Fast time-resolved infrared spectroscopy (TRIR) is used to probe the v(CO) spectrum of ClRe(CO)3(4,4'-bipyridyl)2 in the lowest MLCT (metal-to-ligand charge transfer) excited state. The three ground-state v(CO) bands all shift up in frequency, but not by the same amount. The energy-factored force field (EFFF) of the ground state is accurately solved by employing ,3CO-enrichment. Approximate methods yield information on the force field of the excited state; the principal EFFF force constants (¿co(ami) and fcco(equatoriai)) change by the same amount on excitation. This leads to a new interpretation of the resonance Raman spectrum of the compound. has been time-resolved resonance Raman (TR3) spectroscopy. Classic experiments have probed the structure of the excited states of a range of ruthenium complexes, and have shown, for instance, that in the lowest excited state of [Ru(bpy)3]2+ there is charge transfer from Ru to one of the bpy groups.7 Detailed isotopic studies8 have unravelled the details of the excited state structure. There is, however, a limitation of resonance Raman spectroscopy: only certain of the vibrational modes in the excited state will be resonance enhanced, partly because of the nature of the

The remarkable photochemistry of fac-XMn(CO)sub3(alpha-diimine) (X=halide). Formation of Mnsub2(CO)sub6(alpha-diimine)sub2 via the mer-isomer and photocatalytic disproportionation in the presence of PRsub3 Stor, G.J.; Morrison, S.L.; Stufkens, D.J.; Oskam, A. Published in: Organometallics DOI:10.1021/om00019a021Link to publication Citation for published version (APA):Stor, G. J., Morrison, S. L., Stufkens, D. J., & Oskam, A. (1994). The remarkable photochemistry of facXMn(CO)sub3(alpha-diimine) (X=halide). Formation of Mnsub2(CO)sub6(alpha-diimine)sub2 via the mer-isomer and photocatalytic disproportionation in the presence of PRsub3. Organometallics, 13, 2641-2650. DOI: 10.1021/om00019a021 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. This article describes the remarkable photochemistry of complexes fac-XMn(CO)&~-diimine) (X = C1, Br, I) upon irradiation into their lowest-energy CT band. The primary photoprocess is loss of CO, as was established by flash photolysis and low-temperature IR spectroscopy. The CO-loss product reacted thermally and photochemically to give mer-XMn(CO)s(a-diimine), which in turn transformed thermally into thefac isomer at temperatures above 213 K. Irradiation of mer-XMn(CO)&~-diimine) resulted in the formation of the 16-electron radical complexes Mn+(CO)s(a-diimine*-), which were identified at room temperature by ESR spectroscopy and which dimerized to give Mn&O)&-diimine)2 for a-diimine = bpy. At low temperatures these radical complexes formed rather stable adducts Mn+(C0)3(a-diimine0-)(PR3) with PRs (R = nBu, OMe). At room temperature these adducts initiated the catalytic substitution of X-by PR3 in the starting complex fac-XMn(CO)s(a-diimine). The primary photoprocess of facXMn(CO)s(a-diimine) (loss of CO) most likely occurs from the lowest LF state. Contrary to this, irradiation of mer-XMn(CO)s(a-diimine) gives rise to homolysis of the Mn-X bond. This remarkable difference in photochemical behavior of the fuc and mer isomers is discussed.

The frequencies of the v(C0) bands of W(CO)5L (L = pyridine and piperidine) in the lowest ligand field (LF) excited states have been obtained by fast time-resolved IR spectroscopy of the species dissolved in low-temperature glasses, and the shifts from the ground state indicate that the C-0 bonds lengthen on excitation, contrary to the interpretation of the pre-resonance Raman spectroscopy on the ground state.There has been extensive study of the excited state and photochemical properties of the complexes of general formula M(CO)SL, where M = Cr, Mo or W, and L is a nitrogen donor ligand.l-6 It is generally agreed that for W(CO)SL, if L is pyridine 1 or piperidine 2, then the lowest excited state is ligand field (LF) in character ('Al --+ 3E; weak absorption ca. 442 nm for both 1 and 2), too short-lived to be measured at room temperature but with a lifetime, based on emission studies, quoted as: 2.5 1 and 3.1 2 ps in MCH (methyl cyclohexane) at 77 K;1 0.86 1 and 0.82 2 us in EPA at 77 K;2 3.4 1 ps in argon 9 This is because in the LUMO there is considerable interaction between the pz metal orbital and the four equatorial n* orbitals on the CO groups.

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