Unusual Bonding in Platinum Carbido Clusters

Decomposition of guaiacol on a subnanometric platinum cluster: a DFT investigation followed by microkinetic analysis

The use of biomass as renewable feedstock for commodity chemicals may largely benefit from the successful development and application of heterogeneous catalysts for decomposition processes. The present investigation combines density functional theory and Christiansen-like microkinetic analysis to describe, at the atomistic level, the mechanisms related to the conversion of oxygenated biomass compounds to deoxygenated and semi-saturated hydrocarbons on a subnanometric Pt10 cluster. The DFT calculations and the kinetic analysis based on the evaluated free energy variations, associated with both elementary step barriers and rearrangement/desorption processes occurring on the cluster, suggest that benzene is the preferred product, together with a compound still bearing oxygen, cyclopentadienone, which would form as a minor product only at high temperature. Other than highlighting the role of the peculiar interaction between carbon and platinum, the reported investigation underlines the importance of cluster fluxionality and reorganization ability in promoting catalyzed reactions.

Analogy of C-Pt and C-O Chemical Bonding in the Diatomic CPt and CO

The conjugate-pair molecules of CO and CPt provide a prototype of the autogenic isolobal relationship between the O and Pt atoms that can rationalize the structure and reactivity trends of platinum carbides. Herein, the photoelectron detachment at 532 nm has been recorded for the gas-phase CPt- by using the photoelectron velocity-map imaging spectroscopy. The vibrationally resolved ground-state transition reveals a wealth of information concerning the electronic ground states of CPt0/-1. Although the triple bonding characters in both CPt and CO have fortified the autogenic isolobal relationship between O and Pt, further detailed bonding comparisons have revealed the subtle nuance in the triple bonding. The triple bonds of CO comprise one σ donor bond from the O atom to the C atom and two degenerate π electron-sharing bonds. In contrast, the triple bonds of CPt involve three dative bonds, including one σ donor bond from the C atom to the Pt atom and two degenerate π back-donation bonds from the Pt atom to the C atom.

Isoelectronic IrC3-, PtC3, and AuC3+ Clusters Featuring the Structural and Bonding Resemblance to OC3

The IrC₃^- and PtC₃^- anions generated by laser vaporization were identified and characterized by gas-phase photoelectron spectroscopy and quantum-chemical calculations. The straight-chain structures with an MCCC (M = metal; C = carbon) connectivity are found for the isoelectronic IrC₃^-, PtC₃, and AuC₃⁺ clusters. Further elaborate analyses manifest the strikingly structural and bonding similarities between MC₃^-/0/+ clusters and OC₃ revealed. This finding has broadened the notion of autogenic isolobality to the gas-phase clusters that contain Ir^-, Pt, Au⁺, and C centers.

Account of chemical bonding and enhanced reactivity of vanadium-doped rhodium clusters toward C–H activation: a DFT investigation

The chemical bonding and enhanced reactivity of vanadium-doped rhodium clusters toward C–H activation were investigated using DFT.

Structural and electronic properties of bulk and low-index surfaces of zincblende PtC

Transition metal carbides have been extensively used in diverse applications over the past decade. Their versatility is in part thanks to their unique bonding, which displays a mixture of ionic, metallic and covalent character. While the bulk structure of zincblende (ZB) PtC has been investigated several times, a detailed understanding of the electronic and structural properties of its low-index surfaces is lacking. In this work, we present an ab initio investigation of the properties of five crystallographic ZB PtC surfaces (Pt/C-terminated PtC(1 0 0), PtC(1 1 0) and Pt/C-terminated PtC(1 1 1)). Upon geometry optimization, both polar and nonpolar surfaces undergo a mild interlayer relaxation, without extensive reconstructions. Calculated vacancy formation energies indicate facile C removal on the (1 1 1) surface while Pt-vacancy formation is endothermic. Finally, atomic O adsorption energies on all surfaces reveal a high affinity of the C-terminated surfaces towards this species.

The nature of structure and bonding between transition metal and mixed Si-Ge tetramers: A 20-electron superatom system

A novel superatom species with 20-electron system, Six Gey M(+) (x + y = 4; M = Nb, Ta), was properly proposed. The trigonal bipyramid structures for the studied systems were identified as the putative global minimum by means of the density functional theory calculations. The high chemical stability can be explained by the strong p-d hybridization between transition metal and mixed Si-Ge tetramers, and closed-shell valence electron configuration [1S(2) 1P(6) 2S(2) 1D(10) ]. Meanwhile, the chemical bondings between metal atom and the tetramers can be recognized by three localized two-center two-electron (2c-2e) and delocalized 3c-2e σ-bonds. For all the doped structures studied here, it was found that the π- and σ-electrons satisfy the 2(N + 1)(2) counting rule, and thus these clusters possess spherically double (π and σ) aromaticity, which is also confirmed by the negative nucleus-independent chemical shifts values. Consequently, all the calculated results provide a further understanding for structural stabilities and electronic properties of transition metal-doped semiconductor clusters. © 2016 Wiley Periodicals, Inc.

Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

Carbenes of platinum and palladium, PtC3 and PdC3 , were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty-six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au(+) , and Pt atoms.

Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

Carbenes of platinum and palladium, PtC3 and PdC3, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty-six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au+, and Pt atoms.

Vibrational spectra and structures of SinC clusters (n = 3–8)

The geometries of C-doped silicon clusters determined from infrared spectroscopy and computational chemistry reveal the stable Si₃C unit as a common structural motif.

Endohedral fullerene with μ3-carbido ligand and titanium-carbon double bond stabilized inside a carbon cage

In all metallofullerenes known before this work, metal atoms form single highly polar bonds with non-metal atoms in endohedral cluster. This is rather surprising for titanium taking into account the diversity of organotitanium compounds. Here we show that the arc-discharge synthesis of mixed titanium-lutetium metallofullerenes in the presence of ammonia, melamine or methane unexpectedly results in the formation of TiLu2C@I(h)-C80 with an icosahedral Ih(7) carbon cage. Single-crystal X-ray diffraction and spectroscopic studies of the compound reveal an unprecedented endohedral cluster with a μ3-carbido ligand and Ti-C double bond. The Ti(IV) in TiLu2C@I(h)-C80 can be reversibly reduced to the Ti(III) state. The Ti = C bonding and Ti-localized lowest unoccupied molecular orbital in TiLu2C@Ih-C80 bear a certain resemblance to titanium alkylidenes. TiLu2C@I(h)-C80 is the first metallofullerene with a multiple bond between a metal and the central, non-metal atom of the endohedral cluster.