Tin 4. crystal structure

Figure 8.5.1 A body-centered tetragonal crystal structure adopted by white tin. crystal structure (Fig. 8.5.2).

J. H. Horner, P. J. Squatritto, N. McGuire, J. P. Riebenspies, and M. Newcomb, Organometallics, 10, 1741 (1991). Macrocycles Containing Tin. Crystal Structures and Molecular Mechanics Calculated Structures of Macrocyclic Lewis Acidic Hosts. 

The major alloy of tin recovered from archaeological sites is pewter. This can be divided into those containing lead and lead-free alloys. The former could have a lead content ranging from 67 % (equivalent to plumbers solder) down to 15%. The French in Elizabethan times kept the lead of their wine goblets to below 18% as above this, the wine would become tainted As the lead and tin are insoluble in one another, they are classed as a two-phase alloy and articles could only be manufactured by casting. The lead-tree pewter was invariably an alloy of tin with a small amount of copper (0.5-7% for pewter recovered from the Maty Rose). The copper dissolved in the tin crystal structure resulted in a single-phase structure, which was considerably harder than pure tin. Hence this class of pewter could be subjected to a limited amount of mechanical working to achieve the final shape. 

Another example of epitaxy is tin growdi on the (100) surfaces of InSb or CdTe a = 6.49 A) [14]. At room temperature, elemental tin is metallic and adopts a bet crystal structure ( white tin ) with a lattice constant of 5.83 A. However, upon deposition on either of the two above-mentioned surfaces, tin is transfonned into the diamond structure ( grey tin ) with a = 6.49 A and essentially no misfit at the interface. Furtliennore, since grey tin is a semiconductor, then a novel heterojunction material can be fabricated. It is evident that epitaxial growth can be exploited to synthesize materials with novel physical and chemical properties. 

Metallurgists, also, were slow to feel at ease with the new techniques, and did not begin to exploit X-ray diffraction in any significant way until 1923. Michael Polanyi (1891-1976), in an account of his early days in research (Polanyi 1962) describes how he and Herman Mark determined the crystal structure of white tin from a single crystal in 1923 just after they had done this, they received a visit from a Dutch colleague who had independently determined the same structure. The visitor vehemently maintained that Polanyi s structure was wrong in Polanyi s words, only after hours of discussion did it become apparent that his structure was actually the same as ours, but looked different because he represented it with axes turned by 45° relative to ours . 

When there is electronic resonance, the bond lengths, bond angles, and nuclear positions are intermediate between those corresponding to the individual resonance structures, as found in the crystal structure of the tin dimer.32 This type of bond, that is, a single bond plus a resonating unshared electron pair, was subsequently found to occur on the 100 surfaces of silicon.33... 

Fig. 4. Crystal structure of bis(pentamethylcyclopentadienyl)-tin(II) (3). Reprinted with permission from Chem. Ber. 113, 760 (1980). Copyright by Verlag Chemie...

Fig. 5. Crystal structure of bis[di-(trimethylsilyl)methyl]tin(II) (14). Reprinted with permission from J. Chem. Soc., Chem. Commun, 1976, 261. Copyright by The Chemical Society...

The structures of these stannylene complexes closely resemble those of carbene complexes. In Fig. 12 the crystal structure of the stannylene complex 4 is displayed the tin atom, the two carbon and the chromium atoms are equi-planar 30). 

A number of chemical elements, mainly oxygen and carbon but also others, such as tin, phosphorus, and sulfur, occur naturally in more than one form. The various forms differ from one another in their physical properties and also, less frequently, in some of their chemical properties. The characteristic of some elements to exist in two or more modifications is known as allotropy, and the different modifications of each element are known as its allotropes. The phenomenon of allotropy is generally attributed to dissimilarities in the way the component atoms bond to each other in each allotrope either variation in the number of atoms bonded to form a molecule, as in the allotropes oxygen and ozone, or to differences in the crystal structure of solids such as graphite and diamond, the allotropes of carbon. 

Another element that exhibits allotropy because of variations in the crystal structure is tin. The common allotrope is tin metal, also known as a alpha) tin, which is stable at ambient temperatures. The other allotrope, which generally occurs as a gray powder and is known as p beta) tin, but also as tin pest, is formed only at very low temperatures when tin cools down to temperatures below -18°C, the ordinary allotrope, a tin, is converted to p tin, and the transformation is irreversible under ordinary temperatures. Tin objects exposed to temperatures below -18°C in very cold regions of the world, for example, are generally severely damaged when part of the tin converts to tin pest. In extreme cases, when exposure to low temperatures extends for long periods of time, the allotropic conversion may result in the transformation of tin objects into heaps of gray p-tin powder. 

At atmospheric pressure, pure solid tin adopts two structures or allotropes, depending on temperature. At room temperature white metallic tin is stable but, at temperatures below 13°C, white tin undergoes a phase transformation into gray tin. White tin (also known as / -tin) adopts a body-centered tetragonal crystal structure (Fig. 8.5.1). Allotropic gray tin (a-tin) crystallizes in a cubic diamond... 

Figure 8.5.2 A cubic diamond crystal structure adopted by gray tin.

X-ray Crystal Structure and GED Data of the Decamethylmetallocenes of Silicon, Germanium, Tin, and Lead... 

For the digermenes, Lappert later reported520 the full crystal structure of R2Ge=GeR2, R = Bsi and a refinement of the tin structure while Masamune has characterized the analog... 

S. Patai (Ed.), The Chemistry of Functional Groups, Supplement A The Chemistry of Double-bonded Functional Groups, Vol.2. (esp. pp.1-52) Wiley, Chichester, 1989 F. Hartley and S. Patai (Eds.), The Chemistry of the Metal-carbon Bond, Wiley, Chichester, 1982 P. A. Cusack, P. J. Smith, J. D. Donaldson and S. M. Grimes, A Bibliography of X-Ray Crystal Structures of Tin Compounds, International Tin Research Institute Publication 588, 1981 Organotin Cluster Chemistry, R. R. Holmes, Acct. Chem. Research, 22, 190 (1989). 

Structural Characterization. The tridentate coordination geometry of di-terf-butyl tin pz, 62a, is evident in the crystal structure (Fig. 10). The Sn-N and S-S bond lengths are larger due to this unusual coordination... 

Working first with Polanyi, Weissenberg, and Brill, and later as the leader of the Textile Chemistry Section, Mark successively published papers on the crystal structures of hexamethylenetetramine, pentaerythritol, zinc salts, tin, urea, tin salts, triphenylmethane, bismuth, graphite, sulfur, oxalic acid, acetaldehyde, ammonia, ethane, diborane, carbon dioxide, and some aluminum silicates. Each paper showed his and the laboratory s increasing sophistication in the technique of X-ray diffraction. Their work over the period broadened to include contributions to the theories of atomic and molecular structure and X-ray scattering theory. A number of his papers were particularly notable including his work with Polanyi on the structure of white tin ( 3, 4 ), E. Wigner on the structure of rhombic sulfur (5), and E. Pohland on the low temperature crystal structure of ammonia and carbon dioxide (6, 7). The Mark-Szilard effect, a classical component of X-ray physics, was a result of his collaboration with Leo Szilard (8). And his work with E. A. Hauser (9, 10, 11) on rubber and J. R. 

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