Highs and lows of bond lengths: Is there any limit?

Abstract

We argue that two distinct points on the potential energy curve (PEC) of a pairwise interaction, the zero‐energy crossing point and the point where the stretching force constant vanishes, allow to anticipate the range of possible distances one can expect between two atoms in diatomic, molecular moieties and crystalline systems. We show that these bond stability boundaries are unambiguously defined and correlate with topological descriptors of electron density‐based scalar fields, and we put forward a practical method to calculate them easily using generic PECs. Chemical databases and quantum‐mechanical calculations are used to analyze a full set of diatomic bonds of atoms from the s‐p main block. Emphasis is placed on the effect of substituents in C‐C covalent bonds, concluding that distances shorter than 1.14 Å or longer than 2.0 Å are unlikely to be achieved, in agreement with ultra‐high‐pressure data and transition state distances, respectively. Presumed exceptions, often due to changes in the reference state or ill‐defined dissociation energies (e.g. O 2 2+ ), are used to place our model in the correct framework and to formulate a conjecture for chained‐interactions, which offers a first explanation for the multimodal histogram of O‐H distances reported for hundreds of chemical systems.