Quantum-chemical investigation of structure and stability of [<Emphasis Type="Italic">n</Emphasis>]-prismanes and [<Emphasis Type="Italic">n</Emphasis>]-asteranes

The study by DFT [B3LYP/6-311G(2df,p)] method of structural and energy characteristics peculiar to [n]-prismanes and [n]-asteranes demonstrated that prismanes of n = 3–10 and asteranes of n = 3–7 possessed a stable structure of D_nh-symmetry; the D_nh-geometry was distorted in the subsequent terms of the series.     

The molecular designs and properties of asymmetric heterocycles (HBrBN<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1-4)

The structures and properties of asymmetric heterocycles (HBrBN₃) _n (n = 1-4) are systematically studied at the B3LYP/6-31G* level. The molecules (HBrBN₃) _n (n = 2-4) have the core structures of a 2n-membered ring with alternating boron and α-nitrogen atoms. The relationships between geometrical parameters and oligomerization degree n are discussed. The calculated IR spectra have four main characteristic regions. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed. Thermodynamic analysis of the gas-phase oligomerizations shows that formation of the most stable heterocycles (HBrBN₃) _n (n = 2-4) is enthalpy driven in the range of 200-800 K.     

Structures and magnetic properties of Ni<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 36-40) clusters from first-principles calculations

A genetic algorithm (GA) coupled with a tight-binding (TB) interatomic potential is used to search for the low-energy structures of medium-sized Ni _n (n = 36-40) clusters. Structural candidates obtained from our GA search are further optimized with first-principles calculations. The medium-sized nickel clusters ranging from 36 to 40 atoms are found to favor the double-icosahedron-based structures with a Ni₇ core (a pentagonal bipyramidal structure) except Ni₃₈ cluster. The lowest-energy structure of Ni₃₈ can be considered to be a magic cluster, which is a typical face-centered cubic structure with large stability and magnetic moment.     

Synthesis and structures of benzo[<Emphasis Type="Italic">cd</Emphasis>]furo[2,3-<Emphasis Type="Italic">f</Emphasis>]indol-4(5<Emphasis Type="Italic">H</Emphasis>)-one derivatives

A procedure was developed for the synthesis of derivatives of the new heterocyclic system, benzo[cd]furo[2,3-f]indole, based on the cyclodehydration of 6-acylmethyloxy-1-alkyl-benzo[cd]indol-2(1H)-ones. Either 7- or 8-aryl derivatives of benzo[cd]furo[2,3-f]indol-4(5H)-ones can be prepared depending on the reaction conditions. The molecular and crystal structures of 7- and 8-phenylbenzo[cd]furo[2,3-f]indol-4(5H)-ones were established by X-ray diffraction.     

Calculated properties of neutral and charged Al<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> clusters by density functional theory

Density functional calculations are performed to study the structures and electronic properties of Al _n Co _m clusters with n = 1–7 and m = 1–2. Frequency analysis is also performed after structural optimization to make sure that the calculated ground states are real minima. The corresponding total and binding energies, adiabatic electron affinities and ionization potentials are presented and discussed to aid the identification of our calculations. The BSSE correction is also considered in our calculation. Among Al _n Co _m , Al _n Co _m ⁻, and Al _n Co _m ⁼ clusters (n = 1–7 and m = 1–2), Al₄Co⁻, Al₆Co⁻, Al₂Co₂, and Al₆Co₂ are predicted to be more stable. Our results are consistent with the available experimental data.     

Structure of A Coordination Polymer [Cu(En)<Subscript>2</Subscript>CrO<Subscript>4</Subscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

The crystal structure of [Cu(En)₂CrO₄]_n (En is ethylenediamine) is determined: a = 14.7359(4) Å, b = 9.8083(3) Å, c = 14.2664(4) Å, V = 2061.98(10) ų, space group Cmce, Z = 8, d_x = 1.931 g/cm³. It is demonstrated that the studied phase is isostructural with [Сu(Еn)₂SO₄]_n. A pseudotetragonal copper atom coordination (Cu–N 2.0204 Å and 2.0244 Å, ∠N–Cu–N 84.73°) is completed to distorted octahedral by two oxygen atoms of chromate anions (Cu–O 2.433 Å and 2.380 Å).     

Spatial structure and stability of Mo<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Si<Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> nanoparticles

By means of the ab initio DMol³ method Mo _n Si _m nanoparticles and fragments of Mo₃Si and MoSi₂ crystal lattices are theoretically modeled. For both crystals a few neutral Mo₄Si₆ and Mo₆Si₆ fragments of different shapes and symmetry are considered. In each case, after cluster separation its geometry is optimized, as a result of which the geometric structure noticeably changes and its stability increases. In order to theoretically search for the spatial configurations of Mo₄Si₆ and Mo₆Si₆ nanoparticle, two approaches are used: 1) in the most stable Fe₄C₆ and Fe₆C₆ isomers found previously, iron and carbon atoms are replaced by molybdenum and silicon respectively and then the geometry is optimized to obtain new equilibrium distances and angles; 2) the search for main Mo₄Si₆ and Mo₆Si₆ configurations is performed using the binominal scheme, starting from Mo₂, MoSi, and Si₂ dimers. The nanoparticle structures are found to contain metal atom chains and isolated pairs and triples of silicon atoms. In most cases, the nanoparticle stability proves to be higher than that of the crystal clusters.     

Octafluorocyclohexa derivatives of [60]fullerene: C<Subscript>60</Subscript>(C<Subscript>4</Subscript>F<Subscript>8</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 2, 3, 4, and 6)

Fluorocyclohexa adducts C₆₀(C₄F₈) _n were synthesized by high-temperature reaction of fullerene C₆₀ with 1,2-C₂F₄I₂ or 1,4-C₄F₈I₂ in sealed tubes. Their separation by HPLC allowed us to determine molecular structure (X-ray diffraction) of four new compounds C₆(C₄F₈) _n (n = 2, 3, 4, and 6). Structures of isomers C₆₀(C₄F₈) _n were discussed in terms of a concept of consecutive addition of C₄F₈ groups to the fullerene cage.     

A Systematic Search for Structures and Stabilities of Asymmetric Clusters (HfInN<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1-6)

In order to find single source precursors (SSP), the structures, relative stabilities, and IR spectra of small asymmetric clusters (HFInN₃) _n (n = 1–6) are systematically investigated by means of the density functional theory at the B3LYP level. The obtained geometries show that the frameworks of clusters (HFInN₃) _n (n = 2–6) prefer to be 2n-membered ring with alternating indium and α-nitrogen atoms. The averaged binding energies reveal that all of asymmetric clusters (HFInN₃) _n (n = 1–6) can continue to gain energy as the cluster size n increasing. The second-order difference of energy (Δ₂E) and the HOMO-LUMO energy gap (E_gap) as a function of the cluster size n both exhibit a pronounced even-odd alternation phenomenon. The influences of cluster size n and temperature T on the thermodynamic properties of clusters are discussed. Judged by enthalpies and Gibbs free energies, the formations of the most stable clusters (HFInN₃) _n (n = 2–6) from the monomer are thermodynamically favorable in the range of 200–800 K.     

Synthesis of 6-methyl-8<Emphasis Type="Italic">H</Emphasis>-dibenzo[<Emphasis Type="Italic">a</Emphasis>,<Emphasis Type="Italic">g</Emphasis>]quinolizin-8-imines <Emphasis Type="Italic">via Reissert</Emphasis> compounds

Alkylation of Reissert compounds derived from 3-methylisoquinolines with several 2-cyanobenzylbromides followed by hydrolytic cleavage provided the corresponding 1-benzyl-3-methylisoquinolines. Treatment of the latter with methylmagnesiumiodide caused cyclization to the title compounds rather than formation of 2-acetylbenzylisoquinolines.     

Crystal structure of [Bi(<Emphasis Type="Italic">N</Emphasis>-ethylthiourea)<Subscript>4</Subscript>(ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>]ClO<Subscript>4</Subscript>

The structure of the bismuth(III) complex with N-ethylthiourea (Ettu) has been determined for the first time. We found that the crystal structure of [Bi(Ettu)₄(ClO₄)₂]ClO₄ is built of distorted octahedral cations [Bi(Ettu–S)₄(ClO₄)₂]ClO₄]⁺ and anions ClO₄^-. The deviation of one of the two independent Ettu molecules from the plane structure is explained by the mutual repulsion of the ligands and the formation features of hydrogen bonds. The C₂H₅(Ettu) group is in the cis position relative to the thiocarbonyl group.     

Reactions of ethyl 6,6-dialkyl-8,9-dioxo-5,6,8,9-tetrahydrobenzo[<Emphasis Type="Italic">f</Emphasis>]pyrrolo[2,1-<Emphasis Type="Italic">a</Emphasis>]isoquinoline-10-carboxylates with <Emphasis Type="Italic">N</Emphasis>-nucleophiles

Reaction of enaminoesters, derivatives of 2,2-dialkyl-1,2,3,4-tetrahydrobenzo[f]isoquinoline, with oxalyl chloride leads to the formation of ethyl 6,6-dialkyl-8,9-dioxo-5,6,8,9-tetrahydrobenzo[f]pyrrolo[2,1-a]-isoquinoline-10-carboxylates. At reaction of the latter with ammonia and cyclic amines opening of pyrroledione cycle occurs and the formation of enaminoketoamides, and the reaction with o-phenylenediamine furnishes a fragment of benzimidazole. Hydroxylamine behaves as binucleophile and attacks not only lactam, but also the ester group, affording heterocyclic system of isoxazine-3,4,6-trione.     

Reactions of 2-(2-propynylsulfanyl)-5,6,7,8-tetrahydrobenzo[<Emphasis Type="Italic">b</Emphasis>]thieno[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidin-4(<Emphasis Type="Italic">3H</Emphasis>)-one with arylsulfenyl chlorides

2-(2-propynylsulfanyl)-5,6,7,8-tetrahydrobenzo[b]thieno[2,3-d]pyrimidin-4(3H)-one with arylsulfenyl chlorides in chloroform gave products of anti-Markownikoff Ad _E-addition. The use of nitromethane as solvent in the presence of lithium perchlorate additives favored intramolecular electrophilic cyclization into 1-arylsulfanyl-1,2,6,7,8,9-hexahydro-4H-benzo[4,5]thieno[3,2-e][1,3]thiazolo[3,2-a]-pyrimidin-5-one.     

A DFT study of H<Subscript>2</Subscript>CO and HCN adsorptions on 3<Emphasis Type="Italic">d</Emphasis>, 4<Emphasis Type="Italic">d</Emphasis>, and 5<Emphasis Type="Italic">d</Emphasis> transition metal-doped graphene nanosheets

The binding of 3d (Sc, Ti, V), 4d (Y, Zr, Nb), and 5d (La, Hf, Ta) transition metals on graphene nanosheet (TM–GNS) with hydrogen-terminated edges and the adsorption of H₂CO and HCN molecules on the pristine and TM-doped GNSs were theoretically studied using a density functional theory method. The calculation showed that all TM atoms had strong binding with GNS, in which the Ta atom displayed the strongest interaction with GNS. The H₂CO and HCN molecules showed much stronger adsorption on the TM–GNSs than that on the pristine GNS. The H₂CO showed stronger interactions with TM–GNSs than that of HCN, in which the Ta-doping displayed the strongest interactions between the GNS and H₂CO or HCN. The adsorption interactions induced dramatic changes of TM–GNS electronic properties. The results revealed that the adsorption strength and sensor ability of GNS can be greatly improved by introducing appropriate TM dopants. Therefore, TM-doped GNSs are suitable for application in H₂CO and HCN storage and sensor.     

Isothermal solubility of individual light fullerenes in the homologous series of <Emphasis Type="Italic">n</Emphasis>-alkanes, <Emphasis Type="Italic">n</Emphasis>-alkanols, <Emphasis Type="Italic">n</Emphasis>-alkylcarboxylic acids,and arenes

Available published data on isothermal solubility (at 20°C) of individual light fullerenes in a homologous series of n-alkanes, n-alkanols, n-alkylcarboxylic acids, and arenas were systematized. A correlation between the parameter of Hildebrand’s cohesion and the logarithm of the mole fraction of the fullerene in the saturated solution was revealed.     

Coordination Polyhedra MC<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (M Is <Emphasis Type="Italic">s</Emphasis>-Metal Atom) in Crystal Structures

The crystallochemistry of compounds containing s-metal atoms in the carbon environment has been analyzed using the method of Voronoi–Dirichlet intersecting sectors and polyhedra. The chemical nature of the s metal has been found to affect the characteristics of the Voronoi–Dirichlet polyhedra. It is shown that the volume of Voronoi–Dirichlet polyhedron is practically independent of the coordination number of the s-metal atom.     

Speciation studies of nitric acid and U(VI) third phases in <Emphasis Type="Italic">n</Emphasis>,<Emphasis Type="Italic">n</Emphasis>-dialkyl amides/<Emphasis Type="Italic">n</Emphasis>-dodecane systems

Conventionally composition of the actinide-extractant solvate is assumed to be the same in the unpartitioned organic phase and the formed third phase. For example, if a m:n solvate has formed during extraction, the solvate is expected to be in the same state even during the third phase condition. However contemporary analysis, based on the spectroscopy measurements and empirical observations, has indicated the presence of an extended solvate. In this article, the proposed speciation in nitric acid and U(VI) third phase formation in n–n dialkyl amide/dodecane-nitric acid systems has been modeled with empirical correlations.     

Reactions of 3-Aroylpyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxaline-1,2,4(5<Emphasis Type="Italic">H</Emphasis>)-triones with 2,3-Dihydrofuran and 3,4-Dihydro-2<Emphasis Type="Italic">H</Emphasis>-pyran

3-Aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones reacted with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran to give mixtures of the corresponding hetero-Diels–Alder (furo- and pyrano[3″,2″: 5′,6′]pyrano- [4′,3′: 2,3]pyrrolo[1,2-a]quinoxalines) and Michael adducts (furyl- and pyranylpyrrolo[1,2-a]quinoxalines).