Coordination nanotubes self-assembled from cucurbit[7]uril and lanthanide cations

Abstract

A series of complexes based on the macrocyclic ligand cucurbit[7]uril (Q[7]) with formulas {La₂(H₂O)₁₂Q[7]}·2(ZnCl₄)·2Cl·31H₂O (1), {Ln₂(H₂O)₁₂Q[7]}·2(ZnCl₄)·2Cl·xH₂O [isomorphous with Ln = Ce (2), Pr (3) and Nd (4), x = 25 (2), 29 (3) and 25 (4)], and {Ln₂(H₂O)₁₀Q[7]}·2(ZnCl₄)·2Cl·xH₂O [isomorphous with Ln = Sm (5), Gd (6), Tb (7), Er (8), Tm (9), Yb (10) and Lu (11), x = 24 (5), 27 (6), 27 (7), 33 (8), 27 (9), 18 (10) and 29 (11)], have been synthesized by the self-assembly of Q[7] with the corresponding lanthanide species in the presence of ZnCl₂. The single-crystal X-ray diffraction analyses reveal that the eleven complexes are separated into three types of coordination nanotubes given different coordination environments of the lanthanide(III) ions. The eleven complexes display interesting structural progressions, which are mainly ascribed to the effect of lanthanide contraction. Their thermal and IR properties were also examined.