Promethium compounds

Other promethium compounds that have been isolated include the hydroxide Pm(OH)3 [which adopts the 9-coordinate structure of Nd(OH)3] and hydrated salts including... 

Question 7.6 Suggest why the synthetic routes and spectroscopic methods shown for the binary promethium compounds in Section 7.6 were employed. 

Question 7.7 Why are the structures of promethium compounds determined by powder methods and not by single-crystal methods ... 

Some compounds of promethium are luminescent. Luminescence is the property of giving off light without giving off heat. The light of a firefly is an example of luminescence. Promethium compounds are luminescent because of the radiation they give off... 

There are two reasons why this sub-section has 1947 in its title. One is that in that year promethium compounds prepared from fission products were fully described (Marinsky et al. 1947) although several radioactive nuclei had been reported... 

As a consequence of its radioactivity great care is required when handling the element Several promethium compounds have been prepared but very little is known about the properties of the metal itself The isotope Pm is, however, commercially available and has been tested in miniature batteries for guided missiles. The useful... 

The crystal structure of the rare earth oxyorthosUicates has been determined from single crystals prepared using Bi203 as a flux material (Buisson and Michel, 1968). The oxyorthosilicates from praseodymium to terbium are isomorphic and crystallize in the monocUnic space group P2 /c with Z = 4. According to Ananeva et al. (1981) dysprosium can also have this structure type (A) too, but more often has another structure type (B). It is not clear whether or not lanthanum has a structure of its own. The unit cell dimensions of lanthanide oxyorthosilicates, except those of cerium and promethium compounds, are presented in table 9. 

The preparation of promethium trihalides has been mentioned by Scherer (9). However, the radioactive nature of these compounds has prevented any calorimetric or solubility investigations so far, and they make only one fleeting appearance in this review. 

The main oxidation state for promethium is +3. At least 30 compounds of promethium have been identified, but none are commercially available. Three examples of typical rare-earth metal compounds are as follows ... 

Table 1 shows the assignment of the various lanthanide elements in the numbering of the compounds in this article. As usual, scandium and yttrium have been included because of their chemical similarity with the lanthanides. Not included was the radioactive promethium for which no complex containing heteroallylic ligands has so far been reported. 

Of various rare earth 2-selenenoylacetone chelates luminescence was found only in the europium compounds. Physicochemical properties and IR spectra of 2-selenenoylacetonates of rare earths (except cerium and promethium) give information regarding the structure of these complexes as a function of the metal. 

PmCl3.xH20, Pm(N03)3.xH20, and Pm(C2O4)3.10H2O. It would be expected that promethium would form some stable compounds in the +2 oxidation state, though they are unlikely to be made in aqueous solution. No definite evidence has yet been obtained, since studies have been hindered both by the small quantities of the element available and by its radioactivity. The properties of promethium fit neatly into position between neodymium and samarium it is a microcosm of lanthanide chemistry in general. 

Question 7.8 The visible spectrum of a promethium(iii) compound (Figure 7.7) contains a considerable number of bands. How could you show that none of these were caused by impurity ... 

Answer 7.8 Wait for a few years ( ), then remeasure the spectrum, any bands due to decay products will have become stronger and genuine bands due to Pm + will have diminished. Next, purify the promethium by ion exchange, then reprepare the compound the impurity bands should have vanished. 

It would be expected that promethium would form some stable compounds in the -1-2 oxidation state, but no definite evidence has yet been obtained since studies have been hindered both by the small quantities available and by its radioactivity. 

In the modified Hill system as used by Chemical Abstracts today the arrangement of symbols in formulas is alphabetic, except that in carbon compounds C always comes first, followed immediately by H if hydrogen is also present. For deuterium and tritium compounds, D and T, respectively, are used. These are placed alphabetically in formulas the exception in arrangement made for H is not extended to include these isotopes, Glutamic-d acid is therefore written C5H8DNO4, The names of certain elements and their respective symbols are given preference over former names. The preferred names are astatine, beryllium, niobium, hafnium, and promethium (but not wolfram) (7). 

The lanthanide series of metals includes the 15 elements with atomic numbers 57-71, plus yttrium (atomic number 39). The lanthanides occur in the earth s crust at concentrations exceeding some commonly used industrial elements making the term rare earths something of a misnomer. For example, yttrium, cerium, lanthanum, and neodymium are present in the earth s crust at higher concentrations than lead. Of the 15 lanthanides, only promethium does not occur in nature - it is a man-made element. All of the lanthanides have similar physical and chemical properties. Because of similarities in their chemistry and toxicity, the characteristics of the lanthanides are often described as a group. Within the lanthanide group, however, there are differences between the toxicity of the individual lanthanide elements and their compounds. 

Double chromates of lanthanum, promethium and neodymium of the type RbLn-(Cr04)2 have been found to be anhydrous. The samarium compound crystallized with 0.5 molecules of water whilst those from europium to lutetium had the composition RbLn(Cr04)2,H20. Y-Ray and i.r. studies showed the existence of three structural types as the rare earth element series was transversed. 

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