Synthesis, characterization, reactivity, and sensing properties of 4-formylbenzoate complexes of copper(II), zinc(II), and cadmium(II) possessing the 1,10-phenanthroline ancillary ligand are studied. The crystal structures of the (1,10-phenanthroline)bis(4-formylbenzoate)(aqua)copper(II) and (1,10-phenanthroline)bis(4-formylbenzo-ate)zinc(II) and a novel molecular complex comprising an assembly of mononuclear and dinuclear species of (1,10-phenanthroline)bis(4-formylbenzoate)cadmium(II) are reported. These zinc and cadmium complexes are fluorescent; they show differentiable sensitivity to detect three positional isomers of nitroaniline. The mechanism of sensing of nitroanilines by 1,10-phenanthroline and the complexes are studied by fluorescence titrations, photoluminescence decay, and dynamic light scattering. A plausible mechanism showing that 1,10-phenanthroline ligand-based emission quenched by electron transfer from the excited state of 1,10-phenanthroline to nitroaniline is supported by density functional theory calculations. In an anticipation to generate a fluorescent d10-copper(I) formylbenzoate complex by a mild reducing agent such as hydroxylamine hydrochloride for similar sensing of nitroaromatics as that of the d10-zinc and cadmium 4-formylbenzoate complexes, reactivity of d9-copper(II) with hydroxylamine hydrochloride in the presence of 4-formylbenzoic acid and 1,10-phenanthroline is studied. It did not provide the expected copper(I) complex but resulted in stoichiometry-dependent reactions of 4-formylbenzoic acid with hydroxylamine hydrochloride in the presence of copper(II) acetate and 1,10-phenanthroline. Depending on the stoichiometry of reactants, an inclusion complex of bis(1,10-phenanthroline)(chloro)copper(II) chloride with in situ-formed 4-((hydroxyimino)methyl)benzoic acid or copper(II) 4-(hydroxycarbamoyl)benzoate complex was formed. The self-assembly of the inclusion complex has the bis(1,10-phenanthroline)(chloro)copper(II) cation encapsulated in hydrogen-bonded chloride-hydrate assembly with 4-((hydroxyimino)methyl)benzoic acid.

Solid-state and solution studies were carried out to reveal the interactions of tetrabutylammonium halides with a sulfadiazine-derived urea, namely 4-{[(4-nitrophenyl)carbamoyl]amino}-N-(pyrimidin-2-yl)benzene-1-sulfonamide, influencing the selectivity in the optical detection of fluoride ions in solution. The self-assemblies of two dimethylformamide (DMF) solvates, three ionic cocrystals, and a salt of the sulfadiazine-derived urea were studied. Both solvates had one DMF molecule anchored by bifurcated hydrogen bonds with the urea moiety, whereas the 1:2 solvate had the second DMF in the interstitial spaces. The structures of the three isostructural ionic cocrystals, namely the tetrabutylammonium halide 4-{[(4-nitrophenyl)carbamoyl]amino}-N-(pyrimidin-2-yl)benzene-1-sulfonamide, where halide is chloride, bromide, and iodide, respectively, were determined. However, the corresponding ionic cocrystal was not formed with tetrabutylammonium fluoride; it afforded the salt tetrabutylammonium (4-{[(4-nitrophenyl)carbamoyl]amino}benzene-1-sulfonyl)-(pyrimidin-2-yl)azanide, which was also structurally characterized. Each ionic cocrystal had charge-assisted hydrogen bonds between the respective halide ion and the N−H bonds of the urea moiety. Homodimeric synthons of the parent compound were observed in the ionic cocrystals; hence, the geometrical adjustment of the dimeric synthons due to the slight changes in the angular shape of the host has the prime role of making available room with the required extra space to accommodate the spherical halide ions with different ionic radii. The fluoride, being basic, caused deprotonation to provide the salt. 1 H NMR and UV−visible spectroscopy was used to discern hydrogen bonds formed by the sulfadiazine-based urea with different halides and the deprotonation by tetrabutylammonium fluoride.

Two polymorphs of a dimethylformamide solvate of the N-(5-methyl-1,2-oxazol-3-yl)-4-{[(4-nitrophenyl)carbamoyl]amino}benzene-1-sulfonamide (HSMZU) were studied to elucidate their structures, thermal stability and desolvation. The two synthon polymorphs of the solvate had distinguishable assemblies...