# “Hydridic Hydrogen-Bond Donors” Are Not Hydrogen-Bond Donors

## TL;DR

This paper argues that hydridic hydrogen-bond donors are not true hydrogen bonds and belong to other types of chemical interactions.

## Contribution

The study provides a new theoretical analysis showing that hydridic hydrogen interactions are not hydrogen bonds but Lewis acid/base interactions.

## Key findings

- Protonic Y–Hδ+ and hydridic Y–Hδ− fragments have fundamentally different bonding mechanisms.
- Hydridic Y–Hδ− fragments are better classified as Lewis acid/base acceptors, not hydrogen-bond donors.
- Redshift in Y–H stretching frequency is not exclusive to hydrogen bonds.

## Abstract

Herein, we dismiss a recent proposal by Civiš,
Hobza, and
co-workers to modify the IUPAC definition of hydrogen bonds in order
to expand the scope from protonic Y–Hδ+ to
hydridic Y–Hδ− hydrogen-bond donor
fragments [J. Am. Chem. Soc.2023, 145, 8550]. Based on accurate Kohn–Sham molecular
orbital (KS-MO) analyses, we falsify the conclusion that interactions
involving protonic and hydridic hydrogens are both hydrogen bonds;
they are not. Instead, our quantitative KS-MO, energy decomposition,
and Voronoi deformation density analyses reveal two fundamentally
different bonding mechanisms for protonic Y–Hδ+ and hydridic Y–Hδ− fragments which
go with charge transfer in opposite directions. On one hand, we confirm
the IUPAC definition for regular hydrogen bonds in the case of protonic
Y–Hδ+ fragments. On the other hand, complexes
involving Y–Hδ− fragments are, in fact,
acceptors in other well-known families of Lewis-acid/base interactions,
such as halogen bonds, chalcogen bonds, and pnictogen bonds. These
mechanisms lead to the same spectroscopic phenomenon in both the Y–Hδ+ and Y–Hδ− fragments,
that is, the redshift in the Y–H stretching frequency, which
is, thus, not an exclusive indicator for hydrogen bonding.