Atoms Cap Research Articles

Evolution of Vibrational Spectra in the Manganese-Silicon Clusters Mn2Sin, n = 10, 12, and 13, and Cationic [Mn2Si13

A comparison of DFT-computed and measured infrared spectra reveals the ground state structures of a series of gas-phase silicon clusters containing a common Mn2 unit. Mn2Si12 and [Mn2Si13]+ are both axially symmetric, allowing for a clean separation of the vibrational modes into parallel (a1) and perpendicular (e1) components. Information about the Mn–Mn and Mn–Si bonding can be extracted by tracing the evolution of these modes as the cluster increases in size. In [Mn2Si13]+, where the antiprismatic core is capped on both hexagonal faces, a relatively simple spectrum emerges that reflects a pseudo-D6d geometry. In cases where the cluster is more polar, either because there is no capping atom in the lower face (Mn2Si12) or the capping atom is present but displaced off the principal axis (Mn2Si13), the spectra include additional features derived from vibrational modes that are forbidden in the parent antiprism.

Projector-Free Capped-Fragment Scheme within Density Functional Embedding Theory for Covalent and Ionic Compounds.

Quantum-mechanics-(QM)-based simulations now routinely aid in understanding and even discovering new chemistries involving molecules and materials exhibiting desired functionalities. Ab initio correlated wavefunction (CW) theories systematically improve QM methods, with many exhibiting high accuracy. However, execution of CW methods requires expensive computations that typically scale poorly with system size. Divide-and-conquer approaches partition large systems into smaller fragments; a lower level of theory treats fragment interactions while a preferred higher level of theory describes the important fragment. These methods offer ways to incorporate CWs into chemical simulations of large systems, e.g., biomolecules, surfaces, large inorganic clusters, bulk crystals, etc. Here we propose a partitioning protocol that utilizes capping atoms to saturate severed covalent bonds at fragment interfaces and density functional embedding theory (DFET) to describe fragment interactions. The capping groups in each fragment provide an ad-hoc potential that approximates the effects of the environment. An embedding potential optimized via DFET then serves as an augmentation of the capping group to simulate the effects of the environment. We concurrently use an auxiliary fragment (a separate system comprised of only the combined capping groups) to account for, and thereby correct, the electron density contributions of all the capping groups added to all of the fragments. This method depends only on the capped-subsystem and auxiliary-fragment electron densities, forgoing, as with the original DFET developed for metallic systems, orbital-based projector approaches that determine a nonlocal action of the embedding potential onto the fragment electrons. By using an auxiliary fragment, the method maintains a purely electron-density-dependent embedding potential, substantially lessening the cost and leading to simpler implementation. Here, we demonstrate the utility of our capped-DFET and ensuing capped embedded CW method in two contrasting systems, namely, an organic molecule and an ionic metal oxide cluster.

Syntheses, characterization and properties of two new dodeca-niobates presenting unprecedented features.

Two new dodeca-niobate materials, K3[Nb2O2][H7SiNb12O40]·16H2O (1) and [Cu(en)2]9[(VNb12V1.69Nb0.31O42en0.31)2]·20.69H2O (2) (en = ethylenediamine), have been obtained under hydrothermal conditions and characterized by IR, UV-Vis, XRD, and single crystal X-ray diffraction analysis. Single crystal X-ray analysis reveals that compound 1 presents a reasonable bridging layer structure model and that K plays a great role in the three-dimensional structure. Compound 2 is the first capped Keggin POM with organic ligand chelating the capping atom. The photocatalytic hydrogen evolution and styrene epoxidation catalytic properties of the two compounds were also assessed. Additionally, compound 1 is also a good photocatalyst to degrade RhB.

12-Vertex Zwitterionic Bis-phosphonium-nido-carborates through Ring-Opening Reactions of 1,2-Diphosphetanes.

Carborane-substituted 1,2-diphosphetanes (Ia,b) react with elemental lithium in THF with cleavage of the P-P bond to give a deep red solution from which, in the case of Ia, red crystals of a lithiated intermediate, [{1-Li(THF)PtBu-6-PtBu-4,1,6-closo-Li(THF)C2 B10 H10 }{Li(THF)3 }]2 ⋅2 THF (2 a), are obtained. The compound is dimeric, C2 -symmetric and contains six lithium and four phosphorus atoms. Two lithium atoms cap the six-membered C2 B4 faces, resulting in two 13-vertex closo-clusters (according to Wade's rules) with docosahedral geometry. The addition of methyl iodide resulted in the formation of zwitterionic bis-phosphonium-nido-carborates 7,10-bis(tert-butyldimethylphosphonium)dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1 a) and 7,10-bis(N,N-diisopropylaminodimethylphosphonium)dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1 b) in moderate to good yields. Compounds 1 a and 1 b exhibit short Ccluster -P bonds and large Ccluster ⋅⋅⋅Ccluster distances in the solid state. Further insight into the ring opening and reduction potential of the alkyl halide was obtained from methylation reactions of different 1,2-bis-phosphinocarboranes. The reaction of rac-/meso-1,2-bis(tert-butylmethylphosphino)-1,2-dicarba-closo-dodecaborane(12) (3 a) with two equivalents of methyl iodide also resulted in the formation of 1 a (as shown by NMR spectroscopy), whereas the reaction of 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane(12) with methyl triflate afforded the phosphonium salt 1-methyl-diphenylphosphonium-2-diphenylphosphino-1,2-dicarba-closo-dodecaborane(12) triflate (4) without reduction of the cluster.

Probing cluster surface morphology by cryo spectroscopy of N2 on cationic nickel clusters.

We present the cryogenic (26 K) IR spectra of selected [Nin(N2)m]+ (n = 5-20, m = 1 - mmax), which strongly reveal n- and m-dependent features in the N2 stretching region, in conjunction with density functional theory modeling of some of these findings. The observed spectral features allow us to refine the kinetic classification [cf. J. Mohrbach, S. Dillinger, and G. Niedner-Schatteburg, J. Chem. Phys. 147, 184304 (2017)] and to define four classes of structure related surface adsorption behavior: Class (1) of Ni6+, Ni13+, and Ni19+ are highly symmetrical clusters with all smooth surfaces of equally coordinated Ni atoms that entertain stepwise N2 adsorption up to stoichiometric N2:Nisurface saturation. Class (2) of Ni12+ and Ni18+ are highly symmetrical clusters minus one. Their relaxed smooth surfaces reorganize by enhanced N2 uptake toward some low coordinated Ni surface atoms with double N2 occupation. Class (3) of Ni5+ and Ni7+ through Ni11+ are small clusters of rough surfaces with low coordinated Ni surface atoms, and some reveal semi-internal Ni atoms of high next-neighbor coordination. Surface reorganization upon N2 uptake turns rough into rough surface by Ni atom migration and turns octahedral based structures into pentagonal bipyramidal structures. Class (4) of Ni14+ through Ni17+ and Ni20+ are large clusters with rough and smooth surface areas. They possess smooth icosahedral surfaces with some proximate capping atom(s) on one hemisphere of the icosahedron with the other one largely unaffected.

Eight‐Electron Silver and Mixed Gold/Silver Nanoclusters Stabilized by Selenium Donor Ligands

AbstractThe first atomically and structurally precise silver‐nanoclusters stabilized by Se‐donor ligands, [Ag20{Se2P(OiPr)2}12] (3) and [Ag21{Se2P(OEt)2}12]+(4), were isolated by ligand replacement reaction of [Ag20{S2P(OiPr)2}12] (1) and [Ag21{S2P(OiPr)2}12]+ (2), respectively. Furthermore, doping reactions of 4 with Au(PPh3)Cl resulted in the formation of [AuAg20{Se2P(OEt)2}12]+ (5). Structures of 3, 4, and 5 were determined by single‐crystal X‐ray diffraction. The anatomy of cluster 3 with an Ag20 core having C3 symmetry is very similar to that of its dithiophosphate analogue 1. Clusters 4 and 5 exhibit an Ag21 and Au@Ag20 core of Oh symmetry composed of eight silver capping atoms in a cubic arrangement and encapsulating an Ag13 and Au@Ag12 centered icosahedron, respectively. Both ligand exchange and heteroatom doping result in significant changes in optical and emissive properties for chalcogen‐passivated silver nanoparticles, which have been theoretically confirmed as 8‐electron superatoms.

Eight-Electron Silver and Mixed Gold/Silver Nanoclusters Stabilized by Selenium Donor Ligands.

The first atomically and structurally precise silver-nanoclusters stabilized by Se-donor ligands, [Ag20 {Se2 P(Oi Pr)2 }12 ] (3) and [Ag21 {Se2 P(OEt)2 }12 ]+ (4), were isolated by ligand replacement reaction of [Ag20 {S2 P(Oi Pr)2 }12 ] (1) and [Ag21 {S2 P(Oi Pr)2 }12 ]+ (2), respectively. Furthermore, doping reactions of 4 with Au(PPh3 )Cl resulted in the formation of [AuAg20 {Se2 P(OEt)2 }12 ]+ (5). Structures of 3, 4, and 5 were determined by single-crystal X-ray diffraction. The anatomy of cluster 3 with an Ag20 core having C3 symmetry is very similar to that of its dithiophosphate analogue 1. Clusters 4 and 5 exhibit an Ag21 and Au@Ag20 core of Oh symmetry composed of eight silver capping atoms in a cubic arrangement and encapsulating an Ag13 and Au@Ag12 centered icosahedron, respectively. Both ligand exchange and heteroatom doping result in significant changes in optical and emissive properties for chalcogen-passivated silver nanoparticles, which have been theoretically confirmed as 8-electron superatoms.

Synthesis, X-ray structure and reactivity of the vinyl-terminated iron(II) clathrochelate precursors and their cage derivatives with non-equivalent capping groups

A novel vinyl-terminated boron, antimony-capped iron(II) tris-dimethylglyoximate with labile triethylantimony cross-linking group was prepared using two-step synthetic procedure including template condensation of dimethylglyoxime and triethylantimony(V) dibromide on an iron(II) ion as a matrix followed by transmetallation with 4-vinylphenyl boronic acid. This labile clathrochelate precursor and its bis-methoxyboron-capped analog underwent the same capping group exchange (transmetallation) reactions with more strong Lewis acids, such as trigonal boron compounds or hafnium(IV) phthalocyaninate (HfPc), giving the macrobicyclic iron(II) tris-dimethylglyoximates with non-equivalent capping groups and a binuclear HfPc-capped phthalocyaninoclathrochelate, respectively. The complexes obtained were characterized using elemental analysis, 1H and 13C{1H} NMR, MALDI-TOF MS, IR and UV–vis data as well as by single crystal X-ray diffraction. The number, positions and multiplicity of the signals in the solution 1H and 13C{1H} NMR spectra of these clathrochelates as well as the ratios of their integral intensities in 1H NMR spectra confirmed the composition and symmetry of the macrobicyclic molecules, suggesting the presence of their molecular C3 symmetry pseudoaxis. In the 1H NMR spectrum of a hybrid phthalocyanine-capped cage complex, the π-electron current in its apical macroheterocyclic fragment caused the substantial high-field shifts of the signals of protons of the ribbed methyl substituents because their nuclei are located in its shielding region. Single crystal X-ray diffraction data for the monovinyl-terminated mixed Sb, B- and Hf, B-capped iron(II) cage complexes suggest that their FeN6-coordination polyhedra possess the geometry of a rotationally distorted truncated trigonal pyramid that is close to intermediate between a trigonal prism and a trigonal antiprism with slightly expanded trigonal bases, which are connected with a heavy (Sb or Hf) atom. The encapsulated iron(II) ion is slightly shifted from the center of these polyhedra in the direction of such capping atom.

Towards a standardized setup for surface energy calculations

High-throughput design of new materials with desired electronic properties, based on screening of large collections of crystal structures organized in the from of libraries or databases require fast, widely applicable, consistent and unsupervised methods to calculate the property of interest. In this work we present an approach for the calculation of surface energies of two-dimensional periodic crystal lattices which meets all these requirements. For materials slabs which are terminated with two identical surfaces, the task of calculating the surface energy is trivial. More problematic are the cases where both terminating surfaces are different, as there is no single established method allowing for equal treatment of a wide range of surface morphologies and orientations. Our proposed approach addresses this problem. It relies on appropriately chosen capping atoms, whose bonding energy contributions are used to approximate the total energy of the surface. The choice of the capping atoms is governed by a set of simple guidelines that are applicable for surfaces with different terminations. We present the results for different semiconductor materials and show that our approach leads to surface energies with errors that are below 10%, and that are as low as 2% in many cases. We show that hydrogen is not always the best choice for a capping atom if accurate surface energies are the target of the calculations.

Anion-templated nanosized silver clusters protected by mixed thiolate and diphosphine.

S2-, MoO42-, and Mo6O228- were successfully employed as templates in the formation of six high-symmetry polynuclear silver clusters as exemplified in the single-crystal X-ray structures of [S@Ag18(tBuC6H4S)16(dppp)4]·DMF·5CH3CN·3CH3OH (1), [MoO4@Ag24(MeC6H4S)12(dppm)6(MoO4)4]·2BF4·C2H5NO (2), [MoO4@Ag24(MeC6H4S)12(dppm)6(MoO4)4]·2CF3SO3 (3), [MoO4@Ag24(MeC6H4S)12(dppf)6(MoO4)4]·2CF3SO3 (4), [MoO4@Ag24(MeC6H4S)12(dppb)6(MoO4)4]·2CF3SO3 (5) and [Mo6O22@Ag46(tBuC6H4S)32(dppm)4(CH3CN)8]·6CF3SO3 (6) (dppp = 1,3-bis(diphenylphosphino)propane, dppm = bis(diphenylphosphino)methane, dppf = 1,1'-bis(diphenylphosphino)ferrocene and dppb = 1,4-bis(diphenylphosphino)butane). Cluster 1 is a S2--centered octadecanuclear banana-shaped molecule. Clusters 2-5 have similar structures consisting of a tetrahedron of a MoO42- core and four MoO42- where three silver atoms cap each face and a pair sits on each edge, giving tetraicosanuclear ball-shaped molecules. Although different diphosphine ligands and silver salts were used in the syntheses, 2-5 contain a common building cluster unit with similar geometry and nuclearity. With (Bu4N)2Mo6O19 as a template, a giant 46-silver-atom cluster encapsulates an in situ modified Mo6O228- unit. The nuclearity and geometry depend on the size and shape of the templates. High-resolution electrospray mass spectrometry (HR-ESI-MS) analyses of 4 indicate its exceptionally high stability in acetonitrile. The solid-state luminescence of 1 as a function of the temperature exhibits thermochromism from red to yellow due to the different intensities of the two bands. This work established a new strategy for the construction of polynuclear silver clusters using an anionic template and mixed S- and P-donor ligands where a promising approach for building novel dual emissive materials is unraveled.

Au102+ and Au6X42+ clusters: Superatomic molecules bearing an SP3-hybrid Au6core

The octahedral Au6 core is explored for the formation of novel SP3-hybrid superatomic molecules by considering Au102+ and Au6 X42+ clusters (X= F, Cl, Br, I). The bonding between the four capping atoms and the Au6 core requires a combination of 1S and 1P shells of the core leading to a set of four equivalent hybrid orbitals. Thus, combining the superatom concept with both the Lewis structure model and VSEPR theory contributes to the rationalization of structure and bonding in metal clusters. For example, our results consider the Au6 X42+ clusters as analogues of the simplest perhalogenated hydrocarbon, CX4.

La2NiSb – A Ternary Ordered Version of the Bi3Ni Type with Highly Polar Bonding

Abstract The lanthanum-rich antimonide La2NiSb was synthesized by annealing a cold-pressed pellet of the elements in a sealed silica glas tube at 1120 K. La2NiSb was characterized by powder and single-crystal X-ray diffraction: ordered Bi3Ni type, Pnma, Z =4, a=825.6(3), b=452.2(2), c=1195.5(4) pm, wR=0.0695, 856 F2 values, 26 variables. The nickel atoms form infinite zigzag chains (259 pm Ni-Ni) with trigonal-prismatic lanthanum coordination for each nickel atom. The antimony atoms cap the rectangular faces of the lanthanum prisms (336 pm La-Sb) and thereby coordinate also the nickel atoms (271 pm Ni-Sb). These rods run parallel to the b axis and form a herringbone pattern, similar to the FeB-type structure of GdNi. Although metallic conductivity is expected for La2NiSb from DFT-based band structure calculations, the real-space bonding analysis shows prominent localization of electrons on antimonide anions and positively charged lanthanum cations. The chain substructure is strongly bonded by polar covalent Ni-Sb and multicenter Ni-Ni interactions. The nickel atoms, which are involved in multicenter bonding with adjacent nickel and lanthanum atoms, provide a conductivity pathway along the prismatic strands. 121Sb Mössbauer spectroscopic data at 78 K show a single signal at an isomer shift of -7.62(3)mms-1, supporting the antimonide character. La2NiSb shows weak paramagnetism with a susceptibility of 2.5 x 10-3 emu mol-1 at room temperature.

Synthesis, structures, and solution dynamics of tetrasubstituted nine-atom germanium deltahedral clusters.

Reported are the rational synthesis, structures, and solution dynamics of three tetrasubstituted and neutral Ge9-based deltahedral clusters [Ge9R3R'](0), where R = Si(SiMe3)3 and R' = Et (1), Sn(n)Bu3 (2), or Tl (3). The first step of the synthesis is a reaction of an acetonitrile suspension of the intermetallic precursor compound K4Ge9 with {Si(SiMe3)3}Cl which produces the trisubstituted monoanions [Ge9{Si(SiMe3)3}](-). A benzene suspension of the latter is then reacted with Sn(n)Bu3Cl or TlCp to produce 2 and 3, respectively, while the same acetonitrile solution is reacted with EtBr in order to produce 1. All three structures can be viewed as tricapped trigonal prisms of Ge9 with the three "hypersilyl" substituents, Si(SiMe3)3, exo-bonded to the capping atoms. The fourth substituent in 1, the ethyl group, is exo-bonded to one of the six available Ge atoms with the Ge-C bond positioned radially to the Ge9 core. In the case of 2, on the other hand, the tin fragment is found above one of the triangular bases of the prism interacting with one or more Ge atoms in three crystallographically different molecules in the structure. Lastly, the Tl atom in the structure of 3 is found capping a pseudosquare face between two hypersilyl substituents. NMR spectroscopy indicates that all three compounds are dynamic at room temperature. Variable-temperature studies suggest that the process in 1 and 2 is intramolecular while the process in 3 involves dissociation of the Tl(+) ion from the molecule followed by association at the same or another equivalent pseudosquare face of the molecule. Thus, the latter compound may be considered to a large extent to be ionic as it is made of a thallium cation and a trisubstituted cluster anion.

Electrostatically Embedded Molecular Tailoring Approach and Validation for Peptides.

We add higher-order electronic polarization effects to the molecular tailoring approach (MTA) by embedding each fragment in background charges as in combined quantum mechanical and molecular mechanical (QM/MM) methods; the resulting method considered here is called electrostatically embedded MTA (EE-MTA). We compare EE-MTA to MTA for a test peptide, Ace-(Ala)20-NMe, and we find that including background charges (embedding charges) greatly improves the performance. The fragmentation is performed on the basis of amino acids as monomers, and several sizes of fragment are tested. The fragments are capped with either hydrogen cap atoms or tuned fluorine cap atoms. The effective core potential of the tuned fluorine cap atom is optimized so as to reproduce the proton affinity for seven types of tetrapeptide, and the proton affinity calculated with the tuned cap atom shows a lower mean unsigned error than that obtained by using a hydrogen cap atom. In the application to the test peptide, these generically tuned cap atoms show better performance compared with the hydrogen cap atom for both the electronic energy and the energy difference between an α helix and a β sheet (in the latter case, 1.0% vs 2.7% when averaged over three sizes of fragments and two locations for cut bonds). Also, we compared the accuracy of several charge redistribution schemes, and we find that the results are not particularly sensitive to these choices for the Ace-(Ala)20-NMe peptide. We also illustrate the dependence on the choice of charge model for the embedding charges, including both fixed embedding charges and embedding charges that depend on conformation.

Tuned and Balanced Redistributed Charge Scheme for Combined Quantum Mechanical and Molecular Mechanical (QM/MM) Methods and Fragment Methods: Tuning Based on the CM5 Charge Model.

Tuned and balanced redistributed charge schemes have been developed for modeling the electrostatic fields of bonds that are cut by a quantum mechanical-molecular mechanical boundary in combined quantum mechanical and molecular mechanical (QM/MM) methods. First, the charge is balanced by adjusting the charge on the MM boundary atom to conserve the total charge of the entire QM/MM system. In the balanced smeared redistributed charge (BSRC) scheme, the adjusted MM boundary charge is smeared with a smearing width of 1.0 Å and is distributed in equal portions to the midpoints of the bonds between the MM boundary atom and the MM atoms bonded to it; in the balanced redistributed charge-2 (BRC2) scheme, the adjusted MM boundary charge is distributed as point charges in equal portions to the MM atoms that are bonded to the MM boundary atom. The QM subsystem is capped by a fluorine atom that is tuned to reproduce the sum of partial atomic charges of the uncapped portion of the QM subsystem. The new aspect of the present study is a new way to carry out the tuning process; in particular, the CM5 charge model, rather than the Mulliken population analysis applied in previous studies, is used for tuning the capping atom that terminates the dangling bond of the QM region. The mean unsigned error (MUE) of the QM/MM deprotonation energy for a 15-system test suite of deprotonation reactions is 2.3 kcal/mol for the tuned BSRC scheme (TBSRC) and 2.4 kcal/mol for the tuned BRC2 scheme (TBRC2). As was the case for the original tuning method based on Mulliken charges, the new tuning method performs much better than using conventional hydrogen link atoms, which have an MUE on this test set of about 7 kcal/mol. However, the new scheme eliminates the need to use small basis sets, which can be problematic, and it allows one to be more consistent by tuning the parameters with whatever basis set is appropriate for applications. (Alternatively, since the tuning parameters and partial charges obtained by the new method do not depend strongly on basis set, one can continue to use available CM5-tuned parameters even when one changes the basis set.) Furthermore, we found that, as compared to Mulliken charges, the CM5 charges describe the charge distributions in test molecules better, and they reproduce the dipole moments of full quantum mechanical calculations better; therefore the new tuning procedure is more physical and should be more reliable and robust.

Dispersion corrections in the boron buckyball and nanotubes

We have investigated structural and electronic properties of the B80 buckyball and boron nanotubes by means of dispersion-corrected density-functional calculations. Our analysis reveals the vibrational stability for the icosahedral B80 with the inclusion of dispersion corrections, in contrast to the instability to a tetrahedral B80 with puckered capping atoms from preceding density-functional theory calculations. Similarly, the dispersion-corrected density-functional calculations yield non-puckered boron nanotube conformations and an associated metallic state for zigzag tubes. Our study indicates that the incorporation of long-range dispersive interactions is particularly important to the structural and electronic properties of boron fullerenes and nanotubes.

Encapsulation of Small Base Molecules and Tetrahedral/Cubane-Like Clusters of Group V Atoms in the Boron Buckyball: A Density Functional Theory Study

A density functional theory study of small base molecules and tetrahedral and cubane-like group V clusters encapsulated in B(80) shows that the boron buckyball is a hard acid and prefers hard bases like NH(3) or N(2)H(4) to form stable off-centered complexes. In contrast, tetrahedral and cubane-like clusters of this family are metastable in the cage. The most favorable clusters are the mixed tetrahedral and cubane clusters formed by nitrogen and phosphorus atoms such as P(2)N(2)@B(80), P(3)N@B(80), and P(4)N(4)@B(80). The boron cap atoms are electrophilic centers, and prefer mainly to react with electron rich nucleophilic sites. The stability of the complexes will be governed by the size and electron donating character of the encapsulated clusters. B(80) forms stable complexes with hard materials where a bidentate interaction of the encapsulated molecule with two boron cap atoms is preferred over a single direct complex toward a single endohedral boron.

The leapfrog principle for boron fullerenes: a theoretical study of structure and stability of B112

Two leapfrog isomers of a B(112) boron fullerene are constructed from small C(28) fullerenes (T(d) and D(2) symmetries) by the leapfrog transformation combined with omnicapping of the new hexagons. Their electronic structure is analyzed using the density functional theory at the B3LYP/SVP and BHLYP/SVP levels. Both isomers are characterized as minima on the potential energy hypersurface with a HOMO-LUMO gap at B3LYP/SVP of 1.7 eV and 1.6 eV (3.1 and 3.0 eV at BHLYP/SVP), respectively. The optimized structure of the helical D(2)-leapfrog is asymmetric, due to radial displacements of the capping atoms. The computed cohesive energies amount to -4.2 eV (∼0.04 eV lower than B(80)). The B(112) isomers are isoelectronic to T(d)-C(84) and D(2)-C(84), and HOMO and LUMO orbitals in both isomers closely resemble those of their C(84) homologues. Energetic stability of leapfrog boron fullerenes depends on the isolation of empty hexagon criterion, which is defined by the empty hexagon index based on the total number of empty hexagon pairs and empty hexagon-pentagon fused pairs. The switch of the cap atom to the nearest or farthest empty hexagon destabilizes the cage by 1.6 and 2.7 eV, respectively. The destabilization becomes more enhanced in non-leapfrog structures wherein more caps are displaced.

Photoelectron spectroscopy and density-functional study of Sc 2Si n− ( n = 2–6) clusters

We conducted a photoelectron spectroscopy and density-functional study on Sc 2Si n − ( n = 2–6) clusters. The adiabatic detachment energies of Sc 2Si 2–6 − were estimated to be 1.42 ± 0.08, 1.37 ± 0.08, 1.33 ± 0.08, 1.9 ± 0.2, and 2.0 ± 0.2 eV respectively from their photoelectron spectra. Comparison of theoretical and experimental results indicates that each of these clusters has more than one isomer in the experiments. In the most stable structures of Sc 2Si 3–6 − clusters, the silicon atoms form an n-membered silicon ring, and the two Sc atoms cap to the opposite sides of the ring. The Sc–Sc interaction in Sc 2Si n − clusters is very weak comparing to the strong V–V interaction in V 2Si n − clusters.

Quantum chemistry study of symmetric methyne substitution patterns in the boron buckyball

We report the electronic structure of methyne boron buckyballs B 68(CH) 12, B 72(CH) 8 and B 76(CH) 4 obtained by substituting, respectively, 12, 8 and 4 boron cap atoms by methyne CH groups on the boron buckyball B 80. DFT calculations and minimization techniques have been employed to characterize the structural and electronic properties of endo and exo isomers of these molecules in T h and T symmetry. A vibrational frequencies analysis predicts that only endo-B 72(CH) 8 and endo-B 76(CH) 4 correspond to a true minimum on the potential energy hypersurface with a cohesive energy similar to the boron buckyball. The stable substitutions are characterized by six rhombohedral B 4 bonding motifs.