Supramolecular polymorphism of the 1:1 molecular salt (adamantane-1-carboxylate-3,5,7-tricarboxylic acid)·(hexamethylenetetraminium). A "failed" crystal engineering attempt.

The tetrahedral arrangement of hydrogen bonding donor and acceptor groups is used to rationalise the design of a diamondoid network; however, a single proton transfer renders the four sites inequivalent, and results in two polymorphs of the title molecular salt utilizing similar intermolecular synthons.