Subvalence electrons

In Table 2.1 are listed many of the common isotopes examined by NMR techniques, together with their nuclear constants. Notice that a bare proton has the largest y value of any nuclear particle, while heavier nuclei, surrounded by many subvalence electrons, tend toward lower values. This... 

B. de Courcy, J. P. Dognon, C. Clavaguera, N. Gresh, and J. P. Piquemal, Int. J. Quant. Chem., 111(6), 1213-1221 (2011). Interactions within the Alcohol Dehydrogenase Zn(II)-Metalloenzyme Active Site Interplay between Subvalence, Electron Correla-tion/Dispersion, and Charge Transfer/Induction Effects. 

Where are the lone-pair electrons in subvalent fourth group compounds S. W. Ng and J. J. Zucker-man, Adv. Inorg. Chem. Radiochem., 1985, 29, 297 (178). 

A correct description of Pauli repulsive interactions between valence, subvalence, and core electrons as well as of electrostatic interactions is an essential requirement for accurate quantum chemical predictions. We now show that a proper analysis of steric repulsion—Pauli repulsion in nonbonded... 

Bredig [67] considered two categories of metal-molten salt mixtures metallic and nonmetallic solutions. In metallic solutions the metal dissolves without interacting strongly with the melt. Metal ions and partially free electrons are formed. The electrical conductivity of these mixtures increases strongly due to the presence of very mobile partially free electrons. Therefore an electronic conductivity appears in these melts. In nonmetallic solutions the metal reacts with the melt under the formation of subvalent ions or subvalent compounds. The electrical conductivity of these mixtures depends only to a small extent on the concentration of dissolved metal. The variation of properties of the metal-molten salt mixtures shows a continuous change from the metallic solutions to the nonmetallic if the temperature is sufficiently high. 

WHERE ARE THE LONE-PAIR ELECTRONS IN SUBVALENT FOURTH-GROUP COMPOUNDS ... 

A subsidiary goal from the outset was to identify those systems in which the lone-pair electrons present in these subvalent species show no stereochemical activity that is, in which the fourth-group atoms occupy sites of perfect symmetry in the solid state. Our search brought forth various scattered examples of such structural systems, and reading of their unusual properties heightened our interest. However, with the fortuitous synthesis by C. Janiak in our own laboratory... 

For systems which possess stereochemically active lone-pair electrons in the crystalline state, a definitive experimental answer to the title question is at least in principle available from difference density analysis of X-ray results where the potential for deriving electron distributions from elastic diffraction data is now being realized (13, 31, 104). In one application to subvalent molecules (164), (CH3)2TeCl2 was shown to possess a peak of 0.27 e/A3 centered at 0.9 A from the Te(IV) atom in the position expected for a lone pair of electrons (175). 

The focus of this section will be molecular subvalent dinuclear compounds, rings, and chains in which the composition and structure can be accounted for by localised electron-pair (2c,2e) bonds between adjacent atoms. Cluster compounds with a 3-dimensional architecture, some of which require a more delocalized bonding description, will be discussed in Sections 4 and 5. 

Closo, nido, and arachno boranes form series with formulae B H2 +4, and B H2 +6 coirfirming their status as formally subvalent componnds. Boranes and carboranes (in which one or more boron atoms in the cluster have been replaced by a carbon atom) have been extensively researched and described, and will not be discussed further here. In an example of the application of Wade s rules to a heavier main group cluster, 805 nses 10 of the total 22 valence electrons in 5 lone pairs. This allows 12 electrons, or 2n 4- 2 for n = 5 for cluster bonding and specifies a closo structure, matching the observed Z>3h trigonal bipyramidal structure. 

Further examples of formally subvalent main group compounds that contain element-element bonds but not necessarily clusters are the Zintl phases. The bonding in these has been described as the octet rule for all atoms . The archetypal Zintl compound is NaTl, in which charges are assigned as Na+ and Tl, representing a formal transfer of electrons from the more to the less electropositive element. The Tl ion can be considered to be a group 14 pseudoelement, and in fact exists in NaTl as a three-dimensional polyanionic diamond framework (TN) stuffed with Na+ cations. The Zintl concept is extended more broadly to other binary and ternary solid-state compounds, whose structures show the formation of element-element bonds in one, two, or three dimensions. ... 

As is seen, the most noticeable differences between the all-electron and pseudopotential eigenvalues are observed for the molecular orbitals containing the s-type AOs of Pd by symmetry. It appears to be related to the non-core character of the 4s states in the second transition series atoms therefore, one could take into account for the subvalence shells when constructing pseudopotential [17] or to use some extended basis in such cases. 

Where Are the Lone-Pair Electrons in Subvalent Fourth-Group Compounds ... 

Formally subvalent compounds of boron containing a boron-boron single bond are intermediate in structural complexity between simple monoboron derivatives and the polyhedral electron-deficient compounds of the element. The properties of such compounds, particularly the simple derivatives of the B2X4 type, have attracted the attention of several groups of workers since Stock s initial discovery of BjCL some 45 years ago (96). These materials provide the simplest examples of catenation in boron chemistry and offer suitable systems in which to study the properties of the covalent B—B bond and the characteristic chemistry of compounds containing this linkage. 

Effect on Subvalence Valence electrons Molecular Molecular... 

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