Adducts formed by tetrahedral anions and protonated forms of 1,4,7-triazacyclononane: competition with chloride anions

Abstract

Five adducts formed by 1,4,7-triazacyclononane ([9]aneN₃, L) and four tetrahedral anions have been crystallized from aqueous solutions containing (H₃L)Cl₃ and the appropriate acid, viz. (H₃L)(CuCl₄)Cl·H₂O (1), (H₃L)(ClO₄)Cl₂ (2), (H₃L)(HSO₄)Cl₂ (3), (H₃L)(HSO₄)₂Cl (4) and (H₃L)(H₂PO₄)₃ (5). Their X-ray crystal structures have provided an indication of the stable conformations of the protonated macrocycles and its binding preferences when faced with the option of two different anions as guests. The inclusion of competitive anions (such as phosphate and sulfate) with greater hydrogen bonding abilities has the effect of excluding chloride from the lattice in favor of the formation of more highly connected networks. Also revealed are the tendencies of the anions and macrocycles to form supramolecular architectures through hydrogen bonding and electrostatic interactions, such a tripodal co-ordination pyramid formed by chloride anions and η-2 chelation by the macrocycle of a single oxygen on hydrogen sulfate and hydrogen phosphate anions. The series shows hydrogen bonded 2D sheets, 3D networks and an isolated (HSO₄⁻)₄ cluster is found in 4.