Valence electron rule

Keywords Valence electron rule, Metal ring, Metal cluster, AN +2 valence electron rule, 8/V +6 valence electron rule, 6N +14 valence electron rule, Pentagon stability, Cyclopentaphosphane, Hydronitrogen, Polynitrogen, Triazene, 2-Tetrazene, Tetrazadiene, Pentazole, Hexazine, Nitrogen Oxide, Disiloxane, Disilaoxirane, 1,3-Cyclodisiloxane, Metallacycle, Inorganic heterocycle... 

Alkali and Alkaline Earth Metals 4N + 2 Valence Electron Rule. 299... 

Valence electron rules have been theoretically proposed for three- and four-membered atomic rings [7], The p, p and p orbital arrays are of the Hiickel or Mobius conjugation (Scheme 2) [9, 10], The splitting patterns of the energy levels are well known... 

The 8V + 6 valence electron rule has been completely substantiated by the calculated four-membered species in Table 2 [7], Boldyrev, Wang, and their collaborators presented experimental and theoretical evidence of aromaticity in the Al/ [19] Ga/" [20], In " [20] and isoelectronic heterosystems, XAl [21], The Al/" unit (14e) was found to be square planar and to possess two n electrons, thus conforming to the (An + 2)n electron counting rule for aromaticity. The n electron counting rule would be more powerful if we could predict the number of n electrons of metal atomic rings in an unequivocal manner. Our SN+6 electron rule only requires the number of valence electrons in Al/, which is easy to count. 

The and dianions have 20 (= 6 x 1 + 14) valence electrons and satisfy the 6N + 14 valence electron rule. The Al dianion possesses an geometry [60], Wade rules are not applicable to the stable geometry of Al ". The instability of the 0 geometry of Ga in disagreement with the rule can be attributed to similar magnitudes of the interaction between the p -orbitals and that between the p-orbitals which gives a very small HOMO-LUMO gap [8],... 

The octahedron is classified into the c/o o-structure by Wade [3,4]. Closo-structures with n skeletal atoms are stable when they have 4n-i- 2 valence electrons. Wade s rules predict that the 26 (= 4 x 6 + 2) valence electrons could stabilize the regular octahedrons since n is 6 for the octahedron. This prediction is contained in our 6N + 14 (N= 2) valence electron rule. Our rule also predicts the stability of octahedral metal clusters with the other numbers (14 and 20) of valence electrons. 

Electron counts according to the 18-electron rule are restricted to mono- and dinuclear complexes if the latter have no /iMigands. For triple- and tetra-decker complexes the 18-electron rule has to be transformed into the 30- and 42-valence-electron rule by adding d6 + tt (or o-8) electrons once and twice. 

Acyl derivatives of transition metals are usually encountered when the oxidation state of the metal is low (between —I and II) and therefore these compounds obey the 18-valence electron rule and are diamagnetic. These compounds are characterized by... 

We conclude that the assignment ofaM=M double bond in tmm-[ CpM(CO) (jU-PRR )2] is not in agreement with the observed chemical shift values in the P-NMR spectrum, and largely due to a desire to fulfill the 18 valence electron rule. 

VALENCE ELECTRON RULES FOR COMPOUNDS WITH TETRAHEDRAL STRUCTURES AND ANIONIC TETRAHEDRON COMPLEXES... 

Examples for polycatlonic valence compounds (VEC/ > 8) with defect tetrahedral structures. Except for the high pressure form of B2O with diamond-like stmcture (Endo, Sato Shimada, 1987), no polycatlonic valence compounds with normal tetrahedral structure are known. As examples for compounds with defect tetrahedral structure we discuss here GaSe and "InsS/. The latter compound served as a test case for the validity of these valence electron rules. 

To this formula correspond the values N i bo = and CC = 8/5. However, if one uses the valence electron rules and bases the calculation on the reported composition "InsS/ different values for N, bo and CC are obtained ... 

Assuming that the valence electron rules are correct, the error had to be looked for either in the crystal structure or in the composition of the compound. Since 11 84 had been prepared in a bath of liquid tin the possibility could not be excluded, that some Sn atoms had been incorporated in the crystals and that the true chemiceil composition might be different. Taking instead of "10584" as composition lri4SnS4 one calculates the following values ... 

For all the compounds discussed in Figures 7 to 10 the observed structural features, in particular the features of the base tetrahedron which can be used to construct the complete anionic tetrahedron complex, are in perfect agreement with the predictions based on the valence electron rules. 

Definition of a base tetrahedron. In the examples given above we have demonstrated how one can use the two valence electron rules to predict certain structural features of a compound assuming that an anionic tetrahedron complex is formed. In particular, for each compound we had given a list of calculated parameters and had presented a corresponding graph of a base tetrahedron with which the anionic tetrahedron complex of the compound can be constructed. 

Limits for the application of the valence electron rules. For the fruitful application of these valence electron rules certain assumptions have to be made which can be summarized as follows ... 

Inspite of certain limitations for the application of the valence electron rules, they have been found very useful to systematize and classify structures with anionic tetrahedron compiexes. They have been of heip to point out inconsistencies between reported structure and composition and they offer an aid in the synthesis of new compounds with particuiar structurai features. 

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