Synthesis, Structure, and Topological Studies of Solvates and Salts of a Chiral Zwitterionic Host N‑(2-Imidazol-5-yl-1-carboxyethyl)-1,8-naphthalimide

A chiral carboxylic acid, (−)-N-(2-imidazol-5-yl-1-carboxyethyl)-1,8-naphthalimide (Hbnap), bearing imide and imidazole functionalities with some structural relevance to tryptophan and histidine amino acids, was designed. Various solvates and salts of Hbnap were synthesized and structurally characterized, namely, Hbnap·H₂O (1), 4Hbnap­·MeOH­·3H₂O (2), Hbnap·DMSO {DMSO = dimethyl sulfoxide} (3), Hbnap·DMF {DMF = N,N′-dimethylformamide} (4), Hbnap·DMA {DMA = N,N′-dimethylacetamide} (5), Hbnap­·2quinoline (6), Hbnap­·pyridine (7), bnap·Hdbu·2H₂O {dbu = 1,8-diazabicyclo­[5.4.0]­undec-7-ene} (8), [H₂bnap]­Br­·0.5MeOH (9), [H₂bnap]­I­·0.5MeOH (10), [H₂bnap]₂SO₄­·DMF­·H₂O (11), and [H₂bnap]­NO₃ (12). Their packing patterns were analyzed in detail, showing that an interplay of hydrogen bonds, aquation, and π-stacking control the formation of distinct one-, two-, or three-dimensional (1D, 2D, or 3D) supramolecular assemblies. The H-bonded 2D underlying networks of solvates 1–8 were topologically classified revealing three distinct topological types, namely, an undocumented topology in 1 and the 3,4L127 and skl topologies in 2 and 3–8, respectively. In contrast, the [H₂bnap]⁺ salts 9–12 show H-bonded underlying networks that are quite distinct not only in the topology (2C1 in 9 and 10, kgd in 11, and lon in 12) but also in the dimensionality that increases from 1D in halide salts 9 and 10 to 2D in sulfate derivative 11 and 3D in nitrate compound 12. Thermogravimetric analysis studies on the removal of DMSO, DMA, and dbu show that packing by the zwitterionic form of the Hbnap host and the formation of salts impede the elimination of solvent in comparison with conventional hydrogen bonded hosts. UV–vis and fluorescence emission studies were also performed showing that different solvates and salts exhibit strong emission bands with distinct maxima in the 428–487 nm region. A significant enhancement of the fluorescence intensity in comparison with the free Hbnap host molecule occurred in all compounds.