Growth behavior and properties of (HF)1–16 clusters

Structural Chemistry - HF cluster is a typical hydrogen bond system. (HF)1–16 clusters have been studied by MP2/aug-cc-pvdz//B3LYP/6-311++G(d,p) method. The global minimum structures of them...     

Laser ionization spectra and electronic structure of Kn and NaKn−1 clusters

Photoionization of small K_n and NaK_n−1 clusters with n ⩽ 34 has been achieved in a crossed laser-molecular-beam experiment. The relative ion peak intensities in mass spectra reveal fragmentation effects which are wavelength-dependent. The vertical ionization profiles in the threshold region give some insight into the electronic structure.     

π plasmon modes inC 60 clusters

We study collective excitations of electrons in the fullerene molecule, by using the sum rule approach and linear response theory. The results for the excitation spectrum are discussed in relation to experimental data and to other theoretical approaches.Unité de Recherche des Universités Paris XI et Paris VII associée au CNRS     

Do all-metal antiaromatic clusters exist?

As shown by detailed nucleus-independent chemical shift (NICS) analyses of the contributions of each molecular orbital, the very recently reported gas-phase all-metal Al4Li3- anion and its relatives (Kuznetsov, A.E.; Birch, K.A.; Boldyrev, A.I.; Li, X.; Zhai, A.I.; Wang, L.S. Science 2003, 300, 622) are aromatic rather than antiaromatic. The paratropic (antiaromatic) four-pi-electron contribution is overcome by the predominating diatropic effects of sigma aromaticity. However, true antiaromatic all-metal clusters, such as Sn62- (Schiemenz, B.; Huttner, G. Angew. Chem., Int. Ed. Engl. 1993, 32, 297), do exist.     

Au-doped carbon clusters AuC n with n = 1–11: a theoretical investigation

The hybrid HF/DFT method B3LYP has been employed to investigate the geometrical and electronic structures of AuC _n (n = 1–11) clusters. The properties such as geometrical parameters and electronic energies are determined for open-chain and cyclic species. Our results indicate that the open-chain structures with low spin states (doublet) are more stable than the cyclic ones for the small sizes clusters (n ≤ 9), as the cluster sizes increase (n = 10, 11), the cyclic species are more stable. The incremental binding energies show a smooth even–odd alternation phenomenon for open-chain species, n-even (n is the numbers of C atom in the clusters) species have the stronger stabilities relative to the adjacent odd-numbered ones. In addition, the most favorable dissociation channels are determined by calculating the fragmentation energies accompanying various possible pathways. The studied clusters incline to be dissociated to Au + C _n and AuC _n?3 + C₃ fragments.     

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.     

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.     

High resolution electron attachment to CO₂ clusters

Electron attachment to CO? clusters performed at high energy resolution (0.1 eV) is studied for the first time in the extended electron energy range from threshold (0 eV) to about 10 eV. Dissociative electron attachment (DEA) to single molecules yields O(-) as the only fragment ion arising from the well known (2)Π(u) shape resonance (ion yield centered at 4.4 eV) and a core excited resonance (at 8.2 eV). On proceeding to CO? clusters, non-dissociated complexes of the form (CO?)(n)(-) including the monomer CO?(-) are generated as well as solvated fragment ions of the form (CO?)(n)O(-). The non-decomposed complexes appear already within a resonant feature near threshold (0 eV) and also within a broad contribution between 1 and 4 eV which is composed of two resonances observed for example for (CO?)(4)(-) at 2.2 eV and 3.1 eV (peak maxima). While the complexes observed around 3.1 eV are generated via the (2)Π(u) resonance as precursor with subsequent intracluster relaxation, the contribution around 2.2 eV can be associated with a resonant scattering feature, recently discovered in single CO? in the selective excitation of the higher energy member of the well known Fermi dyad [M. Allan, Phys. Rev. Lett., 2001, 87, 0332012]. Formation of (CO?)(n)(-) in the threshold region involves vibrational Feshbach resonances (VFRs) as previously discovered via an ultrahigh resolution (1 meV) laser photoelectron attachment method [E. Leber, S. Barsotti, I. I. Fabrikant, J. M. Weber, M.-W. Ruf and H. Hotop, Eur. Phys. J. D, 2000, 12, 125]. The complexes (CO?)(n)O(-) clearly arise from DEA at an individual molecule within the cluster involving both the (2)Π(u) and the core excited resonance.     

Ortho-metallation of η-pyrrolylmetal complexes with triosmium clusters

The cluster [O₃(CO)₁₀(MeCN)₂] reacts with (η-cyclopentadienyl)(η-pyrrolyl)iron [azaferrocene, Fe(C₅H₅)(C₄H₄N) under mild conditions to give the oxidative addition product [Os₃H{(C₄H₃N)Fe(C₅H₅)}(CO)₁₀]. The group (C₄H₃N)Fe(C₅H₅) acts as a three-electron donor through the ortho-metallated pyrrolyl ring. An analogous compounds, [Os₃H{(C₄H₃N)Mn(CO)₃}(CO)₁₀], is obtained by the reaction of [Os₃(CO)₁₀(MeCN)₂] with [Mn(η-pyrrolyl)(CO)₃].     

Lanthanide contraction in linear lanthanide–oxygen clusters

Five coordination polymers containing linear lanthanide–oxygen clusters 1–5 have been synthesized by a hydrothermal reaction of 3-(quinolin-8-yloxy) phthalic acid (H₂L) with the respective lanthanide salt. The X-ray single crystal structural analyses revealed that these five crystalline materials belong to two isostructures with formulas [LnHL₂(H₂O)₂]_n (Ln1, where Ln = La 1, Ce 2, Pr 3) and [Ln(HL)(L)(H₂O)]_n (Ln2, where Ln = Nd 4, Sm 5), respectively, which are attributed to the effect of lanthanide contraction. In both structures, the lanthanide cations were bridged by two carboxyl groups of L^2? through Ln–O bonds to form 1-D linear lanthanide–oxygen clusters, which were further connected by intermolecular π–π stacking interactions between quinolinyl units to generate 3-D supramolecular polymers with moderate luminescence and high thermal stability.     

Structure and stability of AuXe n Z (n = 1–3, Z = −1, 0, +1) clusters

We have explored the structures and stabilities of AuXe _n ^Z (n = 1–3, Z = ?1, 0, +1) cluster series at CCSD(T) theoretical level. The electron affinities and ionization potentials are correlated to the HOMO–LUMO gaps. The role of the interaction was investigated using the natural bond orbital analysis.     

A computational study on CunN0,±1 (n=1–4) clusters by density functional methods

Clusters of the type Cu_nN^0,±1 (n=1–4) are investigated computationally using density functional theory methods. Equilibrium geometries are optimized under the constraint of well-defined point-group symmetries at the B3LYP level employing a pseudo-potential method in conjunction with double-zeta basis sets. In this article, different molecular properties such as total energies, electron affinities, ionization potentials, fragmentation energies and equilibrium geometries of the Cu_nN^0,±1 (n=1–4) clusters are systematically calculated and discussed. In particular, the photoelectron spectra of the anionic Cu_nN⁻¹ (n=2–4) clusters are calculated showing a good agreement with the available experimental results. In addition, Mulliken and natural orbital population analyses, and natural orbital configurations are calculated in order to elucidate the charge distributions in the clusters.     

Bonding in [CuNRR′]_4 type clusters

In the past three decades, more than one hundred polynuclear Cu(I) complexes, organometallics and clusters have been synthesized[1]. In many of these compounds there are relatively short Cu-Cu distances of 0.238—0.32 nm (Cu-Cu in metal 0.240 nm). Since Cu(I) has a closed d10 electronic sub-shell, the nature of d10-d10 interactions has also been studied theoretically[2], but the problem whether there is direct or no direct covalent Cu-Cu bonding is still not clear. The same situation also …     

Intramolecular penning ionization in benzonitrile—rare gas clusters

A supersonic beam of benzonitrile (Bn) seeded into He, Ar or Kr was ionized by VUV photons from the electron storage ring BESSY at Berlin. Photoionization efficiency curves were measured for Bn, Bn₂, Bn-Ar and Bn-Kr. Resonance peaks in the PIE curves show that excitation energy of the rare gas atom is transferred to the Bn molecule within the heterogeneous cluster, leading to ionization of the molecule and fragmentation of the cluster.     

Molecular orbital calculations on platinum—gold heterometallic clusters

The bonding in some platinum—gold cluster compounds has been analysed using semi-empirical molecular orbital calculations. In (PtAu₂(PR₃)₄Cl]⁺ (I) and [Pt₂Au₂(PR₃)₄(CNR′)₄]²⁺ (II) the platinum—gold bonding involves three-centre two-electron bonds between the bonding orbital of the Au₂(PR₃)₂ dimer and the frontier orbitals of the T-shaped platinum fragments. The observed distortions in II have been satisfactorily rationalised. In [Pt₃Au(μ-CO)₃(PR₃)₄]⁺ (III) and [Pt₃Au(μ-SO₂)₂Cl(PR₃)₄] (IV) the AuPR₃⁺ fragments cap the Pt₃ triangles by utilising the acceptor orbital of a₁ symmetry localised on gold. The observed differences in bond lengths for these 54 and 56 electron clusters have been accounted for on the basis of the reduced overlap populations.     

Adsorption — desorption kinetics on epitaxially oriented palladium clusters

Palladium clusters with a low size dispersion and a single crystallographic shape have been obtained by epitaxial growth on (100) MgO. The isothermal adsorption — desorption kinetics of CO is obtained by a molecular beam method allowing the direct determination of the global adsorption probability and of the mean life time of CO molecules on the clusters. Three main results are deduced from these measurements: — an increase of the adsorption rate of CO on the clusters by the capture of CO molecules physisorbed on the substrate, — a faster desorption rate from (100) than from (111) facets at high coverage, — an increase of the adsorption energy for clusters smaller than 3 nm.     

Density functional study of small bimetallic Ag–Pd clusters

The geometric and electronic properties of small Ag_mPd_n clusters with m + n = 2–5 are studied within the framework of density functional theory in conjunction with two hybrid and one GGA exchange–correlation functional. For every composition, the global minimum is identified by using geometry optimization for a collection of initial structures. Results indicate that, for bimetallic tetramers and pentamers, the clusters shift from two-dimensional to three-dimensional structures with the addition of a second Pd atom. Ag₂Pd₂ is identified as the most stable tetramer by the calculation of the excess energy and second energy difference of bimetallic clusters. Concerning the fragmentation channels it is seen that the most favourable route in the majority of cases is via the evaporation of a single atom. Density of states calculations reveal that the increase of Pd content depletes the isolated s states close to the Fermi level, while at the same time shifts the d states to higher energies.