Anion control in the complexation of cucurbit[6]uril with Cu(II) salts

Abstract

Based on the coordination ability of SCN−, Cl− and NO3–, three coordination complexes, namely, (C36H36N24O12)·{Cu[(SCN)4(H3O)]}2·2(H3O)·35H2O (1), {(C36H36N24O12)·[CuCl(H2O)3]2}·2Cl·10H2O (2), {(C36H36N24O12)·Cu2(H2O)5}·2(NO3)·2Cl·7H2O (3), have been synthesized through the reaction of cucurbit[6]uril (Q[6]) with transition metal ion Cu(II) at different anion conditions. In the structure of complex 1, the thiocyanate anion preferentially coordinate with the Cu(II) ion, which disables the Cu(II) ion to coordinate directly with the Q[6]. For the complex 2, the chloride anion enhances the coordination ability of the Q[6] to the Cu(II) ion, resulting a coordination tube of Q[6] with Cu(II) ion. In the case of complex 3, in the presence of the noncoordinating nitrate anion, the Cu(II) ion coordinate directly with the Q[6], generating a discrete binuclear complex. These structures unequivocally indicate that the coordinative nature of the anions is the key factor controlling the complexation of Q[6] with Cu(II) ion.