Metal rhenium

Some molybdenum contain from 0.002% to 0.2% rhenium. More than 150,000 troy ounces of rhenium are now being produced yearly in the United States. The total estimated Free World reserve of rhenium metal is 3500 tons. Rhenium metal is prepared by reducing ammonium perrhentate with hydrogen at elevated temperatures. 

Rhenium hexafluoride is readily prepared by the direct interaction of purified elemental fluorine over hydrogen-reduced, 300 mesh (ca 48 pm) rhenium powder at 120°C. The reaction is exothermic and temperature rises rapidly. Failure to control the temperature may result in the formation of rhenium heptafluoride. The latter could be reduced to rhenium hexafluoride by heating with rhenium metal at 400°C. 

Rhenium hexafluoride is used for the deposition of rhenium metal films for electronic, semiconductor, laser parts (6—8), and in chemical vapor deposition (CVD) processes which involve the reduction of ReF by hydrogen at elevated (550—750°C) temperatures and reduced (<101.3 kPa (1 atm)) pressures (9,10). 

In earlier procedures, the ReO anion was precipitated from water as the relatively insoluble potassium salt. Reduction of KReO with hydrogen gas gives rhenium metal, but the metal is contaminated with ca 0.4 wt % potassium that cannot be separated easily. Although suitable for some purposes, rhenium formed from KReO is found to be unsatisfactory in appHcations such as those for use in filaments in mass spectrometer systems. The route involving NH ReO avoids this problem. 

Rhenium metal exhibits a very low paramagnetism which is field-iadependent and almost temperature-iadependent. In the range 79—471 K, magnetic susceptibiUty data for two independent samples were shown to correspond, when Tis ia Kelvin, to the following equations (5) ... 

Pyrolysis of Re2(CO)2Q at 400°C in vacuo or in an inert atmosphere has been used to obtain pure rhenium metal. 

Salts of perrhenic acid may be obtained in acid—base reactions, and may include the tetrahedral ReO anion or the octahedral anion ReO , eg, in Ba (ReOg)2 [13598-09-9], Ammonium perrhenate and perrhenic acid, as well as rhenium metal, are sold by the primary suppHers of this element. 

World production of rhenium in 1993 and 1994 was estimated to be 34 and 35 metric tons, respectively. The price of rhenium metal in 1995 varied in the range 825— 1600/kg. Price is based on form, purity, and quantity. The price for the most commonly used salt, NH ReO, was 550— 770/kg. Dirhenium decacarbonyl and perrhenic acid are also commercially available. 

Tme supported catalysts are not favored for this reaction, but it can be effected by the use of finely divided rhenium metal or rhenium (VI) oxide as well as hydrated mthenium (IV) oxide. 

The use of various heterocyclic additives in the MTO-catalyzed epoxidation has been demonstrated to be of great importance for substrate conversion, as well as for the product selectivity. With regard to selectivity, the role of the additive is obviously to protect the product epoxides from deleterious, acid-catalyzed (Brons-ted or Lewis acid) ring-opening reactions. This can be achieved by direct coordination of the heterocyclic additive to the rhenium metal, thereby significantly decreasing its Lewis acidity. In addition, the basic nature of the additives will increase the pH of the reaction media. 

Pertechnetate forms a blue complex and perrhenate a brownish-yellow complex with K4[Fe(CN) ] in presence of bismuth amalgam. This permits the spectrophotometric determination of both elements in the same solution . The adsorption maxima of the technetium and rhenium complexes are at 680 and 420 nm, respectively. The molar extinction coefficients are 10,800 for technetium and 4,000 for rhenium. Metals forming color or precipitates with K4[Fe(CN) ] must first be removed. 

The element was discovered in 1925 by Walter Noddack, Ida Tacke Noddack, and 0. Berg. They detected it by x-ray examination of platinum ores. X-ray studies also showed its occurrence in columbite and other minerals. It was named after the German river Rhine, called Rhenus in Latin. In 1929, Walter and Ida Noddack produced Ig of rhenium metal from 660 kg of Norwegian molybdenite. 

Dithiol melanotropin peptide cyclized via rhenium metal coordination PDB ID IBOQ... 

The most interesting aspect of these compounds is their structure (Fig. 16.57), which possesses two unusual features. The first is the extremely short Re—Re distance of 224 pm compared with an average Re—Re distance of 275 pm in rhenium metal and 248 pm in Re,Cl. The second unexpected feature is the eclipsed configuration of the chlorine atoms. One might have supposed that since the short Re—Re bond requires that the chlorine atoms lie at distances ( 330 pm) which are less than the sum of their van der Waals radii (—340-360 ppm), the staggered configuration would be preferred (the chlorine atoms would then form a square antiprism rather than a cube). Cotton explained both phenomena by invoking a quadruple bond.147... 

Isolation of 3-cyclopropenyl metal compounds by this method has been achieved so far for iron and rhenium metals only. Thus, the reaction of Na[CpFe(CO)J (NaFp) with cyclopropenylium salts at -70 °C, in THF, gave 3-Fp-cyclopropene complexes (equation 194)2 267. The X-ray crystal structure of the most stable iron complex 3-Fp-C3Ph3 exhibits a regular cyclopropene C—C single and double bond distances (151 and 129 pm), and a characteristic distance of 208 pm for the Fe—C (T-bond267. The H NMR (CS2) spectrum of the 3-Fp-C3Ph,H complex displays a singlet at S = 2.63 ppm, of the cyclopropen yl proton at the 3-position. ... 

This preparation of cadmium rhenium(V) oxide consists of two steps. The first step is the oxidation of rhenium metal in a stream of oxygen to its heptaoxide Re207. The second step is the vapor-phase reaction of cadmium metal and rhenium(VII) oxide. 

Both steps are carried out in a silica tube (1-cm. i.d. X 60 cm. long). A thin wad of glass wool is inserted about 20 cm. from the oxygen input end of the tube. Powdered rhenium metal, 0.4655 g. 

Rare earth chlorides, anhydrous, 28 Rare earth metals, 18 amalgams, concentration of, 17 Rhenium, metallic, 175 by reduction of ammonium per-rhenate, 177... 

Figure 9.5. Contour plot of the two-dimensional PES for dissociative adsorption of N2 on a rhenium metal surface. Broken line indicates the seam between valleys. (From Haase et al. [1989].)...

Lakowicz JR, Gryczynski I, Tolosa L, Dattelbaum JD, Castellano FN, Li L, Rao G. Advances in fluorescence spectroscopy multi-photon excitation, engineered proteins, modulation sensing and microsecond rhenium metal-ligand complexes. Acta Physica Polonica A 1999, 95, 179-196. 

The synthesis of pentacarbonyl rhenium(I) halides, Re(CO)5X, succeeded from simple and complex rhenium halides below 200 atm of CO at 200° C. The compounds are extraordinarily stable and form easily, often quantitatively, from carbon monoxide and rhenium metal in the presence of other heavy metal halides or halogen sources such as CC14. Later we prepared the corresponding carbonyl halides of manganese (67) and technetium (68) from their respective carbonyls. It was found that the corresponding binuclear tetracarbonyl halides [M(CO)4X]2 (M = Mn, Re) could be made by heating the mononuclear M(CO)5X complexes (15, 69), as well as by other methods. 

As most laboratories use commercially obtained rhenium metal rather than a material prepared in situ, the following modifications are used. The rhenium metal is heated in a stream of hydrogen at 1000°C. for an hour to remove surface oxides, and the reaction of rhenium metal and chlorine is carried out at 650°C. Because of these temperatures, a Vycor combustion tube is necessary. 

FIGURE 16 Re L3-edge XANES of rhenium metal (Re0)—5d5 (solid) Re02 (Re4+)—5d (dashed) and NH4Re04 (Re7+)—5d° (dash-dot). The XANES spectra have been aligned in energy to allow a more direct comparison of the white line intensities. 

Previous preparations of Re3Cl9 have involved driving the rhenium halides horizontally along bulb trains.1 2 The present procedure is a considerable improvement on these, because it involves decomposition of refluxing rhenium pentachloride in the reaction bulb. Yields are very high and, using the method for the preparation of rhenium pentachloride given in Sec. 11, yields of over 90% from rhenium metal are possible. 

The coordination chemistry of rhenium, the last of the stable elements to be discovered (in 1925), has in the last 25 years undergone a tremendous growth. This element now occupies an important place in contemporary inorganic chemistry. Entry into its chemistry is usually afforded by access to the commercially available (but relatively expensive) perrhenate salts NH4Re04 and KRe04, although rhenium metal is sometimes used as the starting material,... 

The HNCC of rhenium, [Re6C(CO)igH2] ", [Re,C(CO)2i] -, and [RegC(CO)24] , have been produced in high yields from the solution thermolysis of [Re(CO)4H2] 2-4). In contrast, vacuum pyrolysis of Re2(CO)io (182-300°C) has been shown to yield only rhenium metal 41), unless pyrolyzed in the presence of metallic indium, in which case Re4(CO)i2 InRe(CO)5 4 was obtained in good yield (279). 

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