(BMI)_3LnCl_6 Crystals as Models for the Coordination Environment of LnCl_3 (Ln = Sm, Eu, Dy, Er, Yb) in 1-Butyl-3-methylimidazolium Chloride Ionic-Liquid Solution

摘要

A series of (BMI)_3LnCl_6 (Ln = Sm, Eu, Dy, Er, Yb) crystals was prepared from solutions of LnCl_3 dissolved in the ionic liquid, 1-butyl-3-methylimidazolium chloride (BMICl). Crystals with Ln = 5% Sm + 95% Gd and with Ln = 5% Dy + 95% Gd were also grown to assess the importance of cross-relaxation in the Sm and Dy samples. The crystals are isostructural, with monoclinic space group P21/c and four formula units per unit cell. The first coordination sphere of Ln~(3+) consists of six Cl~- anions forming a slightly distorted octahedral LnCl_6~(3-) center. The second coordination sphere is composed of nine BMI~+ cations. The emission spectra and luminescence lifetimes of both (BMI)_3LnCl_6 crystals and LnCl_3 in BMICl solution were measured. The spectroscopic similarities suggest that crystalline (BMI)_3LnCl_6 provides a good model of the Ln~(3+) coordination environment in BMICl solution.