Investigation of Molecular Iridium Fluorides IrFn (n=1–6): A Combined Matrix-Isolation and Quantum-Chemical Study

The photo-initiated defluorination of iridium hexafluoride (IrF₆) was investigated in neon and argon matrices at 6 K, and their photoproducts are characterized by IR and UV-vis spectroscopies as well as quantum-chemical calculations. The primary photoproducts obtained after irradiation with λ=365 nm are iridium pentafluoride (IrF₅) and iridium trifluoride (IrF₃), while longer irradiation of the same matrix with λ=278 nm produced iridium tetrafluoride (IrF₄) and iridium difluoride (IrF₂) by Ir−F bond cleavage or F₂ elimination. In addition, IrF₅ can be reversed to IrF₆ by adding a F atom when exposed to blue-light (λ=470 nm) irradiation. Laser irradiation (λ=266 nm) of IrF₄ also generated IrF₆, IrF₅, IrF₃ and IrF₂. Alternatively, molecular binary iridium fluorides IrF_n (n=1–6) were produced by co-deposition of laser-ablated iridium atoms with elemental fluorine in excess neon and argon matrices under cryogenic conditions. Computational studies up to scalar relativistic CCSD(T)/triple-ζ level and two-component quasirelativistic DFT computations including spin-orbit coupling effects supported the formation of these products and provided detailed insights into their molecular structures by their characteristic Ir−F stretching bands. Compared to the Jahn-Teller effect, the influence of spin-orbit coupling dominates in IrF₅, leading to a triplet ground state with C_4v symmetry, which was spectroscopically detected in solid argon and neon matrices.     

ChemInform Abstract: A Matrix Isolation and Computational Study of Molecular Palladium Fluorides: Does PdF6 Exist?

Binary palladium fluorides from PdF to PdF₆ are investigated by matrix‐isolation methods using thermal evaporation and laser ablation to generate Pd atoms for reaction with F₂‐doped Ar and Ne matrices as well as neat F₂ matrices.     

Quantum chemical calculations and the structure of Ni n (C2H2) complexes (n = 1–4)

Complexes of nickel atoms and small clusters with acetylene molecules are studied within the density functional theory. A trend toward the predominant formation of structures with bridge hydrogen atoms is observed in reactions between Ni _n and acetylene with rising n.     

Quantum Chemical Study on Geometry and Property of Cluster Ni_4P

1INTRODUCTION Amorphous alloys attractive to scientists have worked in the field of materials and catalysts since they have many excellent physical and chemical pro-perties,such as high magnetic susceptibility,high specific heat,high strength,ductile in compression,low coefficient of friction,high corrosion resistance,super plasticity within the range,ferromagnetism and super conductivity[1~5].Especially,amorphous alloys as catalytic materials have shown either hig-her activity or selectiv…     

Quantum Chemical Study of CnAl2^± （n=1～10） Clusters： Structure and Stability

Geometries, electronic structures and vibrational frequencies of CnAl2± clusters have been investigated by using the B3LYP-DFT method in the range of n = 1～10. At the B3LYP/6-311G level, the ground state structures of CnAl2± clusters are planar or linear with terminal aluminum atom. In these structures, the C–C bonds are alternately changed between double and triple. The changing magnitude of the averaged bond length decreases with the increase of cluster size. The energetic analysis showed that CnAl2± clusters with even n are more stable than those with odd n.     

Heats of formation for Fe(CO)n(n=1–4)

The dissociation energies of Fe(CO)_n (n=2–4) are computed using correlation consistent basis sets and the CCSD(T) approach. The dissociation energies are extrapolated to the CBS limit and are corrected for core–valence (CV), scalar relativistic, spin–orbit, zero-point, and thermal effects. Our iron carbonyl bond strengths agree with experiment within the respective error bars. We use our dissociations energies at 298 K to obtain the heats of formation of Fe(CO)_n (n=1–4).     

An ab Initio Study on the Chemical Bond and Reactivity of Molybdenum–Sulfur Clusters with a Mo2O n S4−n (n=1–3) Core

Using the ab initio method and natural bond analysis, the reactivity and chemical bond of dinuclear molybdenum sulfur clusters with Mo₂O _n S_4–n (n=1–3) core were studied. The results show that the Mo--Mo bonds in these clusters are significantly affected by the delocalization effects of the multicenter d--p and Mo--X ₁ bonds, besides the direct interactions between Mo atoms. The substitution reactions of the cluster core are also discussed, and it is indicated that sulfur atoms have a preference for the bridging sites and the oxygen atoms tend to attach to the terminal sites.     

Theoretical study of silicon–sulfur clusters (SiS2)n (n = 1–6)

 The possible geometrical structures and relative stability of (SiS₂) _n (n=1–6) silicon–sulfur clusters are explored by means of density functional theory quantum chemical calculations. The effects of polarization functions and electron correlation are included in these calculations. The electronic structures and vibrational spectra of the most stable geometrical structures of (SiS₂) _n are analyzed by the same method. As a result, the regularity of the (SiS₂) _n cluster growth is obtained, and the calculation may used for predicting the formation mechanism of the (SiS₂) _n cluster. Received: 17 November 1999 / Accepted: 3 November 2000 / Published online: 3 May 2001     

Ab Initio Study of Neutral and Charged Copper Bromide (CuBr) n (+) Clusters (n?=?1–6)

A theoretical study in the framework of the density functional theory is performed to investigate the stability, the structural and electronic properties of both neutral and cationic copper bromide clusters (CuBr) _n ⁽⁺⁾, n = 1–6. The most stable isomers are found to be cyclic arrangements. Calculated infrared frequencies are compared with the available experimental spectra. The nature of the ionio-covalent bonding is characterized. The fragmentation, the ionization potentials are also investigated.     

Superhalogen properties of PdFn (n=1–7) clusters using Quantum chemical method

In this work the interaction of Palladium (Pd) atom with Fluorine (F) has been studied using density functional theory. Up to seven F atoms are bound to a single Pd atom which results in increase of electron affinities of given molecule successively, reaching a peak value of 8.54 eV for PdF₇. By using HOMO–LUMO gap, molecular orbital analysis, binding energy of these clusters, we examined its stability and reactivity. It is found that energy required for dissociation of F₂ molecules are higher than energy required for dissociation of F atoms. The unusual properties brought about by involvement of inner shell 4d-electrons, which not only allow PdF_n clusters to belong to the class of superhalogens but also show that its valence can exceed the nominal value of 1.     

On the Catalytic Performance of (ZrO)n (n=1–4) Clusters for CO Oxidation: A DFT Study

The unique characteristic of superatoms to show chemical properties like those of individual atoms opens a new avenue towards replacing noble metals as catalysts. Given the similar electronic structures of the ZrO superatom and the Pd atom, the CO oxidation mechanisms catalysed by (ZrO)_n (n=1–4) clusters were investigated in detail to evaluate their catalytic performance. Our results reveal that a single ZrO superatom exhibits superior catalytic ability in CO oxidation than both larger (ZrO)_n (n=2–4) clusters and a Pd atom, indicating the promising potential of ZrO as a “single-superatom catalyst”. Moreover, the mechanism of CO oxidation catalysed by ZrO^+/− suggests that depositing a ZrO superatom onto the electron-rich substrates is a better choice for practical catalysis application. Accordingly, a graphene nanosheet (coronene) was chosen as a representative substrate for ZrO and Pd to assess their catalytic performances in CO oxidation. Acting as an “electron sponge”, this carbon substrate can both donate and accept charges in different reaction steps, enabling the supported ZrO to achieve enhanced catalytic performance in this process with a low energy barrier of 19.63 kcal/mol. This paper presents a new realization on the catalytic performance of Pd-like superatom in CO oxidation, which could increase the interests in exploring noble metal-like superatoms as efficient catalysts for various reactions.     

Theoretical study of the stability and electronic structure of Al(BH4)n=1→4 and Al(BF4)n=1→4 and their hyperhalogen behavior

Using density functional theory (DFT), we have systematically calculated the equilibrium geometries, electronic structure, and electron detachment energies of Al(BH(4))(n=1→4) and Al(BF(4))(n=1→4) at the B3LYP/6-311+G(2d,p) level of theory. The electron affinities of Al(BH(4))(n) not only exhibit odd-even alternation, just as seen in (BH(4))(n), but also, for n = 3 and 4, show a remarkable behavior: whereas the electron affinities of BH(3) and BH(4) are, respectively, 0.06 and 3.17 eV, those of Al(BH(4))(3) and Al(BH(4))(4) are 0.71 and 5.56 eV. Results where H is replaced by F are also very different. The electron affinities of BF(3) and BF(4) are, respectively, -0.44 and +6.86 eV, and those of Al(BF(4))(3) and Al(BF(4))(4) are 1.82 and 8.86 eV. The results demonstrate not only marked difference when H is replaced by F but also substantially enhanced electron affinities by almost 2 eV when BH(4) and BF(4) units are allowed decorate a metal atom, confirming the recently observed hyperhalogen behavior of superhalogen building blocks.     

IR Spectroscopic Study of Chemical Transformations upon Irradiation of the Poly(vinyl chloride)–Triallyl Cyanurate System

Chemical transformations resulting from irradiation of the poly(vinyl chloride) (PVC)–triallyl cyanurate (TAC) system were studied by IR spectroscopy. It was shown that crosslinking was accompanied by scission of the network structure formed in the initial dose range, and the scission process occurred even at small irradiation doses. The scission is assumed to be localized at the interface boundary between PVC and poly(iso-TAC) or poly(TAC).     

Spatial structure and electronic spectrum of TiSi n − clusters (n = 6–18)

Results from optimizing the spatial structure and calculated electronic spectra of anion clusters TiSi _n ^? (n = 6–18) are presented. Calculations are performed within the density functional theory. Spatial structures of clusters detected experimentally are established by comparing the calculated and experimental data. It is shown that prismatic and fullerene-like structures are the ones most energetically favorable for clusters TiSi _n ^? . It is concluded that these structures are basic when building clusters with close numbers of silicon atoms.     

Theoretical study on the structures and properties of (Br2AlN3) n (n = 1–4) clusters

To look for the single-source precursors, the structures and properties of (Br₂AlN₃) _n (n = 1–4) clusters are studied at the B3LYP/6-311+G* level. The optimized (Br₂AlN₃) _n (n = 2–4) clusters all possess cyclic structures containing Al-N_α-Al linkages. The relationships between the geometrical parameters and the oligomerization degree n are discussed. The gas-phase structures of the trimers prefer to exist in the boat-twisting conformation. As for the tetramer, the most stable isomers have the S ₄ symmetry structure. The IR spectra are obtained and assigned by the vibrational analysis. The thermodynamic properties are linearly related with the oligomerization degree n as well as with the temperature. Meanwhile, the thermodynamic analysis of the gas-phase reaction suggests that the oligomerization be exothermic and favorable under high temperature.     

Interactions between Ni n (n = 1–4) clusters and molecules of methane,water, and hydrogen peroxide

Quantum chemical computations and study of IR spectra of systems Ni₄ + CH₄, Ni₄ + H₂O, and Ni₄ +H₂O are performed. The results are discussed conjointly with analogous data for products of reactions with Ni _n (n=1–3). It is shown that formation of complexes with either hydrogen atoms or CH₃ and OH radicals in a bridged position is characteristic of these systems. It is essential that the ground state of the nickel frame formed in Ni₄ systems has the form of a flat rhombus, which is different from the main isomer form of Ni₄ having pyramidal structure.     

Theoretical Study of the Structural,Electronic, and Magnetic Properties of Zirconium-doped Aluminum Clusters:Al_nZr(n = 1～14)

The geometrical structures, stabilities, electronic and magnetic properties of Al_nZr(n = 1~14) clusters have been systematically investigated using density functional theory. It is found that for the optimized clusters the zirconium atom prefers to remain on the surface, and the growth patterns are organized as follows: Zr substituted Al_(n+1) clusters or Zr capped Aln clusters as well as Al added Al_(n-1)Zr clusters. All doped clusters exhibit relatively larger average binding energies and magnetic behaviors compared with pure Al_(n+1) counterpart. The calculated fragmentation energies and second-order difference of energies exhibit pronounced odd-even alternation behavior as a function of the cluster size when n = 3~13. In all Al_nZr clusters, there exits internal hybridization in both Al and Zr atoms and charge transfer from Al to Zr atom, which reflects the strong interactions between the two kinds of atoms. The magnetic property analysis shows that the 4d electrons of Zr atom are the main origin for cluster magnetism.     

A density functional theory investigation of CrSin (n=1–6) clusters

Clusters of the form CrSi_n (n=1–6) were investigated computationally using a density functional approach. In particular, geometry optimizations were carried out under the constraint of well-defined point group symmetries at the B3LYP level employing a pseudopotential method in conjunction with double zeta basis sets. In this article, the resulting total energies, Mulliken atomic net populations, overlap populations, fragmentation energies and geometries of CrSi_n (n=1–6) are presented and discussed, together with natural populations and natural electron configurations. In addition, we comment on the charge transfer within the clusters. From this analysis, the 3d orbital of the Cr atom in CrSi_n (n=1–6) cluster absorbs electrons. From this tendency, conclusions are drawn with respect to the electronic populations and the chemical bond between Si and Cr as well as Si and Si.     

Spectroscopic and Structural Study of the 1:2 Aluminium(III) Complex of Quercetin

Quercetin (3, 3’, 4’, 5, 7-pentahydroxyflavone) is one of the most common flavonols present in nature. The complexation of Al(III) by various flavonoids has been suggested to reduce the overload of aluminum in the diet, a metal which has been implicated…