Tetranuclear Lanthanide Aqua Hydroxo Complexes with Macrocyclic Ligand Cucurbit[6]uril

Abstract

Tetranuclear lanthanide aqua hydroxo complexes with two structural types of core – {Ln4(μ3-OH)4(μ2-OH)4}4+ [Ln = Pr (1), Nd (2), Eu (3), Gd (4), Tb (5)] and {Ln4(μ3-OH)4(μ2-OH)2}6+ [Ln = Er (6), Yb (7)] – were prepared by heating (130 °C) of aqueous solutions of lanthanide(III) chlorides, cucurbit[6]uril (C36H36N24O12, CB[6]), and 4-cyanopyridine. The formation of Ln4 complexes results from the combined influence of the tetradentate coordination of the polycation by the portals of the macrocyclic ligand CB[6] and the chelating effect of the carboxylate ligands of isonicotinic acid generated as a result of hydrolysis of 4-cyanopyridine. X-ray diffraction analysis of 1–7 revealed the sandwich structure with the tetranuclear lanthanide complex situated between two macrocyclic molecules. The compounds were characterized by elemental analysis, IR, and electrospray ionization (ESI) mass spectrometry. Luminescence spectra of 3 and 5 and magnetic properties of 4 were also studied.