Technetium physical properties

Physical Properties. Molybdenum has many unique properties, leading to its importance as a refractory metal (see Refractories). Molybdenum, atomic no. 42, is in Group 6 (VIB) of the Periodic Table between chromium and tungsten vertically and niobium and technetium horizontally. It has a silvery gray appearance. The most stable valence states are +6, +4, and 0 lower, less stable valence states are +5, +3, and +2. 

It should be noted that the above classification system of technetium cluster compounds is not the only possible one. In section 4 another classification is described, which is based on thermal stability and the mechanism of thermal decomposition. Section 2.2 is concerned with the classification based on methods of synthesizing cluster compounds. The classifications based on specific properties of clusters do not at all belittle the advantages of the basic structural classification they broaden the field of application of the latter, because for a better understanding and explanation of any chemical, physico-chemical and physical properties it is necessary to deal directly or indirectly with the molecular and/or electronic structures of the clusters. 

Manganese is a reactive metal that has several oxidation states (2, 3, 4, 6, and 7) that are responsible for its varied chemical compounds. The chemical and physical properties of manganese are similar to the properties of its companions in group 7—technetium ( jTc) and rhenium ( jRe). 

Rhenium is one of the transition elements, which range from metals to metal-like elements. Its chemical and physical properties are similar to those of technetium, which is above it in the periodic table. It is not very reactive. When small amounts are added to molybdenum, it forms a unique type of semiconducting metal. It is also noncorrosive in seawater. 

Technetium appears to have many physical properties similar to rhenium except that unfortunately all its isotopes are unstable to electron capture or /3 decay. 

Some physical property data of technetium metal are summarized in Table 9.2. A. 

Many compounds of technetium and rhenium are of analogous composition and of corresponding physical and chemical properties. Because of the very similar ionic radii, isotypic crystal structure formation of analogous compounds could often be observed. Technetium remarkably differs from manganese by the high stability of pertechnetate compared with permanganate. Moreover, divalent technetium does not exist as a hydrated ion but only as a stabilized complex. 

As the central member of the triad of metals in group 7, technetium (period 5) has similar physical and chemical properties as its partners manganese (period 4) above it and rhenium (period 6) below it. The sizes of their atomic radii do not vary greatly Mn = 127, Tc = 136, and Re = 137. Neither does their level of electronegativity vary significantly Mn = 1.5, Tc =... 

Binuclear carbonyl complexes with M—M bond analogous to Mn2(CO)io have been prepared for technetium and rhenium. The rhenium analogue has been synthesized by the carbon monoxide reduction of Rc207 or KRe04 (eq (5)) [3] or by reduction of anhydrous Re(III) or Re(V) chloride by sodium under CO pressure (eq (6)). [15]. The physical and structural properties of Tc2(CO),o and Re2(CO)io are listed in Table 9.1. 

Technetium-99m ( Tc) is widely used in radiopharmaceutical preparations due to its excellent physical and chemical properties. In fact, more than 80% of all radiopharmaceuticals used in diagnostic nuclear medicine are based on this short-lived radionuclide, which is obtained by elution of a Mo/ Tc generator system that is available in any radiopharmacy and nuclear medicine facility. 

Council of Europe (2005 a) Technetium ""Tc colloidal rhenium sulphide injection. Emopean pharmacopeia 5.0, monograph, no 126. Council of Europe, Maisonneuve, Sainte-Ruffine Council of Europe (2005 b) Technetimn " Tc sulfur colloid injection. Emopean pharmacopeia 5.0, monograph, no 131. Coimcil of Emope, Maisonneuve, Sainte-Ruffine Haney TA, Ascanio I, Gighotti JA, Gusmano EA, Bruno GA (1971) Physical and biological properties of a " Tc-sulfur colloid preparation containing disodium edetate. J Nucl Med 12 64-68... 

The symbols At and Fr were permanently installed in boxes 85 and 87 of the periodic table and their properties proved to be exactly the same as predicted from the table. But in comparison with their unstable mates born by nuclear physics, technetium and promethium, their position is clearly unfavourable. 

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