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Crystal engineering: Structure, design and function
Current Opinion in Solid State and Materials Science 13 (2009) 35
Contents lists available at ScienceDirect
Current Opinion in Solid State and Materials Science journal homepage: www.elsevier.com/locate/cossms
Editorial overview
Crystal engineering: Structure, design and function Crystal engineering is arguably one of the more contemporary areas of chemical research today. A large number of groups worldwide are engaged in strenuous efforts at designing new structures for molecular solids, of both the organic and metal–organic variety. These structures are, ideally, associated with specific physical and chemical attributes that range from absorption of ions, gases and solvents to mechanical, magnetic, electronic and optical properties or specific novel features that lend themselves to patentability. This last feature is especially noteworthy in the category of compounds known as active pharmaceutical ingredients—drugs and medicinal compounds in common parlance. Crystal engineering is developed and structured around three distinct and yet interconnected themes: (i) the study of intermolecular interactions, which one might liken to supramolecular glue; (ii) the use of these interactions in developing design strategies for the construction of a particular crystal architecture; and (iii) the optimization of specific crystal properties that depend on the structure. The six reviews in this special issue concentrate on recent developments (typically within the last two years) in some important areas of crystal engineering. Fourmigué describes halogen bonding, an interaction type that is similar to hydrogen bonding but where the electrophilic species is not a hydrogen but a halogen atom. Natarajan, Mukherjee and Custelcean describe various facets of the crystal chemistry of co-ordination polymers. Within the subject of crystal engineering, the study of co-ordination polymers remains by far one of the more popular aspects and there are many ramifications of these varied and interesting structures; in these three reviews, host–guest effects, magnetic properties and anion separation are highlighted, respectively. Bharadwaj reviews recent work on hydrates, and also with reference to co-ordination
1359-0286/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.cossms.2009.07.001
polymers; it has been said that in a chemical context water goes beyond being a molecule and that it moves to the level of a philosophical abstraction. With relevance to crystal engineering, water is a very potent species. It is small but supramolecularly very active. There seems to be no end to the types of water. . .water geometries that are found in crystals. Water, it seems, plays not only a static structural role in these cases but perhaps also a functional role that is related to dynamics. These aspects are more pronounced of course in the crystals of biological macromolecules. The final review by Bond describes the enigmatic but evergreen topic of polymorphism. Why do some compounds crystallise in more than one crystal form? What constitutes a difference in crystal structure? How can one control the formation of polymorphs? These questions continue to baffle and challenge us even as the crystal engineer searches for a more complete answer to the riddle of the crystallisation mechanism. Taken together, these reviews constitute a concise summary of some fast moving areas of crystal engineering and it is hoped that this collection will be of use to established practitioners as well as to beginners and students of the subject. Gautam R. Desiraju Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India; Tel.: +91 80 22933311; fax: +91 80 23602306. E-mail address: [email protected] Received 13 July 2009 Accepted 13 July 2009
Contents lists available at ScienceDirect
Current Opinion in Solid State and Materials Science journal homepage: www.elsevier.com/locate/cossms
Editorial overview
Crystal engineering: Structure, design and function Crystal engineering is arguably one of the more contemporary areas of chemical research today. A large number of groups worldwide are engaged in strenuous efforts at designing new structures for molecular solids, of both the organic and metal–organic variety. These structures are, ideally, associated with specific physical and chemical attributes that range from absorption of ions, gases and solvents to mechanical, magnetic, electronic and optical properties or specific novel features that lend themselves to patentability. This last feature is especially noteworthy in the category of compounds known as active pharmaceutical ingredients—drugs and medicinal compounds in common parlance. Crystal engineering is developed and structured around three distinct and yet interconnected themes: (i) the study of intermolecular interactions, which one might liken to supramolecular glue; (ii) the use of these interactions in developing design strategies for the construction of a particular crystal architecture; and (iii) the optimization of specific crystal properties that depend on the structure. The six reviews in this special issue concentrate on recent developments (typically within the last two years) in some important areas of crystal engineering. Fourmigué describes halogen bonding, an interaction type that is similar to hydrogen bonding but where the electrophilic species is not a hydrogen but a halogen atom. Natarajan, Mukherjee and Custelcean describe various facets of the crystal chemistry of co-ordination polymers. Within the subject of crystal engineering, the study of co-ordination polymers remains by far one of the more popular aspects and there are many ramifications of these varied and interesting structures; in these three reviews, host–guest effects, magnetic properties and anion separation are highlighted, respectively. Bharadwaj reviews recent work on hydrates, and also with reference to co-ordination
1359-0286/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.cossms.2009.07.001
polymers; it has been said that in a chemical context water goes beyond being a molecule and that it moves to the level of a philosophical abstraction. With relevance to crystal engineering, water is a very potent species. It is small but supramolecularly very active. There seems to be no end to the types of water. . .water geometries that are found in crystals. Water, it seems, plays not only a static structural role in these cases but perhaps also a functional role that is related to dynamics. These aspects are more pronounced of course in the crystals of biological macromolecules. The final review by Bond describes the enigmatic but evergreen topic of polymorphism. Why do some compounds crystallise in more than one crystal form? What constitutes a difference in crystal structure? How can one control the formation of polymorphs? These questions continue to baffle and challenge us even as the crystal engineer searches for a more complete answer to the riddle of the crystallisation mechanism. Taken together, these reviews constitute a concise summary of some fast moving areas of crystal engineering and it is hoped that this collection will be of use to established practitioners as well as to beginners and students of the subject. Gautam R. Desiraju Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India; Tel.: +91 80 22933311; fax: +91 80 23602306. E-mail address: [email protected] Received 13 July 2009 Accepted 13 July 2009