Browsing by Author "Davidson, Ross James"
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- ItemCyclo- and polyphosphazenes grafted with tridentate ligands coordinated to iron(II) and ruthenium(II) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Palmerston North(Massey University, 2011) Davidson, Ross JamesThis thesis sought to explore the chemical and physical properties of a series of cyclotriand polyphosphazenes with substituted tridentate ligands coordinated to iron(II) and ruthenium(II). There were two main objective of this research i) to graft spin crossover (SCO) groups to a polymer backbone, potentially making a new malleable material, ii) to demonstrate that ruthenium(II) complexes can be used to link groups to a polyphosphazene backbone. Seven cyclotriphosphazene (L1–L7) and four polyphosphazene (L1P–L4P) ligands1 were synthesised with 2,6-di(pyridine-2-yl)pyridine-4(1H)-onate (OTerpy); 4-(2,6- di{pyridin-2-yl}-pyridine-4-yl)phenolate (OPhTerpy); 2,6-di(1H-benzimidazol-2- yl)pyridine-4(1H)-onate (Obbp); and 4-(2,6-di{1H-pyrazol-1-yl}pyridine-4- yl)phenolate (OPhbpp) moieties. These ligands were subsequently coordinated to either iron(II) or ruthenium(II) and the optical, vibrational, electrochemical and magnetic properties of the subsequent small molecule complexes and polymers were measured. Sixteen iron(II) complexes were synthesised by reacting iron(II) salts with the respective ligand (L1–L7). Where X-ray crystal structures have been obtained, each of the small molecule iron complexes were homoleptic. Using electronic absorbance, resonance Raman (rR), magnetic and Mössbauer spectroscopy, it was shown that the polymer complex cores in the resulting cross-linked polymers were the same as those of the small molecule analogues (SMA). In addition, these techniques confirmed that the iron complexes formed with the ligands L1, L2, L1P and L2P were each determined to be low spin (LS), while those formed with L3 displayed SCO, and the iron complex formed with L4 remained high spin (HS) for all temperatures while its polymeric analogue remained LS for all measurable temperatures. Fourteen ruthenium(II) small molecule complexes were synthesised by reacting ruthenium complexes of the appropriate co-ligands (2,2':6',2"-terpyridine (Terpy); 2,6- di(pyridin-2-yl)-4-phenylpyridine (PhTerpy); 2,6-di(1H-benzimidzol-2-yl)pyridine (bbp); and 2,6-di(1H-pyrazol-1-yl)pyridine) with the respective ligand (L1–L4). Using electronic absorption and rR spectroscopy it was determined that only the polymers L1P and L2P formed complexes ([Ru(L1P)(Terpy)]Cl2, [Ru(L1P)(PhTerpy)]Cl2, [Ru(L2P)(Terpy)]Cl2 and [Ru(L2P)(PhTerpy)]Cl2) analogous to that of their SMA ([Ru(L1)(Terpy)](PF6)2, [Ru(L1)(PhTerpy)](PF6)2, [Ru(L2)(Terpy)](PF6)2 and [Ru(L2)(PhTerpy)](PF6)2), and are therefore the most suitable for linking groups to polyphosphazenes. Although the ruthenium-bbp-terpy based complexes proved to be unsuitable for attaching groups to a phosphazene due to the low loading of metal complex on the polymer (L3P), the SMA ([Ru(L1)(bbp)](PF6)2, [Ru(L2)(bbp)](PF6)2, [Ru(L3)(Terpy)](PF6)2 and [Ru(L3)(PhTerpy)](PF6)2) displayed a dependence on the basicity of the solution. As it was increased, the imidazole groups were deprotonated causing a bathochromic shifting of the metal-to-ligand charge transfer, oxidation potential and selected vibrational modes.
- ItemDFT calculations on the interaction of phosphazenes with transition metals : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Chemistry at Massey University, Palmerston North(Massey University, 2007) Davidson, Ross JamesThe electronic structure of substituted cyclic phosphazenes has been investigated using Density Functional Theory (DFT) and Natural Bond Order (NBO) analysis. NBO analysis shows covalent, ionic and negative hyper-conjugation interactions all contribute to the electronic structure of cyclic phosphazenes. The geometric and electronic structural changes that occur when transition metals are coordinated to the nitrogen atom of the phosphazene ring have been analyzed using the NBO model. The bonding of transition metal ions with the ring nitrogen on the phosphazene was investigated by modeling hexakis(2-pyridyloxy)cyclotriphosphazene, hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene and octakis(2- pyridyloxy)cyclotetraphosphazene with different metal ions (Co(II), Ni(II), Cu(II), Zn(II)) in their assorted configurations with DFT as implemented in the Gaussian03 package. First-row transition metals bind to the phosphazene ring with simple s donor behaviour via the ring nitrogen. The lengthening of the PN bonds adjacent to the coordinated metal centre is a result of electron density being removed from the PN bonding orbitals and going into the 4s orbital of the metal ion. Investigating the pyridine substituents on the phosphazene ring showed that these can affect the PN bonds in a similar fashion, although weaker, to the transition metals. This effect is the result of the pyridine nitrogen lone pair affecting the negative hyperconjugation component of the PN bond. Coupling between two metal atoms coordinated to the phosphazene ring was investigated by DFT calculations, which showed molecular orbitals in both the tricyclic and tetracyclic phosphazene capable of providing an ‘electron density bridge’ between the metal centres. These results are in accord with ESR and magnetic susceptibility results, which can be explained in terms of weak antiferromagnetic coupling between metal ions. The cyclic phosphazenes are model compounds for polyphosphazenes and the results obtained from this work will provide insight into the electronic properties of this important class of inorganic polymers.