Dialkyl- and diaryl-platinum(II) complexes with secondary phosphines: Preparation,structure and thermal reaction giving the metallopolymer

Alkyl and arylplatinum complexes with 1,5-cyclooctadiene ligand, [PtR₂(cod)] (R = Me, Ph, C₆H₄-p-CF₃, C₆F₅), react with secondary phosphines, PHR′₂ (R′ = i-Bu, t-Bu, Ph), to afford the mononuclear platinum complexes, cis-[PtR₂(PHR′₂)₂] (1a: R = Me, R′ = i-Bu; 1b: R = Me, R′ = t-Bu; 1c: R = Me, R′ = Ph; 2a: R = Ph, R′ = i-Bu; 2b: R = Ph, R′ = t-Bu; 2c: R = R′ = Ph; 3a: R = C₆H₄-p-CF₃, R′ = i-Bu; 3b: R = C₆H₄-p-CF₃, R′ = t-Bu; 3c: R = C₆H₄-p-CF₃, R′ = Ph; 4a: R = C₆F₅, R′ = i-Bu; 4c: R = C₆F₅, R′ = Ph) in 81–98% yields. Molecular structures of the complexes except for 1a, 1c and 2a were determined by X-ray crystallography. Complex 1b has a square-planar structure with Pt–C(methyl) bonds of 2.083(8) and 2.109(8) Å, while the Pt–C(aryl) bonds of 2b–c, 3a–c, 4a and 4c (2.055(1)–2.073(8) Å) are shorter than them. Thermal decomposition of 1b, 2a–c, and 3a–c releases methane, biphenyl or 4,4′-bis(trifluoromethyl)biphenyl as the organic products, which are characterized by NMR spectroscopy. The solid product of the thermal reactions of 2b and 2c were characterized as the metallopolymers formulated as [Pt(PR′₂)₂]_n (5b: R′ = ^tBu; 5c: R′ = Ph), based on the solid-state NMR and elemental analyses.     

Reactivity of intramolecularly coordinated aluminum compounds to R3EOH (E = Sn,Si). Remarkable migration of N,C,N and O,C,O pincer ligands

The reaction of organoaluminum compounds containing O,C,O or N,C,N chelating (so called pincer) ligands [2,6-(YCH₂)₂C₆H₃]AlⁱBu₂ (Y = MeO 1, ^tBuO 2, Me₂N 3) with R₃SnOH (R = Ph or Me) gives tetraorganotin complexes [2,6-(YCH₂)₂C₆H₃]SnR₃ (Y = MeO, R = Ph 4, Y = MeO, R = Me 5; Y = ^tBuO, R = Ph 6, Y = ^tBuO, R = Me 7; Y = Me₂N, R = Ph 8, Y = Me₂N, R = Me 9) as the result of migration of O,C,O or N,C,N pincer ligands from aluminum to tin atom. Reaction of 1 and 2 with (ⁿBu₃Sn)₂O proceeded in similar fashion resulting in 10 and 11 ([2,6-(YCH₂)₂C₆H₃]SnⁿBu₃, Y = MeO 10; Y = ^tBuO 11) in mixture with ⁿBu₃SnⁱBu. The reaction 1 and 3 with 2 equiv. of Ph₃SiOH followed another reaction path and ([2,6-(YCH₂)₂C₆H₃]Al(OSiPh₃)₂, Y = MeO 12, Me₂N 13) were observed as the products of alkane elimination. The organotin derivatives 4–11 were characterized by the help of elemental analysis, ESI-MS technique, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy and in the case 6 and 8 by single crystal X-ray diffraction (XRD). Compounds 12 and 13 were identified using elemental analysis,¹H, ¹³C, ²⁹Si NMR and IR spectroscopy.     

Versatile Ru-based metathesis catalysts designed for both homogeneous and heterogeneous processes

The synthesis of new ruthenium-based catalysts applicable for both homogeneous and heterogeneous metathesis is described. Starting from the Hoveyda-Grubbs first generation (1) and the Hoveyda-Grubbs second generation (2) catalysts the homogeneous catalysts [RuCl((RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COO)(CH–o-O–iPr–C₆H₄)(SIMes)] (4: R = Et, R′ = H; 5: R = R′ = Me) (SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) were prepared by substitution of one chloride ligand with trialkoxysilyl functionalized silver carboxylates (RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COOAg (3a: R = Et, R′ = H; 3b: R = R′ = Me). These homogeneous ruthenium-species are among a few known examples with mixed anionic ligands. Exchange of both chloride ligands afforded the catalysts [Ru((RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COO)(CH–o-O–iPr–C₆H₄)(SIMes)] (9: R = Et, R′ = H; 11: R = R′ = Me) and [Ru((RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COO)(CH–o-O–iPr–C₆H₄)(PCy₃)] (8: R = Et, R′ = H; 10: R = R′ = Me). The reactivity of the new complexes was tested in homogeneous ring-closing metathesis (RCM) of N,N-diallyl-p-toluenesulfonamide and TONs of up to 5000 were achieved. Heterogeneous catalysts were obtained by reaction of 4, 5 and 8–11 with silica gel (SG-60). The resultant supported catalysts 4a, 5a, 8a–11a showed reduced activity compared to their homogenous analogues, but rival the activity of similar heterogeneous systems.     

Hydrogen production from hydrogen sulfide using membrane reactor integrated with porous membrane having thermal and corrosion resistance

Using mathematical model and experimental method, the thermal decomposition of hydrogen sulfide in membrane reactor with porous membrane which has Knudsen diffusion characteristics was investigated. With mathematical model, the effect of characteristics of membrane reactor and operating conditions on H₂ concentration in the permeate chamber, y_H2, which increases at higher reaction temperature, lower pressure and higher ratio of cross-sectional area of the permeate chamber to that of the reactor, was evaluated. The reaction experiments with ZrO₂–SiO₂ porous membrane were carried out under the following conditions: temperature T, 923–1023 K; pressure in the reactor p^R_T, 0.11–0.25 MPa absolute; pressure in the permeate chamber p^P_T, 5 kPa absolute and inlet flow rate of H₂S f⁰_H2S, 3.2×10⁻⁵–1.5×10⁻⁴ mol/s. At p^R_T=0.11 MPa and f⁰_H2S=6.4×10⁻⁵, y_H2 increased from 0.02 at T=923 K to 0.15 at 1023 K. With the experimental condition, p^R_T=0.11, T=1023 K and f⁰_H2S=3.2×10⁻⁵, y_H2 was 0.22. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.     

A theoretical study on the molecular structure and vibrational (FT-IR and Raman) spectra of a new organic–inorganic compound of 2[N(C3H7)4]SbCl4

The salt bis-tetrapropylammonium tetrachloroantimonate (III) is crystallized in the monoclinic system with the P2₁/c space group. The unit cell dimensions are: a = 18.1973(5) Å, b = 15.7225(4) Å, c = 13.6491(3) Å, β = 91.65(1)° and Z = 4. The vibrational spectra have been measured at room temperature by FT-infrared spectroscopy (4000–400 cm⁻¹) on polycrystalline samples, and by FT-Raman spectroscopy (3500–30 cm⁻¹) on monocrystals. The structure of the 2[N(C₃H₇)₄]SbCl₄ formed by two types of cations (C₃H₇)₄N⁺ and two types of anions [SbCl₄]⁻ was optimized by density functional theory (DFT) using the B3LYP method. Actually the values obtained by the B3LYP/LanL2MB basis with the aid of a calculation of the potential energy distribution (PED) are in good agreement with the experimental data. A root mean square (rms) difference value was calculated and the small differences between experimental and calculated modes have been interpreted by intermolecular interactions with-in the crystal. A comparison between the results of the 2[N(C₃H₇)₄]SbCl₄ compound and the simulated compounds based on the (CH₃)₄N⁺) and (C₂H₅)₄N⁺ fragments, shows an increase in the wavenumber of the bands assigned to the stretching vibration of the (NC) group for the 2[N(C₃H₇)₄]SbCl₄ compound. The comparison between the [N(C₃H₇)₄]Cl ligand and the 2[N(C₃H₇)₄]SbCl₄ compound of the infrared and Raman spectrum shows an increase in the wavenumber for the bands assigned to the stretching vibration of (CH₃) and the bending vibration of (NC₄) groups in the 2[N(C₃H₇)₄]SbCl₄ compound.     

Thermodynamic aspects of solubility,solvation and partitioning processes of some sulfonamides

The thermodynamic aspects of sublimation processes of three sulfonamides with the general structures C₆H₅–SO₂NH–C₆H₄–R (R = 4-NO₂) and 4-NH₂–C₆H₄–SO₂NH–C₆H₄–R (R = 4-NO₂; 4-CN) were studied by investigating the temperature dependence of vapor pressure using the transpiration method. These data together with those obtained earlier for C₆H₅–SO₂NH–C₆H₄–R (R = 4-Cl) and 4-NH₂–C₆H₄–SO₂NH–C₆H₄–R (R = 4-Cl; 4-OMe; 4-C₂H₅) were analyzed and compared. A correlation was derived between sublimation Gibbs free energies and the sum of H-bond acceptor factors of the molecules. Solubility processes of the compounds in water, phosphate buffer with pH 7.4 and n-octanol (as phases modeling various drug delivery pathways) were investigated and corresponding thermodynamic functions were calculated as well. Thermodynamic characteristics of the sulfonamides solvation were evaluated. Also in this case a correlation between solubility/solvation Gibbs free energy values and the sum of H-bond acceptor factors was observed. For the sulfonamides with various substituents at para-position the processes of transfer from one solvent (water or buffer) to n-octanol were studied by a diagram method combined with analysis of enthalpic and entropic terms. Distinguishing between enthalpy and entropy, as is possible through the present approach, leads to the insight that the contribution of these terms is different for different molecules (entropy- or enthalpy-determined). Thus, in contrast to the interpretation of only the Gibbs free energy of transfer (extensively used for pharmaceuticals in the form of the partition coefficient, log P), the analysis of thermodynamic functions of the transfer process provides additional mechanistic information. This may be important for further evaluation of the physiological distribution of drug molecules and may provide a better understanding of biopharmaceutical properties of drugs.     

Synthesis and characterization of a novel three-dimensional open-framework: Metal diphosphonate,Zn[HO3PCH2(C6H4)CH2PO3H]

A novel zinc diphosphonate, Zn[HO₃PCH₂(C₆H₄)CH₂PO₃H] (1) was synthesized from tetraethyl para-xylylenediphosphonate, Et₂O₃PCH₂C₆H₄CH₂PO₃Et₂, and Zn (AcO)₂·2H₂O under solvothermal conditions. The structure of compound 1 was determined by single-crystal X-ray diffraction, which reveals that the structure crystallizes in the monoclinic space group C2/c (No. 15), with a = 22.4844(19) Å, b = 6.4361(5) Å, c = 8.1194(7) Å, β = 102.595(2)°, V = 1146.70(16) Å³, T = 298(2) K, Z = 8. The novel three-dimensional (3D) construction is simply built up from linear inorganic chains of corner-sharing four-rings of tetrahedral [ZnO₄] and [PO₃C] which connected adjacent chains by the organophosphorus ligand para-xylylenediphosphonate. The framework has 10 Å × 4 Å (containing the van der Waals radii of atoms) channels running along the b-axis.     

Ab initio crystal structure of nickel(II) hydroxy-terephthalate by synchrotron powder diffraction and magnetic study

The structure of the new hybrid compound [Ni₃(OH)₂(tp)₂(H₂O)₄]·2H₂O (tp = C₈H₄O₄²⁻) has been determined ab initio from synchrotron powder diffraction data and refined with the Rietveld method: space group P-1, a = 10.2077(6) Å, b = 8.0135(5) Å, c = 6.3337(4) Å, α = 97.70 (1)°, β = 97.21(1)°, γ = 108.77(1)°, D_x = 2.124 g/cm³, Rp = 0.045, R_B = 0.095 (757 independent reflections). H atoms were placed geometrically and their position optimized by DFT calculation. The repeating structural unit is the chain [Ni(1)O₆]₂Ni(2)O₆, consisting of two edges sharing octahedrons related by the symmetry center and linked via μ3-OH to a vertex of Ni(2) octahedron. The Ni(1) coordination is ensured by two oxygen atoms from two water molecules, two OH and two oxygen atoms from carboxylate groups. The linkage of the chains by the tp anions forms infinite layers parallel to the (010) planes. Interchain hydrogen bonds between the water molecules coordinating the metal ensure the cohesion of the 2D structure. The structural and magnetic properties are compared with that of the 3D fumarate-based compound [Ni₃(OH)₂(fum)₂(H₂O)₄]·2H₂O (fum = C₄H₂O₄²⁻).     

Catalytic cyclopropanation of olefins using copper(I) diphosphinoamines

Catalytic cyclopropanation reactions of olefins with ethyl diazoacetate were carried out using copper(I) diphosphinoamine (PPh₂)₂N(R) (R = ⁱPr, H, Ph and –CH₂–C₆H₄–CHCH₂) complexes at 40 °C in chloroform. High yields of the cyclopropanes were obtained in all cases. The rate of the reaction was influenced by the nuclearity of the complex and the binding mode of the ligand which was either bridging or chelating. Comparison of isostructural complexes shows that the rate follows the order R = ⁱPr > H > Ph, where R is the substituent on the N. However, cyclopropane formation versus dimerization of the carbene, and trans to cis ratios of cyclopropane was similar in all cases. The nearly identical selectivity for different products formed was indicative of a common catalytic intermediate. A labile “copper–olefin” complex which does not involve the phosphine or the counterion is the most likely candidate. The differences in the reaction rates for different complexes are attributed to differences in the concentration of the catalytically active species which are in equilibrium with the catalytically inactive copper–phosphinoamine complex. To test the hypothesis a diphosphinoamine polymer complexed to copper(I) was used as a heterogeneous catalyst. Leaching of copper(I) and deactivation of the catalyst confirmed the proposed mechanism.     

Synthesis and characterization of novel intramolecularly O,C,O-coordinated heteroleptic organostannylenes and their tungstenpentacarbonyl complexes

The syntheses are reported of the novel heteroleptic organostannylenes [2,6-(ROCH₂)₂C₆H₃]SnCl (1, R = Me; 2, R = t-Bu) and of their tungstenpentacarbonyl complexes [2,6-(ROCH₂)₂C₆H₃](X)SnW(CO)₅ (3, X = Cl, R = Me; 4, X = Cl, R = t-Bu; 5, X = H, R = Me). The compounds were characterized by means of elemental analyses, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopies, electrospray mass spectrometry and in case of 3 and 4 also by single crystal X-ray diffraction analysis. For the two latter compounds the substituents bound at the ether oxygen atom control the strength of intramolecular O → Sn coordination. Thus, the O–Sn distances amount to 2.391(5)/2.389(5) (3) and 2.464(3)/2.513(3) Å (4).     

Theoretical DFT study of phosphorescence from porphyrins

Geometrical structure of free-base porphin (H₂P) and Mg- and Zn-porphyrins together with their vibrational frequencies and vibronic intensities in phosphorescence are investigated by density functions theory (DFT) with the standard B3LYP functional. These molecules have a closed-shell singlet ground state (S₀) and low-lying triplet (T₁) excited states of ππ* type. The S₀–T₁ transition probability and radiative lifetime of phosphorescence (τ_p) of these molecules are calculated by time-dependent DFT utilizing quadratic response functions for account of spin–orbit coupling (SOC) and electric-dipole transition moments including displacements along active vibrational modes. The infrared and Raman spectra in the ground singlet and first excited triplet states are also studied for proper assignment of vibronic patterns. The long radiative lifetime of free-base porphin phosphorescence (τ_p ∼ 360 s at low temperature limit, 4.2 K) gets considerably shorter for the metalloporphyrins. An order of magnitude reduction of τ_p is predicted for Mg-porphyrin but no change of phosphorescence polarization is found. A forty times enhancement of the radiative phosphorescence rate constant is obtained for Zn-porphyrin in comparison with the H₂P molecule which is accompanied by a strong change of polarization and spin-sublevel radiative activity. A strong vibronic activity of free-base porphin phosphorescence is found for the b_2g mode at 430 cm⁻¹, while the 679 and 715 cm⁻¹ vibronic bands of b_3g symmetry are less active. These and other out-of-plane vibrations produce considerable changes in the radiative constants of different spin sublevels of the triplet state; they also promote the S₁ → T₁ intersystem crossing. Among the in-plane vibrations the a_g mode at 1614 cm⁻¹ is found very active; it produces a long progression in the phosphorescence spectrum. The time-dependent DFT calculations explain the effects of the transition metal atom on phosphorescence of porphyrins and reproduce differences in their phosphorescence and EPR spectra.     

New three-dimensional (3,4)-net zincophosphites templated by linear diammonium cations: H3N(CH2)5NH3·Zn3(HPO3)4 and β-H3N(CH2)6NH3·Zn3(HPO3)4

The mild-condition syntheses, single-crystal structures and properties of H₃N(CH₂)₅NH₃·Zn₃(HPO₃)₄ and β-H₃N(CH₂)₆NH₃·Zn₃(HPO₃)₄ are reported. Both are constructed from (3,4)-nets of ZnO₄ tetrahedra and HPO₃ pyramids, sharing vertices to result in three-dimensional anionic open-frameworks. In both materials, the organic species interacts with the framework by way of N–H⋯O bonds. Crystal data: H₃N(CH₂)₅NH₃·Zn₃(HPO₃)₄, M_r = 620.22, orthorhombic, Pccn (No. 56), a = 9.5364 (9) Å, b = 21.8015 (19) Å, c = 9.1118 (7) Å, V = 1894.4 (3) Å³, Z = 4, R(F) = 0.044, wR(F²) = 0.111. β-H₃N(CH₂)₆NH₃·Zn₃(HPO₃)₄, M_r = 634.25, monoclinic, P2₁/n (No. 14), a = 8.7627 (1) Å, b = 13.8117 (2) Å, c = 16.6187 (3) Å, β = 92.680 (1)°, V = 2009.12 (5) Å³, Z = 4, R(F) = 0.072, wR(F²) = 0.187.     

Synchronous ATR infrared and NIR-spectroscopy investigation of sepiolite upon drying

A new environmental cell allowing for the independent synchronous collection of the near- and mid-infrared spectra (12,000–600 cm⁻¹) in the diffuse reflection and attenuated total reflection (ATR) modes, respectively, is reported. The cell is employed to study in real time the dehydration of the phyllosilicate mineral sepiolite, Mg₈Si₁₂O₃₀(OH)₄(OH₂)₄·wH₂O, in both its natural form and after in situ deuteration at ambient. The spectra are obtained under dynamic purging with dry N₂ and compared to those of the same material conditioned over saturated salt solutions. Sepiolite is an important industrial mineral with a modulated structure of alternating tunnels and ribbons. Its mild drying is associated with pronounced vibrational spectral changes due to the removal of surface and zeolitic H₂O and the concomitant structural relaxation of the ribbons. Detailed assignments are provided for the fundamental, combination and overtone spectrum of H₂O confined in the tunnels of sepiolite, SiOH groups on the external surface of the particles, and Mg₃OH groups in the 2:1 ribbons. The spectra are discussed in comparison to those of palygorskite (modulated phyllosilicate with narrower ribbons and tunnels), talc (trioctahedral magnesian phyllosilicate without modulation) and high-surface area silica. It is demonstrated that sepiolite exhibits three discrete states of zeolitic hydration at ambient temperature: Besides the previously known hydrated (w = 7–8) and dry (w = 0–1) states which dominate the spectra above 30% and below 3% relative humidity, respectively, a hitherto unknown intermediate (w = 4–5) is found in the 3–10% range. The new state is most conveniently identified in the near-infrared by a ν₀₂ Mg₃O-H stretching mode at 7205 cm⁻¹ (ν₀₁ = 3686 cm⁻¹, X = 83.5 cm⁻¹) and a characteristic H₂O combination band at 5271 cm⁻¹ (D₂O: 3908 cm⁻¹).     

Spontaneous resolution of a novel chiral coordination polymer through supramolecular interactions and solvent symmetry breaking

The spontaneous resolution reaction of racemic trans-2,3-dihydro-2,3-dipyridyl-benzo[e]indole 1 with Cd(ClO₄)₂·6H₂O in the presence of 2-butanol under solvothermal reaction conditions favors the formation of crystal 2 [P-Cd(R,R,-1)₂(ClO₄)₂], while a similar reaction in the presence of ethanol only favors the formation of crystal 3 [M-Cd(S,S,-1)₂(ClO₄)₂]. The crystal structural determination shows that both 2 and 3 crystallize in chiral enantiomorphous space groups (P6₁22 and P6₅22) and their structures are 1D infinite chain, and are just enantiomorphous pairs most like. The spontaneous resolution process displays estimated ee values of ca. +0.6 for 2-butanol and ca. −0.4 for ethanol. Enantiomerically pure (S,S)-trans-2,3-dihydro-2,3-dipyridyl-benzo[e]indole (S,S,-1) can be obtained through the decomposition of mechanically separated 3. Additionally (S,S,-1) also crystallizes in a chiral space group (P2₁). The CD (circular dichroism) spectra of both 2 and 3 in the solid state are also approximately enantiomorphous pairs. However, their fluorescent spectra in the solid state display a moderate difference in maximum emission peaks (Δλ = 19 nm). Crystal data for 2: C₄₄H₃₄Cl₂N₆O₈Cd, M = 958.07, hexagonal, P6₁22, a = 10.5488(5), c = 68.256(4) Å, α = γ = 90°, β = 120°, V = 6577.8(6) Å³, Z = 6, D_c = 1.451 mg m⁻³, R₁ = 0.0498, wR₂ = 0.1124, μ = 0.679 mm⁻¹, S = 0.623, Flack χ = −0.02(6). For space group P6₅22, R₁ = 0.0670, wR₂ = 0.1602, S = 0.725 with a Flack value of 1.03(7); Crystal data for 3, C₄₄H₃₄Cl₂N₆O₈Cd, M = 958.07, hexagonal, P6₅22, a = 10.5446(3), c = 68.265(3) Å, V = 6573.3(4) Å³, Z = 6, D_c = 1.452 mg m⁻³, R₁ = 0.0444,wR₂ = 0.1002, μ = 0.679 mm⁻¹, S = 0.558, Flack χ = 0.01(5). For space group P6₁22, R₁ = 0.0501, wR₂ = 0.1178, S = 0.599 with a Flack value of 1.00(5). The low Flack parameter indicates that the absolute configurations of 2 and 3 are stated; Crystal data for (S,S)-1, C₂₂H₁₇N₂, M = 323.39, orthorhombic, P2₁2₁2₁, a = 9.2598(7), b = 9.4617(8), c = 19.1452(16) Å, V = 1677.4(2) Å³, Z = 4, D_c = 1.281 mg m⁻³, R₁ = 0.0417, wR₂ = 0.1191, T = 293 K, μ = 0.077 mm⁻¹, S = 0.862.     

Photochemistry of 1,3,5-trithianes in solution: Steady-state and laser flash photolysis studies

In this work, we characterized the direct photochemistry of a set of five structurally-related 1,3,5-trithianes. The compounds were 1,3,5-trithiane, the α- and β-isomers of the 2,4,6-trimethyl derivatives, and the α- and β-isomers of the 2,4,6-triphenyl derivatives. Under steady-state, 254-nm irradiation of acetonitrile solutions of all five trithianes, dithioesters of the form RC( = S)SCH(R)SCH₂R were identified and shown to be primary photoproducts (R = H, CH₃, or C₆H₅). Shorter dithioesters, RC( = S)SCH₂R, were also identified and shown to be secondary products. The presence of the dithioesters could be monitored by their strong absorption bands in the region of 310 nm. This same band was evident following the laser flash photolysis of the five trithianes. The laser-induced transient spectra showed another absorbing species (I) in all five trithianes. This species was not stable and showed a complementary decay that matched the growth of the stable photoproducts at 310 nm. This suggested that the intermediates (I) are the precursors of the corresponding dithioesters, RC( = S)SCH(R)SCH₂R. These correlated processes were related to monophotonic events. However, in the laser flash photolysis experiments in the triphenyl derivatives, there was an additional pathway for the formation of the dithioesters, and this was biphotonic. When the biphotonic formation of products was compensated for, RC( = S)SCH(R)SCH₂R formation quantum yields from steady-state and laser flash photolysis matched within experimental error. The absorption band of (I) varied systematically with substituents, 320 nm in 1,3,5-trithiane, 340 nm in the 2,4,6-trimethyl derivatives, and 420 nm in the 2,4,6-triphenyl derivatives. The nature of these intermediates (I) were discussed as resulting from CS bond cleavage, probably heterolytic.     

Six-coordinate uranium complexes featuring a bidentate anilide ligand

The synthesis of a new bidentate anilide ligand and four uranium amide complexes utilizing the ligand are reported. The secondary aniline HN[R]Ar_MeL (R = C(CD₃)₂CH₃, Ar_MeL = 2-NMe₂-5-MeC₆H₃) is prepared by condensation of H₂NAr_MeL and acetone-d₆ followed by alkylation of the resulting imine with MeLi. The ligand precursors (Et₂O)Li(N[R]Ar_MeL) and K(N[R]Ar_MeL) are prepared through deprotonation of HN[R]Ar_MeL with n-BuLi and KH, respectively. Treatment of UI₃(THF)₄ with (Et₂O)Li(N[R]Ar_MeL) (2 equiv) provides the uranium(III) -ate complex Li[I₂U(N[R]Ar_MeL)₂] (Li[1]), while treatment of UI₃ with three equiv. of K(N[R]Ar_MeL) provides the neutral uranium(III) complex U(N[R]Ar_MeL)₃ (2). Both uranium(III) complexes are susceptible to 1e oxidation, as is demonstrated by the syntheses of the uranium(IV) derivatives I₂U(N[R]Ar_MeL)₂ (1) and [U(N[R]Ar_MeL)₃][OTf] ([2][OTf]; OTf = CF₃SO₃). The spectroscopic and X-ray structural characterization of all four uranium complexes is described. The structures of 2 and [2][OTf] exhibit a large degree of steric pressure about the uranium center, effectively preventing the [2]⁺ ion from achieving a seven-coordinate structure.     

Electronic absorption study on acid–base equilibria for some pyrimidine derivatives containing semi- and thiosemicarbazone moiety

The UV–vis spectra of recently synthesized 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-one, (I), and 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-thione, (II) were studied in aqueous methanol (5%, v/v methanol). The nature of the electronic transitions and the roles of carbonyl oxygen of I and thiocarbonyl sulfur of II on the behavior of UV–vis spectra were discussed.Acid–base equilibria of the compounds against varying pH and pK_a values related equilibria were determined at an ionic strength of 0.10 M by using the Henderson–Haselbalch equation. The mean acidity constants for the protonated forms of the compounds were determined as pK_a1 = 5.121, pK_a2 = 7.929 and pK_a3 = 11.130 for I and pK_a1 = 4.684, pK_a2 = 7.245 and pK_a3 = 10.630 for II. The preferred dissociation mechanisms were discussed based on UV–vis data and a mechanism was proposed for each compound.     

Measurements of HmE and VmE for (propane + sulphurhexafluoride) in the near critical region

A flow mixing calorimeter followed by a vibrating-tube densimeter has been used to measure excess molar enthalpies H_m^E and excess molar volumesV_m^E of {xC₃H₈ +  (1  − x)SF₆}. Measurements over a range of mole fractionsx have been made at the pressure p =  4.30 MPa at eight temperatures in the rangeT =  314.56 K to 373.91 K, in the liquid region at p =  3.75 MPa andT =  314.56 K, in the two phase region at p =  3.91 MPa andT =  328.18 K, and in the supercritical region at p =  5.0 MPa andT =  373.95 K. The measurements are compared with results from the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on{xCO₂ +  (1  − x)C₂H₆} ,{xCO₂ +  (1  − x)C₂H₄} and{xCO₂ +  (1  − x)SF₆} reported previously.     

New metastable hybrid phase,Zn2(OH)2(C8H4O4), exhibiting unique oxo-penta-coordinated Zn(II) atoms

The metastable phase (phase 1) Zn(OH)₂(tp)₂ (tp = C₈H₄O₄^2?) was found to be an intermediate forming during the hydrothermal synthesis of Zn₃(OH)₄tp (phase 2). Its structure has been determined ab initio from synchrotron powder diffraction data and refined with the Rietveld method: space group P2₁/c, a = 3.48856(2) Å, b = 5.84645(2) Å, c = 22.1331(1) Å, β = 103.46(1)°, D_x = 2.488 g/cm³, R_p = 0.10, R_B = 0.095 (402 independent reflections). The structures of the two analogues were compared. Whereas a mixed coordination of the zinc atoms was found in phase 2, phase 1 exhibits only penta-coordinated Zn(II). Moreover, different optical properties were observed, Zn₂(OH)₂(tp) showing photoluminescence at 378 nm under λ_ex = 316 nm.     

A DFT study on group III and V combined hexagonal clusters as potential building motifs for inorganic nanomaterials

A detail theoretical investigation on the structure and electronic properties of inorganic hexagonal units and their higher order derivatives comprising group III (B, Al and Ga) and V (N, P and As) elements is performed. A series of 45 clusters, formed by a linear combination of hydrogen saturated hexagonal motifs up to five units, (MY)_2n+1H_2n+4 (M = B, Al, Ga; Y = N, P, As; n = 1–5) are considered to look into their metal–insulator–semiconductor (MIS) behavior. It is evident from the present study that the arsenic doped group III hexagonal units clearly have a decisive role in forming semiconductor materials.