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# Photochemical and photophysical studies of transition metal species in low temperature media

Campden, Andrew Kenneth (1989) Photochemical and photophysical studies of transition metal species in low temperature media. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

## Abstract

Spectroscopic studies have been performed on a variety of transition metal complexes in gas matrices, polymer films and Nujol and liquid polymer mulls at ca. 12 and 77K. All of the matrix isolated species were identified from their infrared and u.v.-visible spectra. Irradiation of [(η1-C7H7)Re(CO)5] in Ar, CH4, CO and N2 matrices at ca. 12K, results in successive CO ejection accompanied by an increase in ring hapticity, finally affording [(η7-C7H7)Re(CO)2], the intermediates being the η3 and η5 18-electron species. Similar photochemistry was observed for [(C7H7CO)Mn(CO)5], which after initial CO loss and acyl migration to give [(η1C7H7)Mn(CO)5] followed the same pattern of reaction as the Re species. For Mn the final η5 - η7 step was photochemically reversible. In N2 matrices the final product was [(η5-C7H7)Mn(CO)2(N2)], whilst in 13CO doped matrices isotope scrambling allowed a force field fitting study to be performed. Irradiation of [(η5-C5H5)Mo(CO)3(COCF3)] in Ar, CH4 and CO matrices at ca. 12K, leads to sequential CO ejection, resulting finally in the difluorocarbene species trans-[(η5C5H5)Mo(= CF2)(CO)2(F)]. This is the first reported formation of such a species by an α-fluorine elimination reaction. Photolysis in N_2 and ^13CO doped matrices led also to the formation of cis-[(η5-C_5H_5)Mo(CO)_2(X)(CF_3)] (X = N_2 or ^13CO). U.v. and visible irradiation of the metal-metal bonded dimers [lbrace(η5-C_5H_5)M(CO)_3rbrace_2] (M = Mo and W) in Ar, CH_4, CO and N_2 matrices at ca. 12K, led to the formation of the CO ejection species [(η5-C_5H_5)_2M_2(CO)_5], with two terminal, two semi-bridging and one 4-electron bridging CO ligand. U.v. irradiation of the similar dicyclopentadienyl-methane species [CH_2lbrace(η5-C_5H_5)M(CO)_3rbrace_2] constrained in a cis-configuration, also led to CO ejection and formation of [CH_2lbrace(η5-C_5H_5)_2M_2(CO)_5rbrace] with three terminal and two semi-bridging CO ligands. The concentration dependence of polymer film lq pseudo-matrix quality was investigated using [Ru(bipy)_3]Cl_2 doped into PVA films. Studies were performed at both room temperature and ca. 77K using absorption, emission and excitation spectroscopy, and the measurement of phosphorescence lifetimes. No evidence of aggregation effects was observed across the full range of sample weights studied, all lifetimes being single exponential. Studies were extended to Nujol and liquid polymer mulls which produced good emission and excitation spectra, both for [Ru(bipy)_3]Cl_2 and for K_3[Cr(CN)_6]. A range of studies were performed to illustrate the applications of low temperature polymer film, mull and alkali halide disc lq pseudo-matrices at ca. 12 and 77K. The vibrational fine structure in the absorption spectra of [MO_4]^n- ions (M = Cr, n = 2; M = Mn, n = 1 or 2) was studied in both films and mulls, and light induced high spin - low spin interconversion (LIESST) was investigated using infrared spectroscopy for cis-[Fe(phen)_2(NCS)_2] and [Fe(ptz)_6][BF_4]_2 in polymer films, mulls and alkali halide discs. The LIESST studies were extended to include two nickel (II) complexes in PVC films. An investigation of the benzene lq channel three decay mechanism was conducted using infrared spectroscopy in Ar and Xe matrices at ca. 12K, and in the gas phase. Although no definitive evidence was obtained regarding the identity of the hidden state lq X proposed to be involved in this process, a hot molecule mechanism producing acetylene from benzene by a three photon process in the gas phase was reported for the first time.

Published date: 1989

## Identifiers

Local EPrints ID: 461538
URI: http://eprints.soton.ac.uk/id/eprint/461538
PURE UUID: 69e07fea-1573-4cdf-a4a5-fbeaafa8fa98

## Catalogue record

Date deposited: 04 Jul 2022 18:49

## Contributors

Author: Andrew Kenneth Campden