title: FCl:PCX complexes: old and new types of halogen bonds.
abstract: MP2/aug'-cc-pVTZ calculations have been performed to investigate the halogen-bonded complexes FCl:PCX, for X = NC, CN, F, H, CCH, CCF, CH(3), Li, and Na. Although stable complexes with a F-Cl···P halogen bond exist that form through the lone pair at P (configuration I), except for FCl:PCCN, the more stable complexes are those in which FCl interacts with the C≡P triple bond through a perturbed π system (configuration II). In complexes I, the nature of the halogen bond changes from traditional to chlorine-shared and the interaction energies increase, as the electron-donating ability of X increases. The anionic complex FCl:PC(-) has a chlorine-transferred halogen bond. SAPT analyses indicate that configuration I complexes with traditional halogen bonds are stabilized primarily by the dispersion interaction. The electrostatic interaction is the most important for configuration I complexes with chlorine-shared halogen bonds and for configuration II complexes except for FCl:PCNa for which the induction term is most important. The F-Cl stretching frequency is red-shifted upon complexation. EOM-CCSD/(qzp,qz2p) spin-spin coupling constants have been obtained for all FCl:PCX complexes with configuration I. (1)J(F-Cl) decreases upon complexation. (2X)J(F-P) values are quadratically dependent upon the F-P distance and are very sensitive to halogen-bond type. (1X)J(Cl-P) tends to increase as the Cl-P distance decreases but then decreases dramatically in the chlorine-transferred complex FCl:PC(-) as the Cl-P interaction approaches that of a covalent Cl-P bond. Values of (1)J(F-Cl) for configuration II are reduced relative to configuration I, reflecting the longer F-Cl distances in II compared to those of the neutral complexes of I. Although the F-P and Cl-P distances in configuration II complexes are shorter than these distances in the corresponding configuration I complexes, (2X)J(F-P) and (1X)J(Cl-P) values are significantly reduced, indicating that coupling through the perturbed C-P π bond is less efficient. The nature of F-P coupling for configuration II is also significantly different, as evidenced by the relative importance of PSO, FC, and SD components.
authors.affiliation: Instituto de Química Médica (CSIC), Madrid, Spain. ibon@iqm.csic.es
authors.forename: Ibon
authors.initials: I
authors.lastname: Alkorta
authors.forename: Goar
authors.initials: G
authors.lastname: Sanchez-Sanz
authors.forename: José
authors.initials: J
authors.lastname: Elguero
authors.forename: Janet E
authors.initials: JE
authors.lastname: Del Bene
mesh_terms: D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D056831:Coordination Complexes / Q000737:chemistry; D004583:Electrons; D006219:Halogens / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D006219:Halogens; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen