Planar Four-Coordinate Carbon in Star-Like Perlithioannulenes C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Li<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 3–6)

The structure and stability of perlithioannulenes C _n Li _n (n = 3–6) were examined ab initio [MP2(full)/6-311+G**] and in terms of the density functional theory (B3LYP/6-311+G**). The systems with n = 3, 5, and 6 may be stabilized as planar star-like structures with bridging lithium atoms and hypercoordinate carbon atoms. Star-like structures are the most stable isomers of odd-numbered annulenes (n = 3, 5), while the most stable isomers of even-numbered annulenes (n = 4, 6) have less symmetric nonplanar structures.     

Isomerization reactions of RSNO (R=H,C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>H<Subscript>2<Emphasis Type="Italic">n</Emphasis>+1</Subscript><Emphasis Type="Italic">n</Emphasis>≤ 4)

We have applied various theoretical methods to gain detailed insights into the isomers as well as the transition states (TSs) along the corresponding reaction pathways for RSNO (R=H, C _n H_2n+1 n ≤ 4). On the basis of G2 and G2MP2 results, the relative order of stability for R=H is estimated to be trans-HSNO > cis-HSNO > HNSO > cis-HONS trans-HONS, while it is cis-CH₃SNO trans-CH₃SNO > CH₃NSO > trans-CH₃ONS > cis-CH₃ONS for R=CH₃. A similar trend is also obtained from the B3P86 method with considerably less computing effort if the nearly isoenergetic isomers cis-HONS and trans-HONS are ignored. Based on the results of B3P86, cis-RSNO is more stable than trans-RSNO when R=H is replaced by alkyl groups except for R=t-Bu. Natural bond orbital analyses allow us to explore whether the high reactivity of S-nitrosothiols is due to the strong negative hyperconjugation (). The mesomeric effect of S-nitrosothiols, although non-negligible, does not cause the breakage of N–O bond due to the compensation of columbic attraction between N and O.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

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.     

Gas-phase structures of 1-adamantylphosphines,PH<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>(1-Ad)<Subscript>3−<Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1–3)

The gas-phase structure of 1-adamantylphosphine has been determined by electron diffraction, supplemented with data from ab initio and DFT calculations. The adamantyl fragment was modeled with local C _3v symmetry and the phosphino group was found to be in a position almost bisecting a mirror plane of the adamantyl group, giving the molecule overall approximate C _s symmetry. There is a small displacement of the C–P bond from the local threefold axis of the adamantyl group. Geometry optimizations were also performed for bis-(1-adamantyl)phosphine (C ₁ point-group symmetry) and tris-(1-adamantyl)phosphine (C ₃ symmetry), demonstrating extremely crowded environments around the phosphorus atoms leading to adamantyl groups that were much less symmetric. The adamantyl groups were also found to twist by a significant amount to minimize the strain.     

Fast evaluation of molecular auxiliary functions <Emphasis Type="Italic">A</Emphasis><Subscript>α</Subscript> and <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> by analytical relations

Analytical relations through the initial values are derived for the molecular auxiliary functions A _α (x) and B _n (x), where α =n+ɛ, 0⩽ ɛ < 1 and n=0,1,2,.... These relations are useful in the fast calculation of multicenter molecular integrals over integer and noninteger n Slater type orbitals. It is shown that the formulas obtained are numerically stable for all values of n,ɛ and x.PACS No: 31.15.+q, 31.20.EjAMS subject classification: 81-V55, 81-V45     

Phase Diagrams of the <Emphasis Type="Italic">n</Emphasis>-Decane–<Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane, <Emphasis Type="Italic">n</Emphasis>-Decane–Cyclododecane,and <Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane Systems

The n-decane–n-hexadecane–cyclododecane, n-decane–cyclododecane, and n-hexadecane–cyclododecane systems are studied by means of low-temperature differential thermal analysis using a differential scanning heat flow calorimeter. It is noted that all studied systems belong to the eutectic type. It is concluded that in the n-decane–n-hexadecane–cyclododecane system, the eutectic composition contains 85.0 wt % n-С₁₀Н₂₂, 4.0 wt % n-С₁₆Н₃₄, and 11.0 wt % С₁₂Н₂₄. It has a melting point of ?35.0°C.     

HNO(H<Subscript>2</Subscript>O)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1–4) clusters: a theoretical study

The geometrical structure, binding energy, and vibrational spectra of small clusters of nitrosyl hydride (HNO) and water molecules, HNO(H₂O) _n , where (n = 1–4), have been investigated at the MP2 level of theory, using 6-311++G(2d,2p) basis set. We located three dimers, six trimers, nine tetramers, and three pentamers at the MP2/6-311++G(2d,2p) computational level. Particular attention is given to existence and magnitude of NH···O blue-shifting hydrogen bonds. Blue shifts of the NH stretching frequency upon complex formation in the ranges between 28 and 151 cm⁻¹ is predicted. Cooperative effect in terms of stabilization energy along with the many-body interaction energies analysis was performed for the studied clusters. The Atoms in Molecules (AIM) theory was also applied to explain the nature of the complexes.     

The equilibrium structures of the Li[C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>]<Subscript>1</Subscript> (<Emphasis Type="Italic">n</Emphasis> = 7–12) complexes and their alternation depending on <Emphasis Type="Italic">n</Emphasis>

The equilibrium geometric configurations of the Li[C _n ]₁ (n = 7–12) complexes, where [C _n ]₁ is a cylindrical hydrocarbon containing the simplest zigzag nanotube fragment, were determined by the density functional theory method with the PBE0 exchange-correlation functional. Analytic molecular orbital (MO) estimates were obtained for isolated [C _n ]₁ hydrocarbons in the Hückel approximation. The appearance of nonbonding MOs for hydrocarbons with even n was demonstrated. Equilibrium structure types were found to alternate as n increased. This alternation correlated with the behavior of the frontier orbitals of the [C _n ]₁ hydrocarbon. At odd n, the Li atom was situated near the boundary of the π electron density of the bracelet, and the complex had C _s symmetry. Complexes with even n had the C _2v point group, and lithium was situated in the inner cylinder cavity above the center of one of benzene rings.     

Thermodynamic study of nanoclusters of lead (Pb<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>, <Emphasis Type="Italic">n</Emphasis> = 1–6): adsorption of small molecules on the Pb<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters

Nanoclusters of lead (Pb _n , n = 1–6) were studied theoretically employing MP2 and M062X methods. Structural and thermodynamic properties as well as ionization energies and electron affinities of two isomers of Pb₃, six isomers of Pb₄, seven isomers of Pb₅ and seven isomers of Pb₆ were obtained at 298 K. Rhombic, pyramidal and octagonal structures were the most stable forms of the Pb₄, Pb₅ and Pb₆ clusters, respectively. Proton affinities of the Pb _n clusters were computed, which were in the range of 200–250 kcal/mol. Adsorption of C₂H₂, C₂H₄, CO, CO₂, CH₂O, HNO, O₃, NO, N₂O, NO₂, N₂O₄ and N₂O₅ on the Pb _n clusters was studied. O₃ showed the strongest interaction with the Pb _n clusters with adsorption enthalpies of 80–130 kcal/mol. HNO, O₃, N₂O, N₂O₄ and N₂O₅ were dissociated after adsorption on the Pb _n clusters. N₂O decomposes to adsorbed O atom and a free N₂ molecule, while N₂O₄ and N₂O₅ release a NO₂ molecule.     

Structure of (DMF)<Subscript>m</Subscript>(HCl)<Subscript>n</Subscript> complexes (<Emphasis Type="Italic">m</Emphasis>= 2, <Emphasis Type="Italic">n</Emphasis> = 3–4)

(DMF)₂(HCl)₃ and (DMF)₂(HCl)₄ heterocomplexes were studied for the first time in terms of the B3LYP/6-31++G(d, p) density functional calculation. The resulting data about their structure, stability, strength of intermolecular bonds, and degree of proton transfer in O...H...Cl bridges are compared with the results of a similar calculation fulfilled for (DMF)_m(HCl)_n clusters (m, n = 1–2) and with the experimental data on the structure and properties of acid-base complexes in DMF solutions of HCl. An extremely stable symmetrical cycle of four molecules — (DMF)₂(HCl)₂ — is assumed to be a structure-forming element of solution in the DMF-HCl system in the range of concentrations achievable under normal conditions. When [HCl]₀ > [DMF]₀, the “excess” hydrogen chloride molecules add to the chlorine atoms of this cycle, forming heterocomplexes with a branched structure. Addition of more HCl molecules to the (DMF)₂(HCl)₂ cycle appreciably increases the degree of proton transfer from acid to base molecule.     

Phenyl(trimethylsiloxy)fluorosiloxanes PhSi(OSiMe<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>F<Subscript>3−<Emphasis Type="Italic">n</Emphasis></Subscript>

The siloxane bond splitting reaction in hexamethyldisiloxanes PhSiCl _n F_3?n was studied.     

Investigations of the EPR parameters for Cu<Superscript>2+</Superscript> in [Cu(ipt)(dap)H<Subscript>2</Subscript>O]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>•<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants) for Cu²⁺ in [Cu(ipt)(dap)H₂O] _n ?nH₂O (ipt is isophthalic acid, dap–1,3-diaminopropane) are theoretically investigated from the high order perturbation formulas of these parameters for a 3d ⁹ ion in a rhombically elongated octahedron. The ligand orbital and spin-orbit coupling contributions are included from the cluster approach because of strong covalency of the system. The nearly axial anisotropies of the g factors and hyperfine structure constants are correlated to the significant elongation distortion of the five-fold coordinated Cu²⁺ (in a distorted square pyramidal [CuN₂O₃] group). Nevertheless, the perpendicular anisotropies arising from the nonequivalent planar ligands are largely concealed by the experimental uncertainties. The theoretical analysis of the EPR behaviours for [Cu(ipt)(dap)H₂O] _n ?nH₂O would be helpful to understand the local structures and properties of this and relevant systems.     

New “s<Emphasis Type="Italic">p</Emphasis><Superscript><Emphasis Type="Italic">2</Emphasis></Superscript>-bonded” carbanucleosides

By reaction of 2,3-dichloro-, 2,3,5-trichloro-, 2,5-dichloro-3-phenylsulfonyl-, 2-chloro-3-phenylsulfonyl-4,4-ethylenedioxycyclopent-2-en-1-ones with uracyl 3- and 2-uracyl derivatives were obtained of the corresponding chlorocyclopentenone.     

Kinetics of thermal reaction HOCl ⇄ H(<Superscript>2</Superscript><Emphasis Type="Italic">S</Emphasis>) + OCl(<Emphasis Type="Italic">X</Emphasis><Superscript>2</Superscript>Π<Subscript><Emphasis Type="Italic">i</Emphasis></Subscript>) in gas phase

The kinetics of gas reaction \(HOCl\underset{{k_r }}{\overset{{k_f }}{\longleftrightarrow}}H(^2 S) + OCl(X^2 \Pi _i )\) was analyzed by the MP4 method. In the temperature range of 100–373 K the rate constants k _f and k _r and equilibrium constant K were changed from 1.10 × 10^?220 to 1.17 × 10^?52 s^?1, from 2.89 × 10^?16 to 1.68 × 10^?5s^?1 and from 3.80 × 10^?205 to 6.96 × 10^?48 respectively. In the above temperature range, the activation energy of the forward reaction (E _f) is 105.05 kcal/mol. In the same temperature interval there are two kinetic domains for the reverse reaction with activation energies (E _r1 = 5.53 kcal/mol when T is 100–273 K and E _r2 = 14.50 kcal/mol when T is 273–373 K, respectively.     

Spatial Structure,Electron Energy Spectrum,and Growth of HfSi<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>−</Superscript></Stack> Clusters (<Emphasis Type="Italic">n</Emphasis> = 6–20)

The optimized spatial structure and calculated electronic spectra of anionic clusters HfSi _n ^? (n = 6–20) are presented. The calculations have been performed by the density functional theory method. By comparing the calculated and available experimental data, the spatial structures of the clusters detected in the experiment have been determined. It has been established that the formation of endohedral structures begins with n = 12, when a stable structure of a prism encapsulating a hafnium atom is formed. Clusters with n = 12 and 16 have increased stability and are basic for the construction of clusters with a close number of silicon atoms.     

A density functional theory study on the Ag<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>H (<Emphasis Type="Italic">n</Emphasis> = 1–10) clusters

Density functional GGA-PW91 method with DNP basis set is applied to optimize the geometries of Ag _n H (n = 1–10) clusters. For the lowest energy geometries of Ag _n H (n = 1–10) clusters, the hydrogen atom prefers to occupy the two-fold coordination bridge site except the occupation of single-fold coordination site in AgH cluster. After adsorption of hydrogen atom, most Ag _n structures are slightly perturbed and only the Ag₆ structure in Ag₆H cluster is distorted obviously. The Ag–Ag bond is strengthened and the strength of Ag–H bond exhibits a clear odd–even oscillation like the strength of Au–H bond in Au _n H clusters, indicating that the hydrogen atom is more favorable to be adsorbed by odd-numbered pure silver clusters. The adsorption strength of small silver cluster toward H atom is obviously weaker than that of small gold cluster toward H atom due to the strong scalar relativistic effect in small gold cluster. The pronounced odd–even alternation of the magnetic moments is observed in Ag _n H systems, indicating that the Ag _n H clusters possess tunable magnetic properties by adsorbing hydrogen atom onto odd-numbered or even-numbered small silver cluster.     

Structures and electronic properties of germanium-doped Ni<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters, <Emphasis Type="Italic">n</Emphasis> = 13–23

The magnetic property and electronic properties such as binding energy, charge transfer, ionization potential and electron affinity of the Ni _n–1Ge (n = 13–23) neutral and ionic clusters have been studied using the density functional theory calculations with the PBE exchange-correlation energy functional. The calculated total magnetic moments decrease with the addition of Ge atom. Both the calculated ionization potential and electron affinity exhibit an oscillating behavior as the cluster size increases.     

Electronic spectra of the linear cationic chains NC<Subscript>2<Emphasis Type="Italic">n</Emphasis></Subscript>N<Superscript>+</Superscript> (<Emphasis Type="Italic">n</Emphasis> = 1–7): an ab initio study

The ground-state equilibrium geometries of the linear carbon chain cations NC_2n N⁺ (n = 1–7) have been investigated with B3LYP, CAM-B3LYP, and RCCSD(T) calculations. The ground state (X²П_g/u) and excited state (1²П_u/g) have been optimized by using the complete active space self-consistent field method. The present study reveals that these linear cations generally have the characteristic of bond length alternation in both electronic states. The vertical excited energies for the dipole-allowed (1, 2, 3)²П_u/g ← X²П_g/u transitions as well as the dipole-forbidden 1²Φ_u/g ← X²П_g/u transitions have been computed with the complete active space second-order perturbation theory. The calculated transition energies of 1²П_u/g ← X²П_g/u for NC_2n N⁺ (n = 1–6) in the gas phase are 2.26, 2.09, 1.91, 1.72, 1.56, and 1.39 eV, respectively, which mutually agree well with the available experimental values of 2.11, 2.07, 1.88, 1.67, 1.49, and 1.34 eV. Moreover, the corresponding absorption wavelengths are predicted to have the significant nonlinear size dependence, which is different from the bands origin in NC_2n N (n = 1–7).     

Theoretical study of stepwise chlorinated aluminide clusters Al<Subscript>13</Subscript>Cl<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>−</Superscript></Stack> (<Emphasis Type="Italic">n</Emphasis> = 1–9)

The electronic and geometric structures, energy stabilities, normal mode frequencies, and spin density distributions (in radicals) of different stepwise-chlorinated aluminum clusters Al₁₃Cl _n ^? (n = 1–9) are calculated within the B3LYP approximation of the density functional theory using 6-31G* and 6-311+G* basis sets. The results are compared with analogous computation data on hydrides Al₁₃H _n ^? (n = 1–12) obtained at the same level. The general qualitative pattern for related series of hydrides, chlorides, and iodides (as well as fluorides and bromides) turns out to be similar in many respects. For all Al₁₃X _n ^? clusters with different electronegative substituents X, there is a set of a considerable number of low-lying closely spaced inner isomers (with a centered icosahedral cage), marquee isomers, and outer isomers (capped). The effects found by calculations in centered icosahedral isomers—localization of spin density on the trans-Al* atom in radical anions and its associated trans addition rule for an even substituent and the zigzag (odd-even) dependence of the energies D _n (X) of successive addition of substituents X to the metal cage on n described in the framework of the molecular model of the valence states of the Al ₁₃ ^? superatom—should also be shared by many Al₁₃X _n ^? series with different X’s. The differences between hydrides Al₁₃H _n ^? and chlorides Al₁₃Cl _n ^? of the same type are quantitative. For the hydrides, inner isomers are preferable in the first half of the series (n = 1–6); and in the second half (n = 7–12), outer isomers are more favorable. For the chlorides, icosahedral isomers are preferable only at the very beginning of the series. In the other cases, nonicosahedral structures are most favorable, for which the situation becomes very complicated due to the large number of position isomers and the aforementioned simple rules found for centered icosahedral structures are fulfilled to a considerably less extent or not at all.     

Interaction between threonine and cadmium cation in [Cd(Thr)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>]<Superscript>2+</Superscript> (<Emphasis Type="Italic">n</Emphasis> = 1–3) complexes: density functional calculations

Structures corresponding to energy minima and the binding of cadmium cation to threo- nine (Thr) in model systems [Cd(Thr) _n ]²⁺ (n = 1–3) were studied theoretically. Quantum chemical computations were performed within the framework of the density functional theory using the B3LYP, BLYP, and P functionals. In the optimized structures of the complexes [CdThr]²⁺ and [Cd(Thr)₂]²⁺, threonine acts as a bidentate ligand and cadmium binds to oxygen atoms of carbonyl and hydroxyl groups with the formation of one and two six-mem- bered rings, respectively. In the complex [Cd(Thr)₃]²⁺, cadmium binds to three nitrogen atoms and three oxygen atoms of carbonyl groups in three Thr molecules to form three five-mem- bered rings.