Sr-centered monocyclic carbon ring Sr@C14: A new stable cluster.

The study of stable neutral metal endohedral cyclo[n]carbon is helpful for discovering single-molecule devices. Extensive structural search and density functional theory calculations performed here indicate that the perfect planar alkaline metal-doped complexes Sr@C14 possess the well-defined global minima of the system with the metal atom located exactly at the center of the carbon ring. The configuration and bonding properties of C14 are different from those of pristine cyclo [14]carbon. The significant stabilization when forming Sr@C14 predominantly originates from the electrostatic interaction between Sr2+ and C142-. The detailed molecular orbital, nucleus-independent chemical shift (NICS), and ring current analyses indicate that Sr@C14 is aromatic in nature. The NICS values of Sr@C14 are considerably larger than those of benzene. Ab initio molecular dynamics simulations at different temperatures reveal that this system exhibits certain stability at low or moderate temperatures. The findings of this study effectively enrich the chemical structures and bonding patterns of metal-doped cyclo[n]carbon and provide the knowledge required to obtain novel structures of Sr@C14 in future experiments.

Stable Lanthanide-Organic Frameworks: Crystal Structure, Photoluminescence, and Chemical Sensing of Vanillylmandelic Acid as a Biomarker of Pheochromocytoma.

Several isostructural lanthanide metal-organic frameworks, viz. [Ln(DCHB)1.5phen]n (Ln-MOFs, where Ln = Eu for 1, Tb for 2, Sm for 3 and Dy for 4), are successfully synthesized through the hydrothermal reactions of 4'-di(4-carboxylphenoxy)hydroxyl-2, 2'-bipyridyl (H2DCHB) and lanthanide nitrates as well as chelator 1,10-phenantroline (phen). These structures are characterized by single-crystal X-ray diffraction, and the representative Ln-MOF 1 is a fivefold interpenetrated framework with the uncoordinated Lewis base N sites form DCHB2- ligands. The photoluminescence research studies reveal that Ln-MOFs 1-4 exhibit characteristic fluorescent emissions from ligand-induced lanthanide Ln(III) ions, while the single-component emission spectra of Ln-MOF 4 are all located in a white region under different excitations. The absence of coordinated water and the interpenetration property of the structures are conducive to the structure rigidity, and the results display that Ln-MOF 1 has high thermal/chemical stabilities in common solvents and a wide pH range as well as the boiling water. Notably, luminescent sensing studies reveal that Ln-MOF 1 with prominent fluorescence properties can perform in highly sensitive and selective sensing of vanillylmandelic acid (VMA) in aqueous systems (KSV = 562.8 L·mol-1; LOD = 4.6 × 10-4 M), which can potentially establish a detection platform for the diagnosis of pheochromocytoma via multiquenching mechanisms. Moreover, the 1@MMMs sensing membranes comprised of Ln-MOF 1 and a poly(vinylidene fluoride) (PVDF) polymer can also be facilely developed for VMA detection in aqueous media, suggesting the enhanced convenience and efficiency of practical sensing applications.

Quasi-planar Co atom-doped boron cluster: CoB192.

PURPOSE AND METHODS: A global search for the lowest energy structure of CoB192- clusters was conducted.  RESULTS: Its ground state is a quasi-planar structure with the Co atom surrounded by a B8 ring. The central Co atom has an oxidation state of +1 with d8 electron configuration. The wave function analysis showed that the Co-B interaction is not a covalent bond. The bonding strength of peripheral B-B bonds is stronger than that of inner ones. The inner B8 ring bonds with outer boron atoms via σ- and π-type bonds. CONCLUSION: CoB192- shows remarkable aromatic character.

Structures and Properties of CoB19 +/0/- Clusters.

A global search for the lowest energy structure of Co atom-doped boron clusters (CoB19 +, CoB19, and CoB19 - clusters) was conducted. The lowest energy structures of them are remarkably different from those of B20 and CoB18 - clusters. CoB19 + clusters have a bowl-shaped geometry, where the Co atom is at the bottom of the bowl and is coordinated with eight B atoms. The CoB19 cluster presents seven- and eight-membered B rings. The CoB19 - cluster can be viewed as a structure that evolves from a Co-doped boron plane. The coordination number of CoB19 and CoB19 - clusters are 16 and 14, respectively. Several low-lying isomers have quasi-planar structures for the CoB19 - cluster. Some properties including charge transformation and distribution, HOMO-LUMO gaps, molecular orbital distribution, and stability of neutral CoB19 are discussed. CoB19 + and CoB19 - exhibit magnetism with a net moment of 1.0 and 0.94 µB because of odd number of electrons.

Planarization of B20 clusters by Si and C atom substitution.

An optimization strategy combining a global semi-empirical quantum mechanical search and all-electron density functional theory was adopted to determine the lowest energy structures of B19Si and B19C clusters. The planarization of a B20 cluster by Si and C atom substitution was observed. The structural transition was from the double-ring tubular B20 to an almost perfect planar B19Si and a quasi-planar bowl B19C. B19Si possessed a geometry with a central B atom surrounded by a six-membered ring and a 13-atom outer ring. B19C adopted a geometry with a B5C six-membered hole. Both Si and C atoms occupied peripheral positions. The observed planarization may be attributed to sp2 hybridization, changes in the peripheral bonding, and structural mechanics. Some properties, including the HOMO-LUMO gaps, on-site charge on Si and C atoms, and deformed charge distribution, were discussed.

Analysis of the Structures and Properties of (GaSb)n (n = 4-9) Clusters through Density Functional Theory.

An optimization strategy combining global semiempirical quantum mechanical search with all-electron density functional theory was adopted to determine the lowest energy structure of (GaSb)n clusters up to n = 9. The growth pattern of the clusters differed from those of previously reported group III-V binary clusters. A cagelike configuration was found for cluster sizes n ≤ 7. The structure of (GaSb)6 deviated from that of other III-V clusters. Competition existed between core-shell and hollow cage structures of (GaSb)7. Novel noncagelike structures were energetically preferred over the cages for the (GaSb)8 and (GaSb)9 clusters. Electronic properties, such as vertical ionization potential, adiabatic electron affinities, HOMO-LUMO gaps, and average on-site charges on Ga or Sb atoms, as well as binding energies, were computed.

DFT study on endohedral and exohedral B38 fullerenes: M@B38 (M = Sc, Y, Ti) and M&B38 (M = Nb, Fe, Co, Ni).

The structures, stabilities and electronic properties of endohedral and exohedral B38 fullerenes with transition metal atoms (M = Sc, Y, Ti, Nb, Fe, Co, Ni) are studied using all-electron density functional theory. M@B38 (M = Sc, Y, Ti) possess endohedral structures as their lowest energy structures, while Nb, Fe, Co and Ni atoms favor the coordination of B38 fullerenes in an exohedral manner. Sizable HOMO-LUMO gaps and high binding energies imply the viability of M@B38 towards experimental realization. The distributions of electron density and frontier orbitals are analyzed in detail. The analysis of vertical ionization potential and vertical electron affinity indicates that M@B38 are good electron acceptors and bad electron donors.

Theoretical study on aluminum carbide endohedral fullerene-Al4C@C80.

The possibility of a new endohedral fullerene with a trapped aluminum carbide cluster, Al(4)C@C(80)-I( h ), was theoretical investigated. The geometries and electronic properties of it were investigated using density functional theory methods. The Al(4)C unit formally transfers six electrons to the C(80) cage which induces stabilization of Al(4)C@C(80). A favorable binding energy, relatively large HOMO-LUMO gap, electron affinities and ionization potentials suggested the Al(4)C@C(80) is rather stable. The analysis of vertical ionization potential and vertical electron affinity indicate Al(4)C@C(80) is a good electron acceptor.

First principles studies on the interaction of O2 with X@Al12 (X = Al-, P+, C, Si) clusters.

The interaction of O(2) with the doped icosahedral X@Al(12) (X = Al(-), P(+), C, Si) clusters with 40 valence electrons were investigated using density functional theory methods. A different behavior exhibited between Al(13)(-) and X@Al(12) (X = P(+), C, Si) when they interact with O(2). The dissociation of O(2) on Al(13)(-) is strongly dependent on spin state of oxygen molecule. But X@Al(12) (X = P(+), C, and Si) is not the case. The transform of spin moment from O(2) to Al(13)(-) is much faster. Small molecularly binding energy and relatively high energy barrier show that these clusters are all reluctant reacts with the ground state O(2).