DFT study on the complexation of anions with 1,4,7,10,13,16-hexaazacyclooctodeca-2,5,8,11,14,17-hexaene

Abstract

Macrocyclic compounds have been widely used as anion carriers, as they play important functions in chemical and biological systems. This work reports a theoretical study on free 1,4,7,10,13,16-hexaazacyclooctodeca-2,5,8,11,14,17-hexaene (HAC), as well as its complex with fluoride, chloride, bromide and acetate anions, with and without the presence of the sodium counterion, in the gas phase and implicit solvents (cyclohexane and acetonitrile), at the ωB97X-D/6-311G(d,p) level. The negative ∆G0 values indicate that the crown-anion complex is prone to be formed due to hydrogen bonds in all tested media. Nevertheless, such interactions weaken as the solvent polarity increases. The ΔG0 C6H12 values decrease when the counterion is taken into account, reinforcing the formation of the Na+‒HAC‒X− complex. However, the complexation is disfavored in polar solution, since the presence of the counterion increases the HAC-anion distance. Natural bond orbital analysis, the quantum theory of atoms in molecules and non-covalent interactions methods explored the nature and strength of the hydrogen bond interactions, while spin–spin coupling constant calculations for the fluoride-based complex (1h J F,H(N)) gave insight into the potential of this NMR parameter to experimentally probe the complexation of HAC with fluoride.