Boron rings containing planar octa-and enneacoordinate cobalt,iron and nickel metal elements

For a series of boron rings with planar hyper-coordinate 8th group transition metal atoms, singlet 1FeB8-2, multiplet kFeB9n (n = -1, k = 1; n = 0, k = 2), singlet 1CoB8n(n = -1, 1, 3), multiplet kCoB9n (n = 1, k = 2; n = 0, k = 1) and singlet 1NiB9 , the geometry structures have been optimized to be local minima on corresponding potential hyper-surfaces. The electron structures are discussed by orbital analysis and the aromaticity is predicted by nucleus-independent chemical shifts calculation at both the B3LYP/6-311 G* and BP86/6-311 G* levels of theory, respectively. The results suggest that all these structures with high symmetry planar geometries are stable and have aromatic properties with six π valence electrons.     

Theoretical observation of hexaatomic molecules containing pentacoordinate planar carbon

The smallest molecules up to date containing a D5h pentacoordinate planar carbon (PPC) atom, CBe5 and CBe54-, are presented by means of ab initio calculations. To gain a better understanding about which electronic factors contribute to their stabilization, natural bond orbital (NBO) analysis and the nucleus independent chemical shifts (NICS) were calculated. The data reported here suggest that D5h CBe5 is σ aromaticity in nature, while in D5h CBe54- π aromaticity is dominating. The classical octet rule is well satisfied in both molecules, and is one of the fundamental reasons to understand the stability of the pentagon structures. The Be5 ring serves as σ donor in D5h CBe5, and π-acceptor in D5h CBe54-. The D5h CBe54- possessing 18 valence electrons with a closed-shell electron configuration is the most plau-sible candidate for experimental detection.     

Structures and aromaticity of the planar Al<Subscript>2</Subscript>P<Subscript>2</Subscript><Superscript><Emphasis Type="Italic">n</Emphasis>−</Superscript> (<Emphasis Type="Italic">n</Emphasis>=1–4) clusters

Clusters Al₂P₂ ⁿ⁻ (n = 1–4) were theoretically investigated using density functional theory (DFT) methods at the B3LYP/6-311+G* and B3PW91/6-311+G* levels of theory. The calculated results showed that the planar structure (D _2h symmetry) of Al₂P₂ ⁿ⁻ (n = 1–4) species was the global minimum. And the negative nucleus-independent chemical shift (NICS) value of Al₂P₂ ⁿ⁻ (n = 1–4) species indicated the existence of a ring current in the planar structure (D _2h symmetry). A detailed molecular orbital (MO) analysis revealed that the planar structures (D _2h symmetry) had π aromaticity, which further exhibited the strongly aromatic character for Al₂P₂ ⁿ⁻ (n = 1–4) species.     

MB 8 2− (M = Be, Mg, Ca, Sr, and Ba): Planar octacoordinate alkaline earth metal atoms enclosed by boron rings

Complexes involving planar octacoordinate alkaline earth metal atoms in the centers of eight-membered boron rings have been investigated by two density functional theory (DFT) methods. BeB ₈ ^2? with D _8h symmetry is predicted to be stable, both geometrically and electronically, since a good match is achieved between the size of the central beryllium atom and the eight-membered boron ring. By contrast, the other alkaline earth metal atoms cannot be stabilized in the center of a planar eight-membered boron ring because of their large radii. By following the out-of-plane imaginary vibrational frequency, pyramidal C _8v MgB ₈ ^2? , CaB ₈ ^2? , SrB ₈ ^2? , and BaB ₈ ^2? structures are obtained. The presence of delocalized π and σ valence molecular orbitals in D _8h BeB ₈ ^2? gives rise to aromaticity, which is reflected by the value of the nucleus-independent chemical shift. The D _8h BeB ₈ ^2? structure is confirmed to be the global minimum on the potential energy surface.     

Die Kristallstruktur von W2CoB2 und isotypen Phasen

Zusammenfassung Die Phasen Mo₂CoB₂, Mo₂NiB₂, W₂FeB₂, W₂CoB₂ und W₂NiB₂ kristallisieren in einem neuen Typ (W₂CoB₂-Struktur). Die Zelle ist orthorhombisch, die Raumgruppe D _2h ²⁵ -I mmm. Die Punktlagen sind 4 W in 4 f), 2 Co in 2 a) und 4 B in 4 h). Die strukturellen Bauelemente werden mit jenen von Mo₂FeB₂ (U₃Si₂-Typ) verglichen.

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The ternary compounds Mo₂CoB₂, Mo₂NiB₂, W₂FeB₂, W₂CoB₂ and W₂NiB₂ crystallize with a new type (W₂CoB₂-structure). The elementary cell is orthorhombic, the space group being D _2h ²⁵ -I mmmm. The atomic positions are determined to be 4 W in 4 f), 2 Co in 2 a) and 4 B in 4 h). Both crystal structures W₂CoB₂ and Mo₂FeB₂ (U₃Si₂-type) are compared with respect to the trigonal prismatic surrounding of the boron atoms.

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Mit 1 Abbildung     

Planar or quasi-planar octa- and ennea-coordinate aluminum and gallium in boron rings

An ab initio theoretical investigation has been performed on planar or quasi-planar octa-and ennea-coordinate Al and Ga centered in X@B8- and X@B9 (X=Al, Ga). These high symmetry molecular wheels all turned out to be true minima of the systems and σ+π double aromatic in nature, similar to the previously characterized D8h B@B8- both electronically and geometrically. Adiabatic and vertical detachment energies of the anions and the ionization potentials of the neutrals have been calculated to aid their eventua...     

The Planar CoB18− Cluster as a Motif for Metallo‐Borophenes

Monolayer‐boron (borophene) has been predicted with various atomic arrangements consisting of a triangular boron lattice with hexagonal vacancies. Its viability was confirmed by the observation of a planar hexagonal B₃₆ cluster with a central six‐membered ring. Here we report a planar boron cluster doped with a transition‐metal atom in the boron network (CoB₁₈^?), suggesting the prospect of forming stable hetero‐borophenes. The CoB₁₈^? cluster was characterized by photoelectron spectroscopy and quantum chemistry calculations, showing that its most stable structure is planar with the Co atom as an integral part of a triangular boron lattice. Chemical bonding analyses show that the planar CoB₁₈^? is aromatic with ten π‐electrons and the Co atom has strong covalent interactions with the surrounding boron atoms. The current result suggests that transition metals can be doped into the planes of borophenes to create metallo‐borophenes, opening vast opportunities to design hetero‐borophenes with tunable chemical, magnetic, and optical properties.     

Two-layer molecular rotors: A zinc dimer rotating over planar hypercoordinate motifs

Multi-layer molecular rotors represent a class of unique combination of topology and bonding, featuring a barrier-free rotation of one layer with respect to other layers. This emerging fluxional behavior has been found in a few doped boron clusters. Herein, we strongly enrich this intriguing family followed by an effective design strategy, summarized as essential factors: i) considerable electrostatic interactions originated from a strong charge transfer between layers; ii) the absence of strong covalent bonds between layers; and iii) fully delocalized σ/π electrons from at least one layer. We found that planar hypercoordinate motifs consisting of monocyclic boron rings and metals with σ + π dual aromaticity can be regarded as one promising layer, which can support the suspended X₂ (X = Zn, Cd, Hg) dimers. By detailed investigations of thermodynamic and kinetic stabilities of 60 species, eventually, MB₇X₂⁻ and MB₈X₂ (X = Zn, Cd; M = Be, Ru, Os; Be works only for Zn-based cases) clusters were verified to be the global-minimum two-layer molecular rotors. Especially, their electronic structure analyses vividly confirm the practicability of the electronic structure requirements mentioned above for designing multi-layer molecular rotors.     

Computationally Designed Families of Flat,Tubular, and Cage Molecules Assembled with “Starbenzene” Building Blocks through Hydrogen‐Bridge Bonds

Using density functional calculations, we demonstrate that the planarity of the nonclassical planar tetracoordinate carbon (ptC) arrangement can be utilized to construct new families of flat, tubular, and cage molecules which are geometrically akin to graphenes, carbon nanotubes, and fullerenes but have fundamentally different chemical bonds. These molecules are assembled with a single type of hexagonal blocks called starbenzene (D_6h C₆Be₆H₆) through hydrogen‐bridge bonds that have an average bonding energy of 25.4–33.1 kcal mol^?1. Starbenzene is an aromatic molecule with six π electrons, but its carbon atoms prefer ptC arrangements rather than the planar trigonal sp² arrangements like those in benzene. Various stability assessments indicate their excellent stabilities for experimental realization. For example, one starbenzene unit in an infinite two‐dimensional molecular sheet lies on average 154.1 kcal mol^?1 below three isolated linear C₂Be₂H₂ (global minimum) monomers. This value is close to the energy lowering of 157.4 kcal mol^?1 of benzene relative to three acetylene molecules. The ptC bonding in starbenzene can be extended to give new series of starlike monocyclic aromatic molecules (D_4h C₄Be₄H₄^2?, D_5h C₅Be₅H₅^?, D_6h C₆Be₆H₆, D_7h C₇Be₇H₇⁺, D_8h C₈Be₈H₈^2?, and D_9h C₉Be₉H₉^?), known as starenes. The starene isomers with classical trigonal carbon sp² bonding are all less stable than the corresponding starlike starenes. Similarly, lithiated C₅Be₅H₅ can be assembled into a C₆₀‐like molecule. The chemical bonding involved in the title molecules includes aromaticity, ptC arrangements, hydrogen‐bridge bonds, ionic bonds, and covalent bonds, which, along with their unique geometric features, may result in new applications.     

Theoretical study of the structure and stability of the Na2Cl+, NaCl 2? , Na3Cl 2+ , and Na2Cl 3? ions

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na₂Cl⁺, NaCl ₂ ⁻ , Na₃Cl ₂ ⁺ , and Na₂Cl ₃ ⁻ ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na₂Cl⁺ and NaCl ₂ ⁻ triatomic ions have a linear equilibrium D _∞h configuration. The pentaatomic ions can exist in the form of the D _∞h linear isomer, C _2v planar cyclic isomer, or D _3h bipyramidal isomer. At ∼1000 K the Na₃Cl ₂ ⁺ and Na₂Cl ₃ ⁻ ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions Δ_f H ⁰(0 K) was determined: 230 ± 2 kJ/mol (Na₂Cl⁺), −96 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ), −616 ± 2 kJ/mol (NaCl ₂ ⁻ ), and −935 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ). Original Russian Text Copyright ? 2007 by T. P. Pogrebnaya, A. M. Pogrebnoi, and L. S. Kudin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 6, pp. 1053–1061, November–December, 2007.     

Structural and thermodynamic characteristics of ionic associates in vapors over sodium bromide and iodide

Nonempirical methods are used to calculate the geometric parameters, the frequencies of normal vibrations, and thermochemical characteristics of ions existing in saturated vapors over sodium bromide and iodide: Na₂X⁺, NaX₂⁻, Na₃X₂⁺, and Na₂X₃⁻ (X = Br, I). According to the calculations, Na₂X⁺ and NaX₂⁻ triatomic ions have a linear equilibrium configuration of D _∞h symmetry. Pentaatomic ions can exist in the form of three isomers: linear with D _∞h symmetry, planar cyclic with C _2v symmetry, and bipyramidal with D _3h symmetry. At a temperature of ∼1000 K, Na₃X₂⁺ and NaX₃⁻ pentaatomic ions are shown to be present in vapor mainly in the form of linear isomers. The energies and enthalpies of ion molecular reactions with the participation of the above ions are calculated, and the formation enthalpies of the ions are determined, Δ _f H ^o(0 K): 293±2 kJ/mol (Na₂Br⁺), 354±2 kJ/mol (Na₂I⁺), −536±2 kJ/mol (NaBr₂⁻, −458±2 kJ/mol (NaI₂⁻, 24±5 kJ/mol (Na₃Br₂⁺, 143±5 kJ/mol (Na₃I₂⁺, −810±5 kJ/mol (Na₂Br₃⁻, and −675±5 kJ/mol (Na₂I₃⁻.     

Stabilization of octacoordinate carbon center in metal-containing derivatives of orthocarbonic acid

The electronic and spatial structures of alkali metal compounds CO₃M₂, CO₃M₃ ⁺, and CO₄M₄ (M = Li, Na, K) were investigated by the ab initio (MP2(full)/6-311+G**) and density functional (B3LYP/6-311+G**) methods. The calculated energies of formation decrease in the order E ^Li > E ^Na > E ^K for all structural types, being determined by steric and orbital interactions. Stable structures with octacoordinate carbon are formed in the case of CO₄M₄ salts. Dedicated to Academicians A. L. Buchachenko and N. S. Zefirov on the occasions of their 70th birthdays. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1929–1938, September, 2005.     

Fourier-transform infrared spectroscopic studies of dithia tetraphenylporphine

We present here infrared absorption spectra of dithia tetraphenylporphine and its cation in the 450–1600 and 2900–3400 cm⁻¹ regions. Most of the allowed IR bands are observed in pairs due to overallD _2h point group symmetry of the molecule. The observed bands have been assigned to the porphyrin skeleton and phenyl ring modes. Some weak bands, which are forbidden underD _2h , also appear in the spectra due to the distortion of the molecule from planarity-caused by the out-of-plane positioned N and S atoms. Increased intensity of some phenyl ring bands compared to free-base tetraphenylporphine is explained on the basis of rotation of phenyl rings towards the mean molecular plane. Contrary to the point group symmetry of cation of dithia tetraphenylporphine, certain bands are observed to be degenerate due to identical bonding arrangements in pyrrole rings of the cation     

Ab initio study of bonding trends for f0 actinide oxyfluoride species

 Fully relativistic, four-component Dirac–Fock calculations and quasirelativistic pseudopotential calculations at different ab initio levels are used to study the bonding trends among the naked, triatomic [OAnO] ^q+ groups or the oxyfluorides [AnO _n F _m ] ^q with f ⁰ configurations. The triatomic f ⁰ series is suggested to range from the bent ThO₂ via the linear OPaO⁺ to at least NpO₂ ³⁺, a possible new gas-phase species. The neutral oxyfluoride molecules include the experimentally unknown NpO₂F₃ and PuO₂F₄. The latter is a candidate for the so far unknown oxidation state Pu(VIII), which is found to lie considerably above Pu(VI), but to be locally stable. Their all-oxygen isoelectronic analogues are NpO₅ ³⁻, known in the solid state, and the unknown PuO₆ ⁴⁻. Further possible candidates for Pu(VIII) are PuO₄(D _4h ) and the cube-shaped PuF₈(O _h ). Isoelectronic UF₈ ²⁻ is calculated to be D _4d , in agreement with experiment. Received: 18 May 2001 / Accepted: 21 June 2001 / Published online: 11 October 2001     

Planar D 2h B26H8, D 2h B26H8 2+, and C 2h B26H6: Building Blocks of Stable Boron Sheets with Twin-Hexagonal Holes

The most stable mono-layer boron sheets were predicted to have both the isolated hexagonal hole and the twin-hexagonal hole. Previous investigations indicate that planar B₁₈H _n ^q (n = 3–6, q = n ? 4) are the building blocks of boron sheets with isolated hexagonal holes. Extensive DFT investigations performed in this work show that D _2h B₂₆H₈, D _2h B₂₆H₈ ²⁺, and C ₂ B₂₆H₆, may serve as the building blocks of boron sheets with twin-hexagonal holes. These bicyclic clusters possess planar or quasi-planar geometries at B3LYP/6-311+G(d,p) level, with 16, 14, and 14 delocalized π electrons, respectively. Detailed analyses indicate that they are overall aromatic in nature, with the formation of islands of both σ and π aromaticity. They are analogous to D _2h C₁₆H₁₄ and D _2h C₁₆H₁₄ ²⁺ in π bonding patterns, respectively, but fundamentally different from the latter in σ-bonding. Remarkably, all of them appear to be energetically the lowest-lying isomers obtained, which are promising targets for future gas phase syntheses. These hydroboron clusters, together with B₁₈H _n ^q clusters, establish the molecular basis for modeling the short-range structures, nucleation, and growth processes of monolayer boron sheets. The results obtained in this work enrich the chemistry of boron hydride clusters and expand the analogy relationship between hydroborons and hydrocarbons.     

Hydrogenation of B 120/? : A Planar-to-Icosahedral Structural Transition in B12H n0/? (n?=?1–6) Boron Hydride Clusters

A systematic density functional theory and wave function theory investigation performed in this work reveals a planar-to-icosahedral structural transition between n = 4–5 in the partially hydrogenated B₁₂H _n ^0/− clusters (n = 1–6) upon hydrogenation of all-boron B₁₂^0/−. Coupled cluster calculations with triple excitations (CCSD(T)) indicate that a distorted icosahedral B₁₂H₆ cluster with C₂ symmetry is overwhelmingly favored (by 35 kcal/mol) over the recently proposed perfectly planar borozene (D_3h B₁₂H₆) (Szwacki et al., Nanoscale Res Lett 4:1085, 2009) which proves to be a high-lying local minimum. A similar 2D–3D structural transition occurs to the corresponding boron boronyl analogues of B₁₂(BO) _n with n –BO terminals. Detailed adaptive natural density partitioning (AdNDP) analyses reveal the bonding patterns of these quasi-planar or cage-like clusters which are characterized with delocalized σ and π molecular orbitals. The electron detachment energies of the concerned anions and excitation energies of the neutrals are also predicted to facilitate their future experimental characterizations.     

Synthesis and spectroscopic characterisation of aurichalcite (Zn,Cu2+)5(CO3)2(OH)6; implications for Cu–ZnO catalyst precursors

The Cu–ZnO catalyst precursors with variable Cu:Zn ratio, between Zn-rich and Cu-rich compositions have been investigated by a combination of electronic and vibrational spectroscopy. Synthesized catalyst precursors exhibit two d–d transition bands of Cu²⁺ ions in a distorted octahedral symmetry, at 7,600 and 12,900 cm⁻¹ (1,315 and 775 nm). The effect of structural cation substitution (Zn²⁺ and Cu²⁺) on band shifts is observed in the spectra of the synthetic catalyst precursors. The observation of two broad features at ∼7,600 and 12,900 cm⁻¹ (1,315 and 775 nm) is a strong indication for Zn²⁺ substitution by Cu²⁺ ions. The result of multiple bands in the symmetric stretching and bending regions confirms the reduction of symmetry from D _3h to C _2v /C _s for (CO₃)²⁻ ion in aurichalcite. The synthetic aurichalcite may be used as a standard for identification of spectral properties of naturally occurring anhydrous carbonate minerals.     

Voltammetric and potentiometric studies of some sulpha drug-Schiff base compounds and their metal complexes

The electrochemical behavior of some sulpha drug-Schiff bases at a mercury electrode was examined in the Britton-Robinson universal buffer of various pH values (2.5–11.7) containing 20% v/v) of ethanol using DC-polarography, cyclic voltammetry and controlled-potential electrolysis. The DC-polarograms and cyclic voltammograms of the examined compounds exhibited a single, 2-electron, irreversible, diffusion-controlled cathodic step within the entire pH range which is attributed to the reduction of the azomethine group-CH=N- to -CH₂-NH-. The symmetry transfer coefficient (α) of the electrode reaction and the diffusion coefficient (D ₀) of the reactant species were determined. The electrode reaction pathway of the compounds at the mercury electrode was suggested to follow the sequence: H⁺, e⁻, e⁻, H⁺. The dissociation constant of the sulpha drug-Schiff bases, the stability constant and stoichiometry of their complexes with various divalent transition metal ions (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) were determined potentiometrically at room temperature.      

Magnetic properties of fullerene salts containing d- and f-metal cations (Co2+, Ni2+, Fe2+, Mn2+, Eu2+, Cd2+). Specific features of the interaction between C60·? and the metal cations

The interaction between the radical anions C₆₀ ^·− and divalent d- and f-metal (Co, Fe, Ni, Mn, Eu, Cd) cations in DMF and acetonitrile-benzonitrile (AN-BN) mixture was studied. Black solid polycrystalline salts (C₆₀ ^·−)₂{(M²⁺)(DMF) _x } (x = 2.4–4, 1–6) containing the radical anions C₆₀ ^·− and metal(ii) cations solvated by DMF were prepared for the first time and their optical and magnetic properties were studied. The salts containing Co²⁺, Fe²⁺, and Ni²⁺ are characterized by antiferromagnetic interactions between the radical anions C₆₀ ^·−, which result in unusually large broadening of the EPR signal of C₆₀ ^·− upon lowering the temperature (from 5.55–12.6 mT at room temperature to 35–40 mT at 6 K for Co²⁺ and Ni²⁺). The salts containing Mn²⁺ and Eu²⁺ form diamagnetic dimers (C₆₀ ⁻)₂, which causes a jumpwise decrease in the magnetic moment of the complexes and disappearance of the EPR signal of C₆₀ ^·− in the temperature range 210–130 K. A feature of salt 6 is magnetic isolation of the radical anions C₆₀ ^·− due to the presence of diamagnetic cation Cd²⁺. The salts prepared are unstable in air and decompose in o-dichlorobenzene or AN. Reactions of C₆₀ ^·− with metal(ii) cations in AN-BN mixture result in decomposition products of the salts that contain neutral fullerene dimers and metals solvated by BN. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1909–1919, September, 2008.