As, Sb, Bi

3 Typical structures of elements of the 15th group (As, Sb, Bi). A typical structure shown by various elements of this group is the hR6-As type structure, corresponding to the stable grey (rhombohedral, metallic) oAs modification. 

Atomic positions (in the triple primitive hexagonal cell)  

Around each As atom there are three As at 251.7 pm and three As at 312.0 pm forming a polyhedron, code 64 °. 

This structure can be described as a (puckered) layer type (See Fig. 7.17). In each layer the As-As distance (dx) is considerably shorter than the As-As interlayer 

According to Pearson (1972) the rhombohedral structure of these elements can be considered a distortion of a simple cubic structure in which the d2/d ratio would be 1. The decrease of the ratio on passing from As to Bi, and the corresponding relative increase of the strength of the X-X interlayer bond (passing from a coordination nearly 3, as for the 8 — eat rule, to a coordination closer to 6) can be related to an increasing metallic character. 

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Some elements (S, Se, Te, P, As, Sb, Bi, Ge, Sn, Pb) are conveniently converted into their volatile hydrides before passed into the plasma. The formation of the hydrides by use of sodium tetrahydroborate (sodium borohydride) can be batchwise or continuous. 

Similar reactions have been used to produce organo derivatives of As, Sb, Bi Si, Ge and many other elements. 

The binary compounds of the Group 13 metals with the elements of Group 15 (N, P, As, Sb, Bi) are stmcturally less diverse than the chalcogenides just considered but they have achieved considerable technological application as III-V semiconductors isoelectronic with Si and Ge (cf. BN isoelectronic with C, p. 207). Their stmctures are summarized in Table 7.10 all adopt the cubic ZnS stmcture except the nitrides of Al, Ga and In which are probably more ionic (less covalent or metallic) than the others. Thallium does not form simple compounds... 

A range of shiny metallic compounds featuring trigonal planar anions SnX3 (X = As, Sb, Bi) have been characterized with composition M6(SnX3)Oo.5 (M = Rb, Cs) the Sn and X atoms in SnX3 (isostructural with C03 ) are coordinated by trigonal prisms of 6M+, and the ions occupy octahedral sites in the M+ lattice. 

No completely general and quantitative theory of the stereochemical activity of the lone-pair of electrons in complex halides of tervalent As, Sb and Bi has been developed but certain trends are discernible. The lone-pair becomes less decisive in modifying the stereochemistry (a) with increase in the coordination number of the central atom from 4 through 5 to 6, (b) with increase in the atomic weight of the central atom (As > Sb > Bi), and (c) with increa.se in the atomic weight of the halogen (F > Cl > Br > 1). The relative energies of the various valence-Ievel orbitals may also be an important factor the F(a) orbital of F lies well below both the s and the p valence... 

This last reaction is typical of many in which F3CIO can act as a Lewis base by fluoride ion donation to acceptors such as MF5 (M = P, As, Sb, Bi, V, Nb, Ta, Pt, U), M0F4O, Sip4, BF3, etc. These products are all white, stable, crystalline solids (except the canary yellow PtFe ) and contain the [F2CIO] cation (see Fig. 17.26h) which is isostructural with the isoelectronic F2SO. Chlorine trifluoride oxide can also act as a Lewis acid (fluoride ion acceptor) and is therefore to be considered as amphoteric (p. 225). For example KF, RbF and CsF yield M [F4C10] as white solids whose stabilities increase with increasing size of M+. Vibration spectroscopy establishes the C4 structure of the anion (Fig. 17.29g). 

Phospholes and analogs offer a wide variety of coordination modes and reactivity patterns, from the ti E) (E = P, As, Sb, Bi) through ri -dienic to ri -donor function, including numerous and different mixed coordination modes. Electrophilic substitution at the carbon atoms and nucleophilic properties of the phosphorus atom are well documented. In the ri -coordinated species, group V heteroles nearly acquire planarity and features of the ir-delocalized moieties (heterocymantrenes and -ferrocenes). 

Metals in practice are usually coated with an oxide film that affects the potential, and metals such as Sb, Bi, As, W and Te behave as reversible A//A/,Oy/OH electrodes whose potentials are pH dependent electrodes of this type may be used to determine the solution s pH in the same way as the reversible hydrogen electrode. According to Ives and Janz these electrodes may be regarded as a particular case of electrodes of the second kind, since the oxygen in the metal oxide participates in the self-ionisation of water. 

The diazonio group in an arenediazonium salt can be replaced by one of several transition metal ions in subgroups lb (Cu), Illb (Tl), IVb (Ge, Sn, Pb), or Vb (P, As, Sb, Bi) or by certain compounds of the transition elements. There is only one report of a substitution by a main group metal, magnesium, but the primary product has not been clearly identified (Nesmeyanov and Makarova, 1959). 

The Niccolite Structure. The substances which crystallize with the niccolite structure (B8) are compounds of transition elements with S, Se, Te, As, Sb, Bi, or Sn. The physical properties of the substances indicate that the crystals are not ionic, and this is substantiated by the lack of agreement with the structural rules for ionic crystals. Thus each metal atom is surrounded by an octahedron of non-metal atoms but these octahedra share faces, and the edges of the shared faces are longer than other edges (rather than shorter, as in ionic crystals). Hence we conclude that the bonds are covalent, with probably some metallic character also. 

Single crystal X-ray structure analyses of analogously substituted adducts confirmed the applicability of this model. Adducts of the type EtaAl—E(Tms)3 and f-BuaAl—E(i-Pr)3 (E = P, As, Sb, Bi) were structurally characterized [50], allowing detailed comparisons of their solid state structural parameters. The trends observed for the average Al—C bond lengths and the C— Al—C bond angular sums are summarized in Figs. 5 and 6. 

The synthesis of tetraalkyldipnictines of the type R4E2 (E = P, As, Sb, Bi), containing a central E—E bond, goes back to Cadet s initial discovery of the... 

The heterocycles can be cleaved by reaction with 4-(dimethylamino)pyri-dine, yielding Lewis base-stabilized monomeric compounds of the type dmap—M(R2)E(Tms)2 (M = Al, Ga E = P, As, Sb, Bi). This general reaction now offers the possibility to synthesize electronically rather than kinetically stabilized monomeric group 13/15 compounds. These can be used for further complexation reactions with transition metal complexes, leading to bimetallic complexes of the type dmap—M(Me2)E(Tms)2—M (CO) (M = Al, Ga E = P, As, Sb M = Ni, Gr, Ee). 

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