Stannic tins

Tin, having valence of +2 and +4, forms staimous (tin(II)) compounds and stannic (tin(IV)) compounds. Tin compounds include inorganic tin(II) and tin(IV) compounds complex stannites, MSnX., and staimates, M2SnX, and coordination complexes, organic tin salts where the tin is not bonded through carbon, and organotin compounds, which contain one-to-four carbon atoms bonded direcdy to tin. 

Tin Nitrate. Stannic nitrate, Sn(N03)4, has been reported, but its existence is questionable. A soln contg stannic tin (Sn4+) can be made by dissolving Sn in nitric acid. It decomps on aging, heating or dilution. The existence of stannous nitrate, Sn(N03)2, must also be questioned. A soln of stannous tin (Sn +) in nitric acid can be made which must be kept cold. It is unstable to heat, dilution and aging (Ref 3)... 

Tin in ambient waters may exist as divalent cationic (positively charged) ions (Sn ) or as quadrivalent ions (Sn +). Stannous tin (Sn ) dominates in reduced (oxygen-poor) water, and will readily precipitate as a sulfide (SnS) or as a hydroxide (Sn(OH)2) in alkaline water. Stannic tin (Sn ) readily hydrolyzes, and can precipitate as a hydroxide (Wedepohl et al. 1978). The solubility product of Sn(OH)4 has been measured as approximately 10 g/L at 25°C (Wedepohl et al. 1978). 

The sulpho-salts of arsenic, antimony, and stannic tin are particularly characteristic of these metals. (See Preparation 43 and Experiment 11, page 294.) They are easily produced, and all are soluble. They are stable in neutral or basic solutions, but are decomposed by acids, because the anions of the salts combine with hydrogen ions to produce the very weak sulpho-acids, which, being unstable, decompose at once into the sulphides of the metals and hydrogen sulphide ... 

Furthermore, an undesirable side reaction between tin and technetium may occur. As outlined above, there is a high excess of tin - as Sn(II) and Sn(IV) - over technetium and this fact leads to the idea that mixed-metal complexes maybe formed in radiopharmaceutical preparations. Interest in the question, whether stannous or stannic tin could be involved in the radiopharmaceutical was further stimulated by the formation of a tin-capped Tc-dimethylglyoxime complex, Tc(oxime)3(/i-OH)SnCl3 (Deutsch et al. 1976). However, this compound was prepared under the condition of carrier-added technetium its ready conversion to uncapped species gives no evidence for the existence of mixed-metal type compounds. 

It is clear that some of the Sn cations in the B-site Sn04 groups are reduced but no one has determined the extent of such reduction. It is apparent that only a small fraction of such groups are affected. Otherwise the lattice structure would not be maintained. Note that a significant difference in ionic radius occurs when stannic tin is reduced to stannous tin. X-ray analj is shows no difference between the air-fired and the reduced phosphors. K. Th. Wilke studied this phenomenon in 1957 and proposed the following mechanism, given as 3.1.90. on the next page. 

An excellent account of the effect of tin catalysts on the physical properties of cellular urethanes is given by Mack (1964), who found that stannous tin catalysts are extremely sensitive to exposure to air, and to contamination by ferrous iron these result in chemical oxidation of stannous to stannic tin carboxylate, which in itself was found to be a very poor gelation catalyst. 

Since the Sn — Sn potential is only—0.15 v. tin is easily oxidized to its highest oxidation state and most radiochemical tin procedures deal almost-exclusively with stannic tin. With a single oxidation state predoininating, one would expect the chemistry of tin to be relatively simple. Tin salts may be fairly easily volatilized, however, and stannic tin in aqueous solution has a notable tendency to hydrolyze at the slightest provocation. This behavior, plus the fact that there are very few chemical separation steps which are at all selective for tin, makes tin one of the more difficult elements to obtain radiochemically pure. A more detailed description of the chemical behavior of stannic tin will be presented in subsequent sections. 

Stannic tin forms moderately strong complexes with oxalate ion. The degree of complexing is definitely pH dependent (see section IV. 4. A. 2) but little information is available on the size of the stability constant. E vidence has been presented, however, which indicates that the stannic oxalate complex has the formula Sn(C20 ) 4 41,42... 

Mattock has studied the reactions of stannic tin in solutions of dibasic carboxylic acids and concludes that metal-organic anion complexes in... 

Stannous or stannic tin may be extracted quantitatively by diethyl ether 82 126... 

Bock has published a very detailed study of the extraction behavior of a large number of elements in the thiocyanate-HCl-diethyl ether system. Stannic tin is extracted quantitatively from 0, 5M HCl solutions at all NH SCN concentrations above IM. The extraction of tin and a number of other elements from 0. 5M HCl as a fijnction of NH SCN concentration is shown in... 

In general, cation exchange resins are not at all satisfactory for separating tin. Stannic tin hydrolyzes so readHy that it can be kept in solution only by cbmplexing agents. These agents usually form anionic complexes with tin which, of course, are not.adsorbed by cation exchange resins. 

In basic solution, stannic tin forms sulfide complexes which are very... 

Dissolve uranyl sulfate target material in 0. 5N HCl. Add stannic tin (20 mg) and copper (20 mg) carriers and precipitate the mixed sulfides. 

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