"Synthesis and characterization of new SILVER(I) coordination polymers incorporating a BIS(TRIAZOLYL)-type ligand "

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Extraction and Recovery of Metals from Spent HDS Catalysts: Lab- and Pilot-Scale Results of the Overall Process

The present study proposes an overall recycling process for spent hydrodesulfurization (HDS) catalysts. The process put together stages already known in the technical literature, tested again with samples coming from the roasting stage in a pilot kiln, which is the most limiting stage of metal recovery from spent catalysts. These catalysts contain valuable metals like cobalt (Co), molybdenum (Mo), nickel (Ni), and vanadium (V). In particular, one Co-Mo catalyst was treated in order to optimize the roasting step (time, soda ash, and temperature) at a pilot scale and thus maximize the extraction yield of molybdenum (Mo) and vanadium (V). In particular, a dry Co-Mo catalyst was used. After roasting at 700 °C for 2.5 h, the best conditions, the catalysts underwent water leaching, separating Mo and V from Co and the alumina carrier, which remained in the solid residue. The pregnant solution was treated to remove arsenic (As) and phosphorus (P), representing the main impurities for producing steel alloys. V was precipitated as NH4Cl, and further calcined to obtain commercial-grade V2O5, whereas Mo was recovered as molybdic acid by further precipitation at a pH of around one. Thus, molybdic acid was calcined and converted into commercial-grade MoO3 by calcination. The hydrometallurgical section was tested on a lab scale. The total recovery yield was nearly 61% for Mo and 68% for V, respectively, compared with their initial concentration in the spent Co-Mo catalysts

Unsolvated ruthenium(II) benzene dichloride: The beta polymorph

A novel polymorph of the unsolvated species [Ru2(benzene)2Cl4] (beta form in the following) was serendipitously isolated as a polycrystalline powder. Its molecular and crystal structure was unraveled by means of state-of-the-art X-ray powder diffraction structure determination methods applied to laboratory data, and was compared to those of both the alpha polymorph and the CHCl3 solvate, throwing light on some discrepant results recently appeared in the literature. The thermal behavior of the alpha and beta polymorphs was investigated by coupling thermogravimetric analyses to variable-temperature X-ray powder diffraction experiments. No temperature-stimulated phase transformation could be detected between the two polymorphs, each preserving its structural features up to decomposition, suggesting that kinetic, more than thermodynamic, factors regulate their isolation

Novel Coordination Frameworks Based on Polytopic Heteroaromatic Nitrogen and Carboxylate Ligands

Metal-organic frameworks (MOFs) are comprised of metal clusters and organic ligands. MOFs, similar to zeolite, carbon nanotubes, and activated carbon, have very porous structures. Since MOFs have many more building blocks than materials such as zeolite, their properties can be finely tuned through a careful choice of the ligands. The functionalization of the MOF could be achieved by modifying ligands before the MOF synthesis (pre-synthetically) or after the synthesis (post-synthetically). These functionalized MOFs can be used for numerous applications such as gas storage, gas separation, and catalysis. The advantage of these hybrid materials, over classical (natural and synthetic) porous species (zeolites, active carbons, silica, etc.) resides in the possibility of easy optimization and fine tuning of their functional properties by using modification or substitution strategies of the organic ligands, and through the choice of suitable metallic ions [1, 2]. Moreover, the simultaneous presence of channels (or cavities) and metal ions capable of catalytic activity makes these materials particularly intriguing as heterogeneous catalysts for the transformation of small molecules, and, if the pores are suitably “decorated”, they can display significant size-, regio-, and enantioselectivity [3-6]. In this work we report the synthesis and characterization of a series of pyrazolylbased ligands, namely 3,3',5,5'-tetramethyl-1H,1'H-4,4'-bipyrazole (H2Me4BPz), 1H-pyrazole-3,4,5-tricarboxylic acid (H4PzTc), 1H,1'H-4,4'-bipyrazole (H2Pz) and their MOFs with late transition metals (Co2+, Ni2+, Zn2+, Cu2+, Ru++) characterized by the presence of diverse counterions

Novel Coordination Polymers Based on Bis- and Tris-pyrazolyl Ligands

Several pyrazole-based ligands of both rigid and flexible nature have been exploited for the preparation of multifunctional coordination polymers with assorted dimensionality (from 1D to 3D) through either conventional synthetic procedures or solvothermal routes. They were found to display permanent microporosity and remarkable thermal resistance. They were successfully exploited for CO2 adsorption and as solid-state photoluminescence materials

1,3-Bis(1,2,4-triazolyl)adamantine-based Coordination Polymers

The hybrid organic-inorganic materials known as coordination polymers are continuously gaining ground of scientific research, especially due to the interesting and promising functionalities they possess, e.g. magnetic, optical, electrical, redox, and luminescence properties, as well as, when permanent porosity is present, gas adsorption or separation, catalytic activity, and drug delivery. The reaction of the flexible ligand 1,3-bis(1,2,4-triazolyl)adamante (tr2ad, Scheme 1) with chlorides of different late transition metals, either following conventional routes or under solvothermal conditions, afforded the coordination polymers having the general stoechiometric formula of the type M(tr2ad)Cl2 (M = Zn,1; Cu, 2; Cd, 3; Ni, 4; Co, 5). Preliminary ab initio X-ray powder diffraction analyses revealed that 1 developes into a 1-D polymeric chain, while 2 features a 2-D polymeric structure. Thermal-gravimetric analyses (TGA) showed relevant thermal robustness of all these materials, peaking up to the onset of decomposition set at 350 °C

Investigating the Structural Features and Spectroscopic Properties of Bis(tetrazolato)-Based Coordination Polymers

The luminescent compound xylene-bis(2H-tetrazol-5-yl) (H2BTZPX) was prepared and employed in the construction of the novel coordination polymers (CPs) Zn(BTZPX), Ag2(BTZPX), and Hg(BTZPX), containing d10 transition metal ions. Powder X-ray diffraction (PXRD) structure determination enabled us to disclose the crystal and molecular structure of the three CPs: while Zn(BTZPX) features a 3-D polymeric network, Ag2(BTZPX) and Hg(BTZPX) show 2-D corrugated layers. Thermogravimetric analysis and variable-temperature PXRD revealed the appreciable thermal robustness of the three CPs, peaking up to 370 \ub0C, in air, in the case of Ag2(BTZPX). Given the sizable fluorescence emission of the ligand in the solid state, both H2BTZPX and the three CPs were characterized as to their electronic-state transition spectroscopic properties. UV\u2013visible absorption unveiled a bathochromic shift for both the ligand and the CPs with respect to the absorption maximum of the main chromophore of the spacer, i.e., the benzene ring. In order to understand this peculiarity, quantum mechanical calculations were performed using the time-dependent density-functional theory approach. Furthermore, absorption spectra of H2BTZPX in different organic solvents were recorded. To investigate how the luminescence properties of H2BTZPX are influenced by complexation, the fluorescence emission spectra of H2BTZPX and the three CPs were recorded, and the fluorescence quantum yields determined by comparison to anthracene. Zn(BTZPX) exhibited enhanced fluorescence with respect to the ligand, while fluorescence was notably reduced for Ag2(BTZPX) and barely detectable for Hg(BTZPX). This occurrence suggests different decay pathways, which were further investigated by reconstructing the time-resolved fluorescence decays by means of time-correlated single-photon counting

New Coordination Polymers of Zinc(II), Copper(II) and Cadmium(II) with 1,3-Bis(1,2,4-triazol-4-yl)adamantane

The new coordination polymers (CPs) [Zn(tr(2)ad)Cl-2](n), {[Cu(tr(2)ad)Cl]Cl center dot 4H(2)O}(n), [Cd-2(tr(2)ad)Cl-4](n), {[Cu(tr(2)ad)(NO3)](NO3)}(n) and {[Cd(tr(2)ad)(NO3)](NO3)center dot H2O}(n) were obtained in the form of air- and moisture-stable microcrystalline powders by the solvothermal reactions of zinc(II), copper(II) and cadmium(II) chlorides or nitrates with the ligand 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr(2)ad). Investigation of the thermal behaviour assessed the thermal stability of these CPs, with [Cd-2(tr(2)ad)Cl-4](n) starting to decompose only around 365 degrees C. As retrieved by powder X-ray diffraction, while [Zn(tr(2)ad)Cl-2](n) features 1-D chains along which the metal centre shows a tetrahedral geometry and the spacer is exo-bidentate, the other CPs contain 2-D double-layers in which the metal ions possess an octahedral stereochemistry and the linker is exo-tetradentate. A comparative structural analysis involving known coordination compounds containing the tr(2)ad ligand enabled us to disclose (i) the versatility of the ligand, as far as the coordination modes are concerned; (ii) the variability in crystal structure dimensionality, ranging from 1-D to 3-D; (iii) the fact that, to the best of our knowledge, [Zn(tr(2)ad)Cl-2](n) is the first Zn-II-based CP containing the tr(2)ad spacer

Metal azolate/carboxylate frameworks as catalysts in oxidative and C-C coupling reactions

The five metal azolate/carboxylate (MAC) compounds [Cd(dmpzc)(DMF)(H2O)] (Cd-dmpzc), [Pd(H2dmpzc)2Cl2] (Pd-dmpzc), [Cu(Hdmpzc)2] (Cu-dmpzc), [Zn4O(dmpzc)3]·Solv (Zn-dmpzc·S), and [Co4O(dmpzc)3]·Solv (Co-dmpzc·S) were isolated by coupling 3,5-dimethyl-1H-pyrazol-4-carboxylic acid (H2dmpzc) to cadmium(II), palladium(II), copper(II), zinc(II), and cobalt(II) salts. While Cd-dmpzc and Pd-dmpzc had never been prepared in the past, for Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S we optimized alternative synthetic paths that, in the case of the copper(II) and cobalt(II) derivatives, are faster and grant higher yields than the previously reported ones. The crystal structure details were determined ab initio (Cd-dmpzc and Pd-dmpzc) or refined (Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S) by means of powder X-ray diffraction (PXRD). While Cd-dmpzc is a nonporous 3D MAC framework, Pd-dmpzc shows a 3D hybrid coordination/hydrogen-bonded network, in which Pd(H2dmpzc)2Cl2 monomers are present. The thermal behavior of the five MAC compounds was investigated by coupling thermal analysis to variable-temperature PXRD. Their catalytic activity was assessed in oxidative and C-C coupling reactions, with the copper(II) and cadmium(II) derivatives being the first nonporous MAC frameworks to be tested as catalysts. Cu-dmpzc is the most active catalyst in the partial oxidation of cyclohexane by tert-butyl hydroperoxide in acetonitrile (yields up to 12% after 9 h) and is remarkably active in the solvent-free microwave-assisted oxidation of 1-phenylethanol to acetophenone (yields up to 99% at 120 °C in only 0.5 h). On the other hand, activated Zn-dmpzc·S (Zn-dmpzc) is the most active catalyst in the Henry C-C coupling reaction of aromatic aldehydes with nitroethane, showing appreciable diastereoselectivity toward the syn-nitroalkanol isomer (syn:anti selectivity up to 79:21)