Non-Covalent Interactions, Dative Bonding, and Electron Affinities: A Multi-Method Computational Study of Boron Tetrahalides

Ezell, Lance R (2014) Non-Covalent Interactions, Dative Bonding, and Electron Affinities: A Multi-Method Computational Study of Boron Tetrahalides. Undergraduate thesis, under the direction of Gregory Tschumper from Chemistry and Biochemistry, The University of Mississippi.

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Abstract

This study focuses on boron tetrahalides of the form BFXClY, where X + Y = 4, using the B3LYP, M06-2X, and MP2 methods with the aug-cc-pVTZ basis set. The various neutral and anionic species were constructed and optimized using the Gaussian 09 software package, and the equilibrium geometries, harmonic vibrational frequencies, and energetics (specifically the electron affinity, vertical attachment and detachment energies, and stability with respect to dissociation) of each system are presented. The anionic species, due to their closed-shell electron configurations, have relatively high symmetry: Td for BF4- and BCl4-, C3v for BF3Cl- and BFCl3-, and C2v for BF2Cl2-. The symmetries of the open-shell neutral species, which consist of two isomers (one featuring a non-covalent interaction between the boron and the fourth halogen and one marked by completely covalent bonds) are lower: including C1, Cs, and C2v. B—F and B—Cl covalent bond distances range between 1.30 to 1.45 Å and 1.70 to 2.00 Å, respectively, while the non-covalent B!!!Cl bond distances range between 2.9 and 4.0 Å. All neutral van der Waals isomers are metastable with respect to dissociation, and covalent isomers are less stable, or unstable in the case of BF4. The electron affinities and vertical attachment energies generally increase with increasing number of chlorine atoms, after an initial decrease between BF4 and BF3Cl, while the vertical detachment energies generally decrease with increasing number of chlorine atoms, with a dramatic increase at BCl4.

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