Clusters electron deficient

A novel and far-reaching type of isomerism concerns the possibility of valence isomerism between nonclassical (electron-deficient) clusters and classical" organoboron structures. Thus, n-vertexed /do-boranes. have cluster structures... 

The electrostatically favored cation (Li) and anion (RE) arrangement implies the presence of two different E-, Si- and Li sorts, which has been established by solution and solid-state NMR spectroscopy. The electronic structures of the mixed-valent pnictides 10 and 11 have been simply described as electron-deficient clusters with delocalized framework electrons. Formally the latter consist of two low-valent anediyl moieties RE and eight andiides (RE)2- (E = P, As). The relatively large E-E distances of >4 A exclude the occurrence of localized E-E bonds. However, delocalization of the cluster valence electrons is achieved without Li-Li bonds via Li-mediated multiple bonding. Evidence for this has been seen in the NMR spectra (31P, 7Li, 29Si), which are in accordance with the electron delocalization model (see later discussion). 

The lower reactivity of 5a versus 10 reflects the stronger close packing of the anionic and cationic centers than that in the electron deficient cluster 10. Similar relations have been observed for analogous arsenic compounds (36). 

Ru3 i3-CC(0)R ( i-C0)3Cp/3 (R = H, OH) occurs, while among the many products obtained from reactions with CO, both Ru3 i3-CC(0)[0Ru (CO)2Cp] ( i-CO)3Cp3 and Ru2(p-CO)(CO)2CpMe (p4-C=C) MoRu(p-0)(0)(C0)CpCpMe were isolated. The unusual electron-deficient cluster Mo3 i3-C2[Ru(CO)2CpMe] ( i-CO)(Cl)2(CO)Cp3 was obtained from a reaction with tetrachloroethene. 

The chemistry of reduced Nb and Ta hahdes is rich in clusters with various structures. The metal atoms assemble with metal metal distances close to those in the metal into triangular and tetranuclear clusters but the dominant structural motif is that of the octahedral M6X12 and NbeIg types. Binary, ternary, and quaternary compounds aU crystallize in that type. The Me clusters are characteristic of the chemistry of the lower oxidation states of Nb and Ta, although not restricted to them. These electron-deficient clusters are based on metal ions with average oxidation numbers between III and I. 

In contrast to the later elements, B forms a large number of so-called electron-deficient cluster compounds, the bonding in which poses problems within valence bond theory we introduce these compounds in Section 12.11. 

In this section, we introduce electron-deficient clusters containing boron, focusing on the small clusters [BgHg], B5H9 and B4H10. A comprehensive treatment of borane and carbaborane clusters is beyond the scope of this book, but more detailed accounts can be found in the references cited at the end of the chapter. 

There is an interesting relation between TiO and compounds composed of discrete electron deficient clusters which are stabilized by interstitial atoms. TiO is an obvious borderline case. Having only a few electrons which can be used for M-M bonding, the arrangement with only empty clusters is easily transformed into a (statistically disordered) rocksalt structure at elevated temperature. Now, a portion of the ligand atoms plays the role of the interstitials. 

The electron-deficient cluster H20s3Pt(CO)ioP(cyclo-C6Hn)3 adds one mole H2 yielding the 60 electron compound H40s3Pt(CO)io(cyclo-C6Hn). This reaction which occurs under a pressure of 200 bar H2, can be reversed in a N2-atmosphere. 

In this Chapter, some of the different possibilities that Main Group Elements offer for building atomic conglomerates will be analyzed. In such a context examples of electron-deficient cluster species such as the clusters formed by the alkali metals and some complementary aspects of the chemistry of boranes and... 

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