Doctor of Philosophy
School of Chemistry
Alcock, Leighton J., Metal Complexes of Expanded Cavity Cage Ligands, Doctor of Philosophy thesis, School of Chemistry, University of Wollongong, 2017. https://ro.uow.edu.au/theses1/44
This thesis explored the electronic and structural properties of transition metal complexes of Me8tricosane and related ligands in order to gain a better understanding of the factors which contribute to the remarkable properties of complexes such as [Co(Me8tricosane)]2+.
Electronic spectra and solid state structures were determined for [Co(Me5tricosanetriimine)]3+ and [Co(Me5tricosanetriiminetriOH)]3+. These two complexes were found to have very similar structures, with average Co-N bond distances of 1.976 ± 0.016 Å and 1.976 ± 0.007 Å, respectively. An electronic spectrum was also acquired for [Co(Me5tricosanetriOH)]3+. The observed d-d transitions at 26631 and 18957 cm-1 were much lower in energy than is typically observed for cobalt(III) hexaamines. Theoretical investigations on [M(NH3)6]n+ (Mn = CrII, FeII, FeIII, CoIII, NiII) showed that sensitivity to changes in the M-N bond distance varied by metal, with red shifts ranging from 570 to 265 cm-1 per 0.01 Å elongation of the M-N bond distance.
The solid state structures of [Zn(Me8tricosane)]2+, [Cd(Me8tricosane)]2+, and [Hg(Me8tricosane)]2+ were also determined. The latter two complexes were found to adopt the rare trigonal prismatic geometry with a twist angle of 0°, while [Zn(Me8tricosane)]2+ adopted a distorted octahedral geometry with a twist angle of 46.1 ± 0.5°. Computational studies found that where the M-N bond distance exceeds 2.35 Å, complexes of Me8tricosane will adopt the trigonal prismatic geometry due to the steric requirements of the ligand. Despite the high degree of symmetry in their solid state structures, the NMR spectra of all three complexes had a large number of resonances. This was attributed to the presence of multiple species in solution, including one or more with asymmetric structures. The relative energies of different diastereoisomers of the complexes were determined using DFT methods, and showed that inversion of the stereochemistry at one or more of the nitrogen atoms was a likely cause of the complexity of the NMR spectra. These techniques were subsequently extended to [Co(Me8tricosane)]2+, which was also shown to give NMR spectra that were highly dependent on the properties of the solvent.