Chains, Layers, Channels, and More: Supramolecular Chemistry of Potent Diphosphonic Tectons with Tuned Flexibility. The Generation of Pseudopolymorphs, Polymorphs, and Adducts

Naphthalene-1,5-diphosphonic acid
[C10H6(PO3H2)2, H4NDP­(1,5), 1] and its more flexible counterpart,
naphthalene-1,5-bis­(methylphosphonic)
acid [C10H6(CH2PO3H2)2, H4NDP­(1C,5C), 2], have
been synthesized, characterized, and used as building blocks in supramolecular
assemblies with 4-(N,N-dimethylamino)­pyridine
(DMAP) and morpholine. The two acids generate two distinct solvatomorphs
each, with and without dimethyl sulfoxide (DMSO) molecules. The two
adducts of H4NDP­(1,5) with DMAP (3A and 3B) reveal conformational polymorphism caused by the rotation
of phosphonic groups. The two adducts of H4NDP­(1C,5C) show
unexpected structural diversity, generating a symmetric hydrogen bond
and creating a layered structure, 4A, or a channel structure, 4B. The adducts of both acids with morpholine (5A and 5B) allow for observing the influence of the conformational
flexibility of the acids on the dimensionality of a final hydrogen
bond network, which is in general higher for H4NDP­(1C,5C).
The structural motifs and trends are analyzed in terms of the geometric
criteria of these interactions. For the first time, Hirshfeld surface
analysis has also been applied for the investigation of supramolecular
interactions of phosphonic acids in different protonation states.