Influence of substrate morphology on organic layer growth: PTCDA on Ag(1 1 1)

By UV-excited photoelectron emission microscopy (UV-PEEM) we investigated the microscopic growth behavior of organic thin films using 3,4,9,10-perylene-tetracarboxylicacid dianhydride (PTCDA) on a Ag(1 1 1) single crystal substrate as example. Direct, real time observation allows to correlate the initial growth modes and the related kinetic parameters with substrate properties like terrace width, step density, and step bunches from the submonolayer range up to 5 layers or more. Above room temperature PTCDA grows in a Stranski–Krastanov fashion: after completion of the first two stable layers three-dimensional islands are formed. The nucleation density strongly depends on the temperature and the substrate morphology thus affecting the properties of the organic film.     

Ground state of the Si(0 0 1) surface revisited—is seeing believing?

The stable structure of clean Si(0 0 1) surface around 100 K is the c(4 × 2) arrangement constructed by buckled dimers. This structure was widely accepted as the ground state in 1990’s. The view was challenged at the beginning of 2000’s by the observations of a p(2 × 1) structure below 20 K with scanning tunneling microscopy (STM). Recent experimental studies confirm that the dimer is buckled below 30 K. Large tip–surface interaction, and/or tunneling current induced dynamical effect are now experimentally evident in the STM images at low temperatures. Moreover, a current induced structure transformation is discovered below 40 K even in the study by low energy electron diffraction. Dynamical electronic and vibrational effects are theoretically studied for accounting the observation of a p(2 × 1) structure below 20 K.     

Molecular structure and IR absorption spectra of perfluorinated aldehyde hydrates (n-CxF2x+1CH(OH)2, x = 1-4)

Structures and IR absorption spectra of the conformational isomers of perfluorinated aldehyde hydrates, n-C_xF_2x+1CH(OH)₂, (x = 1-4) have been calculated using density functional theory (DFT) and compared to experimental FT-IR measurements. Two absorption peaks around 3600-3700 cm⁻¹ were observed and are assigned to OH stretching modes of OH groups with, and without, intramolecular hydrogen bonding. For n-C₃F₇CH(OH)₂, two absorption bands around 900-1000 cm⁻¹ were observed in the experimental spectra, whereas only a single in-phase stretching mode of the (CF₃)(C₂F₄CH(OH)₂) and (C₃F₇)(CH(OH)₂) bonds was calculated for each conformer. The experimental spectra were well described by composite spectra of the thermal equilibrium mixture of different conformational isomers of n-C_xF_2x+1CH(OH)₂ calculated by DFT.     

Synthesis of single-crystal silver slices with predominant (1 1 1) facet and their SERS effect

In this article, single-crystal silver slices with predominant (1 1 1) facet were synthesized at room temperature with chitosan by a facile, one-pot, and totally green method. XRD, UV-visible and infrared spectroscopy have been employed for identifying chitosan-protected silver nanoparticles (NPs), while SEM, TEM were used to confirm silver NPs orientation along the (1 1 1) direction to form various shapes such as hexagon, trapezium, triangle and so on. The results showed that chitosan, a novel environmentally benign and excellently biocompatible material, serves not only as a reducing agent but also as a stabilizer for the growth of anisotropic silver NPs. The single-crystal silver slices with major facet of (1 1 1) can be used as a surface-enhanced Raman scattering (SERS) substrate, and crystal violet (CV) as a Raman probe to evaluate its enhancement ability. It was found that the enhancement ability of the silver slices was remarkable.     

Study of oxygen adsorption on β-Si3N4(0 0 0 1) by the density functional theory

The density functional theory (DFT) B3LYP method is used to theoretically investigate the interaction of O₂ with the β-Si₃N₄ surface (0 0 0 1) at 1200 °C. All the calculations have been performed at the 6-31G^∗ basis set level using H-saturated cluster. From the total energy minimization, the chemisorption on the center of the molecule lying above an Si site and the molecular axis paralleling to the surface is the most stable. After adsorption, the O–O bond is easier to dissociate compared to the free O₂. The electron transferred from the substrate to the O₂ molecule occupies the O₂ anti-bonding orbital, thus leading to a weakening off the bond strength, which is reflected by the elongated O₂ bond length. The changing trend of the O–O population and vibrational frequency is consistent with the change of the O–O bond length. The significant chemisorption energy and the short adsorption bond length indicate that the oxidation occurs on the β-Si₃N₄(0 0 0 1) surface at 1200 °C more easily.     

Structural and electronic properties of CenO2n (n = 1-5) nanoparticles: A computational study

Understanding the electronic structures and properties of different size CeO₂ nanoparticles is very important for further application in the field of catalysis used in several promising materials. In this study, we have elucidated the electronic analyses of (CeO₂)_n (n = 1-5) nanoparticles through first-principle density-functional theory approach. All structures with the global minimal energies are obtained by fire algorithm combining simulated annealing method and then are further re-optimized by DMol³ program with double numerical atomic basis sets. Two useful analyzed methods (Fukui function and electronic density of state) are calculated to explain the chemical reactivity of different sites for (CeO₂)_n (n = 1-5) nanoparticles.     

Liquid phase equilibria of (water + phosphoric acid + 1-butanol or butyl acetate) ternary systems at T = 308.2 K

(Liquid + liquid) equilibria and tie lines for the ternary systems of (water + phosphoric acid + 1-butanol) and (water + phosphoric acid + butyl acetate) were measured at T = 308.2 K. The experimental ternary (liquid + liquid) equilibrium data were correlated with the UNIQUAC model. The reliability of the experimental tie lines was confirmed using Othmer-Tobias correlation. The average root-mean-square deviation (RMSD) values of (water + phosphoric acid + 1-butanol) and (water + phosphoric acid + butyl acetate) systems were 2.17% and 2.16%, respectively. Distribution coefficients and separation factors were measured to evaluate the extracting capability of the solvents. The results show that butyl acetate may be considered as a reliable organic solvent for the extraction of phosphoric acid from aqueous solutions.     

Syntheses,structures and luminescent properties of four copper(I) cyanide coordination polymers based on 2-(n-pyridyl)benzimidazole ligands (n = 2, 3, 4)

Four copper(I) cyanide coordination polymers containing 2-(n-pyridyl)benzimidazole ligands, namely [Cu₂(CN)(2-PyBIm)]_n (1), [Cu₂(CN)₂(3-PyHBIm)]_n (2), {[Cu₃(CN)₃(4-PyHBIm)₄] · 2H₂O}_n (3) and [Cu₅(CN)₃(4-PyBIm)₂]_n (4), have been synthesized and characterized by X-ray crystallography. Complex 1 is a one-dimension coordination polymer in which 2-(2-pyridyl)benzimidazole is deprotonated and adopts a bridging tridentate coordination mode. Complex 2 has ladder-like structure in which 2-(3-pyridyl)benzimidazole does not deprotonate and acts as a bidentate bridge. Complex 3 displays a saddle-shaped helical chain constructed through μ₂-cyanide group and the outstretched neutral 2-(4-pyridyl)benzimidazole monodentate ligand. Complex 4 shows two-dimension layer polymeric structure in which deprotonated 2-(4-pyridyl)benzimidazole acts as a tridentate bridging ligand. The cyanide groups in four complexes all act as bidentate bridging ligands. These complexes are thermal stable and display luminescence in the solid states.     

Structure–composition sensitivity in “Metallic” Zintl phases: A study of Eu(Ga1−xTtx)2 (Tt=Si, Ge, 0≤x≤1)

Two isoelectronic series, Eu(Ga_1−xTt_x)₂ (Tt=Si, Ge, 0≤x≤1), have been synthesized and characterized by powder and single-crystal X-ray diffraction, physical property measurements, and electronic structure calculations. In Eu(Ga_1−xSi_x)₂, crystal structures vary from the KHg₂-type to the AlB₂-type, and, finally, the ThSi₂-type structure as x increases. The hexagonal AlB₂-type structure is identified for compositions 0.18(2)≤x<0.70(2) with Ga and Si atoms statistically distributed in the polyanionic 6³ nets. As smaller Si atoms replace Ga atoms while the number of valence electrons increases, the lattice parameters, unit cell volumes, and Ga–Si distances in this phase region decrease significantly. Although aspects of X-ray diffraction results suggest puckering of the 6³ nets for the Si-richest example of the AlB₂-type Eu(Ga_1−xSi_x)₂, the complete experimental evidence remains inconclusive. On the other hand, in Eu(Ga_1−xGe_x)₂, six different structural types were observed as x varies. In addition to EuGa₂ (KHg₂-type; space group Imma) and EuGe₂ (own structure type, space group P3¯m1), the ternary phases studied show four different structures: the AlB₂-type for Ga-rich compositions; the YPtAs-type structure for EuGaGe; and two new structures, which are intergrowths of the YPtAs-type EuGaGe and EuGe₂, for Ge-rich compositions. These two Ge-rich phases include: (1) Eu(Ga_0.45(2)Ge_0.55(2))₂ containing two YPtAs-type motifs of EuGaGe plus one EuGe₂ motif; and (2) Eu(Ga_0.40(2)Ge_0.60(2))₂ containing one YPtAs-type motif alternating with a split site at and z=0.4798(2) with ca. 50% site occupancy by Ga and Ge along the c-axis. Magnetic susceptibilities of three Eu(Ga_1−xGe_x)₂ compounds display Curie–Weiss behavior above ca. 100 K, and show effective magnetic moments indicative of divalent Eu with a 4f⁷ electronic configuration, consistent with. X-ray absorption spectra (XAS). Density of states (DOS) and crystal orbital Hamilton population (COHP) analyses, based on first principles electronic structure calculations, rationalize the observed homogeneity ranges of the AlB₂-type phases in both systems and the structural variations as a function of Tt content.     

Self assembly of asymmetric tetranuclear Cu(II) [2 × 2] grid-like complexes and of a dinuclear Ni(II) complex from pyridyl-phenol Schiff base ligands

Self assembly of N-salicylidene 2-aminopyridine (L1H) with Cu(NO₃)₂·3H₂O affords [Cu₄(L1)₄(NO₃)₃(CH₃OH)][Cu(L1)(NO₃)₂](2-aminopyridinium)(NO₃)·5CH₃OH (1) which is composed of an asymmetric [2 × 2] grid-like cationic complex that co-crystallizes with a Cu(II) mononuclear anion. This remarkable tetranuclear unit presents three penta-coordinated and one hexa-coordinated Cu(II) sites. This quadruple helicate structure reveals strong anti-ferromagnetic coupling (J = −340(2) cm⁻¹) between Cu(II) ions through a double alkoxo bridge. Reacting L1H with Cu(NO₃)₂·3H₂O in slightly different conditions affords however a more symmetric tetranuclear grid-like complex: [Cu₄(L1)₄(NO₃)₂(OH)₂](2-aminopyridinium)(OH)·CH₃OH) (2). A dinuclear Ni(II) complex, [Ni₂(L2)₂(L2H)₂(NCS)₂(CH₃OH)₂]·2CH₃OH (3), obtained with another related donor ligand (L2H = N-salicylidene 3-aminomethylpyridine) was also prepared.     

Dinitrogen extrusion from diazidophenylborane: Computational analysis of PhBNx (x = 6, 4, 2) isomers

The energies and structures of possible intermediates in the dinitrogen extrusion from diazidophenylborane 4a to give phenylborylene 11a were determined using density functional (B3LYP), multiconfigurational (CASSCF and MRMP2), and coupled cluster (CCSD(T)) computations in conjunction with basis sets of up to cc-pVTZ quality. Formation of 11a and nitrogen from 4a is an exothermic process (−21 kcal mol⁻¹). The triplet electronic ground state of azidophenylborylnitrene 5a (PhBN₄) is only 26 kcal mol⁻¹ higher in energy than 4a and the phenyl shift in 5a to yield N-azidophenyliminoborane 7a is highly exothermic.     

Cyclometallation of phenylhydrazones: Synthesis, reactivity, crystal structure analysis and novel trinuclear palladium(II) cyclometallated compounds with [C, N, N′] terdentate ligands

Reaction of the ligand C₆H₅N(H)NCMe(C₅H₄N) (a) with palladium(II) acetate in toluene gave the mononuclear cyclometallated complex [Pd{C₆H₄N(H)NCMe(C₅H₄N)}(AcO)] (1a). Reaction of 1a with sodium chloride gave the analogous chlorine compound [Pd{C₆H₄N(H)NCMe(C₅H₄N)}(Cl)] (3a) which could also be prepared by reaction of a with lithium tetrachloropalladate and sodium acetate in methanol for 48 h; whereas shorter reaction times afforded the non-cyclometallated complex [Pd{C₆H₅N(H)NCMe(C₅H₄N)}(Cl)₂] (2a). Reaction of the ligand 2-ClC₆H₄N(H)NCMe(C₅H₄N) · HCl (b), with palladium(II) acetate, or with lithium tetrachloropalladate and sodium acetate, yielded the cyclometallated complex [Pd2-ClC₆H₃N(H)NCMe(C₅H₄N)(Cl)] (1b). Treatment of 3a and 1b with silver trifluoromethanesulphonate (triflate) and triphenylphosphine in acetone gave the mononuclear complexes [Pd{2-RC₆H_nN(H)NCMe(C₅H₄N)}(PPh₃)][CF₃SO₃], (R = H, n = 4, 4a; R = Cl, n = 3, 2b) with the ligand as C,N,N′ terdentate and substitution of chlorine by triphenylphosphine. Reaction of 3a and 1b with silver triflate and the tertiary diphosphine Ph₂P(CH₂)₄PPh₂ (dppb) in a 2:1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-RC₆H₃N(H)NCMe(C₅H₄N)]}₂(μ-Ph₂P(CH₂)₄PPh₂)][CF₃SO₃]₂ (R = H, 5a; R = Cl, 3b) with a μ₂-diphosphine bridging ligand. Similarly, treatment of 3a and 1b with silver triflate and the tertiary triphosphines MeC(CH₂PPh₂)₃ (tripod) and (Ph₂PCH₂CH₂)₂PPh (triphos), in 3:1 molar ratio, gave the novel trinuclear complexes [{Pd[C₆H₄N(H)NCMe(C₅H₄N)]}₃{μ₃-MeC(CH₂Ph₂)₃}][CF₃SO₃]₃ (6a) and [{Pd[2-ClC₆H₃N(H)NCMe(C₅H₄N)]}₃{μ₃-(PPh₂CH₂CH₂)₂PPh}][CF₃SO₃] ₃ (4b) regioselectively, with the phosphine as a μ₃-bridging ligand. When the reaction between 3a and triphos was carried out in 1:1 molar ratio the mononuclear complex [Pd{C₆H₄N(H)NCMe(C₅H₄N)}{(PPh₂CH₂CH₂)₂PPh-P,P,P}][ClO₄] (7a) was obtained. The crystal structures of 2b, 3a and 4a have been determined by X-ray crystallography.     

First-principles study of the electronic and magnetic properties of oxygen-deficient rutile TiO2(1 1 0) surface

Based on first-principles electronic structure calculations we find that the bridging oxygen vacancies on the (1 1 0) surface is more favorable and may be responsible for the unexpected ferromagnetism in undoped rutile TiO₂. Our results show that the ferromagnetism largely originates from the d orbitals of low-charge-state Ti ions converted from Ti⁴⁺ ions induced by the surface oxygen vacancies. The second-nearest neighbors of these ions (fivefold coordinated Ti) also contribute to the total magnetic moments. The spins induced by the local oxygen vacancies form a ferromagnetic arrangement.     

New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: structural characterizations of 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph, Pr, Et)

Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T < −90 °C) followed by a quench with a slight excess of ClPPh₂ afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1) in good yields. Reacting 1 with two equivalents of BuLi followed by a quench with a slight excess of ClPR₂ yield novel 1,2,4,5-tetrakis(phosphino)-3,6-difluorobenzenes 1,4-(PPh₂)₂-2,5-(PR₂)₂-C₆F₂ (R = Ph (2a); R = ⁱPr (2b); R = Et (2c)) in moderate yields. Compounds 1 and 2a-c were characterized by multinuclear NMR spectroscopy and elemental analyses. In addition, molecular structures of 2a-c have been determined by single crystal X-ray crystallography. Phosphorus atoms of PPh₂/PR₂ substituents in 2a-c are displaced from the plane of the central phenyl ring due to steric interactions with neighboring groups.     

Thermodynamic properties on quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1: XCl + MgCl2 + CaCl2 + H2O with (X ≡ Na; NH4)

In this investigation, the quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1 with a cation (Na⁺; NH₄⁺; Mg²⁺; Ca²⁺) have been studied using the hygrometric method at 298.15 K. The water activities of the systems NH₄Cl + MgCl₂ + CaCl₂ + H₂O and NaCl + MgCl₂ + CaCl₂ + H₂O are measured at total molalities from 0.60 mol kg⁻¹ to saturation for different ionic-strength fractions NH₄Cl or NaCl, y = 0.20, 0.50, 0.80, and z ratio ionic-strength for other solutes, with z = 0.20, 0.50 and 0.80 for each y. The obtained data allow the deduction of osmotic coefficients.     

Solubility of carbon dioxide in the solvent system (2-amino-2-methyl-1-propanol + sulfolane + water)

New sets of data for the solubility of CO₂ in the amine solvent system of 2-amino-2-methyl-1-propanol (1) + sulfolane (2) + water (3) were presented in this work. The measurements were done at temperatures of 313.2, 333.2, 353.2, and 373.2 K and CO₂ partial pressures up to 193 kPa. The investigated compositions were as follows: (i) w₁=16.5%$w_1=16.5\%$, w₂=32.2%$w_2=32.2\%$; (ii) w₁=8.2%$w_1=8.2\%$, w₂=41.2%$w_2=41.2\%$; (iii) w₁=22.3%$w_1=22.3\%$, w₂=27.7%$w_2=27.7\%$; and (iv) w₁=30.6%$w_1=30.6\%$, w₂=19.4%$w_2=19.4\%$, where w$w$ is the mass percent of the component. The present solubility data was correlated by a modified Kent–Eisenberg model. The model reasonably represents the present solubility data, not only over the considered conditions, but also for a wider range of temperatures, partial pressures, and compositions.     

Molecular complexes of octafluoronaphthalene with catenated chalcogen-nitrogen compounds C6H5-X-NSN-SiMe3 (X = S, Se)

Mismatched molecular 1:1 complexes of C₁₀F₈ with catenated chalcogen-nitrogen compounds C₆H₅-X-NSN-SiMe₃ (X = S, Se) were prepared and characterized by X-ray crystallography. The complexes provide examples of structurally non-rigid polyheteroatom molecules involved in non-covalent arene-polyfluoroarene π-stacking interactions. In going from homocrystals to the co-crystals, the molecular Z, E configuration of the catenated compounds changes from noticeably non-planar to perfectly planar, i.e. C₁₀F₈ acts as “molecular iron”. On the other hand, C₁₀H₈ does not produce complexes with C₆F₅-X-NSN-SiMe₃ (X = S, Se).     

Complex formation of crown ethers with cations in the (water + organic solvent) mixtures: Part IX. Thermodynamics of interactions of Na ion with benzo-15-crown-5 ether in {(1 − x)DMA + xH2O} at T = 298.15 K

The thermodynamic functions of complex formation of benzo-15-crown-5 ether with sodium cation in {(1 − x)DMA + xH₂O} at T = 298.15 K have been calculated. The equilibrium constants of complex formation of benzo-15-crown-5 ether with sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by calorimetric method at T = 298.15 K. The complexes are enthalpy stabilized and entropy destabilized. A simple model has been proposed to describe the relationship between the thermodynamic functions of complex formation of crown ethers with sodium cation and the structural and energetic properties of the mixed water-organic solvent. The linear enthalpy-entropy relationship for complex formation is also presented. The solvation enthalpy of the complex in {(1 − x)DMA + xH₂O} is discussed.     

Structural and optical properties of Ga2O3:In films deposited on MgO (1 0 0) substrates by MOCVD

Ga₂O₃:In films with different indium (In) content x [x=In/(Ga+In) atomic ratio] have been deposited on MgO (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). Structural analyses revealed that the film deposited with actual In content (x′) of 0.09 was an epitaxial film and the films with x′=0.18 and 0.37 had mixed-phase structures of monoclinic Ga₂O₃ and bixbyite In₂O₃. The absolute average transmittance of the obtained films in the visible region exceeded 95%, and the band gap was in the range of 4.74-4.87 eV. Photoluminescence (PL) measurements were performed at room temperature, in which the visible luminescences were strong and could be seen by the naked eye. The strong emissions in the visible light region were proposed to originate from the gallium vacancies, oxygen deficiencies and other defects in these films.