Mahbod Morshedi

The effect of H2S on the selectivity of light alkenes in the FE-Mn-catalyzed Fischer-Tropsch synthesis

Iron-manganese oxides are prepared using a co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effect of a range of preparation variables is investigated in details. In this investigation, sulfur absorption and effect of sulfur poisoning on Fe-Mn catalysts have been studied. In the Fischer-Tropsch synthesis process, the poisoning of the catalyst is one of the important parameters causing a decrease in the catalyst activity, declaring the sulfur compounds as virulent poisons in this process. In the present investigation, poisoning of Fe-Mn catalysts were performed in a gas circulation system and H2S was injected into a circulation loop. The prepared catalysts were exposed to a mixture of H2S and N2 at about 450°C in the stainless-steel micro reactor via co-precipitation method. H2S was produced by addition of H2SO4 to Na2S × H2O and this gas was mixed with an inert carrier gas (N2). Comparing the activity and selectivity of fresh and poisoned catalysts, indicates that the selectivity and CO conversion are affected by high-level sulfur adsorbed on the catalysts. The results show that the CO conversion and selectivity with respect to methane production and coke formation were decreased, but the selectivity of light alkenes such as propylene was increased over poisoned catalysts. Characterization of both precursors and calcined catalysts by powder X-ray diffraction, BET specific surface area and thermal analysis methods such as TGA and DSC showed that the poisoning of Fe-Mn catalysts influenced the catalyst structure.

Syntheses, Spectroscopic, Electrochemical, and Third-Order Nonlinear Optical Studies of a Hybrid Tris{ruthenium(alkynyl)/(2-phenylpyridine)}iridium Complex.

The synthesis of fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡CH)}3] (10), which bears pendant ethynyl groups, and its reaction with [RuCl(dppe)2]PF6 to afford the heterobimetallic complex fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡C-trans-[RuCl(dppe)2])}3] (11) is described. Complex 10 is available from the two-step formation of iodo-functionalized fac-tris[2-(4-iodophenyl)pyridine]iridium(III) (6), followed by ligand-centered palladium-catalyzed coupling and desilylation reactions. Structural studies of tetrakis[2-(4-iodophenyl)pyridine-N,C1′](μ-dichloro)diiridium 5, 6, fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CH)}3] (8), and 10 confirm ligand-centered derivatization of the tris(2-phenylpyridine)iridium unit. Electrochemical studies reveal two (5) or one (6–10) Ir-centered oxidations for which the potential is sensitive to functionalization at the phenylpyridine groups but relatively insensitive to more remote derivatization. Compound 11 undergoes sequential Ru-centered and Ir-centered oxidation, with the potential of the latter significantly more positive than that of Ir(N,C′-NC5H4-2-C6H4-2)3. Ligand-centered π–π* transitions characteristic of the Ir(N,C′-NC5H4-2-C6H4-2)3 unit red-shift and gain in intensity following the iodo and alkynyl incorporation. Spectroelectrochemical studies of 6, 7, 9, and 11 reveal the appearance in each case of new low-energy LMCT bands following formal IrIII/IV oxidation preceded, in the case of 11, by the appearance of a low-energy LMCT band associated with the formal RuII/III oxidation process. Emission maxima of 6–10 reveal a red-shift upon alkynyl group introduction and arylalkynyl π-system lengthening; this process is quenched upon incorporation of the ligated ruthenium moiety on proceeding to 11. Third-order nonlinear optical studies of 11 were undertaken at the benchmark wavelengths of 800 nm (fs pulses) and 532 nm (ns pulses), the results from the former suggesting a dominant contribution from two-photon absorption, and results from the latter being consistent with primarily excited-state absorption.

Synthesis, crystal structure, and electrochemical properties of Cu(I) coordination polymers with two new (NS)2 Schiff-base ligands containing long flexible spacers

Two new (NS)2 Schiff bases, (4-NO2Ph)2dapte (N,N′-di-(4-nitrobenzaldimine)-1,2-di(o-aminophenylthio)ethane) (1) and (thio)2daptx (N,N′-di-(thiophenedimine)-1,4-di(o-aminophenylthio)xylene) (2), and their 1-D copper(I) coordination polymers [Cu2(μ-Br)2(μ-(4-NO2Ph)2dapte)] n (3), [Cu2(μ-I)2(μ-(4-NO2Ph)2dapte)] n (4), and [Cu2(μ-I)2(μ-(thio)2daptx)] n (5) have been synthesized and characterized by elemental analyses and IR, UV-Vis, and 1H NMR spectroscopy. The structures of 4 and 5 have been determined by X-ray crystallography and were shown to consist of Cu2(μ-I)2 secondary building units (SBUs) bridged by (4-NO2Ph)2dapte or (thio)2daptx ligands. The CuNSI2 coordination sphere is a distorted tetrahedral in both cases. Both (4-NO2Ph)2dapte and (thio)2daptx are N2S2-bis-bidentate chelating ligands with the two imine nitrogens and two thioether sulfurs in a trans configuration generating dinuclear [Cu2(μ-(4-NO2Ph)2dapte)] and [Cu2(μ-(thio)2daptx)]. These units are connected by two bridging iodides to form 1-D copper(I) coordination polymers. The electrochemical properties of 3–5 are also reported and discussed.

Hydrogen bond-Driven Self–Assembly between Amidinium Cations and Carboxylate Anions: A Combined Molecular Dynamics, NMR Spectroscopy, and Single Crystal X-ray Diffraction Study

A combination of molecular dynamics (MD), NMR spectroscopy, and single crystal X-ray diffraction (SCXRD) techniques was used to probe the self-assembly of para- and meta-bis(amidinium) compounds with para-, meta-, and ortho-dicarboxylates. Good concordance was observed between the MD and experimental results. In DMSO solution, the systems form several rapidly exchanging assemblies, in part because a range of hydrogen bonding interactions is possible between the amidinium and carboxylate moieties. Upon crystallization, the majority of the systems form 1D supramolecular polymers, which are held together by short N-H⋅⋅⋅O hydrogen bonds.

Mixed halide/oxoanion-templated frameworks

A tetrahedral tetra-amidinium compound 14+ was crystallised in the presence of a range of anions (Cl−, Br−, NO3−, oxalate2−) giving a range of interesting solid state structures assembled through amidinium⋯anion hydrogen bonding interactions. Mixing the chloride or bromide salts of 14+, i.e.1·4Cl or 1·4Br, and inorganic oxalate salts in water gave crystals of ordered three-dimensional network structures containing both oxalate and halide anions. These interesting “mixed anion” frameworks exhibit high thermal stability to heat and hydrolysis but are not significantly porous. Importantly, these materials are significantly more robust than the analogous terephthalate-containing framework materials.

Phosphine, isocyanide, and alkyne reactivity at pentanuclear molybdenum/tungsten-iridium clusters

The trigonal bipyramidal clusters M2Ir3(μ-CO)3(CO)6(η(5)-C5H5)2(η(5)-C5Me4R) (M = Mo, R = Me 1a, R = H; M = W, R = Me, H) reacted with isocyanides to give ligand substitution products M2Ir3(μ-CO)3(CO)5(CNR′)(η(5)-C5H5)2(η(5)-C5Me4R) (M = Mo, R = Me, R′ = C6H3Me2-2,6 3a; M = Mo, R = Me, R′ = (t)Bu 3b), in which core geometry and metal atom locations are maintained, whereas reactions with PPh3 afforded M2Ir3(μ-CO)4(CO)4(PPh3)(η(5)-C5H5)2(η(5)-C5Me4R) (M = Mo, R = Me 4a, H 4c; M = W, R = Me 4b, H), with retention of core geometry but with effective site-exchange of the precursors’ apical Mo/W with an equatorial Ir. Similar treatment of trigonal bipyramidal MIr4(μ-CO)3(CO)7(η(5)-C5H5)(η(5)-C5Me5) (M = Mo 2a, W 2b) with PPh3 afforded the mono-substitution products MIr4(μ-CO)3(CO)6(PPh3)(η(5)-C5H5)(η(5)-C5Me5) (M = Mo 5a; M = W 5b), and further reaction of the molybdenum example 5a with excess PPh3 afforded the bis-substituted cluster MoIr4(μ3-CO)2(μ-CO)2(CO)4(PPh3)2(η(5)-C5H5)(η(5)-C5Me5) (6). Reaction of 1a with diphenylacetylene proceeded with alkyne coordination and C≡C cleavage, affording Mo2Ir3(μ4–η(2)-PhC2Ph)(μ3-CPh)2(CO)4(η(5)-C5H5)2(η(5)-C5Me5) (7a) together with an isomer. Reactions of 2a and 2b with PhC≡CR afforded MIr4(μ3–η(2)-PhC2R)(μ3-CO)2(CO)6(η(5)-C5H5)(η(5)-C5Me5) (M = Mo, R = Ph 8a; M = W, R = Ph 8b, H; M = W, R = C6H4(C2Ph)-3 9a, C6H4(C2Ph)-4), while addition of 0.5 equivalents of the diynes 1,3-C6H4(C2Ph)2 and 1,4-C6H4(C2Ph)2 to WIr4(μ-CO)3(CO)7(η(5)-C5H5)(η(5)-C5Me5) gave the linked clusters [WIr4(CO)8(η(5)-C5H5)(η(5)-C5Me5)]2(μ6–η(4)-PhC2C6H4(C2Ph)-X) (X = 3, 4). The structures of 3a, 4a–4c, 5b, 6, 7a, 8a, 8b and 9a were determined by single-crystal X-ray diffraction studies, establishing the core isomerization of 4, the site selectivity for ligand substitution in 3–6, the alkyne C≡C dismutation in 7, and the site of alkyne coordination in 7–9. For clusters 3–6, ease of oxidation increases on increasing donor strength of ligand, increasing extent of ligand substitution, replacing Mo by W, and decreasing core Ir content, the Ir-rich clusters 5 and 6 being the most reversible. For clusters 7–9, ease of oxidation diminishes on replacing Mo by W, increasing the Ir content, and proceeding from mono-yne to diyne, although the latter two changes are small. In situ UV-vis-near-IR spectroelectrochemical studies of the (electrochemically reversible) reduction process of 8b were undertaken, the spectra becoming increasingly broad and featureless following reduction. The incorporation of isocyanides, phosphines, or alkyne residues in these pentanuclear clusters all result in an increased ease of oxidation and decreased ease of reduction, and thereby tune the electron richness of the clusters.

Crystal structure of ({4-[(4-bromophen-yl)ethynyl]-3,5-diethylphenyl}ethynyl)-triisopropylsilane

The title compound, C29H37BrSi, was synthesized by the Sonogashira coupling of [(3,5-diethyl-4-ethynylphenyl)ethynyl]triisopropylsilane with 4-bromo-1-iodobenzene. In the structure, the two phenyl rings are nearly parallel to each other with a dihedral angle of 4.27 (4)°. In the crystal, π–π interactions between the terminal and central phenyl rings of adjacent molecules link them in the a-axis direction [perpendicular distance = 3.5135 (14); centroid–centroid distance = 3.7393 (11) Å]. In addition, there are weak C—H⋯π interactions between the isopropyl H atoms and the phenyl rings of adjacent molecules.

Theoretical and experimental study of the protonated 2,4,6-tri(2-pyridyl)-1,3,5-triazine [TPTZH 2 ] 2+

The reaction between 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) and sulfuric acid in the presence of NH4PF6 yielded crystals of [TPTZH2](PF6)2·H2O, characterized by spectroscopic methods and single-crystal X-ray diffraction. The structural data indicate that the diprotonated form, [TPTZH2]2+, is more planar than the neutral TPTZ molecule. Due to the presence of PF6− anions located between neighboring dications, the triazine and/or pyridyl rings in each dication cannot interact in a π–π fashion. The proton affinity of TPTZ was computed using density function theory (B3LYP hybrid functional). Calculated thermochemical results and proton affinities indicate that for the first protonation, the favorable N atoms are different from those obtained from calculations based on Merz-Kollman atomic charges. For the second protonation, the proton affinities show a clear preference of the protonation on two N atoms, this time not contradicted by Merz-Kollman atomic charges, and in agreement with the experimental data. In the UV–Vis spectrum, two visible absorption bands of [TPTZH2](PF6)2·H2O are most likely arising from an outer-sphere charge-transfer. The photoluminescence properties of TPTZ and [TPTZH2](PF6)2 were studied at room temperature in CH3CN solution.Graphical abstract

Anion-templated 2D frameworks from hexahydroxytriphenylene

Hexahydroxytriphenylene (HHTP) forms 2D frameworks through O–H⋯anion hydrogen bonds with a range of anions. In all cases, 1 : 1 co-crystals of HHTP and tetraalkylammonium·anion salts are obtained, which have a layered 2D structure. When HSO4− was used as anion, an unprecedented methylation reaction was observed giving crystals containing the methylsulfate anion (MeOSO3−).

Dynamic Permutational Isomerism in a closo‐Cluster

Permutational isomers of trigonal bipyramidal [W2RhIr2(CO)9(η(5)-C5H5)2(η(5)-C5HMe4)] result from competitive capping of either a W2Ir or a WIr2 face of the tetrahedral cluster [W2Ir2(CO)10(η(5)-C5 H5)2] from its reaction with [Rh(CO)2(η(5)-C5HMe4)]. The permutational isomers slowly interconvert in solution by a cluster metal vertex exchange that is proposed to proceed by Rh-Ir and Rh-W bond cleavage and reformation, and via the intermediacy of an edge-bridged tetrahedral transition state. The permutational isomers display differing chemical and physical properties: replacement of CO by PPh3 occurs at one permutational isomer only, while the isomers display distinct optical power limiting behavior.