Mining the Cambridge Structural Database for Matched Molecular Crystal Structures: A Systematic Exploration of Isostructurality

The
Cambridge Structural Database (CSD) is the world leading collection
of small-molecule crystal structures and represents an invaluable
resource for crystal engineers. It enables structures to be readily
compared and new insights to be gained from the comparison. In order
to search the database for pairs of structures that are related by
the same chemical transformation, and to systematically investigate
the effect of this transformation on crystal packing, a repository
of matched molecular crystal structures has been derived from the
CSD. This makes it easy to find all pairs of structures differing
by the same chemical change or, alternatively, all available chemical
modifications to a given CSD entry. Our analysis shows one of the
many possible applications of these data. An extensive, yet not exhaustive,
exploration of isostructurality across the entire CSD has been carried
out with the aim of identifying packing features within crystals that
maintain isostructurality. With particular focus on terminal chemical
modifications observed between single-component structures with Z′ equal to 1, packing similarity has been calculated
with an enhanced version of existing software. Across the entire data
set of approximately 125 000 matched molecular pairs, 4% of
the pairs were isostructural. Several cases showed an enrichment with
respect to this baseline value, and examples have been discussed to
illustrate some of the questions which can be asked and how they can
be answered using the data set. This will open up avenues of research
for the future and increase our understanding of the impact of functional
groups on crystal packing.