Palladium carbene complexes, CX₂=PdX₂, are prepared along with the insertion products, CX₃–PdX, in reactions of laser-ablated Pd atoms with tetrahalomethanes and identified from matrix infrared spectra and density functional frequency calculations. The carbon–metal bonds of the CCl₂=PdCl₂ and CClF=PdCl₂ complexes are essentially double bonds with effective bond orders of 1.9, near those for the Pt and Ni analogues, as calculated by CASPT2 methods. On the other hand, only insertion complexes are generated from mono-, di-, and trihalomethane precursors. While the carbenes have staggered allene-type structures, many insertion complexes containing C–Cl bonds reveal distinct bridged structures, which indicate effective coordination of Cl to the metal center.

Nickel carbene complexes, CX₂ = NiX₂, are prepared along with the insertion products, CX₃ – NiX, in reactions of laser-ablated Ni atoms with tetrahalomethanes. These reaction products are identified from matrix infrared spectra and density functional frequency calculations. In agreement with the previously studied Pt cases, the carbon – nickel bonds of the Ni carbene complexes are essentially double bonds with CASPT2-computed effective bond orders of 1.8 – 1.9. On the other hand, only insertion complexes are generated from dihalomethane and trihalomethane precursors. The nickel carbenes have staggered structures, and several insertion complexes containing C – Cl bonds reveal distinct bridged structures similar to those observed in the corresponding Fe products, which indicate effective coordination of Cl to the metal center. The unique F-bridged CH₂F – NiCl structure is also observed.

Laser-ablated late lanthanide metal atoms were condensed with pure hydrogen at 4 K, and new infraredabsorptions are assigned to binary metal hydrides on the basis of deuterium substitution and density functionaltheory frequency calculations. The dominant absorptions in the 1330-1400 cm^-1 region are identified asLnH₃ complexes with very weak ligand bands near 3900 cm^-1. With ytterbium, YbH and YbH₂ were themajor initial products, but YbH₃ increased at their expense upon sample irradiation. Evidence is also presentedfor the LuH and ErH molecules and the tetrahydride anions in solid hydrogen.

The results of a combined spectroscopic and computational study of lanthanide hydrides with the general formula MH_x(H₂)_y, where M = La, Ce, Pr, Nd, Sm, Eu, and Gd, x = 1−4, and y = 0−6 are reported. To understand the nature of the dihydrogen complexes formed with lanthanide metal hydride molecules, we have first identified the binary MH_x species formed in the ablation/deposition process and then analyzed the dihydrogen supercomplexes, MH_x(H₂)_y. Our investigation shows that the trihydrides bind dihydrogen more weakly than the dihydrides and that the interaction between the central lanthanide and the H₂ molecules occurs via a 6s electron transfer from the lanthanide to the H₂ molecules. Evidence is also presented for the SmH and EuH diatomic molecules and the tetrahydride anions in solid hydrogen.

Laser-ablated Th atoms react with molecular hydrogen to give thorium hydrides and their dihydrogen complexes during condensation in excess neon and hydrogen for characterization by matrix infrared spectroscopy. The ThH₂, ThH₄, and ThH₄(H₂)_x (x = 1−4) product molecules have been identified through isotopic substitution (HD, D₂) and comparison to frequencies calculated by density functional theory and the coupled-cluster, singles, doubles (CCSD) method and those observed previously in solid argon. Theoretical calculations show that the Th−H bond in ThH₄ is the most polarized of group 4 and uranium metal tetrahydrides, and as a result, a strong attractive “dihydrogenâ€� interaction was found between the oppositely charged hydride and H₂ ligands ThH₄(H₂)_x. This bridge-bonded dihydrogen complex structure is different from that recently computed for tungsten and uranium hydride super dihydrogen complexes but is similar to that recently called the “dihydrogen bondâ€� (Crabtree, R. H. Science 1998, 282, 2000). Natural electron configurations show small charge flow from the Th center to the dihydrogen ligands.

The codeposition of laser-ablated tungsten atoms with neat hydrogen at 4 K forms a single major product with a broad 2500 cm^-1 and sharp 1860, 1830, 1782, 1008, 551, and 437 cm^-1 absorptions, which are assigned to the WH₄(H₂)₄ complex on the basis of isotopic shifts and agreement with isotopic frequencies calculated by density functional theory. This D_2d structured complex was computed earlier to form exothermically from W atoms and hydrogen molecules. Annealing the matrix allows hydrogen to evaporate and the complex to aggregate and ultimately to decompose. Comparison of the H−H stretching mode at 2500 cm^-1 and the W−H₂ stretching mode at 1782 cm^-1 with 2690 and 1570 cm^-1 values for the Kubas complex W(CO)₃(PR₃)₂(H₂) suggests that the present physically stable WH₄(H₂)₄ complex has more strongly bound dihydrogen ligands. Our CASPT2 calculations suggest a 15 kcal/mol average binding energy per dihydrogen molecule in the WH₄(H₂)₄ complex.

The vibrational spectra of UBz and ThBz have been measured in solid argon. Complementary quantum chemical calculations have allowed the assignments of the vibrational spectra. According to the calculations, AcBz are stable molecules, as well as other species like BzAcBz and BzAc₂Bz. Experimentally, there is no evidence for the sandwich compounds BzAcBz and BzAc₂Bz due to the limitations in the reagent concentrations.

Several monouranium and diuranium polyhydride molecules were investigated using quantum chemical methods. The infrared spectra of uranium and hydrogen reaction products in condensed neon and pure hydrogen were measured and compared with previous argon matrix frequencies. The calculated molecular structures and vibrational frequencies were used to identify the species present in the matrix. Major new absorptions were observed and compared with the previous argon matrix study. Spectroscopic evidence was obtained for the novel complex, UH₄(H₂)₆, which has potential interest as a metal hydride with a large number of hydrogen atoms bound to uranium. Our calculations show that the series of complexes UH₄(H₂)_1,2,4,6 are stable.