THE POST-TRANSITION METALS

Attempts to classify carbides according to structure or bond type meet the same difficulties as were encountered with hydrides (p. 64) and borides (p. 145) and for the same reasons. The general trends in properties of the three groups of compounds are, however, broadly similar, being most polar (ionic) for the electropositive metals, most covalent (molecular) for the electronegative non-metals and somewhat complex (interstitial) for the elements in the centre of the d block. There are also several elements with poorly characterized, unstable, or non-existent carbides, namely the later transition elements (Groups 11 and 12), the platinum metals, and the post transition-metal elements in Group 13. 

Several metals that are farther removed from the noble gases in the periodic table form positive ions. These include the transition metals in Groups 3 to 12 and the post-transition metals in Groups 13 to 15. The cations formed by these metals typically have charges of +1, +2, or +3 and ordinarily do not have noble-gas structures. We will postpone to Chapter 4 a general discussion of the specific charges of cations formed by these metals. 

But first the synthesis had to come John was interested in reduced metal halides, particularly for the post-transition metals cadmium, galHum, and bismuth (his Ph.D. dissertation was on anhydrous aluminum halides and mixed halide intermediates, a good start for what was to come ). However, he was not yet actively interested in rare-earth metals and their remarkable solubility in their halides. But these elements lured him one floor below where Adrian Daane headed the metallurgy section of Spedding s empire. He knew how to produce rare-earth metals with high purity and in sufficient quantity and also how to handle tantalum containers. What if one gave it a tr/ and reduced some rare-earth metal halides (John insists that this term is used correctly) from their respective metals at high temperatures under appropriate conditions. 

Metallaborane cluster complexes of the post-transition metals 167... 

The post-transition metals utilize a four-orbital sp3 valence orbital manifold. 

The post-transition metals use a four-orbital sp valence orbital manifold. The inner shell d orbitals are assumed not to be involved in the bonding but instead comprise nonbonding electron pairs. 

Bums RC, Corbett JD (1982) Heteroatomic polyanions of the post transition metals. The synthesis and stmcture of a copound containing Thallium nonastannide and Thallium Ocatastannide with a novel disorder. J Am Chem Soc 104 2804—2810 Critchlow SC, Corbett JD (1982) Heteropolyatomic anions of the post transition-metals -synthesis and stmcture of the Ditindibismuthide(2-) anion, Sn2Bi2 l Inorg Chem 21 3286-3290... 

From the trend in acidities of the hydrogen halides in water, it follows that fluoride is the most basic or nucleophilic of the halides and iodide the least basic if the hydrogen ion is considered the reference acid. It should be recalled (p. 169) that this order of halide basicities is the same as that toward small, multicharged ions with rare-gas structures (for example, Be2+, A 3, and Si4+). A different, and sometimes reversed, order of basicities or nucleophilicities is observed toward certain ions of the post-transition metals (for example, Cu+, Hg +). For a number of ions (for example, Be+2, B+3 and Ta+6), fluoride complexes may exist in aqueous solution, whereas the other halo-complexes do not. Only a few of the elements having positive valence states form no halo-complexes the most important of these are carbon, the rare earths, the alkali metals, and the heavier alkaline-earth metals. 

The Post Transition Metal Effect, Lanthanoid Contraction and... 

If one compares the E(III)/E(V) (E = P, As) bond energies and the ionization energies of oxidation state -f-III P and As compounds, both the diminished stability of the As(V)-element bond [vs P(V)-element] and the unusual high Ip of As(III) compounds [vs P(III) compounds] can best be explained by the post transition metal effect (see above). Two examples from inorganic chemistry (just due to the better accessibility of data) are given in Table 2 . ... 

Bi complexes are summarized in Table 5. The lack of As(V) complexes of the type R3 AsL2 may be explained by the resistance of As to realize high coordination numbers and oxidation states, which are usually discussed on the basis of the post-transition metal effect. Element(V) species of the type R3EL possessing only one carboxylato chelate ligand which coordinates symmetrically show trigonal bipyramidal structures. 

The Post-Transition Metals 23-7 Group HIA Periodic Trends... 

Describe the properties and occurrence of the Group lA metals Describe some important reactions of the Group I A metals Describe some important uses of the Group lA metals and their compounds Describe the properties and occurrence of the Group IIA metals Describe some important reactions of the Group IIA metals Describe some important uses of the Group IIA metals and their compounds Identify the post-transition metals... 

The metals below the stepwise division of the periodic table in Groups IIIA through VA are the post-transition metals. These include aluminum, gallium, indium, and thallium from Group IIIA tin and lead from Group IVA and bismuth from Group VA. Aluminum is the only post-transition metal that is considered very reactive. We will focus our discussion on the metals of Group IIIA. 

Aluminum is the most reactive of the post-transition metals. It is the most abundant metal in the earth s crust (7.5%) and the third most abundant element. Aluminum is inexpensive compared with most other metals. It is soft and can be readily extruded into wires or rolled, pressed, or cast into shapes. 

Inert r-pair effect The tendency of the two outermost r electrons to remain nonionized or unshared in compounds characteristic of the post-transition metals. 

It was also proposed that the significant s and p orbital contraction at row four (Cu) is caused by the post-transition metal effect (d contraction), caused by an increase of the effective nuclear charge for the 4s electrons due to filling the first d shell (3d). A similar interpretation is possible for the row six (Au). This effect is commonly called lanthanoid contraction due to the effect of filling the 4f shell. The traditional explanation for the smaller size of gold (compared to Ag) is the lanthanoid contraction. However, this effect is only sufficient to cancel the shell-structure expansion, to make Au (nonrelativistic) similar to Ag (nonrelativistic). 

All the cited literature references to the above compounds have described solid-state syntheses at temperatures of 700-1200°. Such synthesis conditions will always lead to pyrochlore structure compounds in which all of the octa-hedrally coordinated sites are occupied by the noble metal cation, thus requiring the post-transition metal to noble metal molar ratio always to be 1.0. This paper focuses on solution medium syntheses at quite low temperatures (<75°), thereby stabilizing a new class of pyrochlore compounds in which a variable fraction of the octahedrally coordinated sites are occupied by post-transition element ca-tions.5,6 The specific example here involves the Pb2[Ru2 Pb4+]06 s series. The synthesis conditions may be simply adapted, however, to accommodate preparation of a wider range of pyrochlores which can be described by the formula A2[B2 xAx]07.3> where A is typically Pb or Bi, B is typically Ru or Ir and 0 < 1, and 0 < 1. 

The post-transition metals under consideration use anine-orbital sp d valence orbital manifold. 

The post-transition metals (in their zero formal oxidation states) have a total of 10 + G valence electrons where G is the highest possible oxidation state of the post-transition metal. Thus, germanium, tin, and lead have 10 + 4 = 14 valence electrons arsenic, antimony, and bismuth have 10 + 5 = 15 valence electrons and selenium and tellurium have 10 + 6 = 16 valence electrons. 

Application of this procedure to the post-transition metals forming clusters indicates that bare gallium, indium, and thallium vertices contribute one skeletal electron bare germanium, tin, and lead vertices contribute two skeletal electrons bare arsenic, antimony, and bismuth vertices contribute three skeletal electrons and bare selenium and tellurium vertices contribute four skeletal electrons in 2D and 3D aromatic clusters. Thus, Ge,Sn, and Pb vertices are isoelectronic withBH, Fe(CO)-, andC5H5Co vertices and As, Sb, and Bi vertices are isoelectronic with CH, Co(CO)v and C H Ni vertices in bare metal cluster compounds. 

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