Here, we report the determination of acidity constants of eight amino amides through the use of Nuclear Magnetic Resonance (NMR) to carry out the selective crystallization of diprotonated (a), monoprotonated (b), and neutral species (c) derived from these compounds. Crystallographic studies of compounds 2 a, 6 a, 7 a, 8 a, 2 b, 3 b, 6 b and 2 c revealed that the presence of substituents at the C8 and C10 positions determines the conformation of the molecule regardless of its degree of protonation. Although diprotonated species (a) have the same conformation and similar hydrogen bonding patterns, the supramolecular structures of these compounds are different. Furthermore, chloride ions and solvent molecules play an outstanding role in stabilizing the supramolecular structure of these compounds. This phenomenon restricts the π⋅⋅⋅π interactions between benzimidazole groups and consequently limits the possibility of aggregation in amino amides 1-8.
We report the synthesis of eight indium coordination compounds derived from amino amides 1-8 and InCl 3 . Crystallographic and NMR studies revealed the unusual chelation coordination of the metal ion to the amine and carbonyl groups of the ligands. However, vibrational studies evidenced the presence of formation-breaking equilibria of the C=O!In 3 + coordination bond. Thus, as chelate structures predominate in methanol solutions, In 3 + compounds with open structures prevail in aqueous solutions. Moreover, the Raman spectroscopy and crystallography studies of 2 c and 6 c corroborated that the substitution of a chlorine ion by a methanol molecule in these coordination compounds is feasible and that the interchange equilibrium [HL]InCl 4 + MeOH⇄[L][MeOH]InCl 3 + HCl is present in methanolic solutions. UV spectroscopy proves that the [HL]InCl 4 compounds predominates in methanol solutions. However, fluorescence spectroscopy shows the presence of significant quantities of [L][MeOH]InCl 3 that reduce the intensity of the signals. The formation-breaking and interchange equilibria could facilitate the biological interchange of In 3 + using coordination compounds 1 c-8 c.
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