Control solid-state

Hammetter [91H01] has carried out DTA analysis of a shock-modified but unreacted 2A1 -t- Fe203 mixture and found a preinitiation event, indicating the presence of shock-produced Hercynite (spinel phase FeAl204). These preinitiation events observed in thermal analysis provide direct evidence for the influence of mechanical, shock-induced mixing in controlling solid state chemistry. 

We have already dealt with two of these. Section 2 dealt with formation of a phase boundary while we have just completed Section 4 concerning nuclei growth as related to a phase boundary. We will consider diffusion mechanisms in nuclei and diffusion-controlled solid state reactions at a later part of this chapter. 

The only conclusion that we can draw is that diffusion-controlled solid state reactions tend to produce mixtures of compounds, the relative ratio of which is related to their thermod5rnamic stability at the reaction temperature. Obviously then, if we change the temperature of reaction, we would expect to see somewhat different mixtures of compounds produced. 

It should be clear by comparing the examples for calcium silicate and barium silicate that one cannot predict how the diffusion-controlled solid state reactions will proceed since they are predicated upon the relative thermodsmamic stability of the compounds formed in each separate phase. 

The solid-state polymerization of diacetylenes is an example of a lattice-controlled solid-state reaction. Polydiacetylenes are synthesized via a 1,4-addition reaction of monomer crystals of the form R-C=C-CeC-R. The polymer backbone has a planar, fully conjugated structure. The electronic structure is essentially one dimensional with a lowest-energy optical transition of typically 16 000 cm-l. The polydiacetylenes are unique among organic polymers in that they may be obtained as large-dimension single crystals. 

These schemes have been frequently suggested [105-107] as possible mechanisms to achieve the chirally pure starting point for prebiotic molecular evolution toward our present homochiral biopolymers. Demonstrably successftd amplification mechanisms are the spontaneous resolution of enantiomeric mixtures under race-mizing conditions, [509 lattice-controlled solid-state asymmetric reactions, [108] and other autocatalytic processes. [103, 104] Other experimentally successful mechanisms that have been proposed for chirality amplification are those involving kinetic resolutions [109] enantioselective occlusions of enantiomers on opposite crystal faces, [110] and lyotropic liquid crystals. [Ill] These systems are interesting in themselves but are not of direct prebiotic relevance because of their limited scope and the specialized experimental conditions needed for their implementation. 

Scheme 10.13 Topochemically controlled solid-state synthesis of bisadduct 61 and subsequent cyclopropanation to give [2 4]-hexakisadduct 62. (i) 180°C, 10 min (ii) 40 equiv. diethyl bromomalonate, 40 equiv. DBU.

The polymer-dispersed liquid crystal was used as a modulating medium in optically controlled modulators instead of the liquid crystal [261-264], The sandwiched structure from polyimide photosensitive film and the polymer dispersed liquid crystal film - i.e. the optically controlled solid state modulator -had the characteristics presented in Fig. 36 [261]. Contrast ratio 35 1, response time > 400 ps, decay time 80 ms and sensitivity 5 x 10 sJcm 2 were obtained. 

Prior to the development of tether-directed functionalization methods, Krautler and co-workers developed a very elegant topochemically controlled, solid-state group-transfer synthesis [12,13] to obtain the trans-1 bisanthracene adduct 9 (Figure 2). 

In the last decade, progress has also been made with using superlattices as templates, or structure-directing agents, to kinetically control solid-state reactions. This is accomplished by allowing interdiffusion to reach completion before the occurrence of heterogeneous nucleation, thus trapping the system in the... 

This type of reaction represents the ultimate control solid-state synthetic chemists seek, namely, the bottom-up abUity to build a compound atom by atom. Harris et al. (2003) took advantage of the two dimensional nature of Bi2Te3 and TiTe2, such that their S5mthetic challenge was layer by layer. The secret to their success lies in the fact that two important principles control any synthetic efforts thermodynamics and kinetics. Phase diagrams, which are discussed in Chapter 11, owe allegiance to thermodynamics... 

The goal of this article is to describe ways in which crystal structure, morphology, and crystallization kinetics can be utilized to reproducibly maintain metastable states and control solid-state outcomes. Experimental methods that can be employed to investigate the factors that regulate crystallization from solution will be presented. 

Our approach template-controlled solid-state reactivity 143... 

It is with these ideas in mind that we focus here on the design and construction of finite molecular assemblies in the organic solid state. Our intention is to provide an overview of finite assemblies with emphasis on properties that such assemblies may provide solids. We will begin by outlining general criteria for constructing finite molecular assemblies in both the solid state and solution, and then describe assemblies isolated and characterized in the solid state to date. We will then use recent advances in our laboratory to illustrate how finite assemblies can be used to control solid-state reactivity and direct the synthesis of molecules. 

Fig. 39 Template-controlled solid-state reactivity, X-ray crystal structures of (a) four-component assembly 2(4-bn-res) 2(l,4-bpeb) (b) targeted cyclophane (c) four-component assembly 2(5-OMe-res) 2(l,6-bpht) and (d) targeted [5]-ladderane.

Riegel, J., Neumann, H. and Wiedenmann, H.-M. (2002) Exhaust gas sensors for automotive emission control. Solid State Ionics, 152—153, 783-800. 

The control of charge flow by an electric quantity is a key issue of today s electronics. The concept to electrically specify the conductivity of a resistor by pure solid state effects was already proposed in 1928 by Julius Edgar Lilien-feld in Germany [1], The basic idea was to control the charge carrier density in a solid by an electric field, applied over a third electrode. However, there is no evidence for a practical realisation by Lilienfeld. The first report about a pure electrically controllable solid state device was the well know Germanium transistor from William Shockley, John Bardeen and Walter Brattain [2]. The new term transistor was later explained as a combination of the words transconductance and varistor . Meanwhile a broad variety of different transistor concepts exists, which, however, can be mainly subdivided in two basic operational principles ... 

However, the major impediment to exploration of the factors controlling solid-state photochemistry has been the disinclination of organic chemists to pursue x-ray, computational, and theoretical methods, and this being paralleled by the physical chemists disinclination to study organic reactions involving molecular rearrangements. 

These mechanisms should now be self-evident. We have now described the formation of a phase boundaiy and how it grows (Section I.) and have just completed Section II. concerning nuclei growth. Now, we will consider diffusion mechanisms and diffusion-controlled solid state reactions without concern about how nuclei form or grow in the following section. 

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