Theoretical Studies Of Halogen-bonded Systems Involving Dihalogen Molecules

Due to the broad applications of halogen bond in many fields such as crystal engineering,drug design and nanotechnology,it is of great significance to understand the structure and properties of halogen bond.In the paper,based on the theoretical calculations of quantum chemistry,density functional theory(DFT)and MP2 were carried out to study several typical intermolecular halogen-bonded systems,and the features and nature of interactions can been obtained.The main results consist of three parts:Part one,dihalogen molecule XY(X=Cl and Br and Y=F,Cl and Br)can interact with two CO2 to form ring-shaped CO2?X(Y)?CO2 trimers,in which the X atom simultaneously int eracts with C atom of one CO2 and O atom of the other CO2.Theoretical calculations show that their optimized geometr ies and stretching vibrational frequencies are different from the individual(CO2)2,CO2???XY and YX???CO2 dimers.Their interaction energies are stronger than the sum of the interaction energies of the individual dimers,revealing the cooperativity between the dimers.Their binding distances and interaction strengths are closely associated with the electronegativity of X and Y atoms.Energy decomposition analysis suggests that electrostatic force is the main net contribution to total interaction energy.Quantum theory of atoms in molecules analysis confirms the formation of ring-shaped structures and the cooperativity between the dimers.Molecular electrostatic potential was employed to eluc idate the formation mechanisms of ring-shaped trimers.Part two,a series of four-membered ring-shaped molecular complexes formed by CO2,CO and XY(X=Cl,Br;Y=F,Cl,Br)molecules have been investigated at the moderate M06-2X/6-311++G(2d,2p)level of theory,in which these molecules interact with each other via halogen bond,tetrel bond and van der Waals interaction.The optimized geometry,stretching mode and interaction energy have been obtained and disc ussed.Molecular electrostatic potential and the contour maps of Laplacian ?2ρ were used to reveal the formation mechanisms of these complexes.The cooperativity was found in these complexes because their interaction energies are stronger than the sum of the pair ineraction energies.The electrostatic force was believed to be the main net contribution to the stability of these complexes.Part three,a series of V-shaped molecular complexes formed by NH3,X1X2 and X3Y(X1,X2,X3=Cl,Br;Y=F,Cl,Br)molecu les via two halogen bonds(i.e.,N???X1 and X2???X3 interactions)have been investigated at the MP2/aug-cc-pVTZ level of theory to obtain their optimized geometries,stretching modes and interaction energies.Molecular electrostatic potential was used to illustrate how X1 and X2 act as the halogen bond donor and acceptor in N???X1 and X2???X3 interactions,respectively.The evaluation of the binding distances,interaction energies and the electron density at the bond critical points of the halogen bonds reveals the existence of cooperativity between the two halogen bonds.Subsequently,the concepts of pair interaction and pairwise non-additive contributions to the total interaction energy,and the cooperativity factor were further employed to assess the cooperativity.The formation mechanisms of these complexes were analyzed based on the contour maps of the Laplacian(?2ρ)of electron density.Energy decomposition analysis suggests that the electrostatic force is the main net contribution to the stability of these complexes.