An investigation of gas phase ion-molecule complexes involving novel binding modes

Abstract

In this thesis, an innovative method is introduced to advance the study of gas phase clusters and used to analyse a number of novel binding modes. The systematic sampling of cluster surfaces (SSCS) routine, introduced in Chapter 3, is a computational technique that identifies cluster geometries by examining subsequent additions of solvent molecules along the surface of a core cluster. This technique examines the electrostatic potential of the solvent and cluster to determine favourable sites of interaction. This technique was found to result in a ten-fold increase in efficiency over common Monte-Carlo cluster geometry routines.

Utilizing the SSCS routine, a highly debated topic in gas-phase chemistry was investigated, does electrospray ionization (ESI) sample gas phase or solution phase structures? This topic was investigated in Chapter 4, using deprotonated para-hydroxybenzoic acid and examined the solution phase (carboxylate deprotonated) and gas phase (phenoxide deprotonated) preferred tautomers. Numerous studies have argued for and against tautomer preference, while they missed an important underlying factor, do ESI spray conditions favour one or the other. Six solvents were selected to showcase the transition from the gas phase to the solution phase for one to five solvent molecules. This examination found that both protic and aprotic solvents showed a steady transition to ‘solution phase’ conditions at room temperature. Varying ESI spray conditions found an increase in temperature to result in reduced solution phase preference, with this effect being more drastic for some solvents than others. Thus, the importance of comparing ESI spray conditions is highlighted by this study wherein, electrospray ionization samples structures based off the energy available to the system on-route to the ion trap.

In Chapter 5 and 6, all-cis hexafluorocyclohexane, all-cis pentafluorocyclohexanol, and all-cis hexa-trifluoromethyl-cyclohexane, were studied for their unique ability to bind both cationic and anionic species. It was found that these molecules possess significant dipole moments resulting in substantial propensity for binding ionic species and allowing for the formation of homogeneous dipole bound dimers. These dipole bound dimers were found to readily interact with both cationic and anionic species expanding the number of available binding motifs. These various features lend to a number of novel binding modes with ionic species in the gas phase.

Lastly, Chapter 7 examines the cation-π interactions of inverse Sandwich Cyclopentadienyl Complexes of Sodium in the Gas Phase. This system was found to readily undergo cation-π interactions, with monomer, dimer, and trimer interactions all being found experimentally. The vibrational modes of these systems required a study of anharmonic vibrational modes due to their unconventional nature. Computational investigation found that as the inverse sandwich complexes grew in size, so too did the favourability for binding additional sandwich subunits. Computational limitations prevented the ability to determine at what size the system would no longer readily bind additional subunits.