Electron counting applications

The structure of cluster compounds of transition metals and the limits of applicability of the electron counting rules forpolyhedral molecules. Y. L. Slovokhotov and Y. T. Struchkov, Russ. Chem. Rev. (Engl. Transl), 1985, 54, 323 (150). 

In this review, we present a selection of studies from our own laboratory, intended to introduce a solid-state chemist to both the practical and theoretical considerations that need to be taken into account in XPS measurements of solids with substantial covalent character. Metal phosphides, arsenides, and antimonides represent such a category of solids where the bonding retains some polarity that notions of electron counting derived from the Zintl concept still prove helpful in providing a frame of reference for comparing charge distributions. We also describe the applications of XAS to complementary studies of the electronic structure of these materials. 

A classic example of the application of the above-mentioned rules is given by the borane series B6H62 (octahedron, closo), B5H9 (square pyramid, nido) and B4H10 (butterfly, that is two triangles joined by sharing an edge, arachno). The total electron counts (TEC) result in the three clusters 26, 24 and 22 whereas the skeletal electron... 

New developments in electronic counting in intermetallic compounds It has been recently underlined (Grin 2006) that the understanding the nature of intermetallic compounds is still not complete, mainly due to the strong bias imposed by applications research and to insufficient comprehension about their chemical bonding. 

Hence, these models are somehow of complementary characters and efforts should be directed toward their developments and wider applications, including those situations in which the additivity fails. Extensions of the Pickett s and Lever s models have already been proposed to overcome their limitations, as discussed above, and in some cases the dependency of the ligand parameters on the metal centers and generalizations to types (with different electron-counts, structures, compositions, etc.) of complexes, metal centers and ligands not included in the original proposals, have already been successfully treated. 

The low level comparator will reject pulses of low intensity which are generated by thermoionic emission in the dynodes. It is obvious that an electron emitted by dynode 5 for instance will produce a much smaller avalanche at the anode than an electron emitted by the photocathode but of course thermoionic emission from the photocathode itself would still appear as a genuine pulse, and for this reason PM tubes used in photon counting applications must be cooled down. 

All the standard texts listed in Section A.3 of the Appendix have lengthy sections on coordination and organometallic compounds of the transition elements. See also the books listed in Sections A.10 and A.ll. Bell (1977) gives the fullest account of the chelate effect. Cotton and Wilkinson (1988) (Section A.3) is best for the catalytic applications of complexes. Jolly (1984) (Section A.3) discusses electron-counting in polynuclear carbonyls in some depth. 

Historically, a scheme of skeletal electron-counting was developed to rationalize the structures of boranes and their derivatives, to which the following Wade s rules are applicable. 

A generalized electron-counting scheme, known as the mno rule, is applicable to a wide range of polycondensed polyhedral boranes and heteroboranes, metal -laboranes, metallocenes, and any of their combinations. According to this mno rule, the number of electron pairs N necessary for a macropolyhedral system to be stable is... 

Table 13 4 4. Application of the mno rule for electron counting in some condensed polyhedral boranes and related compounds ...

Exercise 1.5. What is an electron-counting rule derived from application of the closed-shell principle to H or He Why don t you find this rule in textbooks ... 

Another clinical application of conductance is for electronic counting of blood cells in suspension. Termed the Coulter principle, it relies on the fact that the conductivity of blood cells is lower than that of a salt solution used as a suspension medium.The cell suspension is forced to flow through a tiny orifice. Two electrodes are placed on either side of the orifice, and a constant current is established between the electrodes. Each time a cell passes through the orifice, the resistance increases this causes a spike in the electrical potential difference between the electrodes. The pulses are then amplified and counted. 

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