Group 6-12 Elements

Part II Main Group Elements by P. F. Gordon and A. J. Nelson 

A combination of molecular mechanics calculations and electric birefringence (electrooptical Kerr effect) measurements of Group IVB aryl compounds has been used to study conformational effects in these molecules [623]. 

All these elements have four electrons in the outermost shell of their atoms (or the general outer electronic structure ns np, where n is a whole number greater than one). The elements form compounds with similar formulae but they show marked changes in properties, as the group is descended, from carbon to lead. 

The element carbon exists mainly in two allotropic forms, diamond and graphite, and has a very large branch of chemistry (organic chemistry) concerned with the compounds that it forms because of its ability to form long chains by bonding with atoms of itself The ability of the atoms of an element to covalently bond with themselves is called catenation. 

Silicon and germanium are metalloids, whereas tin and lead are metals. Silicon and germanium have structures similar to that of diamond, tin exists in allotropic forms, but lead exists in only one metallic form. 

Below 13 °C, powdery grey a-tin forms on the white, metallic (J-tin allotrope and the metal crumbles. Napoleon s soldiers had tin buttons fastening their jackets and they used tin pots and pans to cook with. During the winter invasion of Russia, in 1812, their buttons and pots crumbled and it was said that this contributed to their defeat. 

Apart from carbon, catenation does not occur to any great degree in the chemistry of the other elements. Si and Ge do form hydrides that might be compared with the lighter hydrocarbons, but they are not as stable. Catenation in these elements involves the formation of Si-Si and Ge-Ge covalent bonds, which are longer and therefore weaker than C-C bonds. 

Elemental copper is used as a dehydrogenation catalyst for the conversion of alcohols into aldehydes or ketones [344]. Its efficiency is en- 

Cuprous chloride CuCl (mp 430 °C), when complexed with amines such as pyridine or phenanthroline, catalyzes the oxidation of alcohols to aldehydes and ketones by air [347]. In the presence of palladium dichloride, l dCl2, in aqueous dimethylformamide, terminal alkenes are converted by oxygen into methyl ketones [348], 

Copper sulfate, CuS04 5H20, is used for the oxidative coupling of terminal acetylenes [5S] for the conversion of a-hydroxy ketones (acyloins) into a-diketones [351, 352] and, in cooperation with potassium peroxy-disulfate, for the selective oxidation of methyl groups on benzene rings to aldehyde groups [355], 

Copper chromite, CuCr204, and mixtures of cupric oxide with chromium sesquioxide and special additives (the Adkins catalyst), dehydrogenate primary alcohols to aldehydes [354, 355] and secondary alcohols to ketones [354, 355, 356]. 

Thermodynamic properties of Mg-Eu solutions have been deduced (953— 1003 K, 0.196 0.945), using vapour-pressure techniques. The en- 

Phase Symmetry Point group Structure type o/nm b/nm clnm pr Ref. 

The Ca-Pb phase diagram has been determined by thermal and X-ray methods. It contains four compounds, of which two melt congruently [CajPb (m.pt. 1476 K) and CaPbs (m.pt. 939 K)], the others decomposing peritectically [CajPba (d., 1400 K) and CaPb (d, 1241K)]. The crystal structures of CajPb, CajPbs, and CaPbg were confirmed and CaPb was found to crystallize with the AuCu-I type structure unit-cell parameters are collected in Table 1. The two eutectics occur at 90.5 mol % Ca (1023 K) and 36.5 mol % Ca (911 K).  

For the most part the scope of the present Report is as defined in Volume 1/ However, since enolates are now discussed in Chapter 2, they are not given duplicate consideration here. 

Lithium.— The major applications of organolithium reagents continue to be in the realm of masked synthons, the appropriate organolithium species frequently being obtained by deprotonation of the conjugate acid with a commercially available organolithium reagent or a readily prepared lithium dialkylamide.  

Larock, Organomercury Compounds in Organic Synthesis, Springer-Verlag, Heidelberg and New York, 1985. 

Organometallie Compounds of Boron, Chapman and Hall Ltd., London, 1985. 

Suzuki and R.S. Dhillon, Selective Hydroboration and Synthetic Utility of Organoboranes thus Obtained, Top. Curr.Chem., 1985, 

Negishi and M.J. Idacavage, Formation of Carbon-Carbon and Carbon-Heteroatom Bonds via Organoboranes and Organoborates,  

Organic Reactions, Vol. 33, Ed. A.S. Kende, John Wiley and Sons, 

Why did I decide to undertake my doctorate research in the exotic field of boron hydrides As it happened, my girlfriend, Sarah Baylen, soon to become my wife, presented me with a graduation gift, Alfred Stock s book. The Hydrides of Boron and Silicon. / read this book and became interested in the subject. How did it happen that she selected this particular book This was the time of the Depression. None of us had much money. It appears she selected as her gift the most economical chemistry book ( 2.06) available in the University of Chicago bookstore. Such are the developments that can shape a career. 

In From Little Acorns Through to Tall Oaks From Boranes Through Organoboranes,  

With these elements, we begin our introduction to the p block, home of all nonmetals (and of a few metals) and of classic covalent chemistry. The elements are chemically rather diverse boron is a moderately electropositive nonmetal, whereas aluminum, gallium, indium, and thallium are all metals. The covalent chemistry we will encounter in this chapter, therefore, will still be somewhat limited, compared to what is to follow in the next chapters. Some general remarks are in order  

Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main-Group Elements, First Edition. Abhik Ghosh and Steffen Berg. 

---

Covalent fluondes of group 3 and group 5 elements (boron, tin, phosphorus, antimony, etc ) are widely used m organic synthesis as strong Lewis acids Boron trifluoride etherate is one of the most common reagents used to catalyze many organic reactions. A representative example is its recent application as a catalyst in the cycloadditions of 2-aza-l,3-dienes with different dienophiles [14] Boron trifluoride etherate and other fluonnated Lewis acids are effective activators of the... 

Some of the important properties of Group 5 elements are summarized in Table 22.1. Having odd atomic numbers, they have few naturally occurring isotopes Nb only 1 and V and Ta 2 each, though the second ones are present only in very low abundance 0.250%, Ta 0.012%). As a consequence (p. 17) their atomic weights have been determined with considerable precision. On the other hand, because of difficulties in removing all impurities, reported values of their bulk properties have often required revision. 

Chemical reactivity and trends Table 22.1 Some properties of Group 5 elements... 

The reason for such a behaviour of arsenic acid is that arsenic is a member of the group 5A elements in the periodic table. Phosphorus and antimony are also group 5 elements and are known to be chemically similar to arsenic. On this basis [8,9], the antimonic acids were found to be poor cassiterite collectors. The alkyl phosphonic acids were not selective collectors. The ethylphenylene phosphonic acid was found to produce similar or better results compared to /7-tolyl arsonic acid. The structural formula for phosphonic acid (Figure 21.5) is similar to that of /7-tolyl arsonic acid but arsenic was replaced with phosphoms. The styrene phosphonic acid radicals are C6H5-CH-CH and p-ethylphenylene CH3-CH2-C6H4. 

Symbol Nb atomic number 41 atomic weight 92.906 a Group VB (Group 5) element a transition metal in the triad of vanadium and tantalum also. 

The standard aqueous redox chemistry of vanadium and the other group 5 elements is summarized in the Latimer diagrams shown in Fig. 1 [2]. Under standard acidic aqueous conditions, the stability of the -1-5 oxidation state increases for the heavier group 5 elements at the expense of the +4 and -L3 states. 

Fig.1 Latimer diagram for the aqueous chemistry of the group 5 elements.

Silyl and polysilyl radicals also combine with nitrogen, arsenic, and other main group 5 elements, as with sulfur and selenium. 

All three Group 5 elements are expected to have +V oxidation states in seawater and are very strongly hydrolysed. The aqueous speciation of Vv in seawater... 

The complex formation of group-5 elements in HF, HC1 and HBr solutions was studied theoretically [165,166]. A motivation for this study was the unexpected behavior of Db (Ha at that time) in the extractions into triisooctyl amine (TIOA) from mixed HC1/HF solutions [176] Db was extracted similarly to Pa and not to Ta. 

The data of Table 19 show the following trend in the complex formation of group-5 elements Pa Nb > Db > Ta. Taking into account the work of transfer of the complexes between the phases, the following trend was predicted for the extraction of group-5 anions by an anion exchanger... 

According to these results, a recommendation was made to conduct the AIX separations in pure HC1 or HF solutions to try to observe the predicted sequence, Equation 32. Accordingly, the amine separations of the group-5 elements were systematically redone by W. Paulus et al. [177]. The reversed extraction sequence Pa > Nb > Db > Ta has been established exactly as theoretically predicted. That was the first time when predictions of extraction behavior of the heaviest elements based on quantum-chemical calculations were made, and also confirmed by specially designed experiments. 

In the discussion of the rather unexpected chemical results [42], it was suggested that the chemical properties of the heaviest elements cannot reliably be predicted by simple extrapolations of trends within a group of elements , and that relativistic, quantum chemical calculations for compounds of Nb, Ta, Pa, and Db are needed to understand in detail the differences in the halide complexing of the group-5 elements . 

Due to the complicated situation in mixed HC1/HF solutions, with possibilities to form mixed chloride/fluoride complexes or even pure fluoride complexes, it was recommended in [44] to repeat the experiments in the pure HC1 system. The original decision of the experimenters to add small amounts of HF to the HC1 solutions was recommended in the literature [45] to prevent hydrolysis and to maintain reproducible solution chemistry of the group-5 elements. 

Liquid-liquid, extraction studies from pure halide solutions As suggested in [44], the amine extractions of the group-5 elements were systematically revisited by W. Paulus et al. [32,49] in pure HF, HC1, and HBr solutions. V. Pershina [29-31], on the basis of an improved model of... 

Group-5 elements are most stable in their maximum oxidation state +5 and therefore form pentahalides, see Figure 7. Most volatile are the pentafluorides, followed by the pentachlorides and the pentabromides. Besides the pure halides, also the oxyhalides (MOX3) are stable in the gas phase. They should be less volatile compared to the pure halides. This was confirmed experimentally for niobium, see Figure 8. 

The known chemical properties of superheavy elements are presented and discussed in Chapter 5 and 7 based upon experimental results obtained from the liquid phase and from the gas phase, respectively. It is quite natural that there is a large body of information on group-4 element 104, rutherfordium, and group-5 element 105, dubnium, which are now under investigation for three decades. However, recent detailed studies demonstrate that these... 

---