Astatine molecule

The first column of the periodic table, Group 1, contains elements that are soft, shiny solids. These alkali metals include lithium, sodium, potassium, mbidium, and cesium. At the other end of the table, fluorine, chlorine, bromine, iodine, and astatine appear in the next-to-last column. These are the halogens, or Group 17 elements. These four elements exist as diatomic molecules, so their formulas have the form X2 A sample of chlorine appears in Figure EV. Each alkali metal combines with any of the halogens in a 1 1 ratio to form a white crystalline solid. The general formula of these compounds s, AX, where A represents the alkali metal and X represents the halogen A X = N a C 1, LiBr, CsBr, KI, etc.). 

C09-0133. Among the halogens, only one known molecule has the formula X 7. It has pentagonal bipyramidal geometry, with five Y atoms in a pentagon around the central atom X. The other two Y atoms are in axial positions. Draw a ball-and-stick model of this compound. Based on electron-electron repulsion and atomic size, determine the identities of atoms X and Y. Explain your reasoning. (Astatine is not involved. This element is radioactive and highly unstable.)... 

When the halogens are in a gaseous state, they occur as diatomic molecules (e.g., Cl ). However, only two of the halogens are gases at room temperature fluorine (F ) and chlorine (Cy. Bromine is a liquid and iodine is a solid at room temperatures. Astatine is the only halogen that is radioactive and is not very important as a representative of the halogens. 

The diatomic molecule Atj, although purported to have been identified (115), is on statistical grounds unlikely to exist, and in terms of organic syntheses there would be a negligible probability of di-astatination occurring. 

In view of the potential therapeutic applications of At vide infra) the synthesis of stable astatinated protein molecules has attracted much effort (see Table VII). Proteins labeled with At can be prepared most reliably and unambiguously via incorporation of previously prepared pora-AtC6H4COOH by an acylation reaction with protein amino groups 53, 156, 158, 159, 178). Labeling proteins by this method was first reported by Hughes et al. 69, 71). 

Astatosteroids. Several complex steroid molecules have been astatinated via their chloromercuriderivatives a mixture of 2-as-tatoestradiol (I), 4-astatoestradiol (II), and 2-astato-4-iodoestradiol (III) was obtained with yields of 55, 19, and 18%, respectively (170). Estradiol was mercurated by Hg(CH3COO)2 in a C2H50H-water solution for 16 hours at room temperature, and then allowed to react with At in H2SO4 in the presence of KI3 for 1 hour. The products were separated and identified by TLC (170). 

Studies of elemental astatine are complicated by the fact (hat the small amounts of astatine present are readily attacked by impunties ih.it normally would not be considered important. Must studies of Attflt involve on excess of iodine which ties the astatine up in All molecules.- - U behaves much as might be expected from the known behavior orl It is readily extractable into CQ4 or CHCli and may be oxidized to positive oxidation states bv reasonably mild oxidizing agents. 

So far as the physical and chemical properties of astatine itself are concerned, not many new data have been published in the last 10-12 years however, a more thorough investigation of the literature has presented quite a few values of physicochemical—mainly thermodynamic—properties of At ions, of the At atom and of the hypothetical At2 molecule so far not commonly known (see Table 1). 

TABLE 1. Some physicochemical properties of astatine ions, atom and molecule (calculated values)... 

In contrast to direct electrophilic substitution in which the astatine attacks one of the C—H bonds, astatination through demetalation can be used to label a substrate at a preferred site in a regiospecific manner not affecting other sensitive sites of the molecule. Since the C—M bond is more sensitive to electrophilic attack than C—H, higher yields can be obtained in short reaction times under milder experimental conditions56. Organometallic compounds of mercury, thallium and tin have been used so far for astatination via demetalation. 

Nothing is yet known of the structural chemistry of astatine. The isotope At is produced by bombardment of Bi by a particles. The formation of compounds has been studied in a time-of-flight mass spectrometer, those observed being HAt, AtCH3, AtCl, AtBr, and Atl. There was no evidence for the formation of At2 molecules. ... 

During World War II, more work was done on the elements, particularly as part of the Manhattan Project. After the war, the existence of these new elements was made public. All of the naturally occurring elements from hydrogen to uranium, including the small number of artificially created but low-number elements francium, astatine, and promethium, had been found and put into the periodic table. Combined with the work of Rutherford and Bohr, this work made the physical structure of the atom clear and proved beyond all doubt. Even if physics would start to find smaller parts within the electron, the neutron, and the proton, from a chemical point of view, the atom was complete. Atoms and molecules had been shown to be real, they way they combined was... 

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