.80 mol) were added to a solution of 5-fluoro-2-nitrophenol (3) (94.3 g, 0.60 mol) in DMF (200 mL). The resulting mixture was stirred at 100 8C for 3 h, filtered, and the filtrate diluted with diethyl ether. The organic layer was washed with water and dried with anhydrous magnesium sulfate. Concentration, followed by vacuum distillation (142 ± 146 8C, 0.

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Halogen Bonding versus Hydrogen Bonding in Driving Self-Assembly Processes

Corradi

et al. 2000

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Pre-reactive Complexes in Mixtures of Water Vapour with Halogens: Characterisation of H2O⋅⋅⋅ClF and H2O⋅⋅⋅F2 by a Combination of Rotational Spectroscopy and Ab initio Calculations

et al. 2001

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Complexes H2O...ClF and H2O...F2 were detected by means of their ground-state rotational spectra in mixtures of water vapour with chlorine monofluoride and difluorine, respectively. A fast-mixing nozzle was used in conjunction with a pulsed-jet, Fourier-transform microwave spectrometer to preclude the vigorous chemical reaction that these dihalogen species undergo with water. The ground-state spectra of seven isotopomers (H2 16O...35ClF, H2 16O...ClF, H2 18O...35ClF, D2 16O... 35ClF, D2 16O...37ClF, HDO...35ClF and HDO...37ClF) of the ClF complex and five isotopomers (H2O...F2, H2 18O...F2, D2O...F2, D2 18O...Fi and HDO...F2) of the F2 complex were analysed to yield rotational constants, quartic centrifugal distortion constants and nuclear hyperfine coupling constants. These spectroscopic constants were interpreted with the aid of simple models of the complexes to give effective geometries and intermolecular stretching force constants. Isotopic substitution showed that in each complex the H2O molecule acts as the electron donor and either CIF or F2 acts as the electron acceptor, with nuclei in the order H2O...ClF or H2O...F2. For H2O...ClF, the angle phi between the bisector of the HOH angle and the O...Cl internuclear line has the value 58.9(16)degrees, while the distance r(O...Cl)= 2.6081(23) A. The corresponding quantities for H2O...F2 are phi = 48.5(21)degrees and r(O...Fi) = 2.7480(27) A, where Fi indicates the inner F atom. The potential energy V(phi) as a function of the angle phi was obtained from ab initio calculations at the aug-cc-pVDZ/MP2 level of theory for each complex by carrying out geometry optimisations at fixed values of phi in the range +/-80degrees. The global minimum corresponded to a complex of Cs symmetry with a pyramidal configuration at O in each. The function V(phi) was of the double-minimum type in each case with equilibrium values phie = +/-55.8degrees and +/-40.5degrees for H2O...ClF and H2O...F2, respectively. The barrier at the planar C2v conformation was V0= 174cm(-1) for H2O...ClF and 7cm(-1) for H2O...F2. For the latter complex, the zero-point energy level lies above the top of the barrier.

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