Crystal engineering in IUCrJ 2021: interactions, structures, properties

In 1989, I wrote that crystal engineering is the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding in the design of new solids with desired physical and chemical properties It is interesting to note that just about every one of the 25 odd papers in the chemistry and crystal engineering section of IUCrJ in 2021 continues to deal with themes like interactions, structure and properties taken in the broadest sense. There is increasing appreciation of the fact that a crystal structure is not a unique or distinguishing property of a molecule. A single molecule may have many crystal structures and some of these may be only stable under unusual temperature and pressure conditions. There may be others that only have an existence in silico at least at the present time. Papers have been published that deal with structures under extra-terrestrial conditions, under high pressures and elevated temperatures. Papers on polymorphs especially polymorphs of drugs continue to be popular as also are those that deal with clusters, which may be precursors for crystals for, in the end, the Holy Grail of crystal engineering is to find a general solution to the problem: Given the molecular structure of a compound what are all the possible crystal structures? The crystal engineering papers straddle conventional vertical classifications such as organic chemistry, inorganic chemistry, materials chemistry and nanochemistry indicating that these new ways of looking at traditional subjects might offer better and quicker solutions to problems related to complexity, emergence and other multivariate phenomena in the world of molecular crystals.