Faster Synthesis of Beta-Diketonate Ternary Europium Complexes: Elapsed Times & Reaction Yields

Abstract

β-diketonates are customary bidentate ligands in highly luminescent ternary europium complexes, such as Eu(β-diketonate)3(L)2, where L stands for a nonionic ligand. Usually, the syntheses of these complexes start by adding, to an europium salt such as EuCl3(H2O)6, three equivalents of β-diketonate ligands to form the complexes Eu(β-diketonate)3(H2O)2. The nonionic ligands are subsequently added to form the target complexes Eu(β-diketonate)3(L)2. However, the Eu(β-diketonate)3(H2O)2 intermediates are frequently both difficult and slow to purify by recrystallization, a step which usually takes a long time, varying from days to several weeks, depending on the chosen β-diketonate. In this article, we advance a novel synthetic technique which does not use Eu(β-diketonate)3(H2O)2 as an intermediate. Instead, we start by adding 4 equivalents of a monodentate nonionic ligand L straight to EuCl3(H2O)6 to form a new intermediate: EuCl3(L)4(H2O)n, with n being either 3 or 4. The advantage is that these intermediates can now be easily, quickly, and efficiently purified. The β-diketonates are then carefully added to this intermediate to form the target complexes Eu(β-diketonate)3(L)2. For the cases studied, the 20-day average elapsed time reduced to 10 days for the faster synthesis, together with an improvement in the overall yield from 42% to 69%.

Europium complexes: choice of efficient synthetic routes from RM1 thermodynamic quantities as figures of merit

“…15 Syntheses of lanthanide complexes are frequently carried out by means of ligand displacement reactions. In particular, ternary b-diketonate europium complexes [Eu(b) 3 (L) 2 ], where L stands for a non-ionic ligand, can be prepared by the usual synthetic route: 12,13,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]…”

“…Alternatively, this sequence of reactions can be inverted, with the addition of non-ionic ligands occurring in the rst step. This is the essence of the faster synthetic route introduced by us 17 for the preparation of may take a much longer time to crystallize. 17 The synthesis of [Eu(b) 3 (L) 2 ] performed in this manner leads to faster overall reaction times and larger overall reaction yields.…”

“…This is the essence of the faster synthetic route introduced by us 17 for the preparation of may take a much longer time to crystallize. 17 The synthesis of [Eu(b) 3 (L) 2 ] performed in this manner leads to faster overall reaction times and larger overall reaction yields. 17 Comparing the two synthetic routes to prepare ternary complexes of type [Eu(b) 3 (L) 2 ], we verify that the usual route can be described as a sequence of two reactions, in which the ion complex always has the same coordination number, in this case, coordination number 8.…”

“…17 The synthesis of [Eu(b) 3 (L) 2 ] performed in this manner leads to faster overall reaction times and larger overall reaction yields. 17 Comparing the two synthetic routes to prepare ternary complexes of type [Eu(b) 3 (L) 2 ], we verify that the usual route can be described as a sequence of two reactions, in which the ion complex always has the same coordination number, in this case, coordination number 8. However, the ligand displacement reactions of the faster synthesis, advanced by our research group, are more difficult to treat theoretically because, in the rst step, the complex reactant […”

“…Since the RM1 model is capable of introducing some covalency in the coordinated bonds, the rational is that it should then be possible to assume that the gures of merit follow the trends in the thermodynamic quantities of different types of ligand displacement reactions, including reactions that are non-isodesmic, non-isogyric, and nonisocoordinate, such as the ones that occur in the two steps of the faster synthesis of complexes of the type [Eu(b) 3 (L) 2 ]. 17 We start by addressing the overall reactions to prepare complexes of the type [Eu(b) 3 (L,L 0 )] in order to expose the coordination bond strengths of both ionic and non-ionic ligands involved. 13 Equipped with the insights thus obtained, we nally carry out a complete a priori RM1 theoretical assessment of six possibilities of synthetic routes for the preparation of the completely mixed ionic ligand complex, [Eu(DBM)(BTFA)(TTA)(TPPO) 2 ].…”