Intermetallic Compounds of Antimony and Bismuth

By: Prof. Arthur Mar, ChemFiles Volume 5 Article 13

 

Prof. Arthur Mar
Department of Chemistry
University of Alberta, Edmonton, AB
Canada

Intermetallic compounds consist of combinations of metals in definite stoichiometric proportions. Given the predominance of metallic elements in the periodic table, the number of combinations is enormous. In the last decade, we have investigated the intermetallic chemistry of antimony, and more recently, bismuth. Various antimonides have elicited interest for their physical properties, such as LaFe3CoSb12 (thermoelectric), Eu14MnSb11 (colossal magnetoresistance), and Ce3Pt3Sb4 (heavy fermions). Our interest has focused on structural relationships, bonding, and properties.

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Rare-Earth Compounds

Ternary systems RE-M-Pn consisting of a rare-earth element (RE), a d-block or p-block metal (M), and Sb or Bi (Pn = pnicogen) provide several fascinating examples of compounds where extensive pnicogen–pnicogen bonding occurs in their crystal structures.1 In La13Ga8Sb21 (Figure 1), five-atom-wide ribbons of Sb atoms that are linked by nearly planar Ga6 rings define channels in which assemblies of La6 trigonal prisms reside. Interestingly, La13Ga8Sb21 undergoes a superconducting transition below 2.5 K.2 Related compounds are RE6Ge5–xSb11+x, which contains three- and four-atom-wide Sb ribbons,3 and LaGaBi2, which contains three-atom-wide Bi ribbons.4 When M is a d-block metal, magnetic ordering frequently develops through the coupling of f electrons of the rare-earth atoms via the d electrons of the transitionmetal atoms. For example, ferromagnetic ordering is observed in the series of RECrSb3 compounds.5,6Syntheses of these compounds generally proceed by direct reaction of the elemental components, either by arc-melting or in furnaces at high temperatures (up to 1000 °C).

Figure 1. Crystal structure of La13Ga8Sb21

 

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Transition-Metal Compounds

Although many binary intermetallic systems have been thoroughly investigated, surprises remain to be found. The Zr–Sb binary system is very rich, containing the compounds Zr3Sb, Zr2Sb, Zr5Sb3, Zr11Sb18, and ZrSb2.7 Recently we discovered a new phase of composition Zr7Sb4 by arc-melting of the elements followed by annealing.8 It exists only within a narrow temperature range (1000–1150 °C). The structure of Zr7Sb4 follows an elegant relationship with the W5Si3- type structure (Figure 2). The two-slab-thick slices of Zr7Sb4 are held together by strong Zr–Zr and Zr–Sb interlayer bonding interactions. The W5Si3-type structure is an important and common one for intermetallic compounds that is also adopted by ternary transition-metal antimonides and bismuthides such as Zr5M1–xPn2+x (M = Cr, Mn; Pn = Sb, Bi).9 With four different atomic sites, the W5Si3-type structure allows many possibilities for substitutional variation, so that even-ordered structures can be obtained with quaternary compounds such as Nb4Pd0.5SiSb.2,10

Figure 2. Crystal structure of W5Si3 and Zr7Sd4

 

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Materials

     

References

  1. Mar, A. et al. Coord. Chem. Rev. 2002, 233–234c, 207. 
  2. Mar, A. et al. Chem. Mater. 2001, 13, 1778. 
  3. Mar, A. et al. Inorg. Chem. 2001, 40, 952.
  4. Mar, A. et al. Inorg. Chem. 2003, 42, 1549. 
  5. Mar, A. et al. Chem. Mater. 1998, 10, 3630. 
  6. Deakin, L. et al. Chem. Mater. 2001, 13, 1778.
  7. Garcia, E.; Corbett, J. D. J. Solid State Chem. 1988, 73, 440. 
  8. Tkachuk, A. V.; Mar, A. Inorg. Chem. 2004, 43, 4400. 
  9. Tkachuk, A. V.; Mar, A. J. Solid State Chem. 2004, 177, 4136. 
  10. Mar, A. et. al. Inorg. Chem. 2001, 40, 5199.

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