Computational investigations of the spectroscopy, vibronic coupling, and photo(stereo)chemistry in inorganic systems

Abstract

This thesis focuses on the spectroscopy and photo-stereochemistry of relatively large closed-shell and open-shell transition metal complexes, investigated with an array of modern computational methodologies. The presence of the metal electrons/orbitals results in a greater number of low-lying excited states, and these states are vibronically coupled resulting in Jahn-Teller or pseudo-Jahn-Teller (pJT) effects, or general surface crossings. These features are very challenging to calculate but are vitally important to explain the observed behavior in such systems. Computational investigations using the multiconfigurational CASSCF method on the pJT effect occurring in ammonia, and Mo2(DXylF)2(O2CCH3)2(μ2-O)2 complex are presented. These definitively show that in the latter case the experimentally observed structure is due to a vibronic coupling of the ground electronic state with that of a nondegenerate 1πδ* state, resulting in a rhomboidal rather than square motif at the bimetallic centre. The (BQA)PtMe2I (BQA= bis(8-quinolinyl)amide) complex has been found to undergo unexpected meridial to facial isomerisation induced by light. The TD-DFT method was used to examine the spectroscopy of this system, and the CASSCF method was used to examine excited state relaxation pathways. The system relaxes on an excited state potential energy surface, of an essentially localised ππ* excited state of the BQA ligand, and reaches a facial excited minimum that is located adjacent to a sloped conical intersection connecting the excited and ground electronic states. Chromium (III) complexes have been investigated for many years and many aspects of their photochemistry are still not very well understood. The photochemistry of paradigm Cr (III) complexes, such as chromium oxalate [Cr(C2O4)3]3-, chromium tris- (1,3diaminopropane) [Cr(tn)3]3+ and Cr(tn)2(CN)2, have been investigated using TDDFT and CASSCF methods. Non-radiative relaxation pathways have been documented showing mechanism of both internal conversion in the quartet manifold, as well as inter-system crossing into the doublet manifold. The results explain photostereochemical features of the photo-induced racemization of [Cr(C2O4)3]3- and the photoaquation of [Cr(tn)3]3+ and Cr(tn)2(CN)2.