Multi-decker sandwich

A composite material consists of flat, thin metal plates of uniform thickness glued one to another with a thin, epoxy-resin layer (also of uniform thickness) to form a multi-decker-sandwich structure. Young s modulus of the metal is Ej, that of the epoxy resin is E2 (where E2 < Ej) and the volume fraction of metal is Vj. Find the ratio of the maximum composite modulus to the minimum composite modulus in terms of Ej, E2 and V. Which value of gives the largest ratio ... 

The synthesis of new materials having novel electronic or optical properties is of great current interest. One approach to the synthesis of such materials is to systematically link small sandwich units together to form an extended multi-decker sandwich system. Immediately following the discovery of the triple-decker structure of the Cp3Ni2+ complex in early 1970s,181 Grimes and co-workers synthesized the first neutral triple-decker metallacarborane sandwich compound. Most of the subsequent research in this field, some of which has been described... 

Fig.5 Examples of simple metallocene structures a parallel sandwich, b multi-decker sandwich, c half-sandwich, d bent/tilted sandwich and e compounds with differently bonded cyclopentadienyl ligands...

Multimetallic sandwiches, including polymetallocenes, bis(fulvalene)-dimetal compounds, multi-decker sandwiches, and compounds in which two metals are bonded to a common unsaturated cyclic hydrocarbon are discussed in Section II. Sections III and IV are subdivided according to the metal group, and describe ligand-bridged bimetallics and metal clusters, respectively. Where appropriate, redox potentials have been included. Unless otherwise stated they are referenced versus the aqueous saturated calomel electrode (see). 

Fig. 32 Optimized geometries (B3LYP/6-311+ G ) and some important geometrical parameters (bond length (R, A), and bond angle (A, degree)) of different molecules involved in the formation of multi-decker sandwich complexes. Reprinted with permission from ref. 231. Copyright 2009 John Wiley.

A series of multi-decker sandwich complexes involving Be and Mg systems have been studied (Fig. 32). Aromaticity of all these systems have been confirmed by their NICS values (Table 13). Frontier molecular orbitals highlight the delocalization pattern (Fig. 33). For any given series an increase in the number of layers has been associated with an increase in hardness and a decrease in energy and electrophilicity in most cases (Table 14). The AH and Aco values of the associated formation reactions are presented in Table 15. 

Chattaraj, P. K. Giri, S. Multi-decker sandwich complexes using Bej and Mgj" dianions. Int. J. Quantum Chem. 1. Mayer Special Issue, 2009,109, 2373. 

Species functionalized at boron, such as 50-53, have also been prepared from the corresponding MC2B4 closo clusters via the removal of the apex BH unit (decapitation) with I M Kl)A.54 57 The same approach has been employed to link CoC2B3 units to benzene or other arenes 5 As shown in the following subsection, di- and trinuclear complexes such as 53 and 54 are easily converted to multi-triple-decker sandwich systems. 

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