Crystal engineering: solid state supramolecular synthesis

Crystal structures are built with intermolecular interactions and in this context, there has been a new awareness of the softer, more polarizable variety of hydrogen bonding. Structural robustness derived from N⋯O hydrogen bonding has been established as being responsible for the crystal packing features in several amide and imidazolone families. Intricate topological patterns have been obtained for some trimesic acid derivatives. Crystal engineering has taken a distinct turn towards the design of functionalized solids; materials with useful microporous, chemical and nonlinear optical properties have been reported. At a fundamental level, there is a need to be able to make connections between molecular and supramolecular structure and to achieve general 3D control over crystal packing while, at a practical level, issues such as polymorphism and nonavailability of single crystal samples continue to pose problems.