Lower Limits on Hydrogen Bond Strength. Charge of Bridging H Atom

While it is usually agreed that a major component in the composition of a H-bond is the electrostatic attraction associated with a positive charge on the bridging H, there has recently arisen some question as to whether a true H-bond can exist when this atom bears a negative charge. Quantum chemical calculations address this question for a variety of potential proton donor molecules where the H atom is bonded to atoms covering a wide range of electronegativity, including the halogen, chalcogen, pnicogen and tetrel families, as well as metal atoms. These molecules are bound to Lewis bases by a variety of noncovalent bonds, including tetrel and halogen bonds, but H-bonds are rare, and exceedingly weak when the H atom does not carry a substantial positive charge.