Electron pair inert

Thallous halides offer a unique possibility of studying the stereochemistry of the (chemically) inert electron pair, since their structures and their pressure and temperature-dependent phase transitions have been well established. Thallium (1) fluoride under ambient conditions, adopts an orthorhombic structure in the space group Pbcm which can be regarded as a distorted rocksalt structure (Fig. 2.4). In contrast to TIF, the thallium halides with heavier halogens, TlCl, TlBr and Til, adopt the highly symmetric cubic CsCl structure type under ambient conditions [46]. Both TlCl and TlBr, at lower temperatures, undergo phase transitions to the NaCl type of structure [47]. 

The harder (in Pearson s model ) or the more electronegative the ligand, the more pronounced the stereochemical activity of the inert electron pair localized at the chalcogen atom. 

Second, the spatial requirement of "inert" electron pairs is easily deduced from the table, namely from the entries of In+/In +, T1+/T1 +, Sn +/Sn +, Pb +/Pb +, and Sb +/Sb +, being of the order of 10 cm /mol, about the size of the hydrogen anion, H. Later studies have shown that the latter anion, a strongly polarizable ion depending on the binding partner, also varies greatly in its incremental volume [34]. 

The properties and behavior of p-block metals are less homogenous than those of the s-metals because of their atomic and ionic sizes and other characteristics such as their unusual crystalline structures and the presence of the pair of electrons on the s orbital (s ) of the outermost electron shell. These s orbital electrons do not participate in chemical interactions (covalent or ionic) (inert electron pair). This influence increases with atomic number within a group. 

Metals have positive oxidation numbers (Table 3.1). Generally, the representative metals have oxidation numbers equal to the group A number. The metals from the p-block can have a second oxidation number, two units smaller than the group A number. In the case of these elements (e.g., Tl, Sn, and Pb) the stability of the highest oxidation state decreases down a group due to the ns inert electron pair. The penetration effect is greater for ns orbitals than np orbitals. As a consequence, the ns electrons are more attracted to the nucleus and more inert. 

It is not possible to obtain a stable modification of Pb02 by replacing the inert electron pair by an additional oxygen atom, but if we push the layers somewhat apart and place an additional anion above each lone electron pair, we end up with the layer structure of BiOF or PbFCl [240]. 

Nonbonded electron pair donors (w-donors) are expectedly readily protonated (or coordinated) with superacids. Remarkably, this includes even xenon, long considered an inert gas. The protonation of some 7T-, (T- and -bases and their subsequent ionization to carbocations or onium ions is depicted as follows ... 

The N—>P dative bonds are weak and different in lengths (1.800 A on average), and the triflate anions are effectively extended to consider interaction with the counter ion. Again the phosphorus atom is strongly pyramidalized and features the aspects of an inert nonbonding electron pair. 

In books on inorganic chemistry, the marked increase in the stability of the lower oxidation state (by two units) of heavier elements descending the main groups of the periodic Table is often explained by the inert s-pair effect (see J. E. Huheey U)). For example, elements like In and Sn may use only 1 or 2 electrons for the formation of bonds instead of 3 or 4 (group number), leaving one electron pair in the outer valence shell inert . The electron pair is assumed to occupy an s-orbital. This classification does not very much contribute to the understanding of bonding first... 

In the reaction shown in Eq. (20.93), the dA complex containing Cr2+ is inert owing to electron pairing giving the low-spin state. There is an extreme variation in rates from very slow to very fast depending on the nature of the ligands present, and rate constants may vary from 10 6 to 108 M-1 s 1. 

The term inert pair is often used for the tendency of the 6s2 electron pair to remain formally unoxidized in the compounds of Pb(n) [and also in the case of T1(I) and Bi(m) etc.]. As discussed above, this tendency can be related to relativity. Figure 59 shows the relativistic and non-relativistic valence orbital energies for Sn and Pb. The relativistic increase of the s-p gap leads to a 6s2 inert pair in the case of Pb. However, the situation is more complex if the local geometry at the heavy atom (Pb) is discussed. There are examples for both, stereochemically inactive and stereochemically active s2 lone pairs. 

Because the number of orbitals available for boron is higher than electrons (three electrons, four orbitals) boron is an electron-pair acceptor, a Lewis acid and it is prone to form multi-centre bonds. Boron is inert under normal conditions except for attack by fluorine. 

Most of the reactions of triplet carbenes discussed in this chapter will deal with reactions in solution, but some reactions in the gas phase will also be included. Triplet carbenes may be expected to show a radical-like behaviour, since their reactions usually involve only one of their two electrons. In this, triplet carbenes differ from singlet carbenes, which resemble both carbenium ions (electron sextet) and carbanions (free electron pair). Radical like behaviour may, also be expected in the first excited singlet state Sr e.g. the state in CH2) since here, too, two unpaired electrons are present in the reactive intermediate. These Sj-carbenes are magnetically inert, i.e., should not show ESR activity. Since in a number of studies ESR spectra could be taken of the triplet carbene, the reactions most probably involved the Ti-carbene state. However, this question should be studied in more detail. 

While the contraction resulting from the poor shielding of 4/ electrons ceases at hafnium, the relativistic effect continues across the sixth row of the periodic table. It is largely responsible for the stabilization of the 6. orbital and the inert s pair effect shown by the elements Hg-Bi. It also stabilizes one40 of the 6p orbitals of bismuth allowing the unusual i-l oxidation state in addition to +3 and + 5.4 ... 

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