CO2 Hydrogenation to Formate and Formic Acid by Bimetallic Palladium-Copper Hydride Clusters.

Mass spectrometric analysis of the anionic products of interaction between bimetallic palladium-copper tetrahydride anions, PdCuH4-, and carbon dioxide, CO2, in a reaction cell shows an efficient generation of the PdCuCO2H4- intermediate and formate/formic acid complexes. Multiple structures of PdCuH4- and PdCuCO2H4- are identified by a synergy between anion photoelectron spectroscopy and quantum chemical calculations. The higher energy PdCuH4- isomer is shown to drive the catalytic hydrogenation of CO2, emphasizing the importance of accounting for higher energy isomers for cluster catalytic activity. This study represents the first example of CO2 hydrogenation by bimetallic hydride clusters

Photoelectron spectroscopic study of iron-pyrene cluster anions

Iron-pyrene cluster anions, [Fem(pyrene)n]− (m = 1–2, n = 1–2) were studied in the gas phase by photoelectron spectroscopy, resulting in the determination of their electron affinity and vertical detachment energy values. Density functional theory calculations were also conducted, providing the structures and spin multiplicities of the neutral clusters and their anions as well as their respective electron affinity and vertical detachment energy values. The calculated magnetic moments of neutral Fe1(pyrene)1 and Fe2(pyrene)1 clusters suggest that a single pyrene molecule could be a suitable template on which to deposit small iron clusters, and that these in turn might form the basis of an iron cluster-based magnetic material. A comparison of the structures and corresponding photoelectron spectra for the iron-benzene, iron-pyrene, and iron-coronene cluster systems revealed that pyrene behaves more similarly to coronene than to benzene

Photoelectron spectroscopic and theoretical studies of Fem − (coronene)n (m=1,2, n=1,2) complexes

Fem(coronene)n (m=1,2, n=1,2) cluster anions were generated by a laser vaporization source and studied by anion photoelectron spectroscopy. Density functional theory was used to calculate the structures and the spin multiplicities of those clusters as well as the electron affinities and photodetachment transitions. The calculated magnetic moments of Fe1(coronene)1 and Fe2(coronene)1 clusters suggest that coronene could be a suitable template on which to deposit small iron clusters and that these in turn might form the basis of an iron cluster-based magnetic material. Fe1(coronene)2 and Fe2(coronene)2 cluster anions and their corresponding neutrals prefer the sandwich-type structures, and the ground state structures of these clusters are all staggered sandwiches

Photoelectron spectroscopic and theoretical study of the [HPd(η(2)-H2)](-) cluster anion.

Anion photoelectron spectroscopic and theoretical studies were conducted for the PdH(-) and PdH3 (-) cluster anions. Experimentally observed electron affinities and vertical detachment energies agree well with theoretical predictions. The PdH3 (-) anionic complex is made up of a PdH(-) sub-anion ligated by a H2 molecule, in which the H-H bond is lengthened compared to free H2. Detailed molecular orbital analysis of PdH(-), H2, and PdH3 (-) reveals that back donation from a d-type orbital of PdH(-) to the σ* orbital of H2 causes the H-H elongation, and hence, its activation. The H2 binding energy to PdH(-) is calculated to be 89.2 kJ/mol, which is even higher than that between CO and Pd. The unusually high binding energy as well as the H-H bond activation may have practical applications, e.g., hydrogen storage and catalysis

Photoelectron spectroscopic study of the negative ions of 4-thiouracil and 2,4-dithiouracil

We report the photoelectron spectra of the negative ions of 4-thiouracil (4-TU) − and 2,4-dithiouracil (2,4-DTU) − . Both of these spectra are indicative of valence anions, and they are each dominated by a single broad band with vertical detachment energies of 1.05 and 1.4 eV, respectively. Complementary calculations by Dolgounitcheva, Zakrzewski, and Ortiz (see companion paper) are in accord with our experimental results and conclude that the (4-TU) − and (2,4-DTU) − anions, reported herein, are valence anions of canonical 4-thiouracil and canonical dithiouracil. Comparisons among the anions and corresponding neutrals of 4-thiouracil, 2,4-dithiouracil, 5-chlorouracil, 5-fluorouracil, and uracil itself show that both sulfur and halogen modifications of uracil give rise to significant changes in the electronic structure. The electron affinities of the first four are all substantially larger than that of the canonical uracil

Photoelectron spectroscopy and theoretical studies of [Com(pyrene)n]− (m=1,2 and n=1,2) complexes

Anion photoelectron spectroscopic experiments and density functional theory based calculations have been used to investigate the structural, electronic, and magnetic properties of neutral and anionic [Com(pyrene)n] (m,n=1–2) complexes. The calculated electron affinities and vertical transition energies of Com(pyrene)n are in good agreement with the measured values. Our results provide clear evidence for dimerization of Co atoms and formation of sandwich structures in these complexes. While the calculated spin magnetic moments of neutral Co2(pyrene)n complexes suggest a preference for ferromagnetic coupling between Co atoms, the spin magnetic moment of Co atom in Co(pyrene) and Co(pyrene)2 complexes was reduced to 1μB

Ground state structures and photoelectron spectroscopy of [Com(coronene)]− complexes

A synergistic approach involving theory and experiment has been used to study the structure and properties of neutral and negatively charged cobalt-coronene [Com(coronene)] complexes. The calculations are based on density functional theory with generalized gradient approximation for exchange and correlation potential, while the experiments are carried out using photoelectron spectroscopy of mass selected anions. The authors show that the geometries of neutral and anionic Co(coronene) and Co2(coronene) are different from those of the corresponding iron-coronene complexes and that both the Co atom and the dimer prefer to occupy η2-bridge binding sites. However, the magnetic coupling between the Co atoms remains ferromagnetic as it is between iron atoms supported on a coronene molecule. The accuracy of the theoretical results is established by comparing the calculated vertical detachment energies, and adiabatic electron affinities with their experimental data