Photocrystallographic studies of linkage isomerism

Abstract

The work described in this thesis utilises a new and rapidly developing branch of diffraction experiment called ‘photocrystallography’. Photocrystallography is the study of photo-induced processes in a crystal using X-ray crystallographic techniques. Within this report photocrystallography is used to investigate the structures of photoactivated metastable linkage isomers of transition metal nitro complexes.

Chapter 1 contains a brief review of current state-of-the-art photocrystallography, as applied to molecular complexes. Complementary techniques are described and a detailed description of linkage isomerism is also presented.

Chapter 2 contains the fundamentals of crystallography giving a background and understanding of the experiments reported within this thesis.

The design and implementation of the LED ring, enabling photocrystallographic experiments to be carried out routinely is described in Chapter 3. The LED ring is an array capable of holding six LEDs in close proximity to the crystal without affecting the diffraction experiment and has been used successfully to photoactivate the crystal.

Chapters 4 and 5 describe the research into the binding modes of the nitrite ligand to a metal centre for a series of complexes supported by a range of nitrogen, phosphorus and arsenic based auxiliary ligands. These chapters explore the different nitrite coordination modes adopted from synthesis, the photocrystallographic investigations of the linkage isomers transformation and the temperature dependant equilibrium between the binding modes. Novel in-situ crystallographic experiments of both thermally and photochemically activated transformations have been carried out on the Ni(Et4en2)(η2-ONO)(η1-NO2) complex and have been shown to give rise to the formation of metastable linkage isomers within the single crystal. The first 100% fully reversible linkage isomerism is also reported for Ni(dppe)(NO2)Cl, with a series of related compounds also exhibiting this high single-crystal to single crystal transformation. In Chapter 6, the kinetics of the linkage isomerism transformation is explored by monitoring the peak intensity change upon irradiation, using both powder diffraction and single crystal diffraction techniques.

Date of Award	1 Apr 2011
Original language	English
Awarding Institution	University of Bath
Supervisor	Paul Raithby (Supervisor)