New lanthanide–CB[6] coordination compounds: relationships between the crystal structure and luminescent properties

Abstract

The reaction between cucurbit[6]uril (CB[6]) and lanthanide chlorides (Eu, Sm, Tb and Tm) in acidic aqueous media led to four new structures. The compounds obtained are isostructural with general formula [Ln₂(H₂O)₁₂(H₂O@CB[6])]Cl₆(H₂O)₄ (Ln = Eu³⁺ (1), Sm³⁺ (2), Tb³⁺ (3) and Tm³⁺ (4)) and crystallize in the P2₁/c space group. For the complexes with Eu³⁺, Sm³⁺ and Tb³⁺, the luminescent properties in the solid state and aqueous media were explored and all spectroscopic observations are in excellent agreement with the single crystal structure data. The excitation and emission spectra show the typical f–f transitions characteristic of the trivalent lanthanide ions. The transitions ⁷F_J ← ⁵D₁ (J = 0,1,2) in the europium compound and ⁷F_J ← ⁵D₄ (J = 0,1,2) in the terbium compound, not yet reported in lanthanide–CB[n] compounds, were also observed.