Bismuth elemental halogens

Oxidation of triorganoantimony and -bismuth(V) compounds with elemental halogen or the equivalent... 

A complete set of trihalides for arsenic, antimony and bismuth can be prepared by the direct combination of the elements although other methods of preparation can sometimes be used. The vigour of the direct combination reaction for a given metal decreases from fluorine to iodine (except in the case of bismuth which does not react readily with fluorine) and for a given halogen, from arsenic to bismuth. 

In a manner similar to phosphoms, arsenic, and antimony, the bismuth atom can be either tri- or pentacovalent. However, organobismuth compounds are less stable thermally than the corresponding phosphoms, arsenic, or antimony compounds, and there are fewer types of organobismuth compounds. For example, with R MX, R3MX2, R2MX3, and RMX, where M is a Group 15 (VA) element and X is a halogen, only the first two types have been prepared where M = Bi, but all four types are known where M = P, As, or Sb. 

The effect of a particular element on the odour of its compound seems also to lend support to the residual affinity theory, for it is only the elements which possess residual affinity in certain of their compounds, which function as osmophores. Oxygen, nitrogen, sulphur, phosphorous, halogens, arsenic, antimony, bismuth, etc., whose valencies vary under certain conditions are powerfully osmophoric whereas carbon, hydrogen, and many others which have a constant valency are practically non-osmophoric, and it is very instructive to note that the element is osmophoric when it is not employing its full number of valencies and therefore has free affinity. 

Emilio Gino Segre (1905-1989 Nobel Prize for physics 1959), together with Dale Raymond Corson ( 1914) and Kenneth Ross Mackenzie ( 1912) obtained the element in tiny amounts by bombardment of bismuth with alpha particles. Halogen with no stable isotope. 

In 1940 D. R. Corson, K. R. Mackenzie, and E. Segre at the University of California bombarded bismuth with alpha particles (26, 27). Preliminary tracer studies indicated that they had obtained element 85, which appeared to possess metallic properties. The pressure of war work prevented a continuation of these studies at the time. After the war, the investigators resumed their work, and in 1947 proposed the name astatine, symbol At, for their element. The name comes from the Greek word for unstable, since this element is the only halogen without stable isotopes (28). The longest lived isotope is At210 with a half-life of 8.3 hours and a very high activity. 

Another previously unknown element, astatine (element 85, the heaviest of the halogens) was made at Berkeley in 1940 by bombarding bismuth with alpha particles. Again, Segre was among the team of chemists who showed it was a new element. 

Similar to the other elements in this group, the exchange reactions studied first and most extensively involve the redistribution of bismuth-carbon bonds with bismuth-halogen bonds. Reactions of the type of Eqs. (159) and (160)... 

In 1940, Corson, Mackenzie, and Segre announced the production of an isotope of element 85, astatine (At), which is the last member of the halogen family. This synthesis involved bombardment of bismuth with alpha particles in a cyclotron ... 

The fifth halogen, element 85, may possibly exist in nature as a very short-lived intermediate in a nuclear decay chain, but too few atoms of this element survive at a given time to allow its study, even making use of tracer methods. Workable amounts of this element were first made in 1942 by the bombardment of bismuth metal with high-energy helium nuclei (alpha particles) ... 

The very small amount of the element astatine formed by nuclear bombardment of bismuth may be volatilized off of the bismuth and collected in a solution of nitric acid. The behavior of the new halogen in a number of reactions is determined by treating the solution and tracing the course of the radiation characteristic of the element. The following are typical experiments ... 

Table 13.2 shows some of the properties of the trihalides of the Group VA elements. Several trends in the data shown in Table 13.2 are of interest. For example, the trihalides of phosphorus and arsenic can be considered as covalent molecules. As a result, the intermolecular forces are dipole-dipole and London forces that are weak. Therefore, the melting and boiling points increase with molecular weight as expected. The trifluorides of antimony and bismuth are essentially ionic compounds and the melting points are much higher than those of the halogen derivatives that are more covalent. 

Reaction of elemental bismuth with the halogens at elevated temperatmes leads to the production of BiX3. Properties of the trihalides are summarized in Table 2. Bismnth is first oxidized by P2(g) to BiFs, with conversion to BiFs occming above 600 °C. The latter is the only known homoleptic bismnth(V) halide, although organic derivatives of the form... 

Halides of the type AX6, where A is P, As, Sb, or Bi, and X is F, Cl, Br, or I, may generally be obtained by interaction of the elements. It is also possible to react AX3-type compounds with the corresponding halogen, and this is particularly useful when X = F. The halides SbF6 and BiF6 are made in this way. The compounds SbBr6 (cf. Section II,A,2), Sbl6, and arsenic(V) and bismuth(V) halides other than the fluorides are unknown. 

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