Investigating facile routes for the rapid assembly of novel hydrazinyl and hydrazone complexes.

Alqurashi, Omar Jameel B. 2026. Investigating facile routes for the rapid assembly of novel hydrazinyl and hydrazone complexes. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The thesis demonstrated the development and design of novel fluorescent ligands and their complexes based on a hydrazinylpyridine framework to enable rapid and efficient metal coordination for potential imaging applications. The structural, characterisation, and photophysical studies of those compounds are discussed in relevant chapters. Chapter 1 provides the theoretical and chemical framework for the studies presented in this thesis. It outlines the fundamental principles of coordination chemistry, including metal-ligand bonding, and the coordination geometry of Cu(II), Ni(II), and Zn(II) complexes. A brief overview of Infrared spectroscopy and the principles of electronic absorption and emission spectroscopy is discussed. The Evans method for determining magnetic susceptibility and effective magnetic moments is also introduced. The chapter concludes with an overview of hydrazine and hydrazone chemistry, focusing on their structural characteristics, donor properties and coordination behaviour. Chapter 2 focuses on the coordination chemistry of mono- and bis-hydrazinylpyridine ligands with Ni(II) and Zn(II). Those complexes exhibit stability in their +2 oxidative state. Full characterisation is explored using a variety of techniques, including infrared spectroscopy, nuclear magnetic resonance spectroscopy, the Evans method, which is an NMR method to study the magnetic moments of the complexes, electronic absorption spectroscopy, cyclic voltammetry, and single crystal diffractometry. All complexes have distorted octahedral geometries. Chapter 3 describes the hydrazones derivatives and their complexes with Ni(II), Cu(II), and Zn(II). All hydrazone derivatives act as tridentate ligands, forming stable chelating rings. Full characterisation is achieved. The cyclic voltammograms indicate one quasi-reversible mechanism in the Ni(II) complex, while one reversible wave and one irreversible peak at the anodic region in the Cu(II) complexes. Compounds 3.1 and 3.2 exhibited significant solvatochromic behaviour across a range of solvents. The correlation between the absorption maxima and the ET(30) solvent polarity parameter indicates that solvent polarity strongly influences the observed solvatochromic behaviour. Complex 3.4 showed distinctly different behaviour in the solid state and in solution. X-ray diffraction confirmed a square planar geometry around the Ni(II) centre, consistent with a diamagnetic low-spin (d8) configuration. In contrast, the 1H NMR resonances together with an effective magnetic moment of 2.91 B.M. determined by the Evans method indicate that the compound exists as a paramagnetic species in acetonitrile solution. This change is most likely associated with solvent coordination, which alters the coordination environment of the metal centre, increasing the donor number surrounding the metal centre, leading to a high-spin Ni(II) species. The X-ray data showed that complexes 3.1 and 3.3 adopted a distorted octahedral arrangement, while 3.2 had a distorted square pyramidal environment, and 3.4 and 3.5 had distorted square planar geometries. These compounds exhibit photophysical features that might be used in analytical applications. The fluorescence spectra of these complexes show emission features attributed to a ligand-centred. Chapter 4 explores the design, synthesis and characterisation of two novel tetradentate hydrazinyl-hydrazone ligands, and their coordination to Ni(II), Cu(II), and Zn(II). The cyclic voltammograms show one quasi-reversible system in the Ni(II) complex, while one quasi reversible process and one irreversible peak at the anodic region in the Cu(II) complexes. The fluorescence spectra of Cu(II) and Zn(II) complexes display high emission features assigned to ligand-centred, which are enhanced upon complexation via the chelation enhanced fluorescence process. Structural characterisation by single-crystal X-ray diffraction revealed diverse coordination environments among the metal complexes. Compound 4.1 crystallised with an octahedral geometry, compounds 4.4 and 4.5 adopted square planar geometries, whereas compound 4.6 exhibited a square pyramidal coordination environment.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry Schools > Physical, Chemical & Environmental Sciences
Date of First Compliant Deposit:	4 September 2026
Last Modified:	04 Sep 2026 11:08
URI:	https://orca.cardiff.ac.uk/id/eprint/189393

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