Hydrogen bond
Hydrogen bonds can be intermolecular (occurring between separate molecules) or intramolecular (occurring among parts of the same molecule). Depending on the nature of the donor and acceptor atoms which constitute the bond, their geometry, and environment, the energy of a hydrogen bond can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, and weaker than fully covalent or ionic bonds. This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins.
N-heterocyclic silylene
Atoms in Molecules bond energy at critical point calculations show that the N to Si bonds in an NHSi are significantly ionic, unlike the highly covalent N-C bond in an NHC. Furthermore, the charge density and the Laplacian (∇) at the bond critical points between the silylene and carbene are dissimilar. Silylenes have much lower charge density between Si and N, with a positive Laplacian from Si to N indicating a more ionic interaction, while the Laplacian is negative going from carbon to nitrogen in an NHC indicating a more covalent bond. Upon coordination to a Group 11 metal the covalent character in the Si or C to metal bond is small, but not insignificant, again with a higher covalent character in the carbenic system. Similarly, silicon has a higher Laplacian between it and the group 11 metals than does carbon, indicating a less covalent metal interaction in silyenes as compared to carbenes.