On the lack of correlation between bond lengths, dissociation energies, and force constants: the fluorine-substituted ethane homologues

Martin Kaupp, Sebastian Riedel, "On the Lack of Correlation between Bond Lengths, Dissociation Energies and Force Constants. The Fluorine-Substituted Ethane Homologues" Inorg. Chim. Acta 2004, 6, 1865 - 1872.

Accurate ab initio coupled-cluster (CCSD) calculations have been used to evaluate systematically the E–E bond lengths, homonuclear dissociation energies, and force constants of a series of fluorine-substituted ethane homologues H₃−_nF_nE–EH₃−₃F_n (n=0–3), H₃E–EF₃, and H₃E–EH₂F (E=C, Si, Ge, Sn) in their staggered ethane-like conformations. The pronounced lack of correlation between bond lengths, dissociation energies, and force constants observed previously with E=Sn has also been found for the lighter group 14 homologues. However, each element in the group exhibits a different behavior. Attempts are made to interpret the findings in the context of electronegativity, hybridization defects, as well as negative and geminal hyperconjugation.

There is no physical law that bond lengths, dissociation energies, or force constants necessarily have to correlate, even though this is generally assumed in interpretation of molecular structure. This work provides accurate coupled-cluster ab initio results for simple group 14 ethane homologues that clearly demonstrate the almost complete absence of correlations between the three indicated quantities. Electronic structure analyses are used to provide explanations for the computational results.