Vibrational spectroscopy measurements are described for mass-selected metal cation-molecular complexes using the technique of infrared resonance-enhanced photodissociation (REPD) spectroscopy. We discuss the mechanism of the REPD process in the infrared and how multiphoton techniques or rare gas tagging can be employed to facilitate dissociation processes in strongly bound complexes. Spectra are reported for Fe+(CO2)n complexes that demonstrate the formation of coordination spheres around the metal cation and for Mg+(CO2)n complexes, where the interaction with theory makes it possible to obtain structures for small clusters. Both of these studies investigate the asymmetric stretch region of CO2. Ni+(C2H2)n complexes are studied in the C-H stretch region, demonstrating evidence for intracluster cyclization reactions. Finally, experiments are described for metal ion-benzene (M = V, Al) complexes excited in the benzene ring distortions and C-H bending region. These experiments confirm the ~ -bonded configura...

Infrared spectroscopy to probe structure and dynamics in metal ion-molecule complexes

The chemistry of group 10 metalacycles

The reactivity of ground state iron atoms with respect to atom transfer and adduct formation reactions with a variety of simple molecules in Ar buffer gas near room temperature has been investigated. Iron atoms are produced by visible multiphoton dissociation of iron pentacarbonyl or ferrocene, and their removal by added gases under pseudo‐first‐order conditions is monitored by resonance fluorescence excitation at variable time delay following the photolysis pulse. Upper limits for second‐order rate constants for reaction of ground state iron atoms with O2, CO, H2O, (CH3)2O, C2H2, C2H4, N2O, C2H4O, and CF3Cl at room temperature and 100 Torr total pressure are estimated to be in the range (2–10)× 10−15 cm3 molecule−1 s−1, which corresponds to reaction probabilities of less than ≂10−5 per hard sphere collision. Pseudo‐second‐order rate constants in the range (2–60)× 10−14 cm3 molecule−1 s−1 are found for 1:1 adduct formation reactions of ground state iron atoms with C6H6, 1,3‐butadiene, NH3, and NO. The for...

Chemical reactivity of iron atoms near room temperature

Hydrogen-bonded H···π complexes of C2H2 and C2H4 were studied both computationally and experimentally. Computationally, C2H2-C2H4 clusters ranging from 1:1 to 6:1 stoichiometries were identified. Using matrix isolation infrared spectroscopy, the 1:1 adduct was studied in an argon matrix. Formation of these adducts was evidenced by shifts in the vibrational frequencies of the acetylene and ethylene submolecules in the complex. The molecular structure, vibrational frequencies, and stabilization energies of the complexes were calculated at the HF, MP2, MP2(full), and B3LYP levels of theory by employing basis sets ranging from 6-31G(d,p) to 6-311++G(2d,2p). Both computations and experiments showed that two types of complexes are formed, one in which acetylene acts as a proton donor to the π cloud of ethylene and another in which ethylene acts as the proton donor to the π cloud of acetylene. Structures, interaction energies, and vibrational frequencies have also been obtained for 1:2, 1:4, and 1:6 complexes of...

H-π Complexes of acetylene-ethylene: A matrix isolation and computational study

Ni+(C2H2)n ion−molecule complexes are produced by laser vaporization in a pulsed nozzle source. These ions are mass analyzed and size-selected with a reflectron time-of-flight spectrometer. Infrared excitation with a pulsed OPO/OPA laser induces photodissociation of these complexes that proceeds by sequential loss of C2H2 molecules. IR resonance-enhanced photodissociation (IR-REPD) spectra are measured in the C−H stretch region for Ni+(C2H2)n complexes (n = 3−6). The C−H stretch vibrations are shifted to lower frequencies than those in free acetylene, consistent with the formation of metal cation π-complexes. At the cluster sizes of n = 5 and larger, new bands are measured attributed to surface acetylene molecules. Additional red-shifted bands at n = 5 and beyond are assigned to an intracluster cyclization reaction, forming π-bonded cyclobutadiene.

Infrared Spectroscopy of Ni+(C2H2)n Complexes: Evidence for Intracluster Cyclization Reactions

Matrix-isolation studies of the reactions of iron atoms and iron dimers with acetylene in an argon matrix. The FT-IR spectrum of ethynyliron hydride

The reactions between atomic nickel and acetylene have been investigated in argon matrices at 12 K with Fourier-transform infrared spectroscopy At very low concentrations of nickel and acetylene the nickel atom forms a pi complex with the triple bond of acetylene This pi complex photorearranges upon visible photolysis with lambda greater than or equal to 400 nm to give nickel vinylidene, NiCCH/sub 2/ Photolysis with ultraviolet light causes the reversal of this reaction Isotopic studies with C/sub 2/D/sub 2/, C/sub 2/HD, /sup 13/C/sub 2/H/sub 2/, and /sup 12/C/sup 13/CH/sub 2/ support these findings The FTIR spectrum of a dinickel-acetylene pi complex obtained at higher nickel concentrations has also been identified The bond order of acetylene has been reduced to two in both Ni(C/sub 2/H/sub 2/) and Ni/sub 2/(C/sub 2/H/sub 2/), as evidenced from the big shift in the carbon-carbon stretching frequency No photochemistry was observed in the case of the dinickel reaction

FTIR matrix isolation studies of the reactions of atomic and diatomic nickel with acetylene in solid argon. The photosynthesis of nickel vinylidene

Nickel and cyclopropane reactions and photochemistry using matrix-isolation FTIR spectroscopy. Nickelacyclobutane synthesis and photofragmentation

The reactions between atomic nickel and acetylene have been investigated in argon matrices at 12 K with Fourier-transform infrared spectroscopy. At very low concentrations of nickel and acetylene the nickel atom forms a ..pi.. complex with the triple bond of acetylene. This ..pi.. complex photorearranges upon visible photolysis with lambda greater than or equal to 400 nm to give nickel vinylidene, NiCCH/sub 2/. Photolysis with ultraviolet light causes the reversal of this reaction. Isotopic studies with C/sub 2/D/sub 2/, C/sub 2/HD, /sup 13/C/sub 2/H/sub 2/, and /sup 12/C/sup 13/CH/sub 2/ support these findings. The FTIR spectrum of a dinickel-acetylene ..pi.. complex obtained at higher nickel concentrations has also been identified. The bond order of acetylene has been reduced to two in both Ni(C/sub 2/H/sub 2/) and Ni/sub 2/(C/sub 2/H/sub 2/), as evidenced from the big shift in the carbon-carbon stretching frequency. No photochemistry was observed in the case of the dinickel reaction.

Ellen S. Kline

Papers

Matrix-isolation studies of the reactions of iron atoms and iron dimers with acetylene in an argon matrix. The FT-IR spectrum of ethynyliron hydride

FTIR matrix isolation studies of the reactions of atomic and diatomic nickel with acetylene in solid argon. The photosynthesis of nickel vinylidene

Nickel and cyclopropane reactions and photochemistry using matrix-isolation FTIR spectroscopy. Nickelacyclobutane synthesis and photofragmentation

FTIR Matrix Isolation Studies of the Reactions of Atomic and Diatomic Nickel with Acetylene in Solid Argon. The Photosynthesis of Nickel Vinylidene.

Matrix-Isolation Studies of the Reactions of Iron Atoms and Iron Dimers with Acetylene in an Argon Matrix.