Element main-group

1 Main Group Elements The synthesis and crystal structure of the dimer 

The stable l,l -diazastannocene (ii -C4H2N( Bu)2)2 Sn has been obtained from the reaction of lithiated 2,5-di-tert-butylpyrrole and SnCl2. The structures of [(PhCH2)5C5ln]2 and [(PhCH2)sC5Tl]2 have been compared with that of the new stannylene [2,3,5-(CF3)3C6H2]2Sn. The first structurally characterised alkaline earth metal fluorenyl complex, ( 13119)2 Ba(NH3)4, has been prepared in 87% yield directly from Ba and fluorene in liquid ammonia.  

2 Scandium, Yttrium, Lutetium, Lanthanides and Actinides The crystal 

1 Main Group Elements A structural analysis of a camphfH derived cyclo-pentadienyl lithium using variable tenqrerature NMR and MNDO calculations has been performed. The crystal structures of [Cp Mg(thf)p.-Cl]2, Cp Na.3py and Q K. py, py = pyridine have been determined as has that of [Cp Ge(C(SiM63)3)]. Bis(rerf-butyl-cyclopentadienyl)magnesium, calcium, strontium and barium metallocenes have been prepared by metallation.  

Reaction of Cd(acac)2 acac = acetylacetonate with 2 equivalents of LiCp gives CdCp 2. The synthesis of Cp 4Al from [Al.xEt20] has been described. The crystal structure of CpSbQ2 been determined and indicates q -coordination of the cyclopentadienyl ligand. The In and 11 complexes rerr-butylcyclopentadienylindium I and (l,r,3,3 -rerr-butyl-5,S -pentafulvalene)-dithallium have been prepared and structurally characterised. 

DERIVATIVES OF MAIN GROUP ELEMENTS Selection of parent hydrides and their names 

Carbon is, of course, unique in the number of hydrides it forms, but the elements in the proximity of carbon in the Periodic Table have a similar, if more restricted, propensity to form hydrides. Silicon, germanium, boron and phosphorus are obvious examples. For hydrides of these elements, and especially for their organic derivatives, the methods of substitutive nomenclature can be applied to obtain suitable names. 

It is generally an arbitrary matter to decide where to apply substitutive nomenclature in these cases. Table 5.1 shows the elements to which both CNIC and CNOC approve the application. Table 5.2 gives the names of the corresponding mononuclear parent hydrides. The only additional elements to which substitutive nomenclature may sometimes be applied are the halogens, particularly iodine. 

Several of the names for the parent hydrides, although systematic, are not in general use, and alternatives are approved these are azane (ammonia is sanctioned by wide usage), oxidane (water) and sulfane (hydrogen sulfide). 

The names of polynuclear hydrides (i.e. compounds with molecules consisting of chains) are obtained by prefixing the -ane names of Table 5.2 with the appropriate multiplicative prefixes of di-, tri-, tetra-, etc. 

To write the electron configuration of an ion formed by a main group element, we first write the configuration for the atom and either add or remove the appropriate number of electrons. Electron configurations for the sodium and chloide ions ate 

We can also write electron configurations for ions using the noble gas core. 

Sample Problem 7.6 gives you some practice writing electron configurations for the ions of main group elements. 

It is a common error to mislake spedes wAh the same valence electron configuration for isoelectionic species. For example, F and Ne are isoelectronic. r and Cr are not 

Strategy First write electron configurations for the atoms. Then add electrons (for anions) or remove electrons (for cations) to account for the charge. 

A combination of molecular mechanics calculations and electric birefringence (electro-optical Kerr effect) measurements of group IVB aryl compounds has been used to study conformational effects in these molecules12731. 

Structure optimization of main group molecules with generic force fields has the same advantages and problems as molecular mechanics calculations of organic and organometallic compounds with similar approaches on one hand there is no need to fit a specialist force field, on the other hand is the expectation of lower accuracy1279,2801. The structural results are especially poor for molecules where electronic effects are important, e.g., those with hypervalent or dative bonds. 

An area of increasing interest is the selective complexation of Sn2+ and more particularly Pb2+ for the treatment of heavy metal poisoning. Molecular mechanics has been extensively applied to the problem of metal ion selectivity (see Chapter 8) but there have been few studies of lead or tin complexes. The fit of Sn2+ to 18-crown-6 has been considered12811, as has the size selectivity of tetraazamacrocycles with respect to Pb2+ binding131. The binding of Pb2+ to porphyrin-1 has been modeled, though in this case the point of interest was the structural deformations caused by the metal cation11901. 

Section 8.1 broadly discusses properties of the main group elements that inflnence their physical and chemical behavior. 

TABLE 8.1 Top 20 Industrial Chemicals Produced in the United States, 2010  

Sources Data from Chem. Eng. News, July 4, 2011, pp. 55-63 U. S. D artment of the Interior, U.S. Geological Survey, Mineral Commodity Summaries 2011. 

Elements along a rough diagonal from boron to polonium are intermediate in behavior, in some cases having both metallic and nonmetalUc aUotropes these elements are designated as metalloids or semimetals. Some elements, such as silicon and germanium, are capable of having their conductivity finely tuned by the addition of small amounts of impurities and are consequently of enormous importance in the manufacture of semiconductors (Chapter 7) in the electronics industry. 

FIGURE 8.1 Electrical Resistivities of the Main Group Elements. Dashed lines indicate estimated values. 

The 20 industrial chemicals produced in greatest amounts in the United States are main group elements or compounds (Table 8-1), and eight of the top ten may be classified as inorganic numerous other compounds of these elements are of great commercial importance. 

A discussion of main group chemistry provides a useful context in which to introduce a variety of topics not covered previously in this text. These topics may be particularly characteristic of main group chemistry but may be applicable to the chemistry of other elements as well. For example, many examples are known in which atoms form bridges between other atoms. Main group examples include 

In this chapter, we will discuss in some detail one important type of bridge, the hydrogens that form bridges between boron atoms in boranes. A similar approach can be used to describe bridges by other atoms and by groups such as CO (CO bridges between transition metal atoms will be discussed in Chapter 13). 

This chapter also provides examples in which modem chemistry has developed in ways surprisingly different from previously held ideas. Examples include compounds in which carbon is bonded to more than four atoms, the synthesis of alkali metal anions, and the now fairly extensive chemistry of noble gas elements. The past two decades have also seen the remarkable development of the fiillerenes, previously unknown clusters of carbon atoms. Much of the information in this chapter is included for the sake of handy reference for more details, the interested reader should consult the references listed at the end of this chapter. The bonding and stractures of main group compounds (Chapters 3 

FIGURE 8-1 Electrical Resistivities of the Main Group Elements. Dashed lines indicate estimated values. (Data from J. Emsley, The Elements, Oxford University Press, New York, 1989.) 

It is remarkable how pooriy documented, on the whole, are the reactions of phosgene with the main group elements. There are very few classical studies of the reactivity of the elements with phosgene at low temperature, although the number of purely physical investigations are increasing. 

In 1702, William Homberg heated borax with iron(n) sulphate and obtained by sublimation a compound he called sedative salt , though it was not a salt but boric acid.94 The boron hydrides, first studied by A. Stock in 1909, have provided a rich source of new chemistry.95 Pliny described a silvery cup, lighter than any known metal, once owned by the emperor Tiberius. Some have speculated that the Romans might have stumbled on aluminium.96 Though alum was known in antiquity, the 

A good deal of historical work has appeared on the halogens. The work of Scheele, Lavoisier, Berthollet, Gay-Lussac and Davy on chlorine has been briefly reviewed,119 and a more lengthy paper has appeared on the isolation of iodine by B. Courtois in 1811.120 Fluorine became important to the Manhattan Project as a vehicle for separating uranium isotopes.121,122 The centenary of fluorine s isolation by H. Moissan in 1886 created much interest.123-128 

Chemiluminescence is observed during the reactions of aryl Grignard reagents with oxygen 4650 or with aryl peroxides.4656 Analysis of the luminescence spectrum and e.s.r. data indicates that for the oxygen-induced reaction brominated biphenyls are the emitters, whereas in the peroxide case triphenylmethane is the luminescent species. 

It might appear that d orbitals have to be included in the case of hypervalent compounds, such as SFe, PCI5 or SiFg, because the 35, and 3p AOs can be used to form no more than four covalent bonds. Thus, the textbook description of SFe goes back to Pauling s classical paper [2] and postulates six equivalent SF bonds formed after prior sp d hybridization of the sulphur AOs. Doubts 

As the flouride ions approach, retaining symmetry, two electrons of each octet can be utilized for SF bonding. Initially, all twelve bonding electrons are localized in the six MOs of the F combinations the configuration is [a e ]. 

As the ions approach, each of these orbitals interacts favorably and unfavorably with a sulphur orbital of the same irrep, producing a bonding and antibonding combination the six lowest of these are doubly-occupied in the closed shell ground-state. 

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Much effort has been devoted to developing sets of STO or GTO basis orbitals for main-group elements and the lighter transition metals. This ongoing effort is aimed at providing standard basis set libraries which ... 

Dolg Also called Stuttgart sets, this is a collection of ECP sets currently under development by Dolg and coworkers. These sets are popular for heavy main group elements. 

The number of valence elec trons in an atom of a main group element such as nitrogen is equal to its group number In the case of nitro gen this is five... 

PM3, developed by James J.P. Stewart, is a reparameterization of AMI, which is based on the neglect of diatomic differential overlap (NDDO) approximation. NDDO retains all one-center differential overlap terms when Coulomb and exchange integrals are computed. PM3 differs from AMI only in the values of the parameters. The parameters for PM3 were derived by comparing a much larger number and wider variety of experimental versus computed molecular properties. Typically, non-bonded interactions are less repulsive in PM3 than in AMI. PM3 is primarily used for organic molecules, but is also parameterized for many main group elements. 

Other Inorganics. Inorganic species in solution have been studied very effectively by Raman spectroscopy. Work in this area includes the investigation of coordination compounds (qv) of fluorine (qv) (40), the characterization of low dimensional materials (41) and coordinated ligands (42), and single-crystal studies (43). Several compilations of characteristic vibrational frequencies of main-group elements have been pubflshed to aid in the identification of these species (44,45). 

For main group elements the number of framework electrons contributed is equal to (t + a — 2) where v is the number of valence shell electrons of that element, and x is the number of electrons from ligands, eg, for Ff, x = and for Lewis bases, x = 2. Examples of 2n + 2 electron count boranes and heteroboranes, and the number of framework electrons contributed by their skeletal atoms, ate given in Table 1. 

Main Group Element Metallaboranes. A variety of metaHaborane clusters, which incorporate main group metals in vertex positions of polyhedral metaHaborane clusters, have been reported. Examples are (BH BeB H Q (165), MgB2QH22 20(C2H )2 (166), [(CH2)HgB2QH22]A (167),... 

Boranes also form derivatives ia which main group elements occupy a bridging position between two boron atoms, rather than a polyhedral vertex. An extensively studied system is -R MB Hg, where R = H, CH, C2H3, halogen, and M = Si, Ge, Sn, Pb (185). The stmcture of l-Br- J.-[(CH3)3Si]-B3H2... 

Main Group Element Carborane Derivatives. Main group element carborane derivatives have been reviewed (231). Only a few alkaline-earth element metaHacarborane derivatives have been characterized. The icosahedral beryUacarborane, /(9j (9-3-[(CH3)3N]-3,l,2-BeC2B H, shown in Figure 24a, has been prepared via the reaction of nido-1 and Be(CH3)2 [0(C2H3)2]2 followed by reaction of the diethyletherate product and... 

R)C2B4H ions and appropriate main group element haUdes, have stmctures containing central main group elements iu the 4+ oxidation states similar to the bis-dicarboUide sUicon sandwich compound. TThe stmcture of the sUicon sandwich compound commo- ](GH.])fi fZ, fri fii is shown iu Figure 27. 

Heteroboranes, compounds where one or more of the cage borons are replaced by a main group element (33), are not themselves commercially available. However, carborane sdoxanes containing > -carborane [16986-21 -6], C2H22B2Q, are available under the trade name of Dexsd for the stationary phase in gas—Hquid chromotography (qv) (34). The carborane, l,7-dicarba-c/(9j (9-dodecaborane(10) (35), contributes enhanced chemical and thermal stabiHty to the sdoxane polymer. 

Vol 12 PerfluorohaloorganiL Compounds of Main Group Elements Part 2 Compounds of Sulfur (Cuniinuanon) Selenium and Tellurium... 

Supplementary Work, Vol 24 Perfluorohnloorganic Compounds of Mam Group Elements Part 3 Phosphorus, Arsenic, Antirnon and Bismuth Compounds Perfhiorohaloorganic Compounds of Main Group Elements Part 5 Compounds oj Nitrogen (Heteroc clrc Compounds)... 

System No 5 Fluorine Perfluorohaloorganic Compounds of Main Group Elements Supplementary, Vol 1 Compounds with Elements of Mom Groups I to 5 (EKcludtng Nitrogen) and with Sulfur (Partially)... 

Many transition-metal complexes, including Ni(CO)4, obey the 18-electron rule, which is to transition-metal complexes as the octet rule is to main-group elements like carbon and oxygen. It states that... 

Salts of the [NSO] anion can be used for the synthesis of both transition-metal and main group element thionyl imides by metathetical reactions, e.g., Cp2Ti(NSO)2 and Ph3, .As(NSO)x (x = 1,2), respectively (Section 7.6). 

By far the most common CN of hydrogen is 1, as in HCl, H2S, PH3, CH4 and most other covalent hydrides and organic compounds. Bridging modes in which the H atom has a higher CN are shown schematically in the next column — in these structures M is typically a transition metal but, particularly in the Mi-tnode and to some extent in the x3-mode, one or more of the M can represent a main-group element such as B, Al C, Si N etc. Typical examples are in Table 3.3. Fuller discussion and references, when appropriate, will be found in later chapters dealing with the individual elements concerned. 

Hydrogen combines with many elements to form binary hydrides MH (or M H ). All the main-group elements except the noble gases and perhaps indium and thallium form hydrides, as do all the lanthanoids and actinoids that have been studied. Hydrides are also formed by the more electropositive transition elements, notably Sc, Y, La, Ac Ti, Zr, Hf and to a lesser... 

The hydrides of the later main-group elements present few problems of classification and are best discussed during the detailed treatment of the individual elements. Many of these hydrides are covalent, molecular species, though association via H bonding sometimes occurs, as already noted (p. 53). Catenation flourishes in Group 14 and the complexities of the boron hydrides merit special attention (p. 151). The hydrides of aluminium, gallium, zinc (and beryllium) tend to be more extensively associated via M-H-M bonds, but their characterization and detailed structural elucidation has proved extremely difficult. 

Salts of several heavy main-group elements can be reduced to form polyanions such as Na4[Sn9], Na3[Sb3] and Na3[Sb7] (p. 588). 

E. Coates, M. L. H. Green and K. Wade, Organo-meiallh Compounds, Vol. 1. The Main Group Elements, 3rd edn Chap. It. Group II. pp. 71-121. Methuen. London. 1967... 

Derivatives of the boranes include not only simple substituted compounds in which H has been replaced by halogen, OH, alkyl or aryl groups, etc., but also the much more diverse and numerous class of compounds in which one or more B atom in the cluster is replaced by another main-group element such as C, P or S, or by a wide range of metal atoms or coordinated metal groups. These will be considered in later sections. 

This type of transhalogenation reaction, which is common amongst the halides of main group elements, always proceeds in the direction which pairs the most electropositive element with the most electronegative, since the greatest amount of energy is evolved with this combination. 

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