The Cambridge Structural Database and structural dynamics

Abstract

With the availability of the computer readable information in the Cambridge Structural Database (CSD), wide ranging, largely automated comparisons of fragment, molecular, and crystal structures have become possible. They show that the distributions of interatomic distances, angles, and torsion angles for a given structural fragment occurring in different environments are highly correlated among themselves and with other observables such as spectroscopic signals, reaction and activation energies. The correlations often extend continuously over large ranges of parameter values. They are reminiscent of bond breaking and forming reactions, polyhedral rearrangements, and conformational changes. They map—qualitatively—the regions of the structural parameter space in which molecular dynamics take place, namely, the low energy regions of the respective (free) energy surfaces. The extension and continuous nature of the correlations provides an organizing principle of large groups of structural data and suggests a reconsideration of traditional definitions and descriptions of bonds, “nonbonded” and “noncovalent” interactions in terms of Lewis acids interacting with Lewis bases. These aspects are illustrated with selected examples of historic importance and with some later developments. It seems that the amount of information in the CSD (and other structural databases) and the knowledge on the nature of, and the correlations within, this body of information should allow one—in the near future—to make credible interpolations and possibly predictions of structures and their properties with machine learning methods.

Widening the Scope of Structural Correlations by Means of the van der Waals Crust Penetration Indices: The Dimerization of Groups 11 and 12 L–M–X Halo Complexes

“…One of the fields that has most benefited from the visionary endeavor of Olga Kennard is that of Structure Correlations, successfully explored by Bürgi and Dunitz, − Brammer, , Orpen, and many others, which allows us to interpret the correlation between two structural parameters within a family of related compounds as providing snapshots of chemical reaction pathways . Some paradigmatic examples include the proton transfer reaction showcased by O–H···O hydrogen bonds and the S N 2 nucleophilic substitution mechanism at Sn atoms represented by the structures of X-SnR 3 ···Y, X-SnR 3 -Y, and X···R 3 Sn–Y compounds, where the dotted lines indicate nonbonding short contacts or incipient bonds …”