Marmodée Bettina, de Klerk Joost S, Ariese Freek, Gooijer Cees, Kumke Michael U
Institute of Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam-Golm, Germany.
Anal Chim Acta. 2009 Oct 12;652(1-2):285-94. doi: 10.1016/j.aca.2009.06.006. Epub 2009 Jun 9.
Eu(III) luminescence spectroscopy, both in the steady-state and the time-resolved mode, is an appropriate technique to study the properties of complexes between heavy metal ions and humic substances (HS), which play a key role in the distribution of metal species in the environment. Unfortunately, room temperature luminescence spectra of Eu(III) complexes with aromatic and aliphatic carboxylic acids - model compounds of HS binding sites - are too broad to fully exploit their potential analytical information content. It is shown that under cryogenic conditions fluorescence-line-narrowing (FLN) is achieved, and the highly resolved spectra provide detailed information on the complexes. Ten model ligands were investigated. Total luminescence spectra (TLS) were recorded, using the (5)D(0)<--(7)F(0) transition for excitation and the (5)D(0)-->(7)F(1) and (5)D(0)-->(7)F(2) transitions for emission. The energy of the excitation transition depends on the ligand involved and the structure and composition of the complex. For most ligands, discontinuities in the high-resolution TLS indicated that more species, i.e. distinct complex structures, coexisted in the sample. Selective excitation was performed to measure the species-associated luminescence decay times tau. The latter strongly depend on nearby OH oscillators from coordinating water molecules or ligand hydroxyl groups. Furthermore, the asymmetry ratios r, defined as the intensity ratio of the (5)D(0)-->(7)F(2) and (5)D(0)-->(7)F(1) transitions, were calculated and the variation of the excitation energy E(exc) with the splitting of the (7)F(1) triplet (DeltaE) was determined, which yielded the crystal field strength parameter N(nu)(B(2q)), as well as the crystal field parameters B(20) and B(22). An in-depth analysis of the results is presented, providing detailed information on the number of coexisting complexes, their stoichiometry, the number of water molecules in the first coordination sphere and their geometry (symmetry point group).
稳态和时间分辨模式下的铕（III）发光光谱法，是研究重金属离子与腐殖质（HS）之间配合物性质的一种合适技术，腐殖质在环境中金属物种的分布中起着关键作用。不幸的是，铕（III）与芳香族和脂肪族羧酸（HS结合位点的模型化合物）形成的配合物在室温下的发光光谱太宽，无法充分利用其潜在的分析信息含量。结果表明，在低温条件下可实现荧光线窄化（FLN），高分辨率光谱提供了有关配合物的详细信息。研究了十种模型配体。记录了总发光光谱（TLS），使用(^5D_0\leftarrow^7F_0)跃迁进行激发，(^5D_0\rightarrow^7F_1)和(^5D_0\rightarrow^7F_2)跃迁进行发射。激发跃迁的能量取决于所涉及的配体以及配合物的结构和组成。对于大多数配体，高分辨率TLS中的不连续性表明样品中存在更多种，即不同的配合物结构。进行了选择性激发以测量与物种相关的发光衰减时间(\tau)。后者强烈依赖于来自配位水分子或配体羟基的附近OH振荡器。此外，计算了不对称比(r)，定义为(^5D_0\rightarrow^7F_2)和(^5D_0\rightarrow^7F_1)跃迁的强度比，并确定了激发能量(E_{exc})随(^7F_1)三重态分裂(\Delta E)的变化，从而得出晶体场强度参数(N_{\nu}(B_{2q}))以及晶体场参数(B_{20})和(B_{22})。对结果进行了深入分析，提供了有关共存配合物数量、它们的化学计量、第一配位层中水分子数量及其几何形状（对称点群）的详细信息。
