Building materials crystal engineering

Que ley, justicia o razon negar a los hombres sabe privilegio tan suave, excepcion tan principal, que Dios le ha dado a un cristal, a un pez, a un bruto y a un ave  

For what law can so depart From all right, as to deny One lone man that liberty That sweet gift which God bestows On the crystal stream that flows. Birds and fish that float or fly  

Pedro Calderon de la Barca, La vida es sueno (Translation by D. F. MacCarthy) 

When the synthesis of suitable single crystals implies extreme difficulty or when the sought crystallographic phases are metastable, their preparation in the form of thin films becomes the logical alternative. Nano or micrograms of MOMs can 

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Transition metal clusters, however, need still to be tested in the engineering of crystalline materials. Crystal engineering has been defined as the capacity to make crystals with a purpose. In transition metal cluster chemistry this purpose is that of utilizing the distinct characteristics mentioned above to construct crystals that can function as the result of the inter-cluster interactions. To do this the experimentalist needs to conceive ways of directing the crystal-building process towards given architectures, i. e. needs to learn how to make non-covalent crystal synthesis. Clearly, the growth and success of a solid-state chemistry of transition metal clusters depends crucially on a close interaction between synthesis, theory, solid state characterization, and evaluation of properties. 

Because of the vastness of the subject matter, we shall focus our attention on hydrogen bonding interactions between ions and on the possibilities and limitations of their use in the design and construction of molecular materials of desired architectures and/or destined to predetermined functions. Obviously, the crystal engineer (or supramolecular chemist) needs to know the nature of the forces s/he is planning to master, since molecular and ionic crystals, even if constructed with similar building blocks, differ substantially in chemical and physical properties (solubility, melting points, conductivity, mechanical robustness, etc.). 

In this contribution we have also underlined an emerging aspect of solid-state chemistry, namely that solvent-free solid-state synthetic procedures can be exploited to construct bottom-up new materials from molecular or ionic building blocks. This is at the core of molecular crystal engineering [81]. It is fascinating to think that the crystal engineer may free him/herself from operating with solvent to achieve the bottom-up construction of supramolecular materials completely from sohd to sohd . 

The paramount advantage of molecular solids over their more classical inorganic counterparts is that their constituents, the building blocks, are molecules or clusters that can be designed and synthesized in other words they can be intentionally modified. Therefore, we can talk about molecular and crystal engineering and the goal is to be able to produce materials with predetermined physical properties. We are not yet at this desired level but the scientific and technical bases are certainly at hand. 

We saw in the preceding section the crystal engineering of diamondoid arrays arising via halogen bonding, from the use of tetrahedral building blocks. We complete this chapter by a brief discussion of what constitutes a diamondoid array and why they are not just interesting from a materials point of view but also very beautiful. 

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