Photofragmentation of transition-metal-cluster carbonyls in the gas phase

Hollingsworth, William E.; Vaida, Veronica

doi:10.1021/j100398a008

Cited by 21 publications

(5 citation statements)

References 12 publications

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“…These methods rely on ultraviolet (UV) laser photolysis followed by detection methods based on UV absorption (20), chemical trapping (21,22), IR absorption (23,24,25) and ionization (5,6,26,27).…”

Section: Experimental Methodsmentioning

confidence: 99%

Photofragmentation of Transition Metal Cluster Complexes in the Gas Phase

Vaida¹

1987

ACS Symposium Series

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The gas phase photofragmentation of transition metal cluster complexes is discussed. The information available for the gas phase dissociation of Mn 2 (CO) 10 , Co 3 (CO) 9 CCH 3 and Mo 2 (O 2 CCH 3 ) 4 is compared to the well established data base on cluster compounds in condensed phase. The gas phase results are discussed in light of the predictions of electronic structure theory concerning the photofragmentation of these cluster compounds.The study of metal containing compounds proved to be a difficult conceptual and technical task. To the experimentalist the difficulty comes from the fact that standard high resolution spectroscopic methods are often not applicable to the study of organometallic complexes.As experimental chemical physics added to its repertoire sensitive time and energy resolved spectroscopic probes, it opened the way for the exploration of metal containing molecules. At the same time, theoretical chemistry is developing methods able to handle many electron systems necessary for the study of transition metal complexes.The rich photochemistry of transition metal complexes has been used extensively to address questions concerning reactions of molecules in excited electronic states (1). These studies are motivated by expectations that such information will find practical application in the systematic design of organometallic reactions and catalytic processes (2^,4).To date, most of the photochemical data available for transition metal complexes comes from condensed phase studies (1). Recently, the primary photochemistry of a few model transition metal carbonyl complexes has been investigated in gas phase (5.). Studies to date indicate that there are many differences between the reactivity of organometallic species in gas phase (5,6) as compared with matrix (7-10) or solution (11-17) environments. In most cases studied, photoexcitation of isolated transition metal

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Section: Experimental Methodsmentioning

confidence: 99%

Photofragmentation of Transition Metal Cluster Complexes in the Gas Phase

Vaida¹

1987

ACS Symposium Series

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“…They only observed the bare metal cluster ions Mn + , Mn 2 + and Fe + , Fe 2 + , Fe 3 + , respectively, i.e., 7−10 laser photons had to be absorbed by the parent molecule. Vaida and co-workers observed in their MPI experiments on M 2 (CO) 10 (M = Mn, Re) only M + and M 2 + in the mass spectra. , Similar to the mononuclear transition metal carbonyls, the polynuclear species exhibit complete ligand stripping in the gas phase under multiphoton conditions when applying nanosecond laser pulses. Real-time studies in solution with femtosecond laser pulses focused on the decarbonylation dynamics and on geminate recombination induced by the solvent cage. , A landmark study by Zewail and co-workers on Mn 2 (CO) 10 in a molecular beam yielded directly the fragmentation time scales of metal−metal bond cleavage (40 fs) and metal−CO bond breakage (20 fs) when exciting the σ → σ* transition .…”

Section: Introductionmentioning

confidence: 92%

“…Up to now, most investigations on the structure and dynamics of polynuclear transition metal carbonyls have focused on systems which already contain a metal-metal bond. Prototype systems which have been investigated in the gas phase are Mn 2 (CO) 10 and Re 2 (CO) 10 (see, e.g., refs 4-12). These compounds show intense absorption in the region between 330 and 500 nm which is assigned to the σ f σ* transition of the metalmetal bond.…”

Section: Introductionmentioning

confidence: 99%

“…13 Photoexcitation of this transition leads to homolytic cleavage of the metal-metal bond in competition with ligand dissociation. 9 Leutwyler and Even investigated Mn 2 (CO) 10 and Fe 3 (CO) 12 by nanosecond multiphoton dissociation (MPD)/ multiphoton ionization (MPI) using a N 2 -laser pumped dye laser in the region of 380-450 nm. 7 They only observed the bare metal cluster ions Mn + , Mn 2 + and Fe + , Fe 2 + , Fe 3 + , respectively, i.e., 7-10 laser photons had to be absorbed by the parent molecule.…”

Section: Introductionmentioning

confidence: 99%

“…Vaida and co-workers observed in their MPI experiments on M 2 (CO) 10 (M ) Mn, Re) only M + and M 2 + in the mass spectra. 9,10 Similar to the mononuclear transition metal carbonyls, the polynuclear species exhibit complete ligand stripping in the gas phase under multiphoton conditions when applying nanosecond laser pulses. Real-time studies in solution with femtosecond laser pulses focused on the decarbonylation dynamics and on geminate recombination induced by the solvent cage.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Ultrafast Dynamics of Transition Metal Carbonyls. 3. Intracluster Chemistry in [Cr(CO)₆]_n

Gutmann¹,

Dickebohm²,

Janello³

1999

J. Phys. Chem. A

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We report on one-color femtosecond−pump/probe experiments applied to homogeneous chromium hexacarbonyl clusters which are prepared in a molecular beam. The pump pulse initiates bimolecular intra-cluster reactions by ultrafast photodissociation of a CO ligand from Cr(CO)6 in a 1T1u metal-to-ligand charge-transfer state. The resulting reaction products are detected mass-selectively after multiphoton ionization by the probe pulse. In contrast to nanosecond multiphoton ionization (Peifer, W. R.; Garvey, J. F. Int. J. Mass Spectrom. Ion Processes 1990 102, 1), which exclusively leads to appearance of the Cr+ mass peak, a number of novel species which may serve as interesting model systems for catalysis and surface chemistry are detected. In addition to mononuclear fragments, metal cluster ions, and coordinatively unsaturated polynuclear metal carbonyls, metal oxides and carbides are observed in the femtosecond mass spectra. The appearance of these species can be rationalized by formation of asymmetric π-bridging CO ligands in the neutral manifold. The dynamics extracted from the transients of different reaction products is interpreted using concepts of surface and inorganic cluster chemistry. Ultrafast metal−metal bond formation on a time scale much faster than our laser pulse width (ca. 150 fs) can be observed. Site exchange of CO from terminal to bridging positions on the picosecond time scale is proposed to occur in coordinatively unsaturated polynuclear metal carbonyls. Experiments at different center wavelengths (280 and 262.5 nm) reveal energy-dependent reaction channels which are closed when exciting the clusters at 280 nm. When exciting at 262.5 nm, impulsive formation of the corresponding products and decay on the picosecond time scale is observed.

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