Magnetic and spectroscopic properties of lanthanoid coordination compounds with tripicolylamine ligands
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2025
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Melbourne Authors
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School of Chemistry
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PhD thesis
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© 2025 Jonay Gonzalez Sanchez
Abstract
This thesis presents a comprehensive study of the magnetic and spectroscopic properties of several families of lanthanoid-tris(2-methylpyridyl)amine (tpa) complexes, with a particular focus on their luminescence decay dynamics and energy transfer processes in the solid state.
Two closely related families of heteroleptic compounds, [Ln(tpa)(NO3)3] and [Ln(tpa)Cl3], are investigated to elucidate the influence of ligand environment and local symmetry on both magnetic and optical behaviour. Despite their similar structural motifs, these compounds exhibit markedly different properties. The nitrato-containing complexes display more intense and longer-lived luminescence, while the chloro analogues show enhanced single-molecule magnet (SMM) behaviour. These differences are attributed to subtle variations in the crystal field imposed by the coordinating ligands and small changes in the symmetry of the lanthanoid ion environment.
Building on this detailed characterisation, mixtures of selected complexes were prepared to probe energy transfer mechanisms and concentration quenching effects on luminescence properties. The cocrystallised compound [Tb0.6Yb0.4(tpa)(NO3)3] was used to investigate intermetallic energy transfer between Tb3+ and Yb3+, with downshifting emission observed in the solid state. A series of diluted [ErxY1-x(tpa)(NO3)3] samples was synthesised to systematically examine the impact of spectroscopically active ion concentration on emission intensity and excited-state lifetimes.
Two additional families of fluorinated complexes, [Ln(tpa)(hfac)3] and [Ln(tpa)(hfac)2(tfa)], were subsequently explored to enhance emission performance and facilitate detailed studies of energy transfer dynamics. These compounds exhibit significantly improved luminescence properties relative to the non-fluorinated analogues, which is attributed to reduced phonon-mediated non-radiative decay arising from the fluorinated ligands. Their favourable optical properties enabled the investigation of energy transfer in cocrystallised Er3+/Yb3+ mixtures, with metal ratios determined by magnetometry and energy transfer pathways elucidated through time-resolved luminescence measurements.
Overall, this thesis demonstrates how targeted modification of the ligand environment and metal-ion composition can be used to tune both the magnetic relaxation behaviour and luminescence dynamics of lanthanoid complexes, providing insight into the interplay between structure, crystal field effects, and energy transfer processes in multifunctional lanthanoid materials.
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Lanthanoid, Energy transfer, Luminescence, Single-molecule magnetism, Time-resolved emission, Coordination compound