Magnetostructural correlations in polynuclear complexes of phtalazine based tetra- and hexadentate ligands

Sheppard, Christopher Lorenzo (1998) Magnetostructural correlations in polynuclear complexes of phtalazine based tetra- and hexadentate ligands. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis describes the synthesis, spectroscopic and crystallographic characterisation, and magnetism of a series of polynuclear Cu(II) complexes of the ligand 1,4-bis(3'-methyl-2’-pyridy)aminophthalazine (PAP3Me), and a series of Ni(II) and Mn(II) complexes of the ligand 1,4-bis((6-methylpyridine-2-carboxaldiimino)amino)phthalazine (PHP6Me), with particular interest in µ₂-1,1 azide bridged systems. In addition, a series of Extended Hūckel molecular orbital calculations investigating the variation of magnetic behaviour with changes in the geometry of the binuclear centre in the phthalazine / µ₂-1,1 azide bridged Cu(II) binuclear system was also undertaken. -- Part A is an introduction, consisting of three chapters. Chapter 1 provides an introduction to the study of polynuclear metal complexes. The role of these complexes as a bridge between the physics of molecular magnetism and the biochemistry of metalloenzymes is emphasised, and the theory of magnetism introduced. Chapter 2 develops the theory of molecular magnetism of binuclear metal complexes, including quantitative expressions for magnetic exchange, factors influencing the magnitude and sign of exchange interactions, and computational models (Extended Hūckel) of these interactions. Chapter 3 is an overview of the magnetic properties of binuclear and polynuclear complexes linked via azide or thiocyanate bridges. -- Part B consists of experimental results, and contains two chapters. Chapter 4 describes the synthesis of complexes based on a Cu₂PAP3Me core, in which the binuclear Cu(II) centres are bridged by phthalazine and azide or phthalazine and some other exogenous bridge. The X-ray diffraction structures of four Cu(II) complexes, along with infrared, UV / Vis and variable temperature magnetism studies of these four, and five other complexes, are presented. In particular, it is found that the variable temperature magnetic data of the µ₂-1,1 azide bridged complexes cannot be fitted to the Bleaney-Bowers equation, whereas the data for the non-azide complexes can. Several other attempts to understand the anomalous magnetism of the azide systems suggests that using a variable temperature -2J best models the observed behaviour. A variable temperature X-ray diffraction study was undertaken in an attempt to rationalise this behaviour in terms of changing bridge geometry, but the results indicate that this is not the case. Extended Hūckel molecular orbital calculations were also carried out and showed that magnetic coupling in phthalazine / µ₂-1,1 azide bridged Cu(II) systems is a function of not only the µ₂-1,1 azide bridge angle, but of other geometric distortions of the azide bridge. Chapter 5 presents the synthesis, preliminary X-ray diffraction studies, spectroscopic studies, and magnetism of Ni(II) and Mn(II) complexes of the ligand PHP6Me, plus either azide or thiocyanate. Due to a lack of firm structural data, the results are inconclusive, and attempts to establish unequivocally an antiferromagnetic realm for µ₂-1,1 azide bridged Ni(II) and Mn(II) complexes proved unsuccessful.

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