Cage Clusters Research Articles

SPIN-POLARIZED DENSITY FUNCTIONAL STUDY ON HETEROFULLERENE AND METALLOFULLERENE CLUSTERS

The fullerene cage clusters C 60 and C 70 become magnetic and half metallic when doped with B and N atoms. The five-atom transition metal clusters of Mn , Fe , Co , and Ni encapsulated inside fullerene cages have higher magnetic moment, while that of Cr become nonmagnetic as compared to corresponding isolated clusters. These clusters encapsulated inside fullerene cages get distorted. The distortion in a cluster inside C 70 is larger as compared to that inside C 60, C 59 B , and C 59 N cages. These clusters also distort the hexagons and pentagons of fullerene cages. The fullerene cages expand but retain their shapes. The energy calculations show that Mn and Cr clusters encapsulated inside C 60 and C 59 N are stable.

Molecular Alloys, Linking Organometallics with Intermetallic Hume−Rothery Phases: The Highly Coordinated Transition Metal Compounds [M(ZnR)n] (n≥ 8) Containing Organo−Zinc Ligands

This paper presents the preparation, characterization and bonding analyses of the closed shell 18 electron compounds [M(ZnR)(n)] (M = Mo, Ru, Rh, Ni, Pd, Pt, n = 8-12), which feature covalent bonds between n one-electron organo-zinc ligands ZnR (R = Me, Et, eta(5)-C(5)(CH(3))(5) = Cp*) and the central metal M. The compounds were obtained in high isolated yields (>80%) by treatment of appropriate GaCp* containing transition metal precursors 13-18, namely [Mo(GaCp*)(6)], [Ru(2)(Ga)(GaCp*)(7)(H)(3)] or [Ru(GaCp*)(6)(Cl)(2)], [(Cp*Ga)(4)RhGa(eta(1)-Cp*)Me] and [M(GaCp*)(4)] (M = Ni, Pd, Pt) with ZnMe(2) or ZnEt(2) in toluene solution at elevated temperatures of 80-110 degrees C within a few hours of reaction time. Analytical characterization was done by elemental analyses (C, H, Zn, Ga), (1)H and (13)C NMR spectroscopy. The molecular structures were determined by single crystal X-ray diffraction. The coordination environment of the central metal M and the M-Zn and Zn-Zn distances mimic the situation in known solid state M/Zn Hume-Rothery phases. DFT calculations at the RI-BP86/def2-TZVPP and BP86/TZ2P+ levels of theory, AIM and EDA analyses were done with [M(ZnH)(n)] (M = Mo, Ru, Rh, Pd; n = 12, 10, 9, 8) as models of the homologous series. The results reveal that the molecules can be compared to 18 electron gold clusters of the type M@Au(n), that is, W@Au(12), but are neither genuine coordination compounds nor interstitial cage clusters. The molecules are held together by strong radial M-Zn bonds. The tangential Zn-Zn interactions are generally very weak and the (ZnH)(n) cages are not stable without the central metal M.

Size- and Temperature-Dependent Magnetic Response of Molecular Cage Clusters: Manganese-Doped Tin Clusters

Endohedral clusters, formed by incorporating a single Mn atom into a cage of tin atoms, have been generated in the gas phase. Mass spectrometry reveals that a cage size of 10 tin atoms is necessary for the efficient incorporation of one Mn atom. Some of the cluster compounds with one Mn atom attached to the tin clusters display large intensities compared to the pure tin clusters, indicating that the compound clusters are particularly stable. The manganese-doped tin cluster assemblies Mn@Sn12, Mn@Sn13, and Mn@Sn15 have been further analyzed within a molecular beam magnetic deflection experiment. Interestingly, although the effect of the magnetic field on the behavior of Mn@Sn12 is quite different from that of Mn@Sn13 and Mn@Sn15, the magnetic dipole moments are the same within the uncertainty of the measurements. Magnetic dipole moments have been found in close agreement with the spin quantum number S = 5/2 predicted by theory for Mn@Sn12, indicating that the magnetic moment of the Mn atom is not quenched. This supports the idea that within a tin cluster cage a single Mn atom can be encapsulated, resulting in the formation of endohedral clusters consisting of a central Mn2+ ion surrounded by a particularly stable Zintl-ion cage Sn(N)(2-). The observed molecular beam profiles indicate that at a nozzle temperature of 55 K the magnetic moment is strongly locked to the molecular framework of Mn@Sn12; in contrast, the magnetic moment of Mn@Sn13 and Mn@Sn15 tends to align with the magnetic field. The experiments therefore demonstrate that the size of a presumably nonmagnetic cluster cage might have a fundamental influence on the magnetization dynamics of paramagnetic species. The influence of vibrational excitation on the Stern-Gerlach profile of Mn@Sn12 is further analyzed, and it is shown that the behavior of Mn@Sn12 at elevated nozzle temperatures changes continuously toward a nonlocked moment, pointing to size- and temperature-dependent magnetization dynamics.

3 d transition metals: Which is the ideal guest for Si n ( [formula omitted]) cages?

The configurations, stability, and electronic structures of Si 15 and Si 16 cages with encapsulated 3 d transition metal atoms, M@Si 15 and M@Si 16 (M = Sc, Ti, V, Cr, Mn, Fe, Co, or Ni), have been investigated within the framework of all-electron density functional theory. The results show that Ti@Si 16 and Ti@Si 15 have the largest embedding energies in this series and relatively large HOMO–LUMO gaps. This suggests that the titanium atom is an ideal guest for Si n ( n = 15 , 16 ) cages as far as stability is concerned. The Mn atom is found to have a large spin moment even when encapsulated, while the spin moments of Ti, Cr, Fe, and Ni are entirely quenched upon doping into the Si 15 and Si 16 cage clusters.

Mixed Metal Nitride Clusterfullerenes in Cage Isomers: LuxSc3−xN@C80 (x = 1, 2) As Compared with MxSc3−xN@C80 (M = Er, Dy, Gd, Nd)

Two isomers of lutetium−scandium mixed metal nitride clusterfullerenes (MMNCFs), LuxSc3−xN@C80(x = 1, 2), have been synthesized and isolated for the first time, and accordingly, the interplay of the cluster structure and cage isomerism is followed. The electronic and vibrational properties of LuxSc3−xN@C80 (I, II, x = 1, 2) are characterized by UV−vis−NIR and FTIR spectroscopies, revealing the effect of the composition of the encaged LuxSc3−xN cluster. A comparative study of LuxSc3−xN@C80 (I) with other MxSc3−xN@C80(I; M = Er, Dy, Gd, Nd) MMNCFs points to the dependence of their electronic and vibrational properties on the encaged metal. The cage structures of LuxSc3−xN@C80 (I, II; x = 1, 2) are determined by 13C NMR spectroscopy. The 45Sc NMR spectroscopic study is carried out to probe the dynamics of the encaged Sc atoms. Finally, DFT computations are used to address the effect of the composition of the encaged LuxSc3−xN cluster on the NMR lines and the structures of LuxSc3−xN@C80 (I, II; x = 1, 2) especially with respect to the carbon atoms.

A small molecule in metal cluster cages: H2@Mgn (n = 8 to 10)

Core-shell isomers of small magnesium clusters "doped" with a hydrogen molecule are theoretically studied and predicted to be weakly stable or metastable for different sizes of the system, allowing a low-temperature release of hydrogen. Evolution of H(2) inside Mg(n) is followed from the molecular species to two H atoms. Among properties analyzed are equilibrium geometries, dissociation energies, charge distributions, vertical energies of electronic excitation, ionization and electron attachment, and vibrational frequencies.

Discrete Polyoxovanadate Cluster into an Organic Free Metal-Oxide-Based Material: Syntheses, Crystal Structures, and Magnetic Properties of a New Series of Lanthanide Linked-POV Compounds [{Ln(H2O)6}2As8V14O42(SO3)]·8H2O (Ln = La3+, Sm3+, and Ce3+)

This article describes the linking propensity of the sulfite encapsulated polyoxovanadate (POV) anion, [As(8)V(14)O(42)(SO(3))](6-), with aqua-lanthanide complex cations [Ln(H(2)O)(6)](3+) in a controlled wet synthesis resulting in a series of organic free metal-oxide-based materials [{Ln(H(2)O)(6)}(2)As(8)V(14)O(42)(SO(3))] x 8 H(2)O, Ln = La(3+) (1), Sm(3+) (2), and Ce(3+) (3). The title compounds have been characterized by elemental analyses, IR, diffuse reflectance, electron paramagnetic resonance, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and single-crystal X-ray diffraction studies. All three compounds crystallize in the monoclinic space group P2(1)/n. Crystal data for 1: a = 13.4839(7), b = 12.3388(6), c = 18.3572(10) A, beta = 108.2570 (10) degrees, V = 2900.4(3) A(3). Crystal data for 2: a = 13.4156(3), b = 12.2588(3), c = 18.2501(4) A, beta = 108.049(3) degrees, V = 2853.8(10) A(3). Crystal data for 3: a = 13.4934(3), b = 12.3983(3), c = 18.3992(4) A, beta = 108.025(3), V = 2927.0(10) A(3). Crystal structure shows that each cluster is surrounded by six [Ln(H(2)O)(6)](3+) complex cations, and each [Ln(H(2)O)(6)](3+) cation is coordinated to three surrounding POV cluster anions. The electron spin resonance spectra of compounds 1-3 show a typical single line (g = 1.9671 for 1, g = 1.9669 for 2, and g = 1.9704 for 3), characteristic for a V(4+) (d(4)) ion; in addition, a supplementary signal appears for compound 2 at g = 5.9238 due to the presence of the Sm(3+) (f(5)) ion. All vanadium atoms exit in +4 oxidation states that have been confirmed by bond valence sum calculations. Variable-temperature magnetic studies for all three compounds 1-3 are performed and are discussed in terms of antiferromagnetic coupling interactions, giving importance to linking/assembling the {V(14)} cluster anions. TGA/mass analyses of compounds 1-3 (linked system) have been compared with that of the starting precursor [NH(4)](6)[As(8)V(14)O(42)(SO(3))] (discrete building unit). Interestingly, the evolution of SO(2) gas takes place for the discrete cluster compound [NH(4)](6)[As(8)V(14)O(42)(SO(3))] in a temperature range of 480-520 degrees C with the decomposition of the POV cluster anion, whereas the same evolution occurs at 520-580 degrees C for compounds 1-3. These comparative TGA/mass studies help to understand how the organic free linker elevates the thermal stability of the sulfite encapsulated POV cluster anion in going from a discrete cluster anion to the linked system (molecule to material). It has also been demonstrated that the stability of the sulfite anion increases to a greater extent when it is included in the cluster cage. The powder XRD studies of compounds 1-3 confirm that these are isostructural materials and provide information about the phase purity.

Structure determination of W-capsulated Si cage clusters by x-ray absorption fine structure spectra

Local structure of transition metal (TM)-encapsulated Si clusters TMSin is investigated by x-ray absorption fine structure. For a series of W-encapsulated Si cluster (WSin) films, the extended x-ray absorption fine structure (EXAFS) results indicate that the W atoms are coordinated by 9–10 Si atoms with a large structural disorder. The x-ray absorption near-edge structure (XANES) spectra exhibit intense white lines for the cluster films, which distinguishes the different local structures from that of amorphous W–Si alloy. Multiple-scattering XANES calculations indicate that the intense white lines are reproduced by the WSin cage clusters with a W atom in the Sin cage centre. Combining the XANES and EXAFS results, it is revealed that the WSin cage structure (n = 8 or 12) is formed, characterized by strengthened covalency consistent with considerable bond contraction.

Towards gold shells shaped by carbon cores: From a gold cage to a core–shell aurocarbon

A new aurocarbon species, C 10Au 18, is investigated in terms of its geometry, stability, charge distribution and properties involving changes of the electronic and charge state. The system consists of a carbon-radical core inside a gold shell. The property variations upon adding the carbon molecular ‘dopant’ to the gold cage cluster of equivalent geometry are analyzed via isolating the effects of the shell shape change and core influence. The charge distribution in the system exhibits interesting, sometimes counterintuitive features. An approximate splitting of the total binding energy into the in-shell and core–shell components is attempted, indicating comparable values for both.

A Conducting Coordination Polymer Based on Assembled Cu9 Cages

We report on a novel highly semiconducting 1D coordination polymer architecture obtained by the reaction of a Cu(II) salt with 2,2'-dipyridyldisulfide under microwave solvothermal conditions. This reaction proceeds with an unusual C-S and S-S bond cleavage of the 2,2'-dipyridyldisulfide ligand. The unprecedented architecture of this coordination polymer consists of a 1D chain formed by the assembling of Cu9 cluster cages. The electrical conductivity behavior of this novel material suggests new perspectives for the use of coordination polymers as electrical conducting materials.

New Molecular Cage Clusters of Pb by Encapsulation of Mg

Endohedral clusters formed from the Zintl ions Pb(10) (2-) and Pb(12) (2-) are particularly stable and therefore suitable for the assembly of larger aggregates. We therefore investigate the formation of Mg-doped lead clusters in the gas phase, and demonstrate that a whole series of new molecular cage clusters of lead can be generated by encapsulation of magnesium. Mass spectrometry reveals that some of the cluster compounds, with one and two Mg atoms attached to the lead clusters, display large intensities compared to the pure lead clusters, which indicates that the compound clusters are particularly stable. The magnesium-doped lead-cluster assemblies were further analyzed within a molecular-beam electric deflection experiment. Almost vanishing permanent dipole moments for MgPb(10-16) support the idea that a single Mg atom could be encapsulated within a highly symmetric lead cage, which results in structures with not only enhanced stability but also increased symmetry compared to the pure lead clusters Pb(N).

Investigation of a Size-Selective Single Hafnium-Encapsulated Germanium Cage

The structures, relative stabilities, and electronic properties of size-selective single Hf-encapsulated germanium caged clusters ( n = 9-24) have been investigated in detail by density functional method for the first time. The dominant growth behavior of the solid nanocluster Hf@Ge n is based on a pentagonal prism instead of a hexagonal prism. Analogous to Hf@Si n , the encapsulated fullerene-like structure of Hf@Ge n begins to appear at 14, which is consistent with the prediction from the reactivity toward water in a recent experiment ( J. Phys. Chem. A 2007, 111, 42). Also, similar to Hf@Si n in the previous experimental observation ( Chem. Phys. Lett. 2003, 371, 490), the binding energy of Hf@Ge n is gradually increased up to the maximum at 16 and tends to be decreased subsequently, suggesting that stabilization of large germanium cages needs to be realized by doping more Hf atoms. The encapsulated Hf will obviously be moved away from the center of the germanium cage if the cluster size of Hf@Ge n is larger than 20. According to analysis of the electron density of size-selective Hf@Ge n , the covalent character in the germanium framework can be affected by the encapsulated position of Hf in the germanium cage. In addition, comparison between typical low-lying size-selective Hf@Ge n and Hf@Si n ( n = 12, 16 and 20) cages indicates that large-scaled divergence exists in stabilities, growth behaviors, electronic properties, and so forth.

Water Clusters Confined in Nonpolar Cavities by Ab Initio Calculations

Encapsulation of (H2O)n clusters (n = 1−22) in fullerene cages of different diameters (0.73−1.41 nm) has been investigated using gradient-corrected density functional theory. A linear relationship between cavity volume and maximum number of the encapsulated water molecules has been obtained. The interaction between water molecules and the fullerene wall was identified as physisorption with an adsorption energy of about 1.1 kcal/mol per molecule. The equilibrium configurations of small confined water clusters (n < 12) roughly resemble those of gas-phase clusters, whereas larger water clusters tend to adopt cage-like configurations when they are encapsulated in fullerene cages of sufficiently large diameter (i.e., >1.4 nm). The dipole moments of water clusters in the confined phase are smaller than those in the gas phase due to the screening effect of the outer fullerene cage. These results might shed some light on the behavior of water clusters confined in the nonpolar cavities of biological interests.

Theoretical study of hydrogenated Mg, Ca@Al12 clusters

The studies on the structure and electronic properties of hydrogenated metal embedded Al(12) cage clusters have been performed by density functional theory calculations. We have investigated aluminum cluster hydrides with 12 and 14 hydrogen atoms, respectively. Insertion of the Mg, Ca alkali metals remarkably enhances the stability of the aluminum clusters. The hydrogen atom prefers to occupy on-top sites along the surface of the clusters. Mulliken population analysis indicates that significant charge transfer occurs between the Mg and Ca atoms and the Al atoms. Our computations suggest that these clusters appear to be physically and chemically stable.

Zeolite-Supported Palladium Tetramer and Its Reactivity toward H2 Molecules: Computational Studies

Effects of zeolite support on reactivity of Pd 4 cluster toward dihydrogen molecules were studied at the DFT level using T6 (six-ring) and T24 (sodalite cage) clusters as models of zeolite FAU. It has been found that Pd 4 cluster binds to O-centers of T6 cluster via eta (3) and eta (2) coordination modes, leading to three different T6/Pd 4 clusters. For the energetically most stable triplet state T6/Pd 4 structures, the energy of interaction between Pd 4 and the constrained T6 ring is calculated to be ca. -5 kcal/mol. Encapsulating Pd 4 in a sodalite cage (T24) with the full relaxation of cluster geometry resulted in the Pd 4-zeolite interaction energy of -7.4 kcal/mol after correcting for basis set superposition error. The H-H bond activation barrier associated with the first H 2 addition to the triplet state T6/Pd 4 clusters (Delta E 0/Delta H, kcal/mol) varies from (2.2/0.7) to (3.2/2.0) to (4.8/3.5), depending on the path. Comparison of the calculated H 2 addition barriers for the T6-supported and gas-phase Pd 4 indicates that embedding of Pd 4 on zeolite reduces this barrier slightly (by 1.8/2.1 kcal/mol). Interestingly, the characteristic gas phase Pd 4-H 2 active site structural motif has been preserved in the T6-supported transition state structures. The heat of the reaction of the addition of first H 2 to the triplet state T6/Pd 4 ranges from (-17.6/-18.9) to (-21.8/-23.5) for the paths considered. The addition of the second, third and fourth H 2 molecules to the respective first H 2 addition products leads to the dissociative addition product only for the continuation of the single first H 2 addition path.

Capture of Periodate in a {W18O54} Cluster Cage Yielding a Catalytically Active Polyoxometalate [H3W18O56(IO6)]6− Embedded with High‐Valent Iodine

Capture of Periodate in a {W₁₈O₅₄} Cluster Cage Yielding a Catalytically Active Polyoxometalate [H₃W₁₈O₅₆(IO₆)]⁶⁻ Embedded with High‐Valent Iodine

Capture of Periodate in a {W18O54} Cluster Cage Yielding a Catalytically Active Polyoxometalate [H3W18O56(IO6)]6− Embedded with High‐Valent Iodine

Periodat im Zentrum: Ein Wolframperiodatcluster der Form β*-[H3W18O56(IO6)]6−, in dem Periodat in einen {W18O54}-Käfig eingeschlossen ist, konnte als erstes [HnW18O56(XO6)]m−-Heteropolyoxowolframat kristallographisch charakterisiert werden. Massenspektrometrische, elektrochemische und Katalysestudien sowie DFT-Rechnungen offenbaren die ungewöhnlichen physikalischen Eigenschaften der Clusterstruktur, die auch in Lösung intakt bleibt.

Investigation of Size-Selective Zr2@Sin (n = 16−24) Caged Clusters

The size-selective Zr(2)Si(n) (n = 16-24) caged clusters have been investigated by density functional approach in detail. Their geometries, relative stabilities, electronic properties and ionization potentials have been discussed. The dominant structures of bimetallic Zr(2) doped silicon caged clusters gradually transform to Zr(2) totally encapsulated structures with increase of the clustered size from 16 to 24, which is good agreement with the recent experimental result (J. Phys. Chem. A. 2007, 111, 42). Two novel isomers, i.e., naphthalene-like and dodecahedral Zr(2)Si(20) clusters, are found as low-lying conformers. Furthermore, the novel quasi-1D naphthalene-like Zr(n)Si(m) nanotubes are first reported. The second-order energy differences reveal that magic numbers of the different sized neutral Zr(2)Si(n) clusters appear at n = 18, 20 and 22, which are attributed to the fullerene-like, dodecahedral and polyhedral structures, respectively. The HOMO-LUMO gaps (>1 eV) of all the size-selective Zr(2)Si(n) clusters suggest that encapsulation of the bimetallic zirconium atoms is favorable for increasing the stabilities of silicon cages.

Reversible electron-transfer reactions within a nanoscale metal oxide cage mediated by metallic substrates

Transition metal oxides exhibit a rich collection of electronic properties and have many practical applications in areas such as catalysis and ultra-high-density magnetic data storage. Therefore the development of switchable molecular transition metal oxides has potential for the engineering of single-molecule devices and nanoscale electronics. At present, the electronic properties of transition metal oxides can only be tailored through the irreversible introduction of dopant ions, modifying the electronic structure by either injecting electrons or core holes. Here we show that a molybdenum(VI) oxide 'polyoxometalate' molecular nanocluster containing two embedded redox agents is activated by a metallic surface and can reversibly interconvert between two electronic states. Upon thermal activation two electrons are ejected from the active sulphite anions and delocalized over the metal oxide cluster cage, switching it from a fully oxidized state to a two-electron reduced state along with the concomitant formation of an S-S bonding interaction between the two sulphur centres inside the cluster shell.

Metal–Oxygen Isopolyhedra Assembled into Fullerene Topologies

Conditions that permit the assembly of metal–oxygen isopolyhedra into fullerene topologies favor the hexagonal bipyramid as the basic building unit. Uranyl hexagonal bipyramids containing two peroxide edges have been used to create a cage cluster with a fullerene topology containing 50 polyhedra (see picture), as well as cage cluster of 40 polyhedra that contains topological squares, pentagons, and hexagons.