Yttrium and lanthanide (Ln = La and Gd) complexes with cucurbit[10]uril: crystals transforming from supramolecular frameworks to coordination nanotubes

Abstract

We report the synthesis and characterization of yttrium (Y³⁺) and lanthanide (Ln = La³⁺ and Gd³⁺) complexes with cucurbit[10]uril (Q[10]) via a self-assembly approach in a 6 M HCl solution. Crystals transforming from the initially formed two-dimensional (2D) supramolecular frameworks to 1D coordination nanotubes were observed. The coordination of Y³⁺ ions with Q[10] first led to the formation of a compound, {Y₄(H₂O)₂₄(Q[10])₃}·12Cl·4H₂O (Q[10]-Y1), with a 2D supramolecular structure built up with an octanuclear complex and metal-free Q[10] via extensive second-shell interactions. Through crystals transforming, Q[10]-Y1 gradually transformed to another compound, {Y₆(H₂O)₂₀(Q[10])}·18Cl·9H₂O (Q[10]-Y2), with a 1D nanotube structure. Similar crystals transforming from supramolecular frameworks to 1D coordination nanotubes (Q[10]-La and Q[10]-Gd) were also observed in La³⁺ and Gd³⁺ complexes with Q[10], suggesting the unique phenomenon is a common feature in the self-assembly of Q[10] complexes with lanthanide ions. The crystal structures of these compounds were revealed by synchrotron single crystal X-ray diffraction and compared to the existing lanthanide and actinide complexes with Q[10].