title: Boron as an Electron-Pair Donor for B⋅⋅⋅Cl Halogen Bonds.
abstract: MP2/aug'-cc-pVTZ calculations were performed to investigate boron as an electron-pair donor in halogen-bonded complexes (CO)2(HB):ClX and (N2)2(HB):ClX, for X=F, Cl, OH, NC, CN, CCH, CH3, and H. Equilibrium halogen-bonded complexes with boron as the electron-pair donor are found on all of the potential surfaces, except for (CO)2(HB):ClCH3and (N2)2(HB):ClF. The majority of these complexes are stabilized by traditional halogen bonds, except for (CO)2(HB):ClF, (CO)2(HB):ClCl, (N2)2(HB):ClCl, and (N2)2(HB):ClOH, which are stabilized by chlorine-shared halogen bonds. These complexes have increased binding energies and shorter B-Cl distances. Charge transfer stabilizes all complexes and occurs from the B lone pair to the σ* Cl-A orbital of ClX, in which A is the atom of X directly bonded to Cl. A second reduced charge-transfer interaction occurs in (CO)2(HB):ClX complexes from the Cl lone pair to the π* C≡O orbitals. Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) spin-spin coupling constants,1xJ(B-Cl), across the halogen bonds are also indicative of the changing nature of this bond.1xJ(B-Cl) values for both series of complexes are positive at long distances, increase as the distance decreases, and then decrease as the halogen bonds change from traditional to chlorine-shared bonds, and begin to approach the values for the covalent bonds in the corresponding ions [(CO)2(HB)-Cl]+and [(N2)2(HB)-Cl]+. Changes in11B chemical shieldings upon complexation correlate with changes in the charges on B.
authors.affiliation: Instituto de Química Médica (IQM-CSIC), Juan de la Cierva, 3, E-28006, Madrid, Spain. ibon@iqm.csic.es.
authors.forename: Ibon
authors.identifier: http://orcid.org/0000-0001-6876-6211
authors.initials: I
authors.lastname: Alkorta
authors.affiliation: Instituto de Química Médica (IQM-CSIC), Juan de la Cierva, 3, E-28006, Madrid, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Elguero
authors.affiliation: Department of Chemistry, Youngstown State University, Youngstown, OH, 44555, USA. jedelbene@ysu.edu.
authors.forename: Janet E
authors.initials: JE
authors.lastname: Del Bene
keywords: EOM-CCSD spin-spin coupling constants; QTAIM; borylenes; charge-transfer energies; halogen bonds