# Strongest hydrogen bond between neutral molecules?

It is known that very strong hydrogen bonds can occur in charged systems, such as $\ce{[F-}\ce{-H+-F-]}$, while hydrogen bonds in neutral systems are much weaker in comparison.

What is the strongest known hydrogen bond within the following specifications?

• both donor and acceptor monomers are neutral, and remain neutral upon association (no ionic bridges);
• heterodimers are allowed (e.g. hydrogen fluoride and ammonia);
• must be a single-site hydrogen bond - excluding dimers stabilized by multiple hydrogen bonds such as nucleobase pairs.
• Well, you should change "possible" to known, otherwise it's speculation. – Mithoron Feb 7 '18 at 0:11
• Also this: chemistry.stackexchange.com/questions/47346/… is highly relevant here. – Mithoron Feb 7 '18 at 0:12
• This sounds like it could be a good target for design golf... – Nicolau Saker Neto Feb 7 '18 at 0:54
• It probably is $\ce{HF}$ and $\ce{NH3}$. It's hard to get a better donor and acceptor pair than that. It's always possible one could find some very obscure system where a hydrogen becomes quite positively charged, but for small molecules I'd be surprised if something beats $\ce{HF}$ and $\ce{NH3}$. – jheindel Feb 9 '18 at 7:04