Molecular structure and conformation of triphenylsilane from gas-phase electron diffraction and theoretical calculations, and structural variations in H4?nSiPhn molecules (n?=?1–4)

The molecular structure of triphenylsilane has been investigated by gas-phase electron diffraction and theoretical calculations. The electron diffraction intensities from a previous study (Rozsondai B, Hargittai I, J Organomet Chem 334:269, 1987) have been reanalyzed using geometrical constraints and initial values of vibrational amplitudes from calculations. The free molecule has a chiral, propeller-like equilibrium conformation of C ₃ symmetry, with a twist angle of the phenyl groups τ = 39° ± 3°; the two enantiomeric conformers easily interconvert via three possible pathways. The low-frequency vibrational modes indicate that the three phenyl groups undergo large-amplitude torsional and out-of-plane bending vibrations about their respective Si–C bonds. Least-squares refinement of a model accounting for the bending vibrations gives the following bond distances and angles with estimated total errors: r _g(Si–C) = 1.874 ± 0.004 ?, 〈r _g(C–C)〉 = 1.402 ± 0.003 ?, 〈r _g(C–H)〉 = 1.102 ± 0.003 ?, and ∠_aC–Si–H = 108.6° ± 0.4°. Electron diffraction studies and MO calculations show that the lengths of the Si–C bonds in H_4−n SiPh _n molecules (n = 1–4) increase gradually with n, due to π → σ*(Si–C) delocalization. They also show that the mean lengths of the ring C–C bonds are about 0.003 ? larger than in unsubstituted benzene, due to a one hundredth angstrom lengthening of the C_ipso–C_ortho bonds caused by silicon substitution. A small increase of r(Si–H) and decrease of the ipso angle with increasing number of phenyl groups is also revealed by the calculations.     

Synthesis and Anticancer Activity of Long-Chain Isonicotinic Ester Ligand-Containing Arene Ruthenium Complexes and Nanoparticles

Arene ruthenium complexes containing long-chain N-ligands L¹ = NC₅H₄–4-COO–C₆H₄–4-O–(CH₂)₉–CH₃ or L² = NC₅H₄–4-COO–(CH₂)₁₀–O–C₆H₄–4-COO–C₆H₄–4-C₆H₄–4-CN derived from isonicotinic acid, of the type [(arene)Ru(L)Cl₂] (arene = C₆H₆, L = L¹: 1; arene = p-MeC₆H₄Pr ⁱ , L = L¹: 2; arene = C₆Me₆, L = L¹: 3; arene = C₆H₆, L = L²: 4; arene = p-MeC₆H₄Pr ⁱ , L = L²: 5; arene = C₆Me₆, L = L²: 6) have been synthesized from the corresponding [(arene)RuCl₂]₂ precursor with the long-chain N-ligand L in dichloromethane. Ruthenium nanoparticles stabilized by L¹ have been prepared by the solvent-free reduction of 1 with hydrogen or by reducing [(arene)Ru(H₂O)₃]SO₄ in ethanol in the presence of L¹ with hydrogen. These complexes and nanoparticles show a high anticancer activity towards human ovarian cell lines, the highest cytotoxicity being obtained for complex 2 (IC₅₀ = 2 μM for A2780 and 7 μM for A2780cisR).     

Mass attenuation coefficients of B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–CaF<Subscript>2</Subscript> glass system at 0.662 and 1.25 MeV gamma energies

The total mass attenuation coefficients, partial interaction and the effective atomic numbers (Z_eff) of glass system (80−x)B₂O₃–10Al₂O₃–10SiO₂–xCaF₂ (where x = 5, 10, 20, 25, 30, 35 and 40 mol %) have been calculated at photon energies 0.662 and 1.25 MeV using the WinXCom software on the basis of mixture rule. Results indicated that the total mass attenuation coefficients showed a decrease with increasing the CaF₂ concentration, due to a decrease in Compton scattering probability, which gave a dominant contribution to the total mass attenuation coefficients for the studied glass samples at both energies. However, the photoelectric absorption and coherent scattering showed an increase with increasing the CaF₂, concentrations at same energies. For a comparison, the total mass attenuation coefficients of the glass system had lower values at the energy 1.25 MeV than that at 0.662 MeV. Z_eff was found to increase linearly with the increase of CaF₂ concentrations. It was concluded that low CaF₂ concentrations in glass system, under study, have Z_eff close to that of human tissue and have higher total absorption coefficients at energy of 0.662 MeV than that at 1.25 MeV. These results are very useful in designing gamma radiation detectors using thermoluminescence technique. Therefore, it is recommended to use low CaF₂ concentration of our glass system as good gamma detectors at energy of 1.25 MeV.     

Synthesis and characterization of 2-phenylaniline cyclopalladated complexes

Reaction of the dinuclear complex [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}Cl]₂ (1) with ligands (L = 4-picoline, sym-collidine) gave the six-membered palladacycles [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}Cl(L)] (2). The complex 1 reacted with AgX (X = CF₃SO₃, BF₄) and bidentate ligands [L–L = phen (phenanthroline), dppe (bis(diphenylphosphino)ethane), bipy(2,2′-bipyridine) and dppp (bis(diphenylphosphino)propane)] giving the mononuclear orthopalladated complexes [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}(L–L)] (3) [L–L = phen, dppe, bipy and dppp]. These compounds were characterized by physico-chemical methods, and the structure of [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}Cl(L)] (L = sym-collidine) was determined by single-crystal X-ray analysis.     

Effect of substituents at the heteroatom on the structure and ligating properties of carbodicarbenes and its silicon analogs: a theoretical study

Density functional calculations have been carried out to investigate the effect of substituents attached to the heteroatoms of N-heterocyclic carbenes (NHCs) on the structure and ligating properties of carbon(0) [C(NHC)₂] and silicon(0) [Si(NHC)₂] compounds. The substituents were found to have a profound role on the structure and ligating properties of these classes of compounds. Fluoro- and chloro-substituted carbon(0) compounds were found to have quasi-linear geometries in which their C(0) characteristics are “masked.” However, their C(0) characteristics become prominent in their protonated species. Large negative charges and shallow bending potential of the central C_c–C₀–C_c angle provide evidence for the “hidden C(0) characteristics” of these two compounds. Electron withdrawing substituents at N-atoms of the two NHCs dramatically decreases the basicity of these compounds. Both natural bonding and atoms in molecules analysis suggest that the most favorable Lewis structure of C(NHC)₂ and Si(NHC)₂ in their equilibrium geometries should be described (portrayed) as L=C=L and L → Si ← L, respectively, where L = NHCs.     

O-Tolyl/benzyl dithiocarbonates of phosphorus(III) and (V): syntheses and characterization

Abstract  

O-Tolyl/benzyl dithiocarbonates, ROCS₂Na (R = o-, m-, or p-CH₃C₆H₄–, and –CH₂C₆H₅), were synthesized and characterized. These new ligands reacted with PCl₃/POCl₃ in refluxing toluene which resulted in the formation of phosphorus(III) and phosphorus(V) tolyl/benzyl dithiocarbonates corresponding to [(ROCS₂) _n PCl_3−n ] and [(ROCS₂) _n POCl_3−n ] (R = o-, m-, or p-CH₃C₆H₄–, and –CH₂C₆H₅; n = 1, 2, 3). These pale yellow liquid compounds were characterized by IR, mass, and NMR (¹H, ¹³C, and ³¹P) spectral studies, which suggest the dithiocarbonate ligands bind in a monodentate mode leading to P–S–C linkages in these derivatives.     

Thermodynamic investigation of room temperature ionic liquid

The molar heat capacities of the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluoroborate (BMIPF₆) were measured by an adiabatic calorimeter in temperature range from 80 to 390 K. The dependence of the molar heat capacity on temperature is given as a function of the reduced temperature (X) by polynomial equations, C _P,m (J K⁻¹ mol⁻¹) = 204.75 + 81.421X − 23.828 X ² + 12.044X ³ + 2.5442X ⁴ [X = (T − 132.5)/52.5] for the solid phase (80–185 K), C _P,m (J K⁻¹ mol⁻¹) = 368.99 + 2.4199X + 1.0027X ² + 0.43395X ³ [X = (T − 230)/35] for the glass state (195 − 265 K), and C _P,m (J K⁻¹ mol⁻¹) = 415.01 + 21.992X − 0.24656X ² + 0.57770X ³ [X = (T − 337.5)/52.5] for the liquid phase (285–390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the BMIPF₆ relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass transition of BMIPF₆ was measured to be 190.41 K, the enthalpy and entropy of the glass transition were determined to be ΔH _g = 2.853 kJ mol⁻¹ and ΔS _g = 14.98 J K⁻¹ mol⁻¹, respectively. The results showed that the milting point of the BMIPF₆ is 281.83 K, the enthalpy and entropy of phase transition were calculated to be ΔH _m = 20.67 kJ mol⁻¹ and ΔS _m = 73.34 J K⁻¹ mol⁻¹.     

A two-dimensional ladder-type network in the 2:1 co-crystal of 1,2,5-thiadiazole-3,4-dicarboxylic acid and 4,4′-bipyridine

Abstract  

The crystal structure of the 2:1 co-crystal of 1,2,5-thiadiazole-3,4-dicarboxylic acid and 4,4′-bipyridine, (C₄H₂N₂O₄S)₂·C₁₀H₈N₂, has been determined by X-ray diffraction at the monoclinic space group C2/c with cell parameters of a = 21.388(7) ?, b = 6.735(2) ?, c = 14.877(5) ?, β = 110.431(3)°, and Z = 4. There are one molecule of thiadiazole and a half molecule of bipyridine in the asymmetric unit. The dihedral angle between the pyridine ring planes is 40.5(3)°. Two intramolecular O–H···N [2.730(7) ?] and O–H···O [2.433(6) ?] hydrogen bonds are observed in the thiadiazole molecule. In the crystal structure, the molecules form a unique two-dimensional ladder-type network linked by intermolecular O–H···N [2.704(4) ?] hydrogen bonds and S···O [3.100(5) ?] heteroatom interactions.     

Three forms of squaric acid with pyrazine and pyridine derivatives: an experimental and theoretical study

Three new squarate salts were synthesized and combined with experimental and theoretical study on molecular, vibrational, and electronical properties. Squaric acid was crystallized as HSQ⁻ [SQ: squarate] monoanion in [(C₁₃H₁₂NO₂)(HC₄O₄)] (I), as uncharged H₂SQ in [(C₅H₅N₃O)(H₂C₄O₄)] (II), and as SQ²⁻ dianion form in [C₆H₉N₂)₂(C₄O₄)] (III). They crystallize in the triclinic and monoclinic crystal system with space group P−1, P2₁/c, and P2₁/c, respectively. Crystal structure analysis reveals that, far from forming discrete ionic species in (I) and (II), it is likely that there is large degree of proton sharing between the two hydrogen squarate anions in (I) and between the neutral moieties in (II), with the H atom lying almost symmetrically between the donor and acceptor sites, as evidenced by the long O–H and N–H bonds and short H···O distances. Ab initio calculations have been carried out for three compounds by using DFT/B3LYP and HF methods at 6-31++G(d,p) basis set. Although the supramolecular interactions have some influences on the molecular geometry in solid state phase, calculated data show that the predicted geometries can reproduce the structural parameters. The results of the optimized molecular structure for three compounds obtained on the basis of two models are presented and compared with the experimental X-ray data. Calculated vibrational frequencies are consistent with each other and experimental IR data. The theoretical electronic absorption spectra have been calculated by both TD–DFT and HF–CIS methods. Molecular orbital coefficients analysis suggest that the electronic transitions are mainly assigned to n → π* and π → π* electronic transitions.     

Theoretical study on the CH3NgF species

Geometrical parameters, harmonic vibrational frequencies, atomic charge distributions, bonding character, and relative stability of the CH₃NgF (Ng = He, Ar, Kr, or Xe) species were investigated at the MP2 level of theory. CH₃HeF was also predicted stable at the CCSD(T) level. All the four CH₃NgF species have C _3v symmetry. Ng–F bond lengths of the CH₃NgF species are all longer than those of the corresponding HNgF species. The calculated infrared intensities of the C–Ng and Ng–F stretching vibrations are much larger than those of the other vibrations, which is advantageous for the experimental spectroscopic identification of the species. The atoms in molecules (AIM) topological analysis indicated that the three Ng–F (Ng = He, Ar, or Kr) bonds are dominated by electrostatic interaction whereas the two C–Ng (Ng = Ar or Kr) bonds are dominated by covalent interaction. In contrast, the bond length analysis seems to indicate that both the Ng–F and C–Ng bonds are dominated by covalent interaction. According to the MP2 calculations, CH₃HeF and CH₃ArF are higher in energy than the dissociation limits CH₃ + He + F and CH₃ + Ar + F by 15.10 and 2.64 kcal/mol whereas CH₃KrF and CH₃XeF are lower in energy than CH₃ + Kr + F and CH₃ + Xe + F by 16.80 and 38.44 kcal/mol, respectively.     

Mechanistic and kinetic study on the ozonolysis of ethyl vinyl ether and propyl vinyl ether

The reaction mechanisms for ozonolysis of ethyl vinyl ether (EVE) and propyl vinyl ether (PVE) have been investigated using the density functional theory (DFT) and ab initio method. Cycloaddition reactions of O₃ to EVE and PVE are highly exothermic by 52.91 and 53.17 kcal/mol, respectively. Major products (formaldehyde, ethyl formate, and propyl formate) resulting from the both reactions are identified by comparing them with the experimental results. Further reactions of the most energy-rich Criegee intermediates (C₂H₅OCHOO and C₃H₇OCHOO) have been proposed in the presence of NO and H₂O in which the main products are ethyl formate and propyl formate. The Multichannel Rice–Ramsperger–Kassel–Marcus (RRKM) approach is employed to calculate the total and individual rate constants for major product channels over a wide range of temperatures and different pressures. In the temperature range of 200–2500 K, the main path is the production of ethyl formate with k _EVE+O3 = 4.67 × 10⁻¹² exp(−3029/T), for the EVE with O₃ reaction and k _PVE+O3 = 3.58 × 10⁻¹² exp(−2858/T) for the PVE with O₃ reaction. At 298 K and 760 torr, the rate constants calculated are 1.80 × 10⁻¹⁶ and 2.45 × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹ for ozonolysis of EVE and PVE, which are consistent with the experimental results. The total rate constants show positive temperature dependence over the temperature range of 200–2000 K but pressure independence in the range of 0.01–10000 Torr. Estimation of branching ratios of several products is also performed. The influence of carbon chain length on reactivity toward ozone is examined.     

A Density Functional Investigation on C2Aun+ (n?=?1, 3, 5) and C2Aun (n?=?2, 4, 6): from Gold Terminals, Gold Bridges, to Gold Triangles

A systematic density functional theory investigation on C₂Au _n ⁺ (n = 1,3,5) and C₂Au _n (n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like C_s C₂Au⁺ (C=C–Au⁺) and D_∞h C₂Au₂ (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C_2v C₂Au₃ ⁺ ([Au–C≡C–Au]Au⁺) and C_s C₂HAu₂ ⁺([H–C≡C–Au]Au⁺). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au₃) in the head-on coordinated C_2v C₂Au₄ (Au–C≡C–Au₃) and the side-on coordinated C_2v C₂Au₅ ⁺ ([Au–C≡C–Au]Au₃ ⁺). Similar –Au₃ triangular units exist in the head-on coordinated C_2v C₂HAu₃ (H–C≡C–Au₃) and D_2d C₂Au₆ (Au₃–C≡C–Au₃). The existence of stable –Au₃ triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au₃ triangles originates from the fact that an equilateral D_3h Au₃ ⁺ cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature. The extension from H/Au analogy to H/Au₃ analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials.     

Optimization of a miniaturized DBD plasma chip for mercury detection in water samples

In this work, an optimization study was conducted to investigate the performance of a custom-designed miniaturized dielectric barrier discharge (DBD) microplasma chip to be utilized as a radiation source for mercury determination in water samples. The experimental work was implemented by using experimental design, and the results were assessed by applying statistical techniques. The proposed DBD chip was designed and fabricated in a simple way by using a few microscope glass slides aligned together and held by a Perspex chip holder, which proved useful for miniaturization purposes. Argon gas at 75–180 mL/min was used in the experiments as a discharge gas, while AC power in the range 75–175 W at 38 kHz was supplied to the load from a custom-made power source. A UV-visible spectrometer was used, and the spectroscopic parameters were optimized thoroughly and applied in the later analysis. Plasma characteristics were determined theoretically by analysing the recorded spectroscopic data. The estimated electron temperature (T _e = 0.849 eV) was found to be higher than the excitation temperature (T _exc = 0.55 eV) and the rotational temperature (T _rot  = 0.064 eV), which indicates non-thermal plasma is generated in the proposed chip. Mercury cold vapour generation experiments were conducted according to experimental plan by examining four parameters (HCl and SnCl₂ concentrations, argon flow rate, and the applied power) and considering the recorded intensity for the mercury line (253.65 nm) as the objective function. Furthermore, an optimization technique and statistical approaches were applied to investigate the individual and interaction effects of the tested parameters on the system performance. The calculated analytical figures of merit (LOD = 2.8 μg/L and RSD = 3.5%) indicates a reasonable precision system to be adopted as a basis for a miniaturized portable device for mercury detection in water samples.     

[C5Li5]Mgn[C5Li5] (n?=?2–8): novel sandwich complexes containing –Mg–Mg– chain

A density functional theory (DFT) investigation on novel sandwich-type D ₅ [C₅Li₅]Mg _n [C₅Li₅] (n = 2–8) complexes containing –Mg–Mg– chain has been performed in this work. The equilibrium geometries, electronic structures, vibrational frequencies, and stabilities of these complexes are researched by B3LYP and BP86 methods at 6-311+G(d) levels of theory. The Mg _n ²⁺ sandwich complexes with D ₅ symmetry are all true minima on the potential energy surface. NBO analyses for the series of complexes reveal that the Mg–Mg bond is a weak σ covalent bond. There are mainly electrostatic interactions between C₅Li₅ ⁻ ligands and Mg _n ²⁺(n = 2–8) nuclear in these complexes. The NICS and NICS_zz computed with GIAO-B3LYP/6-311+G(d) indicates that the C₅Li₅ ⁻ rings in the series of complexes are aromatic. These novel complexes turn out to be strongly thermodynamically favored in the gas phases and may be targeted in future experiments to expand the structural domain of sandwich-type complexes.     

Some studies on the phase formation and kinetics in TiO<Subscript>2</Subscript> containing lithium aluminum silicate glasses nucleated by P<Subscript>2</Subscript>O<Subscript>5</Subscript>

Lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li₂O–71.7SiO₂–7.1Al₂O₃–4.9K₂O–3.2B₂O₃–1.25P₂O₅–1.25TiO₂ were prepared by the melt quench technique. Crystallization kinetics was investigated by the method of Kissinger and Augis–Bennett using differential thermal analysis (DTA). Based on the DTA data, glass ceramics were prepared by single-, two-, and three-step heat treatment schedules. The interdependence of different phases formed, microstructure, thermal expansion coefficient (TEC) and microhardness (MH) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-mechanical analysis (TMA), and microhardness (MH) measurements. Crystallization kinetics revealed that Li₂SiO₃ is the kinetically favored phase with activation energy of 91.10 kJ/mol. An Avrami exponent of n = 3.33 indicated the dominance of bulk crystallization. Based upon the formation of phases, it was observed that the two-stage heat treatment results in highest TEC glass ceramics. The single-step heat treatment yielded glass ceramics with the highest MH.     

Crystallization study of Sn additive Se–Te chalcogenide alloys

Calorimetric study of Se_85−x Te₁₅Sn _x (x = 0, 2, 4 and 6) glassy alloys have been performed using Differential Scanning Calorimetry (DSC) under non-isothermal conditions at four different heating rates (5, 10, 15 and 20 °C/min). The glass transition temperature and peak crystallization temperature are found to increase with increasing heating rate. It is remarkable to note that a second glass transition region is associated with second crystallization peak for Sn additive Se–Te investigated samples. Three approaches have been employed to study the glass transition region. The kinetic analysis for the first crystallization peak has been taken by three different methods. The glass transition activation energy, the activation energy of crystallization, and Avrami exponent (n) are found to be composition dependent. The crystallization ability is found to increase with increasing Sn content. From the experimental data, the temperature difference (T _p − T _g) is found to be maximum for Se₈₃Te₁₅Sn₂ alloy, which indicates that this alloy is thermally more stable in the composition range under investigation.     

A low-temperature heat capacity study of natural lithium micas

Low-temperature heat capacity of natural zinnwaldite was measured at temperatures from 6 to 303 K in a vacuum adiabatic calorimeter. An anomalous behavior of heat capacity function C _p(T) has been revealed at very low temperatures, where this function does not tend to zero. Thermodynamic functions of zinnwaldite have been calculated from the experimental data. At 298.15 K, heat capacity C _p(T) = 339.8 J K⁻¹mol⁻¹, calorimetric entropy S ^o(Т) – S ^o(6.08) = 329.1 J K⁻¹ mol⁻¹, and enthalpy Н ^o(Т) − Н ^o(6.08) = 54,000 J mol⁻¹. Heat capacity and thermodynamic functions at 298.15 K for zinnwaldite having theoretical composition were estimated using additive method of calculation.     

Structural and thermal properties of rare earth complexes with 2,2′-biphenyldicarboxylic acid

Rare earth complexes with 2,2′-biphenyldicarboxylic acid (diphenic acid = H₂dpa) were obtained as hydrated precipitates of the general formula Ln₂(C₁₄H₈O₄)₃∙nH₂O, where n = 3 for the of Y(III) and Ce(III)–Er(III) and n = 6 for La(III), Tm(III), Yb(III) and Lu(III) complexes. On heating in air atmosphere complexes lose all water molecules in the temperature range 30–210 °C in one step and form anhydrous compounds, which are stable up to 315–370 °C. During further heating they decompose to oxides. The trihydrated compounds are crystalline powders whereas the hexahydrated are amorphous solids. The trihydrated complexes crystallize in the monoclinic (Pr(III) and Ce(III) complexes) and triclinic (Y(III) and Nd(III)–Er(III) complexes) crystal systems.