Characterization of Halogen Bonds with Multinuclear Magnetic Resonance in the Solid-State, X-ray Crystallography, and Quantum Chemical Calculations

Abstract

Solid-state nuclear magnetic resonance (SSNMR) has proven to be a useful tool in the characterization of non-covalent interactions such as hydrogen bonding and cation-π interactions. In recent years, the scientific community has manifested a renewed interest towards an important class of non-covalent interaction, halogen bonding (XB), as it has applications in various fields such as crystal engineering and biological processes. This dissertation demonstrates that NMR parameters measured in the solid state are sensitive to changes in electronic structure, which are caused by halogen bonds. A series of halogen bonded compounds exhibiting interactions between different diiodoperfluorobenzenes (p- C6F4I2, o- C6F4I2, sym- C6F3I3, p- C6H4I2) and various halogen bond acceptors have been synthesized as part of this work. These new halogen bonded compounds were characterized with a combined theoretical and experimental SSNMR, X-ray diffraction (XRD) methods. The complete multinuclear magnetic resonance spectroscopy of the nuclei involved directly in the halogen bond (13C, 14/15N, 31P, 77Se, 35/37Cl and 79/81Br) were recorded at multiple magnetic fields (4.7, 9.4, 11.75 and 21.1 T). The specialized SSNMR experiments provided high-resolution spectra of quadrupolar nuclei, which were WURST-QCPMG or solid-echo type experiments combined with the variable offset cumulative spectral (VOCS) method, as for spin 1/2 nuclei cross polarization magic angle spinning (CPMAS) experiments were usually appropriate. This dissertation will discuss successful applications of SSNMR spectroscopy to characterize halogen bonds, it will demonstrate the significant changes in NMR observables in the presence of XB interaction and thus establish that NMR parameters are very sensitive to halogen bonding interaction. Furthermore, this work explains why the NMR parameters are correlated with the halogen bonding interaction. The different trends observed between the NMR observables and the halogen bonding were further understood with a ZORA-DFT natural localized molecular orbital (NLMO) study.