Stannides

For binary compounds the name of the element standing later in the sequence in Sec. 3.1.1.3 is modified to end in -ide. Elements other than those in the sequence of Sec. 3.1.1.3 are taken in the reverse order of the following sequence, and the name of the element occurring last is modified to end in -ide e.g., calcium stannide. 

The disagreement found for the compounds magnesium silicide and magnesium stannide may be explained as the result of the deformation of the anions (mole refraction of Si 4, 950 of Sn 4, 228) or, on the other hand, the crystals may not have the ionic structure assumed. 

By melting the calculated amounts of magnesium and tin in an iron crucible under a mixture of potassium and magnesium chlorides, and cooling slowly, a mass of magnesium stannide was obtained from which individual crystals could be cleaved. The X-ray data were obtained from Laue and spectral photographs, treated as described by Dickinson.3 I wish to express my thanks to Dr. Roscoe G. Dickinson for his advice and active interest in this research. 

Spectral data from a (111) face of a crystal of magnesium stannide are given in Table I. Using the value of 3.591 for the density,2 these data place nz/m = 0.248 for the first reflection. No reflections were found on the Laue photographs with values of n less than 0.26 A. U., calculated for the unit containing four Mg2Sn, with n — 1, and di0o = 6.78 0.02 A. U. 

Crystals of the intermetallic compound magnesium stannide, MgjSn, have been prepared and investigated by means of Laue and spectral photographs with the aid of the theory of space-groups. The intermetallic compound has been found to have the calcium fluoride structure, with dwo = 6.78 0.02 A. U. The closest approach of tin and magnesium atoms is 2.94 0.01 A. U. 

Examples of alkali metal stannides are mainly limited to tris(trimethylsilyl)- and triphenylstannides. NMR studies of trimethyl- and tributylstannide in ether, THF, and hexamethylphosphoramide (HMPA, OP(NMe2)3) reveal the compounds to be monomeric in solution, as indicated by the large Li-Sn coupling. The addition of HMPA produces an... 

General characteristics of alloys such as those presented in Fig. 3.3 have been discussed by Fassler and Hoffmann (1999) in a paper dedicated to valence compounds at the border of intermetallics (alkali and alkaline earth metal stannides and plumbides) . Examples showing gradual transition from valence compounds to intermetallic phases and new possibilities for structural mechanisms and bonding for Sn and Pb have been discussed. Structural relationships with Zintl phases (see Chapter 4) containing discrete and linked polyhedra have been considered. See 3.12 for a few remarks on the relationships between liquid and amorphous glassy alloys. 

Growth of rare earth rhodium stannides from excess Sn The crystals can be leached with dilute HC1. As long as the crystals are in contact with the Sn flux, they remain shiny and metallic. Crystals separated from Sn, however, quickly form a black tarnish containing an amorphous mixture of Rh and Sn. The removal of the crystals from the leaching solution as soon as they are free of Sn flux is therefore necessary. 

Alkali metal silanides, characteristics, 2, 18 Alkali metal stannides, characteristics, 2, 23 Alkaline earth metals... 

There is a distinct difference for these fifteen plumbide systems when compared with the stannide systems (Skolozdra, 1997). This difference becomes already evident when looking at the binary Ni-Sn(Pb) and Cu-Sn(Pb) systems (Massalski, 1986). While binary stannides like NigSn, Ni3Sn2/ NiSn, Ni3Sn4, Cu3Sn,... 

CuioSn3, and Cu6Sn5 (Villars and Calvert, 1991,1997) exist, no binary nickel and copper plumbides are known. This fact is transferred to the ternary R-Ni(Cu)-Pb systems. The plumbides systems contain fewer ternary compounds when compared to the stannide ones. To give an example, 15 stannides have been reported for the Gd-Ni-Sn system (Skolozdra, 1997), while only five plumbides exist in the related system with lead (Gulay, 2003b). This empirical rule is observed for many other ternary systems. 

The structural features of P FeisPb are similar to the stannide Th4Fei3Sri5 (Manfrinetti et al., 1997 Moze et al., 2000 Principi et al., 2001), where a two-dimensional Fei3 cluster unit (243-268 pm Fe-Fe) is separated by layers of condensed SnTIv, octahedra. In both iron-rich compounds, the iron sublattices give a magnetic contribution. 

Some of the plumbides within the Yb3Rh4Sni3 family show complex superstructures. They have the compositions R- Rh Pb ip (R = Y, Pr, Nd, Sm, Yb) (Venturini et al., 1986) and the structure is closely related with the Eri tSnIEr4Rhfl Snis structure (Hodeau et al., 1984 Vandenberg, 1980). This complex structure type crystallizes in space group I4i/acd. All investigated stannide crystals are twinned by recticular pseudomerohedry. So far, the corresponding plumbides have only been studied by X-ray powder diffraction. 

So far more than 180 rare earth-transition metal-plumbides have been reported. They crystallize with 23 different structure types. Apart from the few lead rich plumbides with YbsRlpSnis and related structures, only plumbides with 33 at% or even lower lead content have been reported. Some ternary systems exhibit large liquidus ranges in the lead rich regions at 870 °C. Through phase analytical investigations at lower temperatures one will certainly get access to new lead rich phases. In view of the more than 500 and 850 rare earth-transition metal-stannides and indides, respectively, the lead based systems certainly have a great potential for many more phases to be discovered. 

Only YbAgPb and La4Ni3Pb4 show peculiar structure types, which have first been observed for a plumbide. All other plumbides exhibit relatively simple structure types, which have been observed also for silicides, germanides, stannides, gallides, or indides. We expect that lead characteristic structures will form in the lead rich parts of the ternary systems, similar to the gallium and indium based phase diagrams. 

Skolozdra, R.V. Stannides of rare-earth and transition metals, in Gschneidner Jr., K. A., Eyring, L., editors. Handbook on the Physics and Chemistry of Rare Earths, vol. 24. Amsterdam North-Holland 1997, chap. 164. 

R.V. Skolozdra, Stannides of rare-earth and transition metals 399 Author index 519... 

Insertion reactions of calcium atoms into M14—M14 bonds yield symmetrical or unsym-metrical M14—Ca compounds according to Scheme 144 and equation 6989. A trimethylsi-lyl trimethylstannyl calcium was also characterized chemically in the cocondensation of calcium with trimethylsilyl trimethylstannane90. Calcium bis(stannide) (equation 69) crystallizes in the form of colorless cuboids in a centrosymmetric space group PI. The calcium atom lies on the crystallographic center of inversion in the middle of the linear Sn—Ca—Sn chain. The calcium atom is coordinated in a distorted octahedral fashion by two tin atoms... 

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