Halogen Bonding in the Gas Phase: A Comparison of the Iodine Bond in B⋯ICl and B⋯ICF3 for Simple Lewis Bases B

The Electrophilicities of XCF3 and XCl (X=H, Cl, Br, I) and the Propensity of These Molecules To Form Hydrogen and Halogen Bonds with Lewis Bases: An Ab Initio Study

Equilibrium dissociation energies, De , of four series of halogen- and hydrogen-bonded complexes B⋅⋅⋅XCF3 (X=H, Cl, Br and I) are calculated ab initio at the CCSD(T)(F12c)/cc-pVDZ-F12 level. The Lewis bases B involved are N2 , CO, PH3 , C2 H2 , C2 H4 , H2 S, HCN, H2 O and NH3 . Plots of De versus NB , where the NB are the nucleophilicities assigned to the Lewis bases previously, are good straight lines through the origin, as are those for the corresponding set of complexes B⋅⋅⋅XCl. The gradients of the De versus NB plots define the electrophilicities EXCF3 and EXCl of the various Lewis acids. The determined values are: EXCF3 =2.58(22), 1.40(9), 2.15(2) and 3.04(9) for X=H, Cl, Br and I, respectively, and EXCl =4.48(22), 2.31(9), 4.37(27) and 6.06(37) for the same order of X. Thus, it is found that, for a given X, the ratio EXCl / EXCF3 is 2 within the assessed errors, and therefore appears to be independent of the atom X and of the type of non-covalent interaction (hydrogen bond or different varieties of halogen bond) in which it is involved. Consideration of the molecular electrostatic surface potentials shows that De and the maximum positive electrostatic potential σmax (the most electrophilic region of XCF3 and XCl, which lies on the symmetry axes of these molecules, near to the atom X) are strongly correlated.

Relativistic Effects on NMR Parameters of Halogen-Bonded Complexes

Relativistic effects are found to be important for the estimation of NMR parameters in halogen-bonded complexes, mainly when they involve the heavier elements, iodine and astatine. A detailed study of 60 binary complexes formed between dihalogen molecules (XY with X, Y = F, Cl, Br, I and At) and four Lewis bases (NH₃, H₂O, PH₃ and SH₂) was carried out at the MP2/aug-cc-pVTZ/aug-cc-pVTZ-PP computational level to show the extent of these effects. The NMR parameters (shielding and nuclear quadrupolar coupling constants) were computed using the relativistic Hamiltonian ZORA and compared to the values obtained with a non-relativistic Hamiltonian. The results show a mixture of the importance of the relativistic corrections as both the size of the halogen atom and the proximity of this atom to the basic site of the Lewis base increase.

The rich conformational landscape of perillyl alcohol revealed by broadband rotational spectroscopy and theoretical modelling

We explore the conformational landscape of perillyl alcohol in order to properly account for the sources of the conformers observed.

Multiple Noncovalent Bonding in Halogen Complexes with Oxygen Organics. I. Tertiary Amides

The present work describes the structure and binding of adducts of N,N'-diacetylpiperazine with halogens and interhalogens based on combination of different experimental methods and quantum chemical calculations. On the basis of conductometric and spectro-photometric experimental results, behavior of complexes in the acetonitrile solution was described. The iodine adduct with N,N'-diacetylpiperazine fully degrades into components. Adducts of interhalogens I-X (X = Cl or Br) with N,N'-diacetylpiperazine in acetonitrile partially dissociate to anionic [X-I-X](-) and cationic species. In the solid state, molecules are connected via C═O···I, C-H···I, and Cl···Cl attractive interactions. N,N'-diacetylpiperazine···dihalogen complex is stabilized by simultaneous C═O···I and C-H···I interactions. Such binding mode allows to explain the problems of the direct halogenation of acetyl-containing compounds with molecular halogens as reagents. We believe that the observed binding pattern can be used as prototypical for future design of halogeno complexes.