On the other hand, many synthetic chemists have found new inspiration and new ideas for their synthetic skill and moved from the preparation of molecules to that of solid supramolecular assemblies of higher complexity (Braga, 2017 ).ДЄ crystal engineering project implies the ability to master a variety of energetically different supramolecular bonding interactions. Many structural chemists have found in crystal engineering a good motivation to abandon the (often frustrating) ancillary role of service crystallography to start making their own compounds. While crystallography focuses on the characterization of a solid, crystal engineering focuses on its synthesis, and requires the definition of a target material or target property and of a synthetic strategy to reach such targets.ДЄs a matter of fact, crystal engineering would have gone nowhere without the knowledge and tools of crystallography, but it is also true that crystal engineering has provided appealing alternatives to the work of crystallographers. This is also the basic difference between crystal engineering and crystallography. In both cases, the crystal making process implies the existence of a project and of a design strategy (Braga & Grepioni, 2006 Zhang & Zaworotko, 2014 ). Molecular crystals are mainly built up via the self-assembly of molecules and/or molecular ions capable of intermolecular bonding, while coordination networks are constructed using metal coordination topology and multidentate ligand linkers capable of coordination bonds. However, depending on the category of materials one is aiming to obtain, the construction criteria are different for molecular crystals and coordination networks. The number and type of useful crystalline materials that can be, at least in principle, obtained on the basis of the crystal engineering paradigm is limited only by the imagination of the `crystal maker', and the applications span from photoelectronics to non-linear optics, from chiral materials, pharmaceuticals, agrochemicals, to nutraceuticals and cosmetics, let alone `zeolitic like' materials to filter, trap, activate molecules on a nano scale etc. What this purpose could be depends on the motivations of the experimentalist and could be utilitarian, esthetical or driven by curiosity, or a combination of these (Desiraju, 1989 Desiraju, 1995 Braga et al., 1999 ). Crystal engineering is essentially making crystals with a purpose. Scientists have always dreamt of being able to obtain materials with desired properties starting from a knowledge of the properties of the molecular/ionic components of choice and of their spatial distribution and intermolecular interactions in the solid. Since most useful/utilizable materials are solids, and most solids are crystalline, the strive for the `controlled arrangement of things on a small scale' is essentially an effort to design and construct crystals from preformed molecular building blocks. Feynman, during his famous talk: `There's Plenty of Room at the Bottom', said `I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do' (Toumney, 2009 ).

Crystal engineering is, in essence, the attempt of the chemist to gain control on the assembly of molecular/ionic building blocks in the solid state via non-covalent interactions, forcing the result of a crystallization process towards planned structural and physical properties вЂ“ an extremely ambitious goal.ДЄlmost 60 years ago Richard P.

Ragdoll runners demo unblocked