Coordination complexes based on pentacyclohexanocucurbit[5]uril and lanthanide(iii) ions: lanthanide contraction effect induced structural variation

Abstract

Eight coordination complexes, {LnCl₂(H₂O)₃Q*[5]}·NO₃·18.5H₂O [isomorphous for Ln = La (1), Ce (2) and Pr (3)], {LnCl₂(H₂O)₂Q*[5]}·NO₃·14H₂O [isomorphous for Ln = Nd (4) and Sm (5)], {Dy(H₂O)₂[Cl ⊂ Q*[5]]Dy(H₂O)₆}·5Cl·20H₂O (6), {LnCl(H₂O)[Cl ⊂ Q*[5]]Ln(H₂O)₆}·4Cl·13H₂O [isomorphous for Ln = Ho (7) and Er (8)], were obtained by reactions of the corresponding lanthanide species with the macrocyclic ligand pentacyclohexanocucurbit[5]uril (Q*[5]) in aqueous solution, and their structures were determined by single-crystal X-ray diffraction. Crystal structure analysis reveals that, in complexes 1–5, each Q*[5] coordinates to one lanthanide(III) ion to form an opened molecular capsule structure, and then adjacent molecular capsules bridge each other to form a 1-D coordination polymer structure, while in complexes 6–8, each Q*[5] coordinates to two lanthanide(III) ions to form a 0-D half-opened molecular capsule structure. These complexes show that their structural variations are ascribed to the effect of lanthanide contraction.