Relationships between Bond Strength and Spectroscopic Quantities in H-Bonds and Related Halogen, Chalcogen, and Pnicogen Bonds.

A large number of systems were studied that contain either a H-bond (HB) or the closely related halogen (X), chalcogen (Y), or pnicogen (Z) bond. Many of the same relationships between the strength of the HB and spectroscopic parameters apply as well to the other noncovalent bonds. There is a very nearly linear relationship between the interaction energy and the red shift that occurs within the stretching frequency of the pertinent F-A covalent bond of the Lewis acid (where A refers to H, X, Y, or Z). This vibrational mode also undergoes an intensification in all of these bond types, but this quantity is slightly less indicative of the bond strength for XB, YB, and ZB than it is for HB. On the other hand, most of the various noncovalent bonds display a better relationship between energetics and NMR chemical shifts than do the H-bonds, highly auspicious for the use of NMR spectra in diagnosing the presence and strengths of these bonds. An important element in NMR chemical shifts is the internal geometry change induced by complexation.