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From Molecule to Crystal The Problem of Crystal Engineering Gautam R. Desiraju Solid State and Structural Chemistry Unit Indian Institute of Science Bangalore 560 012 What is Crystal Engineering? It is the design of organic and metal-organic solids Molecular Solids The understanding of intermolecular interactions in the context of crystal packing and in the utilisation of such understanding in the design of new solids with desired physical and chemical properties (Desiraju, 1989) Crystal Engineering The question Given the molecular structure of an organic compound, what is its crystal structure? In other words, how do molecules recognize one another? Why do we start with molecules? O H5C6 H O C6H5 O H O Towards greater complexity O H3C O H O H O O H3C O H CH3 Crystal Engineering The problem The behaviour of a functional group in a molecule during crystallization depends on the nature and positioning of all the other functional groups in the molecule. Therefore crystal structures are not related to molecular structures (functional groups) in simple ways. They are emergent properties. Hydrocarbon residues also count as functional groups in supramolecular chemistry. Crystal Engineering A second problem One → Few → Many → Crystal We do not know how molecular crystals are built up. Are small clusters formed which increase in an orderly way to give larger clusters? Or are the events more irregular? A simplification is required Supramolecular synthons are structural units within supermolecules which can be formed and/or assembled by known or conceivable synthetic operations involving intermolecular interactions Desiraju (1995) Even more complexity Br O O H O O H Br Br O O H S. S. Kuduva et al., J. Am. Chem. Soc, 121, 1936, 1999 The Weak Hydrogen Bond D. Das et al, Cryst. Growth & Des., 3, 675, 2003 D. Das and G. R. Desiraju, Chem. Asian J., 1, 231, 2006 The weak hydrogen bond is an interaction X–H···Y wherein a hydrogen atom forms a bond between two structural moieties X and Y, of which one or even both are of moderate to low electronegativity C–H···O C–H···N O–H···π C–H··· π Os–H···O C–H···Ni Degrees of complexity Supramolecular Synthons Maximise information density With weak interactions both size and complexity increase ome supramolecular synthons O N O O Cl C N H C N N C Cl H C N H N C O C H N H O N H N N H H O H O O N H O N O N O G. R. Desiraju, Angew. Chem. Int. Ed. Engl., 34, 2311, 1995 Br Supramolecular retrosynthesis O I O I N O O I N O O I N O N O O N I N O O O I O N O O I N O V. R. Thalladi et al., Chem. Comm., 401, 1996 I Polymorphism Kinetics and Thermodynamics G. R. Desiraju, Nature Mat., 1, 77, 2002 Efavirenz polymorphs A: Thermodynamic; B and C: Kinetic S. Mahapatra et al., Cryst. Growth Des. 10, 3191, 2010 Phenylacetylene polymorphs T. S. Thakur et al., Cryst. Growth Des. 10, 4246, 2010 Lower level objects may not be the best models for higher entities Universality in the behavior of complex systems often reveals itself in forms that are essentially independent of the details of microscopic dynamics. A representative paradigm of complex behavior in nature is cooperative evolution, seen in structural chemistry as self-assembly and crystallisation (chemical sociology). The interaction of individuals gives rise to a wide variety of collective phenomena that strongly differ from individual dynamics such as demographic evolution, cultural and technological development, and economic activity. Crystal Engineering The Holistic Crystal Students, Post-docs DST, BASF, Rigaku Indian Institute of Science IIAP, AvH Stiftung