Sulfide Complex Research Articles

Mining Exploration with UAV, Low-Cost Thermal Cameras and GIS Tools—Application to the Specific Case of the Complex Sulfides Hosted in Carbonates of Udías (Cantabria, Spain)

The depletion of natural resources implies the need for a constant search for new reserves to satisfy demand. In the mining sector, Unmanned Aerial Vehicles (UAVs) have revolutionised geo-information capture and modelling to allow the use of low-cost sensors for prospecting and exploration for potentially exploitable resources. A very powerful alternative for managing the huge volume of data is the Geographic Information System (GIS), which allows storage, visualisation, analysis, processing and map creation. The research in this paper validates a new quasi-automatic identification of mining resources using GIS thermal-image analysis obtained from UAVs and low-cost sensors. It was tested in a case that differentiated limestone from dolostone with varying iron content, and different thermal behaviour from solar radiation, thereby ensuring that the thermal image recorded these differences. The objective is to discriminate differences in an image in a quasi-automatic way using GIS tools and ultimately to determine outcrops that could contain mineralisation. The comparison between the proposed method with traditional precision alternatives offered differences of only 4.57%, a very small deviation at this early stage of exploration. Hence, it can be considered very suitable.

Влияние рудоподготовки на флотацию минералов меди и мышьяка при переработке сульфидных руд

Monomineral flotation results showed that the use of a new reagent S-cyanoethyl N, N-diethyldithiocarbamate enhances the flotation activity of chalcopyrite, in contrast to flotation with butyl xanthate, and reduced the flotation ability of arsenopyrite, which makes this reagent promising for its use in the selective flotation of complex sulfide ores.

Polypyrrole‑molybdenum sulfide complex as an efficient and transparent catalytic electrode for bifacial dye-sensitized solar cells

A transparent catalytic counter electrode (CE) with excellent properties plays an important role in the performance improvement of bifacial dye-sensitized solar cells (Bi-DSSCs). In this work, pyrrole is combined with molybdenum sulfide (MoS2) by a refluxing technology and subsequently polymerized in situ to construct polypyrrole (PPy)-MoS2 CEs with high transparency. And compared with the original PPy CE, the PPy-MoS2 CE shows higher electrocatalytic activity for triiodide reduction. A superior power conversion efficiency of 9.48% under both-side irradiation is obtained for the Bi-DSSCs assembled with PPy-4 wt‰ MoS2 complex CE, compared to 7.36% bifacial efficiency for PPy-CE based solar cell.

Design of cobalt‐iron complex sulfides grown on nickel foam modified by reduced graphene oxide as a highly effect bifunctional electrocatalyst for overall water splitting

Design of <scp>cobalt‐iron</scp> complex sulfides grown on nickel foam modified by reduced graphene oxide as a highly effect bifunctional electrocatalyst for overall water splitting

Nature and evolution of the ore‐forming fluids in the Shazhou volcanic‐related hydrothermal uranium deposit, Xiangshan ore field, SE China

The Xiangshan uranium (U) ore field in South‐east China has been recognized as the largest volcanic‐related hydrothermal U deposit in China since its discovery in the 1950s. The U mineralization at Xiangshan is mostly hosted in felsic volcanic and sub‐volcanic rocks and occurs mainly in veins, which are controlled by high‐angle normal faults in association with haematite, quartz, fluorite, apatite, and pyrite. Likewise, diverse hydrothermal alterations such as haematitization, silicification, fluoritization, and illitization have been identified adjacent to the ore‐bearing faults and outward for tens to hundreds of metres into the volcanic rocks. Situated to the west in the Xiangshan ore field, the Shazhou deposit is the second‐largest U deposit in the Xiangshan volcanic basin. Based on geological field evidence and petrographic observations, the ore‐forming fluids in the Shazhou U deposit can be classified and separated into three stages (early, main, and late): (a) fluids associated with the early mineralization stage are characterized by the oxidizing feature with U‐O hydroxide complexes as the dominant species; (b) fluids from the main mineralization stage were reducing fluids with black–purple fluorite and sulphide complexes of U‐Ti‐O; and (c) fluids from the late‐stage were weakly oxidizing fluids with light purple fluorite and light red calcite complexes of U‐O as the dominant species in the fluid. Fluid inclusions in alteration minerals from the main and late mineralization stage recorded homogenization temperatures (Th) of 280–340°C and 200–260°C, with salinities of 5–17 and 6–10% NaCleqv, respectively. Ore‐forming fluids contain variable amounts of CO2, O2, and H2, in which the volatile content in the main mineralization stage is higher than that in the late stage. The temperature and salinity of the ore‐forming fluids were fluctuating and gradually decreased as the geologic history of the deposit progressed. The δDW‐SMOW values calculated for the ore‐forming fluids range from −97.4 to −65.1‰. The δ18O values of syn‐ore quartz occur mainly between 5.9 and 15.7‰; calculated δ18OW‐SMOW values are between −1.5 and +8.3‰. The δ34SCDT values of syn‐ore pyrite and galena range from 9.7 to 19.7‰. The ore‐forming fluids in the Shazhou U deposit are derived from different sources with a complex geological evolution history. The ore‐forming fluids from the early mineralization stage with high O2 contents may have been primarily derived from post‐volcanic hydrothermal activity. Subsequently, fluids from the main mineralization stage (with lower O2 and high H2 contents) might have originated from the deep‐sourced fluids, where sulphur was carried from the metamorphic basement. Finally, ore‐forming fluids from the late mineralization stage could have been produced by mixing meteoric hydrothermal fluids. Large‐scale fluid immiscibility and boiling occurred during the main mineralization stage, followed by fluid mixing during the late mineralization stage. Boiling and mixing of fluids were the two dominant mechanisms for the deposition of U in the Shazhou deposit.

Ore‐forming process of the Haigou gold deposit in the eastern Central Asian Orogenic Belt, NE China: Constrains from EPMA and LA‐ICP‐MS analysis of Au‐bearing pyrite

AbstractThe Haigou lode deposit, containing 40 t of gold at an average grade of 3.5 g/t, is one of the largest deposits in the Jiapigou gold belt located along the eastern segment of the northern margin of the North China Craton. The deposit comprises 15 gold‐bearing quartz veins hosted in a Carboniferous monzonite–monzogranite stock. Although many studies relating the genesis of this deposit have been carried previously, the understanding of ore‐forming process remains controversial. In this study, we combined field geological mapping with petrography, Electron Probe Micro Analysis (EPMA) and in situ LA‐ICP‐MS analysis of gold‐bearing pyrite to provide new insight into the genesis of the gold deposit. Our results show that Au in the Haigou gold deposit mainly exists in the form of native gold. LA‐ICP‐MS in situ multi‐element mapping shows that Au has a significant positive correlation with Ag, Te, Bi and Pb in Au‐bearing pyrite, indicating that these elements co‐precipitated with Au in pyrite lattice. The ore‐forming fluid existed under medium to low temperature, aiding complexing of the gold with sulfur, chlorine, and tellurium. Decoupling of sulfide and telluride complexes facilitated gold precipitation in the Haigou area. The abundance of lead and nickel tellurides in the Haigou gold deposits with general absence of tellurium in native gold is indicative of expulsion of tellurium through boiling during the process of fluid migration and evolution. Also, coexistence of Bi in native gold indicates that they were at Au–Bi eutectic. The gold‐bearing pyrite is characterized by dispersed magnetite in and around the fractures. The Au–Te–Bi–Pb element anomalies indicate that fluid oxygen fugacity increases while sulfur fugacity decreases with time, resulting in Au precipitation. Our results provide a new theoretical basis for the establishment of metallogenic model and deep prospecting of the Haigou gold deposit.

Enhanced separation of base metal sulfides in flotation systems using Chitosan-grafted-Polyacrylamides

• Chitosan-grafted-Polyacrylamide (Chi-g-PAM) was prepared and characterized. • Adsorption studies of Chi-g-PAM on metal sulfide surfaces were conducted. • Chi-g-PAM was tested as pyrite’s depressant in metal sulfide flotation. • Chi-g-PAM outperformed other depressants at producing less pyrite-diluted products. In this study, chitosan-grafted-polyacrylamide (Chi-g-PAM), a synthetic biocompatible polymer was investigated as a selective depressant of iron sulfide minerals [i.e., pyrite (FeS 2 )] in the flotation process of base metal sulfide minerals [i.e., galena (PbS), chalcopyrite (CuFeS 2 ), and sphalerite (ZnS)]. Chi-g-PAM was successfully synthesized by grafting polyacrylamide chains onto chitosan backbone. The synthesized polymer was characterized using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), and X-ray Powder Diffraction (XRD) analysis. Adsorption studies of Chi-g-PAM on mineral surfaces were conducted using zeta potential, contact angle, and total organic carbon (TOC) measurements in addition to X-ray Photoelectron Spectroscopy (XPS). Adsorption tests showed that Chi-g-PAM was most selective to pyrite as compared to the base metal sulfides indicating that this polymer may have the potential to be used as pyrite’s depressant in the flotation of base metal sulfides under specific conditions. XPS studies suggested that the depression of pyrite by Chi-g-PAM was due to chemisorption of the amine, amide, and hydroxyl groups of Chi-g-PAM at pyrite-water interface. The impact of Chi-g-PAM on the flotation response of sulfide minerals was investigated in both microflotation and batch flotation systems using model minerals and real sulfide ore, respectively. In microflotation tests of model minerals, the best separation efficiencies between valuable base metal sulfides and pyrite were achieved at pH 7. In batch flotation tests of complex sulfide ore of Mississippi Valley type (MVT) at natural pH (7.8), a separation efficiency of 61% was achieved between galena and pyrite when Chi-g-PAM was used compared to 35% with sodium cyanide (NaCN), the depressant that is commonly applied for this type of ore. However, the separation efficiency between chalcopyrite and pyrite was 15% and 21% with Chi-g-PAM and NaCN, respectively. Comparative studies indicated that Chi-g-PAM outperformed other depressants at producing less pyrite-diluted flotation concentrates.

Biodissolution of metal values from complex sulfides using sulfur-oxidizing bacteria

Bioleaching of a complex sulfide sample was carried out using an acidophilic microorganism namely sulfur-oxidizing bacteria (SOB). Various leaching parameters like initial pH, elemental sulfur, and pulp density were varied in order to evaluate their significance on the bioleaching process. The evaluation was based on the dissolution of elements like copper, zinc, iron, and sulfur present in the complex sulfide sample. All three leaching parameters significantly affected the biodissolution rate of the above elements. The SOB could able to leach 22.2, 33.9, 27.1 and 50.2 %(w/w) of copper, zinc, iron, and sulfur, respectively, at the optimum condition of elemental sulfur, 8 g/L; initial pH, 2.0; and pulp density, 10 %(w/v). The equilibrium contact time of the bioleaching was found to be 25 days. The biodissolution rate of zinc and sulfur was found to be more than that of copper and iron. The leaching rate increased with the increase of elemental sulfur addition and it decreased with the increase of pulp density. However, it increased with the increase of pH from 1.5 to 2.0 and decreased upon further increase of pH due to the maximum bacterial activity at pH 2.0.

A new orogenic gold belt in Southeast Asia: Geology, mineralogy and genesis of the Vangtat gold deposit, Southeastern Laos

AbstractThe Vangtat deposit is the major gold deposit in a new orogenic gold belt discovered and developed in southeastern Laos in the past two decades. Our study of the Vangtat orogenic gold deposit shows that it formed within a convergent margin along the western segment of the Poko suture zone, which marks the collision between the Indochina Terrane and the Kontum Massif. Shear structure and greenschist facies metamorphic rocks are the main hosts for gold mineralization in the Vangtat deposit. High‐grade gold‐bearing quartz‐sulfide veins and wall rock hydrothermal alteration are genetically related, and alteration minerals consist of quartz, carbonate, graphite, white mica, chlorite, and pyrite. The study of fluid inclusions and wall rock alteration assemblages indicate that the Vangtat gold deposit was formed by an aqueous‐carbonic, low salinity, reduced, weakly alkaline to near‐neutral pH fluid, mainly composed of H2O, NaCl, CO2, CH4, N2, H2S, H2, O2, Si, and K. Gold was predominantly carried as a sulfide complex. The precipitation of gold is related to wall rock sulfidation and the further reduction with the carbon‐bearing host rock. The correlation between trapping temperature obtained from arsenopyrite geothermometry (360–395°C) and homogenization temperature obtained from primary fluid inclusion microthermometry (240–250°C), indicates a pressure and depth range for the Vangtat deposit of 380–420 MPa and 11–13 km, respectively. Gold appears as inclusions mainly in pyrite, and auriferous pyrite is homogeneous in textural, chemical, and sulfur isotopic composition. Auriferous pyrite δ34S values range from +4 to +6‰, which is compatible with the δ34S composition of igneous rocks. Together with cobalt/nickel ratios from the Vangtat auriferous pyrite, which are significantly greater than one (avg. 6.3), we suggest that mafic‐ultramafic rocks in the geologic basement of the Vangtat deposit are the plausible source of hydrothermal gold and sulfur. The formation of this orogenic gold deposit is associated with metamorphic dehydration and devolatilization that transported gold to the site of deposition.

Centrifugal Concentration of Mandailing Natal North Sumatera Gold Ores Using Knelson Concentrator

Gravity concentration is the type of separation process of minerals based upon the difference in density. This technique has been known for centuries. It has the ability to separate the valuable minerals with relatively low production cost and little environmental impact, such as gold ores. Separation of gold from gangue minerals by using gravity concentration has been used for decades. In fact, it has the limitation to process fine particles. In attempt to recover fine particles using gravity concentration methods, the technique has been developed by combining centrifugal force. One of wellknown devices, Knelson Concentrator, was used to separate gravity recoverable golds (GRG) from the gangue minerals of Mandailing Natal (North Sumatera) sulfide complex gold ores with -200# of particle size. The head grade of ores was 5 g/t of gold. The ores were separated by using Knelson Concentrator with variation of pulp density, feeding rate, and water fluidization pressure. The results have proved that these three variables have particular impacts on gold recovery. The recovery of gold was increased by the increasing of pulp density until it reached the optimum level in 25% of solid with 86.9% of gold recovered, and then decresed by increasing of pulp density into 84.88% of gold with 30% of solid in pulp. It has the same trends in variation of feeding rate and water fluidization pressure. The highest point with 87.08% of recovery and 17.88 g/t of concentrate grade was anchieved at 25% of solid, 0.7 kg/minutes of feeding rate, and 2.7 kg/cm2 of water fluidization pressure.

Effect of Microwave Pretreatment on Leaching of Tetrahedrite

In mineral processing, the use of microwave radiation is important especially in pre-treatment processes. At present, there is an acceleration of processes as well as an increase in the efficiency of metal recovery. One of the main problems in copper recovery from complex sulphide ores is the removal of impurities such as antimony, arsenic, mercury. In the hydrometallurgical processing scheme, the key step is the leaching. The extraction process can be influenced by the selection of suitable leaching reagents or by suitable pre-treatment of the ore. The article describes the effect of microwave radiation on the leaching Sb, As and Hg of tetrahedrite and tetrahedrite concentrate. The samples were irradiated at the power 900 W for 30 seconds. The leaching of irradiated and non-irradiated samples was realized in an alkaline sodium sulphide. The positive effect of microwave radiation was confirmed by an increase in the recovery of Sb and As already after 15 min of extraction. After microwave leaching of irradiated tetrahedrite samples, the yield of Sb was 43.2 %, in irradiated tetrahedrite concentrate, the yield of Sb was 81.3 %.

Thermodynamic and experimental studies on removal of calcium and sulfate ions from recycling water of complex sulfide flotation operations

A chemical method for removing calcium sulfate saturated solutions (0.016 mol/L CaSO4) using barium chloride (BaCl2·2H2O) and sodium phosphate (Na3PO4) was experimentally studied. The main interest is to remove these ions from the solution through the precipitation of two solid species: sulfate (SO42−) as barite (BaSO4), and calcium (Ca2+) as hydroxyapatite (Ca5(PO4)3OH). Additionally, a solid/liquid separation method (i.e., flotation) was explored, using oleic acid and dodecylamine as collectors. The results show that, the chemical treatment of saturated solutions at 60 °C, pH 11.5 and using 3.9 g/L BaCl2·2H2O and 1.6 g/L Na3PO4, promotes the precipitation of barium sulfate and calcium-deficient hydroxyapatite (Ca10–x(HPO4)x(PO4)6–x(OH)2–x), with residual concentrations of calcium and sulfate below 0.10 and 5 mg/L, respectively. The residual calcium concentration increases to 28 mg/L when using the same amount of reactants, at temperature and pH values below those quoted. The highest flotation recovery of hydroxyapatite with oleic acid at pH 9.5 was about 80%, while that of barite floated with dodecylamine at pH 6.5 was about 90%.

Nanobubble assisted flotation separation of complex Pb–Cu–Zn sulfide ore – Assessment of process readiness

ABSTRACT A considerable difference exists between the flotation separation of artificial minerals and real low-grade ores processing where selectivity would be the main issue. Nanobubble-assisted (NB) flotation investigations have been mostly examined with pure materials and a narrow particle size range, less on complex sulfide ores. This study considered NB flotation for processing complex Pb-Cu-Zn sulfide ore in two different size ranges and various conditions to assess the process readiness. Metallurgical NB flotation responses (recovery, grade, kinetics, and selectivity index) were determined, compared to conventional tests. Outcomes revealed that an inclusive size fraction (−150 µm) could result in a higher selective process than a fine fraction (- 38 µm). In contrast, mass recovery and kinetics were higher for the fine one. In general, adding NBs compared to the conventional (CB) could improve the flotation metallurgical responses; however, the way NBs were generated would be key. NBs generated in the presence of frother (NBF) could produce higher mass and water recoveries while decreasing selectivity. In general, different setups’ flotation products showed the following selectivity order of Pb-Cu sulfides: NB>NBF>CB. These results opened a new approach for considering different NB generation conditions when they are going to use in various flotation stages.

Mechanism of efficient remediation of U(VI) using biogenic CMC-FeS complex produced by sulfate-reducing bacteria

Uranium in groundwater during uranium mining activities urgently needs to be remediated through effective and environmental-friendly approaches. The reduction and immobilization of soluble U(VI) using biogenic carboxymethyl cellulose modified iron sulfide complex (biogenic CMC-FeS complex) is one of the emerging and innovative methods. However, its removal mechanism is largely unknown. Here, biogenic CMC-FeS complex with extracellular polymeric substances (EPS) and CMC was successfully synthesized by sulfate-reducing bacteria (SRB) and showed highly dispersible capacity. The tryptophan and tyrosine, which were the main components in EPS produced by SRB on CMC-FeS surface, significantly increased the U(VI) removal capacity of the biogenic CMC-FeS complex compared with chemically synthesized CMC-FeS. U(VI) removal was attributed to the adsorption of soluble U(VI) by ≡FeO+, CMC, tryptophan, and tyrosine on the biogenic CMC-FeS complex, following its reduction by S2-, S22- and Fe2+. Moreover, biogenic CMC-FeS complex with CMC-to-FeS molar ratio of 0.0005 performed well in the presence of bicarbonate (5 mM), humic acid (10 mg/L), or co-existing cations such as Pb2+, Ni2+, Cd2+, Mn2+, and Cu2+ (200 ug/L) at pH 7.0, and displayed relatively high oxidation resistance and stability ability. This work provides an in-depth understanding of the biogenic CMC-FeS complex for the U(VI) removal and contributes to the development of cost-effective U(VI) remediation technologies.

Obtaining of Nano Gold from Concentrate (Banská Hodruša, Slovakia) Using Algae with Utilization of Mechanochemical Activation

The difficult and predominantly toxic processing of sulphide concentrates with a low gold content has prompted the finding of a more efficient and environmentally friendly method of obtaining this noble metal. This work was therefore focused on the recovery of gold from the concentrate of refractory sulphide complex (Banská Hodruša, Slovakia) using a non-cyanide mechanochemico-biological process. Gold in this complex concentrate is physically located in the intercrystalline space of sulfide minerals and fills in structural defects in sulfides. The precipitation of gold from the complex mineral matrices of the concentrate can be achieved using a mechanochemico-biological process. This innovative process makes it possible to recover gold by applying a thiourea solution, which is a preferred alternative to toxic a cyanidation. The use of a biological process with the application of algae has shown that algae with siliceous structures make it possible to obtain gold from a complex concentrate (Banská Hodruša, Slovakia) with dimensions of the nano. Limnetic algae (diatoms, golden algae) are part of aquatic ecosystems and form the largest of biomass of all plants on Earth. Mechanochemicobiological process is a method that allows to obtain 100 nm gold nanoparticles from refractory sulphide concentrate (Banská Hodruša, Slovakia).

Impact of Industrial Pollution on Radial Growth of Conifers in a Former Mining Area in the Eastern Carpathians (Northern Romania)

The research aims to evaluate the impact of local industrial pollution on radial growth in affected Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) stands in the Tarnița study area in Suceava. For northeastern Romania, the Tarnița mining operation constituted a hotspot of industrial pollution. The primary processing of non-ferrous ores containing heavy metals in the form of complex sulfides was the main cause of pollution in the Tarnița region from 1968 to 1990. Air pollution of Tarnița induced substantial tree growth reduction from 1978 to 1990, causing a decline in tree health and vitality. Growth decline in stands located over 6 km from the pollution source was weaker or absent. Spruce trees were much less affected by the phenomenon of local pollution than fir trees. We analyzed the dynamics of resilience indices and average radial growth indices and found that the period in which the trees suffered the most from local pollution was between 1978 and 1984. Growth recovery of the intensively polluted stand was observed after the 1990s when the environmental condition improved because of a significant reduction in air pollution.

Reactivity of inorganic sulfide species towards a pentacoordinated heme model system

The reactivity of inorganic sulfide towards ferric bis(N-acetyl)- microperoxidase 11 in sodium dodecyl sulfate has been explored by means of visible absorption and resonance Raman spectroscopies. The reaction has been previously studied in buffered solutions at neutral pH and in the presence of excess sulfide, revealing the formation of a moderately stable hexacoordinated low spin ferric sulfide complex that yields the ferrous form in the hour's timescale. In the surfactant solution, instead, the ferrous form is rapidly formed. The spectroscopic characterization of the heme structure in the surfactant milieu revealed the stabilization of a major ferric mono-histidyl high spin heme, which may be ascribed to out of plane distortions prompting the detachment of the axially ligated water molecule, thus leading to a differential reactivity. The ferric bis(N-acetyl)- microperoxidase 11 in sodium dodecyl sulfate provides a model for pentacoordinated heme platforms with an imidazole-based ligand.

Volatilized and Condensed Sb- and As-Bearing Phases Produced During Roasting of Cu-Rich Complex Concentrate in Nitrogen Atmosphere with Oxygen in Traces

A Cu-rich complex sulpfide concentrate (containing Sb as sulphosalts and gudmundite, and As as arsenopyrite) is roasted in Nitrogen atmosphere carrying traces of oxygen ({text{p}}^{{text{O}}_{2}} approx {10}^{-5.3}text{ bar)}. In situ measurements through QMS indicated that the volatilized species are mainly elemental sulfur, S2(g), and gaseous sulfur oxides. Sb- and As-bearing volatilized species could not be detected, owing to their low concentrations in the gas phase. Characterization studies through XRD and SEM-EDS confirmed that the condensates collected at room temperature during the roasting experiments comprised of (1) cyclo-octa sulfur, S8(s) and polysulfur oxides, Sn−xOx(s); (2) amorphous trisulfides of Sb and As; (3) and cubic crystalline trioxides of Sb and As. The solid phases in the condensate were found to be fine-sized (sub-micronic) and widely intermixed. Consequently, quantification of the solid phases in the condensates through direct measurement techniques like QEMSCAN was not possible. A novel approach of partial quantification of solid phases in the condensate through a stochastic model-based calculation approach is also presented. The model results suggested the occurrence of vapor-phase complexation of sulfides of Sb and As in the gas phase. Additional attributes of the volatilized species could be determined through a thermodynamic equilibrium calculation showing that the formation of the complex oxides, As4−nSbnO6(g), would be negligible compared to that of the complex sulfides, As4−nSbnS6(g).

Synthesis, structure, melting and optical properties of three complex orthorhombic sulfides BaDyCuS3, BaHoCuS3 and BaYbCuS3

Complex sulfides BaDyCuS3, BaHoCuS3 and BaYbCuS3 were synthesized in a flow of sulfiding gases (CS2, H2S) at 900оC from standard solutions of lanthanide and copper nitrates, as well as from the same standard Ba(OH)2 solution. The crystal structures of BaDyCuS3, BaHoCuS3 and BaYbCuS3 were obtained by the Rietveld refinement method. All three compounds crystallize in the Cmcm space group (KZrCuS3 structural type) as predicted by the tolerance factor analysis. Their micromorphological, thermal and spectroscopic properties are evaluated. BaDyCuS3 and BaHoCuS3 melt congruently at 1376.5 °C and 1363.8 °C. BaYbCuS3 melts incongruently at 1353.3 °C. The optical band gap is 2.45 eV for BaDyCuS3, 2.37 eV for BaHoCuS3 and 1.82 eV for BaYbCuS3. The low bandgap of BaYbCuS3 is explained by the charge transfer band of Yb at the bottom of conduction band. The vibrational parameters of BaDyCuS3, BaHoCuS3 and BaYbCuS3 crystals were determined with the use of Raman and Infrared spectroscopies.

Asymmetric conjugate addition reactions with chiral oxadiazinones: Unusual conformational properties of the oxadiazinones

Abstract A series of Ephedra based oxadiazinones have been prepared, acylated, and examined in the asymmetric conjugate addition reaction with Grignard reagents in the presence of copper(I) bromide-dimethyl sulfide complex. The highest diastereoselectivity that was obtained in the conjugate addition reaction was observed with the (1R,2S)-ephedrine based N4-methyloxadiazinone (5:1 d.r.) favoring the formation of the (S)-configuration of the conjugate addition product. Efforts to enhance the level of diastereoselection via increasing the steric volume of the stereo-directing N4-substituent of the oxadiazinone (N4- = p-methoxyphenyl or -isopropyl) led to an observed decrease in the level of diastereoselection. A computational study was conducted to examine the conformations adopted by the N4-methyloxadiazinone vs. the N4-isopropyl-oxadiazinone that yielded the lower diastereoselectivity. An argument is made for the stereoelectronic properties of the N4-substituent being the cause of both the moderate diastereoselectivity and the unexpected facial preference for the conjugate addition.