The role of weak interactions in self-assembly of supramolecular associations of benzothiazole derivatives and their coordination compounds

Abstract

New benzothiazole derivatives and their transition metal coordination compounds were synthesized and structurally characterized. The participation of weak interactions, as H-bonding, π-stacking, O → S, N → S and S lone pair···π, on the stabilization of their supramolecular assemble was analyzed. The bis-benzothiazole (ebbtz) derivative was obtained from the reaction of benzothiazole-2-carboxaldehyde and ethylenediamine. When reacting this ligand with copper(II) chloride, an electrophilic addition of methanol, as a methoxy group, gave place to the amino ether derivative on the coordination compound [Cu(MeO-ebbtz)Cl]Cl·4H2O. The supramolecular arrangement of this compound is stabilized by H-bonding, O → S, N → S, lp(S)···π and π-stacking interactions. Whereas, from the reaction in situ of benzothiazole-2-carboxaldehyde, ethylenediamine and copper(II) bromide, the polymeric [Cu2(µ-Br)3(ebtz)Br]n compound was obtained. In this compound, the copper(II) atoms present two different geometries, tetrahedral and octahedral, where a 3D assembly is driven by lp(S)···π and π···π stacking. Two isostructural [M(H2O)2(CH3OH)4]·2(prbtz) (M = CoII and NiII) compounds and a polymeric sodium complex were obtained with 3-(benzothiazol-2-ylthio)-1-propanesulfonate (prbtz). In the [Na2(prbtz)2(H2O)2µ-(H2O)]n polymer, the prbtz− is bound to the metal ion in a bent conformation, presenting a supramolecular arrangement stabilized by H-bonding, N → S, T-shape and lp(S)···π interactions. On the other hand, in the [M(H2O)2(CH3OH)4]·2(prbtz) compounds, prbtz− co-crystallized, presenting an extended conformation, mainly with lp(S)···π interactions. Additionally, theoretical calculations on the association between two ebbtz molecules, were performed. The results indicate that these molecules have a binding energy of 79.49 kJ/mol promoted by lp(S)···π and π···π stacking interactions, taking place at the frontier LUMO and HOMO molecular orbitals.