π‐Hole Bonds: Boron and Aluminum Lewis Acid Centers

MP2/aug‐cc‐pVTZ calculations were performed on complexes of boron and aluminum trihydrides and trihalides with hydrogen cyanide (ZH₃‐NCH and ZX₃‐NCH; Z=B, Al; X=F, Cl). The complexes are linked through the B???N and Al???N interactions, which are named as triel bonds and which are classified as π‐hole bonds. It was found that they possess numerous characteristics of typical covalent bonds, since they are ruled mainly by processes of the electron charge shift from the Lewis base to the Lewis acid unit. Other configurations of the ZH₃‐NCH and ZX₃‐NCH complexes linked by the dihydrogen, hydrogen, and halogen bonds were found. However, these interactions are much weaker than the corresponding π‐hole bonds. The quantum theory of atoms in molecules and the natural bond orbital approaches were applied to characterize the complexes and interactions analyzed. The crystal structures of triel trihydrides and triel trihalides were also analyzed for comparison with the results of calculations.     

Theoretical studies on Lewis acidity scale and bonding character of boron trihalides BX3(X=F,C1, Br,I) by DV-Xα quantum chemical approach

The Lewis acidity scale of boron trihalides BX₃ (X=F, C1, Br, I) and character of the boron-halogen bonds have been studied by means of DV-X_m approach. Present results show that the acid strength of boron trihalides increases in the order BF₃<BCl₃<BBr₃<BI₃, in excellent agreement with experiments. Based on boron-halogen bonding character, the valence of boron atom in boron compounds can be considered M equal to five instead of three which seems to be more reasonable.     

Oligomerization of Aluminum,Gallium, and Indium Trihalides in the Gas Phase: A Quantum-Chemical Study

The structural and thermodynamic properties of oligomers of Group IIIA metal trihalides [MX₃]_n(M = Al, Ga, In; X = F, Cl, Br, I; n = 2, 3, 4) have been obtained by the density functional theory B3LYP/LANL2DZ(d) method. The processes of tri- and tetramerization of trifluorides are exothermic and favorable at low temperatures. The fraction of trimeric molecules in aluminum and gallium chloride vapors is small (~10^?3%). For Al₃Cl₉ and Al₄Cl₁₂, in addition to the expected cyclic structures with three and four chloride bridges, the existence of their high-energy isomers with, respectively, six and eight bridging halogen atoms has been predicted.     

Thermodynamic calculations of the interaction of scandium halides with aluminum

The fundamental characteristics of the reduction of scandium trifluoride and trichloride with aluminum were studied by thermodynamic modeling over wide temperature and pressure ranges (1100–1400 K and 1–10⁶ Pa for ScF₃ and 800–1200 K and 1–10⁵ Pa for ScCl₃). Calculations of the equilibrium compositions of the systems were performed to draw conclusions about the contents of condensed and gaseous components and determine the temperatures of the complete reduction of trihalides with the formation of a two-phase alloy containing a saturated solution of scandium in aluminum and the Al₃Sc intermetallic compound. The results of modeling were in agreement with the available experimental data.     

Carboxylation of indoles and pyrroles with CO2 in the presence of dialkylaluminum halides

The Lewis acid-mediated carboxylation of arenes with CO₂ has been successfully applied to 1-substituted indoles and pyrroles by using dialkylaluminum chlorides instead of aluminum trihalides. Thus, the carboxylation of 1-methylindoles, 1-benzyl-, and 1-phenylpyrroles proceeds regioselectively with the aid of an equimolar amount of Me₂AlCl under CO₂ pressure (3.0 MPa) at room temperature to afford the corresponding indole-3-carboxylic acids and pyrrole-2-carboxylic acids in 61-85% yields, while the same treatment of 1,2,5-trimethylpyrrole affords the 3-carboxylic acid in 52% yield.     

Molecular structure of N,N′-o-phenylene-bis(salicylideneaminato)copper(II) studied by gas-phase electron diffraction and quantum-chemical calculations

The molecular structure of N,N′-o-phenylene-bis(salicylideneaminato)copper(II) (Cu(saloph)) was determined using the combination of gas-phase electron diffraction (GED), mass spectrometry, and quantum-chemical calculations. According to both experimental and theoretical approaches the molecule of Cu(saloph) is planar and possesses C _2v symmetry. Main structural parameters determined by GED experiment are the following (total error is given in a brackets): r _h1(Cu–N) = 1.960(20) Å, r _h1(Cu–O) = 1.913(17) Å, ∠NCuN = 82.7(18)°, ∠OCuO = 91.6(21)°, ∠NCuO = 92.9(9)°. The experimental structural parameters of Cu(saloph) molecules determined by X-ray single crystal analysis and GED experiments were discussed and compared to the theoretical ones.

     

Synthesis and reactivity of ω-haloalkyltin compounds

ω-Haloalkyltin trihalides, X(CH₂)_nSnX₃ (n ≧ 3; X = halogen) can readily be prepared in high yields by the direct reaction of stannous halides with α,ω-dihaloalkanes, catalysed by trialkylantimony compounds. The compounds are versatile starting materials for the synthesis of a variety of ω-functionallysubstituted organotin compounds R_3-mX_mSn(CH₂)_n Y (R = alkyl, phenyl; m = 0-3; X = Cl, Br, O; Y = Br, NMe₂, NEt₂, COOH, CHOHR, R₃Sn). ¹H-NMR spectral data for a series of such compounds are presented. The trends observed in the chemical shifts and the ¹¹⁹Sn—methyl proton coupling constants of Me_3-m Br_mSn(CH₂)_nBr (m = 0-3; n = 3-5) are discussed in terms of inductive effects. Intramolecular coordination between the ω-bromine atom and tin could not be demonstrated.     

New anionic species of tellurium(IV)

Tetrahaloaryltellurates(IV) were prepared by refluxing aryltellurium trihalides with phosphonium, tropylium and telluronium halides in CHCl₃. These compounds, which contain the ArTeX^?₄ anion, may be also prepared from aryltellurium trihalides and aqueous halogen hydride solutions. The phosphonium derivatives can be considered as potential precursors of tellurophosphoranes for Wittig reactions. Halogen exchange reactions allow the interconversion of the complex anions. The ionic nature of the compounds is supported by ion exchange reactions utilizing ion exchange resins, and by conductance measurements. Far infrared and Raman spectral data suggest a square pyramidal configuration for the ArTeX^?₄ anions.     

Push–pull effect on the charge transfer, and tuning of emitting color for disubstituted derivatives of mer-Alq3

To design innovative and novel optical materials with high mobility, two kinds of disubstituted derivatives for meridianal isomer of tris(8-hydroxyquinolinato)aluminum (mer-Alq3) with push–pull (X–Y) substituents have been designed. The structures of tris(4-X-6-Y-8-hydroxyquinolinato)aluminum (type 1) and tris(4-Y-6-X-8-hydroxyquinolinato)aluminum (type 2) (where X = –CH₃/–NH₂ and Y = –CN/–Cl) in the ground (S₀) and first excited (S₁) states have been optimized at the B3LYP/6-31G^* and CIS/6-31G^* level of theory, respectively. All the designed derivatives of type 1 show blue shift while most of the type 2 derivatives show red shift as compared to the mer-Alq3. The emitting color could be tuned from blue to red. We have explained the distribution of HOMOs and LUMOs on different individual ligands. The reorganization energies of tris(4-methyl-6-chloro-8-hydroxyquinolinato)aluminum (1), tris(4-methyl-6-cyano-8-hydroxyquinolinato) aluminum (2), tris(4-chloro-6-methyl-8-hydroxyquinolinato)aluminum (5) and tris(4-cyano-6-methyl-8-hydroxyquinolinato)aluminum (6) are comparable with mer-Alq3. Thus these derivatives might be good candidates for emitting materials possessing comparable charge carrier mobility as mer-Alq3.     

Use of imaging plates (IPs) in the gas-phase electron diffraction (GED) experiments on the EG-100 M apparatus. The tetrachloromethane molecule as a test object

The gas-phase electron diffraction (GED) experiment at the Moscow State University was carried out for the first time using imaging plates (IPs). The response of the Fuji BAS-MP IPs calibrated by means of ¹⁴C standard sources was found to be linear in a broad dynamic interval (larger than 10⁴). The GED study of tetrachloromethane was carried out in order to test the applied technique (IP reader FLA7000) and the developed software. The determined structural parameters of the CCl₄ molecule are in excellent agreement with those obtained in experiments with photographic registration.     

Electron diffraction study of the equilibrium structure of hexamethylenetetramine involving data from quantum chemistry and vibrational spectroscopy

The equilibrium structure of the urotropine molecule is characterized by means of gas electron diffraction (GED) with the involvement of quantum chemistry and vibrational spectroscopy. A structural analysis of the GED data is performed based on the parameters of the intramolecular potential function using of the program complex SYMM/DISP/ELDIFF/LARGE. The quadratic and cubic force constants of the urotropine molecule were obtained earlier on the basis of calculations at the MP2(full)/cc-pVTZ level and assuming molecular symmetry T _d . The values of the equilibrium geometric parameters r _e of the urotropine molecule are found. The experimental structural parameters are in good agreement with those calculated at the MP2(full)/cc-pVTZ level.     

Crystal structures and thermal behavior of complexes of group 13 metal halides with pyridine-type ligands

Complexes of group 13 metal halides with pyridine-type ligands (pyridine, pyrazine, and 4, 4´-bipyridine) have molecular, polymeric, or ionic structures containing metal atoms with a coordination number of 4, 5, or 6 depending on the component ratio, the acceptor ability of the halide, the donor ability and the coordination mode of the ligand. The strongest donor-acceptor bond is formed in the 1 : 1 molecular complexes, and their transition to the gas phase is energetically most favorable. The acceptor ability of Lewis acids in the complexes decreases in the series AlCl₃ > AlBr₃ > GaCl₃ > GaBr₃ > GaI₃. The stability of the complexes with respect to homogeneous dissociation correlates with the donor proton affinity. Group 13 metal trihalides act as catalysts for the pyrolysis of ligands.     

The molecular structure of tris-2,2,6,6-tetramethyl-heptane-3,5-dione indium: gas-phase electron diffraction and quantum chemical calculations

The molecular structure of tris-2,2,6,6-tetramethyl-heptane-3,5-dione indium, or In(thd)₃, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both the DFT calculations and the GED data collected at 387(8) K indicate that the molecules have D ₃ symmetry with a distorted anti-prismatic InO₆ coordination geometry. According to GED refinements, the twist angle θ, i.e. the angle of rotation of the upper and lower O₃ triangles in opposite directions relative to their positions in a regular prism is θ = ±24.9(1.2)° and the bond distances (r _h1) in the chelate ring are In–O = 2.127(4) Å, C–O = 1.268(3) Å and C–C = 1.411(3) Å, respectively. The DFT calculations yielded structure parameters in close agreement with those found experimentally.     

Catalytic effects of Fe,Al and Si on the formation of NO<Subscript>X</Subscript> precursors and HCl during straw pyrolysis

The catalytic effects of iron, aluminum or silicon on the formation of NO_X precursors (HCN, NH₃ and HNCO) and HCl during wheat straw pyrolysis were studied using a thermogravimetric analyzer (TG) coupled with a Fourier transform infrared (FTIR) spectrometer in argon atmosphere. The results show that the presence of iron, aluminum or silicon decreases conversion of straw-N into NH₃ with the sequence of Fe > Si > Al. The iron or silicon addition suppresses N-conversion into HCN and HNCO, and the aluminum addition has no notable influence on HCN emission during pyrolysis. The share of N-conversion to NH₃ and HCN increases, but that to HNCO and NO decreases a little in the presence of added iron, aluminum or silicon. The addition of SiO₂ results in the highest HCl removal efficiency.     

Benzyl-tris(trimethylsilyl)methylzinndihalogenide, {(CH3)3Si}3C(C6H5–CH2)SnHal2 mit Hal = Cl,Br, I

Benzyl-tris(trimethylsilyl)methyl Tin Dihalides, {(CH₃)₃Si}₃C(C₆H₅–CH₂)SnHal₂ with Hal = Cl, Br, I The tin tetrahalides SnHal₄ (Hal = Cl, Br, I) react with base-free tris(trimethylsilyl)methyllithium (Tsi–Li) solved in toluene to form the trihalides Tsi–SnHal₃. But when the reaction is carried out in a 1 : 2 molar ratio at 60 °C in toluene, Tsi–H, Tsi–Hal and benzyl-trisyl tin-dihalides are formed in good yields, respectively. The nmr (¹H, ¹³C, ²⁹Si, ¹¹⁹Sn) and the Raman spectra are discussed, the X-ray structure analyses of the dibromide as well as the diiodide have been measured.     

Alcohol‐Processable Organic Amorphous Electrolytes as an Effective Electron‐Injection Layer for Organic Light‐Emitting Diodes

A new series of monoammonium‐based organic electrolytes with the tetrafluoroborate (BF₄^?) counteranion have been synthesized. Replacing the pendant ethyl groups in the fluorenyl unit with 4‐ethoxyphenyl groups dramatically improves both solubility and morphological stability. The characterization of the alcohol‐processable amorphous ionic compounds as an electron‐injection layer in organic light‐emitting diodes (OLEDs) reveals that the organic electrolyte that comprises a rigid linear‐conjugated unit provides better device performance, with respect to its counterpart containing a branched bulky moiety. The capability of these compounds to facilitate electron injection from air‐stable aluminum metal is preliminarily discussed on the basis of the investigations of the electron‐only devices and photovoltaic experiments.     

Halides of Titanium in Lower Oxidation States

New investigations on the di‐ and trihalides of titanium, TiX₂ and TiX₃ (X = Cl, Br, I), with their 3d² and 3d¹ electronic configurations, confirm the early observations and conclusions of Klemm. At sufficiently low temperatures, Ti–Ti single bonds are formed in the one‐dimensional trihalides, i.e., Ti–Ti dimers are observed. Equally, in the two‐dimensional dihalides, {Ti₃} triangles occur with three single bonds. Phase transitions were detected from single‐crystal or powder X‐ray diffraction data, from magnetic measurements and thermal analysis. Except for the binary halides a number of ternary halides ATiX₃ (extended chains of facesharing octahedra), K₄Ti₃Br₁₂ (triples of face‐sharing octahedra), Na₂Ti₃Cl₈ (triangular trimers), A₃Ti₂X₉ (dimers of face‐sharing octahedra), and A₃TiX₆ (isolated octahedra) as well as the mixed‐valent halides CsTi₂I₇ (tetrahedra and octahedra) and Na₅Ti₃Cl₁₂ (chains of octahedra) have been observed. Except for the triangles in titanium(II) halides, cluster compounds are rare but include K₄[{OTi₄}I₁₂] and {CTi₆}Cl₁₄.     

Enhancement corrosion resistance of (3-methacryloxypropyl)silsesquioxane hybrid films and its validation by gas-molecule diffusion coefficients using MD simulation

In the first part of this work, based on silsesquioxanes (SSO) derived from hydrolytic condensation of (3-methacryloxypropyl)trimethoxysilane (MPMS) and tetraethoxysilane (TEOS), two hybrid films, f-MPMS-SSO (f-MS) and f-MPMS-TEOS-SSO (f-MTS) modified with 15 wt% TEOS, were prepared. The anticorrosion properties (corrosion potential, E _corr, and corrosion current density, I _corr) of the bare aluminum alloy (AA) and the two films on AA were tested by electrochemical measurements with typical potentiodynamic polarization curves. The I _corr values of three samples are significantly different with the order of f-MTS < f-MS < AA which implies that the TEOS addition in the f-MTS coating indeed enhances the electrochemical corrosion resistance. Correlations between the structures of two films and anticorrosion properties were discussed. In the second part of this work, two different 3D-amorphous cubic unit cells, cell(f-MS) and cell(f-MTS), as models were employed to investigate self-diffusion coefficients by molecular dynamics (MD) simulation for the NO₂, SO₂ and H₂O molecules. All three self-diffusion coefficients of NO₂, SO₂ and H₂O diffusing in cell(f-MTS) were less than the coefficients in cell(f-MS), which validates the corresponding anticorrosion-experiment results. Two reasons why the addition of TEOS in the system of f-MTS leads to a lowering of the gas self-diffusion coefficient compared to the f-MS system, were discussed. An erratum to this article can be found at     

Tautomeric and conformational properties of dibenzoylmethane,C<Subscript>6</Subscript>H<Subscript>5</Subscript>–C(O)–CH<Subscript>2</Subscript>–C(O)–C<Subscript>6</Subscript>H<Subscript>5</Subscript>: gas-phase electron diffraction and quantum chemical study

Tautomeric and structural properties of dibenzoylmethane, C₆H₅–C(O)–CH₂–C(O)–C₆H₅, have been investigated by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to cc-pVTZ). Analysis of GED intensities resulted in the presence of 100(5)% enol tautomer at 380(5) K. The enol ring possesses C _S symmetry with a strongly asymmetric hydrogen bond. The two phenyl rings are rotated with respect to the enol ring by 15.1(5.0) and 12.1(5.8)°. The experimental geometric parameters are reproduced very closely by the B3LYP/cc-pVTZ method.     

Molecular structure of N-chlorosuccinimide studied by gas-phase electron diffraction and quantum-chemical methods

The molecular structure of N-chlorosuccinimide has been studied by GED method at the nozzle temperature of 116 °C. Vibrational corrections to the r _a parameters, Δ(r _a − r _e), have been calculated using the scaled quadratic and cubic force constants from B3LYP/6-31G(df,p) calculations. The force field scaling has been carried out using the IR and Raman spectra of the solid N-chlorosuccinimide. The molecular skeleton and the bond conformation around nitrogen were found to be planar within large experimental errors. The equilibrium geometrical parameters derived from the experimental data assuming C _2v molecular symmetry and those from MP2(fc)/6-311G(3df,2pd) calculations are in a good agreement.