Rhenium occurrence

Occurrence and Recovery. Rhenium is one of the least abundant of the naturally occurring elements. Various estimates of its abundance in Earth s cmst have been made. The most widely quoted figure is 0.027 atoms pet 10 atoms of silicon (0.05 ppm by wt) (3). However, this number, based on analyses for the most common rocks, ie, granites and basalts, has a high uncertainty. The abundance of rhenium in stony meteorites has been found to be approximately the same value. An average abundance in siderites is 0.5 ppm. In lunar materials, Re, when compared to Re, appears to be enriched by 1.4% to as much as 29%, relative to the terrestrial abundance. This may result from a nuclear reaction sequence beginning with neutron capture by tungsten-186, followed by p-decay of of a half-hfe of 24 h (4) (see Extraterrestrial materials). 

Occurrence of rhenium and molybdenum together in nature is a consequence of the similarities of these elements. Both elements have a high affinity for sulfide ion. Moreover, the radii of Re" " and Mo" ", 0.74 nm and 0.70 nm, respectively, ate almost identical, so that ReS2 [12038-63-0] and M0S2 have similar crystal stmctures with almost identical dimensions (see Molybdenumcompounds). 

However, like the mp, bp and enthalpy of atomization, it also reflects the weaker cohesive forces in the metallic lattice since for Tc and Re, which have much stronger metallic bonding, the -t-2 state is of little importance and the occurrence of cluster compounds with M-M bonds is a dominant feature of rhenium(III) chemistry. The almost uniform slope of the plot for Tc presages the facile interconversion between oxidation states, observed for this element. 

Rhenium was the last naturally occurring chemical element to be discovered in 1925 by Noddack, Tacke, and Berg in the mineral gadolinite. The name of this extremely rare element (the estimated occurrence in the earth s crust is about 0.7 ppb ) is derived from the Rhine river. Residues from the processing of molybdenum ores represent the main source of the metal. 

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. 

G.E. Boyd and W.V. Larson, Report on the occurrence of technetium on the earth s crust, Journal of Physical Chemistry 60 (1956) 707-715. Translation in K. U. Leuven Archives, Noddack-Tacke Papers, 1316. See also the lists of publications on rhenium and technetium, 1954 and 1956,... 

Niobium metal is typically gray or dull silver in color. It is one of the refractory metals along with tantalum, tungsten, molybdenum, and rhenium, due to its very high melting point. It is estimated that niobium has a natural occurrence in Earth s crust of approximately 20 parts per milhon (ppm). The largest niobium-containing mineral reserves are located in Brazil and Canada. 

Rhenium(VII) complexes, 196-202 amides, 196 deuterides, 201 halides, 201 hydrides, 201 imides, 196 nitrides, 196 thiols, 201 Rhodium occurrence, 902... 

By way of example, we can focus on the cyano complexes. Palladium and platinum can form homoleptic complexes with two, four, or six cyanides, depending on the metal oxidation state zero, two, and four, respectively. Rhenium forms heptacyano complexes in its - -3 and -t-4 oxidation states but forms an octacyano complex in its -t-5 state. Molybdenum and tungsten also appear commonly in octacyano complexes for +4 and - -5 oxidation states, and heptacyano analogs for the - -2 and - -3 cases, with only one occurrence of [Mo(CN)6]" anions in two oxidation states (n = 3, 4). Similar situations can be found with phosphine or carbonyl complexes. For instance, the group... 

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