Structure Of Cs Symmetry Research Articles

Formation of Delocalized Linear M-B-M Covalent Bonds: A Combined Experimental and Theoretical Study of BM2(CO)8+ (M = Co, Rh, Ir) Complexes.

Investigations of transition-metal boride clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The geometric structures and bonding features of heteronuclear boron-containing transition metal carbonyl cluster cations BM(CO)6+ and BM2(CO)8+ (M = Co, Rh, and Ir) are studied by a combination of the infrared photodissociation spectroscopy and density functional calculations at B3LYP/def2-TZVP level. The completely coordinated BM2(CO)8+ complexes are characterized as a sandwich structure composed of two staggered M(CO)4 fragments and a boron cation, featuring a D3d symmetry and 1Eg electronic ground state as well as metal-anchored carbonyls in an end-on manner. In conjunction with theoretical calculations, multifold metal-boron-metal bonding interactions in BM2(CO)8+ complexes involving the filled d orbitals of the metals and the empty p orbitals of the boron cation were unveiled, namely, one σ-type M-B-M bond and two π-type M-B-M bonds. Accordingly, the BM2(CO)8+ complexes can be described as a linear conjugated (OC)4M═B═M(CO)4 skeleton with a formal B-M bond index of 1.5. The three delocalized d-p-d covalent bonds render compensation for the electron deficiency of the cationic boron center and endow both metal centers with the favorable 18-electron structure, thus contributing much to the overall structural stability of the BM2(CO)8+ cations. As a comparison, the saturated BRh(CO)6+ and BIr(CO)6+ complexes are determined to be a doublet Cs-symmetry structure with an unbridged (OC)2B-M(CO)4 pattern, involving a two-center σ-type (OC)2B → M(CO)4+ dative single bond along with a weak covalent B-M half bond. This work offers important insight into the structure and bonding of late transition metal boride carbonyl cluster cations.

High-Level Multireference Investigations on the Electronic States in Single-Vacancy (SV) Graphene Defects Using a Pyrene-SV Model.

The nonplanar character of graphene with a single carbon vacancy (SV) defect is investigated utilizing a pyrene-SV model system by way of complete-active-space self-consistent field theory (CASSCF) and multireference configuration interaction singles and doubles (MR-CISD) calculations. Planar structures were optimized with both methods, showing the 3B1 state to be the ground state with three energetically close states within an energy range of 1 eV. These planar structures constitute saddle points. However, following the out-of-plane imaginary frequency yields more stable (by 0.22 to 0.53 eV) but nonplanar structures of Cs symmetry. Of these, the 1A' structure is the lowest in energy and is strongly deformed into an L shape. Following a further out-of-plane imaginary frequency in the nonplanar structures leads to the most stable but most deformed singlet structure of C1 symmetry. In this structure, a bond is formed between the carbon atom with the dangling bond and a carbon of the cyclopentadienyl ring. This bond stabilizes the structure by more than 3 eV compared to the planar 3B1 structure. Higher excited states were calculated at the MR-CISD level, showing a grouping of four states low in energy and higher states starting around 3 eV.

Establishing the structural motifs present in small ammonium and aminium bisulfate clusters of relevance to atmospheric new particle formation.

Atmospheric new particle formation is the process by which atmospheric trace gases, typically acids and bases, cluster and grow into potentially climatically relevant particles. Here, we evaluate the structures and structural motifs present in small cationic ammonium and aminium bisulfate clusters that have been studied both experimentally and computationally as seeds for new particles. For several previously studied clusters, multiple different minimum-energy structures have been predicted. Vibrational spectra of mass-selected clusters and quantum chemical calculations allow us to assign the minimum-energy structure for the smallest cationic cluster of two ammonium ions and one bisulfate ion to a CS-symmetry structure that is persistent under amine substitution. We derive phenomenological vibrational frequency scaling factors for key bisulfate vibrations to aid in the comparison of experimental and computed spectra of larger clusters. Finally, we identify a previously unassigned spectral marker for intermolecular bisulfate-bisulfate hydrogen bonds and show that it is present in a class of structures that are all lower in energy than any previously reported structure. Tracking this marker suggests that this motif is prominent in larger clusters as well as ∼180 nm ammonium bisulfate particles. Taken together, these results establish a set of structural motifs responsible for binding of gases at the surface of growing clusters that fully explain the spectrum of large particles and provide benchmarks for efforts to improve structure predictions, which are critical for the accurate theoretical treatment of this process.

MOLECULAR STRUCTURE AND VIBRATION SPECTRA OF PIVALIC ACID

The metal carboxylates such as metal pivalates (salts of the pivalic acid (CH3)3CCOOH) attract a great interest as most promising precursors for chemical vapor deposition (CVD) technology. The possibility to use these substances in the CVD technology is specified by their good thermal stability and high volatility. For modeling of chemical reactions with metal pivalates in the gas-phase and the data on molecular structure will be very useful, in particularly information about effect of central metal ion to geometry of pivalic ligands. In the frame of this task the structures of metal pivalate molecules and pivalic acid (H(piv)) in a gas phase should be finding. The aim of present work is theoretical investigation of the geometry and IR-spectrum of H(piv) using density functional theory (DFT) methods. All calculations were performed using the Gaussian 03 program. The optimization of geometry and quadratic force field calculations were carried out using DFT functionals B3LYP, PBE, PBE0 and BP86 with correlation-consistent triple-ζ valence cc-pVTZ basis sets for O, C, and H. Appropriate assignment of vibrational modes was carried out by the potential energy distribution (PED) analysis among internal coordinates using the SHRINK program. According to DFT computations, the H(piv) molecule has an equilibrium structure of Cs symmetry with Гvib=26A'+19A''. The theoretical and experimental IR-spectra are satisfactorily agreed. The comparison of the ten intensities of highest bands in spectra allowed determining linear correlation between peaks position in experimental and modeling IR-spectra. It should be note the complicated composition of vibrational modes.

Electron momentum spectroscopy of cyclopentane: A molecular dynamical investigation

The experimental results of electron momentum spectroscopy studies on the valence orbitals of cyclopentane have been reinterpreted on the basis of Molecular Dynamical simulations employing the classical MM3 force field. Analysis using the produced molecular structures demonstrates that the pseudorotation and the variations of the ring puckering amplitude due to thermally induced vibrational effects have significant influence on the electron momentum distributions for the six highest-energy orbitals 1e2″, 3e1′ and 3e2′. The conformational average of the structures of C2 symmetry and the structures of Cs symmetry is also an equitable model to interpret the valence electron momentum distributions.

Distinctive features of the structure of hemihexaphyrazine complexes with Y, La, and Lu according to quantum chemical data

The molecular structure of Y, La, and Lu complexes with hemihexaphyrazine (Нр), a six-link heteroazaporphyrinoid of АВАВАВ type, has been studied by DFT. It has been found that these MHp (M = Y, La, Lu) complexes have a non-planar structure of Cs symmetry with the metal atom dislocated from the center of the cavity to one of the thiadiazole rings. The average lengths of coordination bonds formed by the metal atom with six nitrogen atoms of the thiadiazole moieties are 2.389, 2.566, and 2.358 Å in YHp, LaHp, and LuHp, respectively. Different degrees of deviation from planar structure have been determined in La complex and Y and Lu complexes, characterized by the values of the NN...NN torsion angle between nonequivalent NN bonds in two thiadiazole rings (38.2, 56.0, and 58.6°, respectively). At the same time the internal circumferences of the macrocycle are the same in all three complexes. It has been shown that the planar structures of the complexes of the D3h symmetry are saddle points on the PES. The transition barriers between the structures of Cs and D3h symmetries have been computed (40.5, 4.6, and 52.4 kJ/mol for YHp, LaHp, and LuHp, respectively).An NBO analysis of the electron density distribution in MHp complexes has been carried out and the nature of coordination bonds in the complexes has been examined. We suppose the coordination bonds in the complexes as three-center ones involving atom M and two nitrogen atoms of Nt-Nt bond in the thiadiazole moieties, and the Hp ligand as a quasi tridentate one, despite the fact that the metal atom is bonded to six nitrogen atoms of the ligand.The value of the lanthanide contraction ΔrLn (0.208 Å) in the examined LnHp complexes with one ligand has been determined, which turned out to be close to ΔrLn values in the series of lanthanide halogenides with three monovalent ligands and in the series of lanthanide compounds with three bidentate ligands.

Dimethyl Sulfide-Dimethyl Ether and Ethylene Oxide-Ethylene Sulfide Complexes Investigated by Fourier Transform Microwave Spectroscopy and Ab Initio Calculation.

The ground-state rotational spectra of the dimethyl sulfide-dimethyl ether (DMS-DME) and the ethylene oxide-ethylene sulfide (EO-ES) complexes were observed by Fourier transform microwave spectroscopy, and a-type and c-type transitions were assigned for the normal, (34)S, and three (13)C species of the DMS-DME and a-type and b-type transitions for the normal, (34)S, and two (13)C species of the EO-ES complexes. The transition frequencies measured for both the complexes were analyzed by using an S-reduced asymmetric-top rotational Hamiltonian. The rotational parameters thus derived for the DMS-DME were found to be consistent with a structure of Cs symmetry with the DMS bound to the DME by two C-H(DMS)···O and one S···H-C(DME) hydrogen bonds. Some high-Ka lines were found to be split, and we have interpreted these splittings in terms of internal rotations of the two methyl groups of the DMS and of the "free", i.e., outer group, of the DME. Some forbidden transitions were also observed in cases where Ka = 3 levels were involved, for the DMS-DME complex in the internal-rotation E state. The barrier height, V3, to internal rotation of the CH3 in the DME thus derived is smaller than that of the DME monomer, while the V3 of the CH3 groups in the DMS is nearly the same as that of the DMS monomer. For the EO-ES complex, the observed data were interpreted in terms of an antiparallel structure of Cs symmetry with the EO bound to the ES by two C-H(ES)···O and two S···H-C(EO) hydrogen bonds. An attempt was also made to observe a-type transitions of the DMS dimer without success. We have applied a natural bond orbital analysis to the DMS-DME and EO-ES to calculate the stabilization energy CT (= ΔEσσ*), which was correlated closely with the binding energy as found for other related complexes.

Intermolecular interaction in the formaldehyde-dimethyl ether and formaldehyde-dimethyl sulfide complexes investigated by Fourier transform microwave spectroscopy and ab initio calculations.

The ground-state rotational spectra of the formaldehyde-dimethyl ether (H2CO-DME) and formaldehyde-dimethyl sulfide (H2CO-DMS) complexes have been studied by Fourier transform microwave spectroscopy. The a-type and c-type rotational transitions have been assigned for the normal and deutrated formaldehyde-containing species of both complexes. In the case of H2CO-DME, doublets were observed with the splitting 10-300 kHz, whereas no such splittings were observed for H2CO-DMS, D2CO-DME, and D2CO-DMS. The observed rotational spectra were found consistent with a structure of Cs symmetry with DME or DMS bound to H2CO by two types of hydrogen bonds: C-H(DME/DMS)---O(H2CO) and O(DME)/S(DMS)---H-C(H2CO). The R(cm) distances between the centers of mass of the component molecules in the H2CO-DME and H2CO-DMS complexes were determined to be 3.102 and 3.200 Å, respectively, which are shorter than those in most related complexes. The spectral and NBO analyses showed that H2CO-DMS has a stronger charge transfer interaction than H2CO-DME does and that the binding energy of H2CO-DMS is larger than that of H2CO-DME.

Molecular structure, infrared spectra, photochemistry, and thermal properties of 1-methylhydantoin.

The structural, vibrational, and photochemical study of 1-methylhydantoin (1-MH, C4H6N2O2) was undertaken by matrix isolation infrared spectroscopy (in argon matrix; 10 K), complemented by quantum chemical calculations performed at the DFT(B3LYP)/6-311++G(d,p) level of approximation. The theoretical calculations yielded the Cs symmetry structure, with planar heavy atom skeleton, as the minimum energy structure on the potential energy surface of the molecule. The electronic structure of this minimum energy structure of 1-MH was then studied in detail by means of the natural bond orbital (NBO) and atoms in molecules (AIM) approaches, allowing for the elucidation of specific characteristics of the molecule's σ and π electronic systems. The infrared spectrum of the matrix-isolated 1-MH was fully assigned, also with the help of the theoretically predicted spectrum of the compound, and its UV-induced unimolecular photochemistry (λ ≥ 230 nm) was investigated. The compound was found to fragment to CO, isocyanic acid, methylenimine, and N-methyl-methylenimine. Finally, a thermal behavior investigation on 1-MH samples was carried out using infrared spectroscopy (10 K until melting), differential scanning calorimetry and polarized light thermal microscopy. A new polymorph of 1-MH was identified. The IR spectra of the different observed phases were recorded and interpreted.

Molecular structure and conformation of 1,3,5-tris(trifluoromethyl)-benzene as studied by gas-phase electron diffraction and quantum chemical calculations

The molecular structure of 1,3,5-tris(trifluoromethyl)benzene (1,3,5-TTFB) was studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP method with 6-31G(d,p) basis set and MP2 method with cc-pVTZ basis set). The best fit of the experimental scattering intensities (RG=4.0%) was obtained for the structure of CS symmetry. The differences between some geometric parameters were constrained at the values calculated at the MP2/cc-pVTZ level. The principal structural parameters rh1(∠h1) determined by GED are (bond lengths in Angstroms and bond angles in degrees with 3σ in parentheses): r(CC)=1.392(4), r(CC)=1.512(4), r(CF)av=1.346(2), ∠CC(CF3)C=120.9(2), ∠CC(H)C=119.1(2), ∠(CCF)av=111.6(2). The structure of the carbon ring deviates from a regular hexagon due to the σ-electronegative effect of the CF3 groups. The geometric parameters of the trifluoromethyl groups deviate considerably from regular tetrahedron arrangement. The experimental structural parameters agree well with the results of B3LYP/6-31G(d,p) and MP2/cc-pVTZ calculations. The electron diffraction data are in agreement with nearly free rotation of the CF3 groups around CmethylCphenyl axis.

Quantum-Chemical Ab Initio Calculations on Ala-(C5H5Al) and Galabenzene (C5H5Ga)

1 Quantum-chemical ab initio and time-dependent density functional theory (TD-DFT) calculations employing various basis sets were used to elucidate the spatial as well as the electronic structure of C5H5Al () and C5H5Ga (2) (ala- and galabenzene). The lowest closed shell singlet states of both compounds were found to have a non-planar structure of C S symmetry with C-X-C bond angles of about 116° (MP2/6-311++G**) and 125° (CCSD/aug-cc-pVDZ). At approximately 103°, the corresponding angles of the lowest triplets are significantly smaller. The lowest triplet state of alabenzene is also non-planar (C S) at the MP2 level while optimization with the CCSD and the CASPT2 method resulted in planar structures with C 2v symmetry. The corresponding state of galabenzene has C 2v symmetry at all levels of optimization. The relative stability of the lowest closed shell singlet and the lowest triplet (ΔE(T 1-S 0)) state is small and its sign even strongly method-dependent. However, according to the highest levels of theory applied in this study the singlet states of both molecules are slightly lower in energy than the corresponding triplets with singlet/triplet gaps between about 0.5 and 5.8 kcal/mol in favour of the singlet states. Most of the applied methods give a slightly smaller splitting for ala- than for galabenzene. Independent of the applied method (TD-DFT/CAM-B3LYP/6-311++G(3df,3pd)//MP2/6- 311++G** or SAC-CI/6-31++G(3df,3pd)//MP2/6-311++G**), the general shape of the calculated UV/VIS spectral curves are quite similar for the lowest singlet states of ala- and galabenzene, and the same applies to the spectra of the normal modes. The calculated UV/VIS spectra of C5H5Al and C5H5Ga are featured by long wavelength bands of moderate intensity around 900 nm at the TD-DFT and between 1300 and 1500 nm at the SAC-CI level. According to both methods these bands are predominantly due to HOMO(π)→LUMO(σ*) transitions. The results of isodesmic bond separation reactions for the singlet states indicate some degree of stabilization due to delocalization in both of the title compounds. With our best values between 29 and 32 kcal/mol this stabilization appears to be only slightly less than the previously reported value for borabenzene (∼38 kcal/mol).

Theoretical Study of Mononuclear Nickel(I), Nickel(0), Copper(I), and Cobalt(I) Dioxygen Complexes: New Insight into Differences and Similarities in Geometry and Bonding Nature

Geometries, bonding nature, and electronic structures of (N^N)Ni(O2) (N^N = β-diketiminate), its cobalt(I) and copper(I) analogues, and (Ph3P)2Ni(O2) were investigated by density functional theory (DFT) and multistate restricted active space multiconfigurational second-order perturbation (MS-RASPT2) methods. Only (N^N)Ni(O2) takes a C(S) symmetry structure, because of the pseudo-Jahn-Teller effect, while all other complexes take a C(2V) structure. The symmetry lowering in (N^N)Ni(O2) is induced by the presence of the singly occupied δ(d(xy)-π(x)*) orbital. In all of these complexes, significant superoxo (O2-) character is found from the occupation numbers of natural orbitals and the O-O π* bond order, which is independent of the number of d electrons and the oxidation state of metal center. However, this is not a typical superoxo species, because the spin density is not found on the O2 moiety, even in open-shell complexes, (N^N)Ni(O2) and (N^N)Co(O2). The M-O and O-O distances are considerably different from each other, despite the similar superoxo character. The M-O distance and the interaction energy between the metal and O2 moieties are determined by the d(yz) orbital energy of the metal moiety taking the valence state. The binding energy of the O2 moiety is understood in terms of the d(yz) orbital energy in the valence state and the promotion energy of the metal moiety from the ground state to the valence state. Because of the participations of various charge transfer (CT) interactions between the metal and O2 moieties, neither the d(yz) orbital energy nor the electron population of the O2 moiety are clearly related to the O-O bond length. Here, the π bond order of the O2 moiety is proposed as a good measure for discussing the O-O bond length. Because the d electron configuration is different among these complexes, the CT interactions are different, leading to the differences in the π bond order and, hence, the O-O distance among these complexes. The reactivity of dioxygen complex is discussed with the d(yz) orbital energy.

Formula omitted] complexes (Ng = He–Xe): An ab initio and DFT theoretical investigation

The HNgOH2+ cations (Ng=He–Xe), formally arising from the insertion of a Ng atom into the O–H bond of H3O+, were characterized by MP2, CCSD(T), B3LYP, and BP86 calculations as ion–dipole complexes, best described by the resonance form (HNg+)(OH2). While the MP2, CCSD(T), and B3LYP methods predict planar structures of C2v symmetry, the BP86 predicts non-planar structures of Cs symmetry. The structural differences are however only minor, and do not affect the bonding situation, as described by the atomic charges, and the AIM bond topologies. The energy decomposition analysis performed by the ETS method at the BP86 level of theory revealed that the interaction between NgH+ and H2O is prevailingly electrostatic for Ng=Ne, Ar, Kr, and Xe, while the electrostatic and the orbital contributions become comparable for Ng=He. The NOCV analysis unraveled also that, for any Ng, the dominant orbital contribution is the donor–acceptor interaction between the σ(O–H) orbital of H2O (3 A1) and the empty σ orbital of NgH+. All the (HNg+)(OH2) are however largely unstable with respect to dissociation into H3O+ and Ng, and only the heaviest (HAr+)(OH2), (HKr+)(OH2), and (HXe+)(OH2) are predicted to be metastable, and conceivably observable at low temperature. The structure and stability of the Ng-H3O+ intermediates involved in the decomposition of the (HNg+)(OH2) were also briefly examined.

Aromaticity of Benzenoid-Borazinoid Hybrids: Current Maps for Hetero-Graphenes

Two isomeric coronene-borazine hybrids C18B3N3H12, in which a central or outer C6-cycle is formally replaced by an alternating B3N3 cycle, are assessed for aromaticity on the ring-current criterion. Calculations for the B3LYP/6-31G** optimized structures (of D3h and Cs symmetry, respectively) at the coupled-Hartree-Fock ipsocentric level for treatment of magnetic response properties show distinct patterns of π-current: central substitution isolates a strongly diatropic C18 perimeter, whereas outer substitution leaves a phenanthrene-like circulation in the carbon-only region of the molecule. Circulations within the B3N3 moiety are limited to localized “lone-pair” circulations on the nitrogen centres. In the limit of the replacement strategy, where all C6 cycles are replaced, as in hexaborazino-coronene (B12N12H12, D3h), all π-currents become localized on nitrogen centers.

Reduced bandwidth chirped-pulse microwave spectroscopy for analysis of weakly bound dimers: Rotational spectrum and structural analysis of CH2ClF⋯FHC[dbnd]CH2

A reduced bandwidth (480MHz) chirped-pulse Fourier-transform microwave spectrometer has been used to record the rotational spectrum of the weakly bound complex between chlorofluoromethane and fluoroethylene (CH2ClF⋯FHCCH2). Spectra of both the 35Cl and 37Cl isotopologues were assigned from a 7 to 18GHz broadband scan. Derived rotational constants (35Cl: A=5602.82(28)MHz, B=918.5894(4)MHz, C=795.1888(4)MHz; 37Cl: A=5453.14(9)MHz, B=913.6372(5)MHz, C=788.4024(4)MHz) are consistent with a Cs symmetry structure in which the CH2ClF is angled toward the fluorine and hydrogen atoms at the end of the fluoroethylene subunit. The CH2ClF hydrogen atoms straddle the fluorine atom on fluoroethylene, while the chlorine atom from CH2ClF points towards the geminal hydrogen atom on fluoroethylene. Dipole moment components of μa=2.342(6)D, μb=0.022(7)D and μtot=2.342(7)D were also determined.

Computational study of the equilibrium geometry and anharmonic vibrational spectra of PbX2 ··· NO and PbX2 ··· ON (X = F, Cl, Br, I) complexes

Equilibrium geometry parameters of the open shell PbX2 ··· NO and PbX2 ··· ON (X = F, Cl, Br, I) complexes have been computed by second-order Z-averaged perturbation theory (ZAPT2) with Stevens–Basch–Krauss–Jasien–Cundari (SBKJC) scalar-relativistic effective core potentials (RECP) and basis sets on all atoms. Equilibrium geometries of both PbX2 ··· NO and PbX2 ··· ON bonding isomers conform to Cs symmetry structure with end-on ligand coordination, and are characterized by Pb-N bond length within 266.6–271.7 pm range, Pb–O distance of 267.8–275.8 pm, Pb–N–O angle within 109.2–120.7° range, and Pb–O–N angle of 117.1–127.8°. Anharmonic vibrational spectra of the PbX2 ··· NO and PbX2 ··· ON complexes have been calculated by direct correlation-corrected vibrational self-consistent field (CC-VSCF) method enhanced with second-order perturbative correction using potential energy surfaces (PESs) determined at ZAPT2/SBKJC+(d) level in curvilinear (internal) coordinates. Fundamental ν(Pb–N) stretching mode has been computed at 232.8 to 209.0 cm−1 within PbX2 ··· NO series. whereas ν(Pb–O) stretching mode fundamental evaluation in PbX2 ··· ON series afforded wavenumbers within 183.2–150.7 cm−1 range. Blue shift of the ν(N=O) stretching mode wavenumber upon PbX2 ··· NO complex formation, computed in anharmonic approximation, 15.8–14.6 cm−1, correctly reproduces the effect observed in the low-temperature Ar matrix spectra of PbX2 ··· NO compounds. Influence of complex formation on the νs(Pb–X) and νas(Pb–X) fundamentals of PbX2 halides has also been discussed. Two-dimensional mapping of the (Qi , Qj ) mode-mode coupling potential has been used to rationalize the origin of mode coupling related anharmonic corrections.

Endohedrally Doped Golden Fullerenes [X@Au32] (X = Li+, Na+, K+, Rb+, Cs+)

The structure, stability, energy partition analysis, and charge redistribution of endohedral complexes formed between Au32 cluster with alkali metal cations, such as Li+, Na+, K+, Rb+, and Cs+, have been investigated using the density functional theory method. All alkali metal cations can be stably encapsulated in both the Ih and the Cs symmetry structural forms [Ih-(X@Au32)+ and Cs-(X@Au32)+]. Smaller cations are found to be more stable in the Cs symmetry structure. A higher charge-transfer characteristic is noted when the Au32 cage is encapsulated with smaller-sized alkali ions than larger-sized ions in both the structures. Vibrational frequency calculation data show imaginary frequency values for Li+ and Na+ ions in the Ih-(X@Au32) system, which indicates the free movements of these ions in the cage, whereas all dopant ions show positive IR frequency values for Cs-(X@Au32), suggesting the existence of weak bonding between dopants and the cage. The analysis of structural, energetic, and charge-transfer ...

A parallel study of Ni@Si12 and Cu@Si12 nanoclusters

The Ni@Si12 and Cu@Si12 clusters are studied in parallel within the framework of the density functional theory using the hybrid functional of Becke-Lee, Parr and Yang (B3LYP), emphasizing the differences and similarities in structural and electronic properties. The dominant structures for both clusters are a distorted hexagonal structure of Cs symmetry and a distorted octahedral structure of D2d. For Ni@Si12 the two structures are practically isonergetic whereas for Cu@Si12 the energy difference of the D2d structure from the lowest Cs structure of hexagonal origin is about 0.7 eV, at the B3LYP/TZVP level of theory. Contrary to Cu@Si12 for which the well known Frank–Kasper (FK) structure of C5v symmetry is a real local minimum of the energy hyper-surface (although higher by more than 1.6 eV from the global minimum), for Ni@Si12 the FK structure is dynamically unstable. The HOMO-LUMO gaps, the binding energies per atom and the embedding energies for Cu@Si12 clusters are smaller by 0.5, 0.1 and 1.1 eV, respectively compared to the Ni@Si12 clusters. This is attributed to different type of bonding in the two clusters.

A Photoelectron Spectroscopic and Computational Study of Sodium Auride Clusters, NanAun‐ (n = 1—3).

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A Photoelectron Spectroscopic and Computational Study of Sodium Auride Clusters, NanAun- (n = 1−3)

Negatively charged sodium auride clusters, NanAun- (n = 1-3), have been investigated experimentally using photoelectron spectroscopy and ab initio calculations. Well-resolved electronic transitions were observed in the photoelectron spectra of NanAun- (n = 1-3) at several photon energies. Very large band gaps were observed in the photoelectron spectra of the anion clusters, indicating that the corresponding neutral clusters are stable closed-shell species. Calculations show that the global minimum of Na2Au2- is a quasi-linear species with Cs symmetry. A planar isomer of D2h symmetry is found to be 0.137 eV higher in energy. The two lowest energy isomers of Na3Au3- consist of three-dimensional structures of Cs symmetry. The global minimum of Na3Au3- has a bent-flake structure lying 0.077 eV below a more compact structure. The global minima of the sodium auride clusters are confirmed by the good agreement between the calculated electron detachment energies of the anions and the measured photoelectron spectra. The global minima of neutral Na2Au2 and Na3Au3 are found to possess higher symmetries with a planar four-membered ring (D2h) and a six-membered ring (D3h) structure, respectively. The chemical bonding in the sodium auride clusters is found to be highly ionic with Au acting as the electron acceptor.