A few years back, I did a post about the Pirkle reagent[cite]10.1039/c39910000765[/cite] and the unusual π-facial hydrogen bonding structure[cite]10.1039/P29940000703[/cite] it exhibits. For the Pirkle reagent, this bonding manifests as a close contact between the acidic OH hydrogen and the edge of a phenyl ring; the hydrogen bond is off-centre from the middle of the aryl ring.

If H3N+-O– is viable compared with its tautomer H2N-OH when carrying water bridges, then why not try H2O+-O– vs HO-OH? https://orcid.org/0000-0002-8635-8390

In the previous post I described how hydronium hydroxide or H3O+…HO–, an intermolecular tautomer of water, has recently been observed captured inside an organic cage[cite]10.1002/chem.201406383[/cite] and how the free-standing species in water can be captured computationally with the help of solvating water bridges.

This is a corollary to the previous post ^‡ exploring how many molecules are needed to ionise HCl. Here I am asking how many water molecules are required to form the ionic ammonium hydroxide from ammonia and water.