Department of Chemistry, Durham University , South Road, Durham DH1 3LE, UK.
Inorg Chem. 2012 Aug 6;51(15):8042-56. doi: 10.1021/ic300147p. Epub 2012 Jul 19.
Nonadentate ligands based on triazacyclononane incorporating pyridyl-2-phosphinate groups form an isostructural series of complexes with Ln ions in the solid state and in solution. The Ln ion is effectively shielded from the solvent environment. Crystal structures reveal a rigid C(3)-symmetric tricapped trigonal-prismatic coordination geometry that is maintained in solution for the methyl and phenylphosphinate series, as shown by multinuclear NMR analysis. Variable-temperature measurements of the field dependence of the water proton relaxivity in gadolinium complexes indicate that these systems exclude solvent from the primary coordination environment and minimize the second sphere of solvation. The electronic relaxation time for the gadolinium methylphosphinate complex has been estimated to be 550 (±150) ps by EPR and NMR methods, compared to values of around 0.30-0.05 ps for the terbium-ytterbium series, deduced by analyzing the field dependence (4.7-16.5 T) of the (31)P NMR longitudinal relaxation times. Values are compared with analogous azacarboxylate ligand complexes, supporting a key role for donor atom polarizability in determining the electronic relaxation. Spectral emission behavior in solution of samarium, europium, terbium, and dysprosium complexes is compared, and the resolved RRR-Λ and SSS-Δ complexes show strong circularly polarized luminescence. The molecular quadratic hyperpolarizability 〈β(HLS)〉 has been measured in solution using hyper-Raleigh light-scattering methods, for the whole series of lanthanide complexes of one ligand. The values of 〈β(HLS)〉 reach a maximum around the center of the series and are not simply dependent on the number of f electrons, suggesting a dominant contribution from the octupolar rather than the dipolar term.
基于三氮杂环壬烷并含有吡啶-2-膦酸酯基团的非齿配体在固态和溶液中与 Ln 离子形成一系列同构的配合物。Ln 离子有效地被溶剂环境屏蔽。晶体结构揭示了刚性的 C(3)对称的三角双锥配位几何形状，在甲基和苯基膦酸酯系列中通过多核 NMR 分析得以保持。在溶液中，对水质子弛豫率的场依赖性的变温测量表明，这些体系将溶剂排除在主配位环境之外，并最小化溶剂化的第二球。通过电子顺磁共振(EPR)和 NMR 方法，对镝甲基膦酸酯配合物的电子弛豫时间进行了估计，为 550(±150)ps，而通过分析钬-镱系列的场依赖性(4.7-16.5 T)，得到的弛豫时间为 0.30-0.05 ps。与类似的氮杂羧酸酯配体配合物的值进行了比较，支持供体原子极化率在决定电子弛豫方面的关键作用。比较了溶液中钐、铕、铽和镝配合物的光谱发射行为，分辨出的 RRR-Λ 和 SSS-Δ 配合物表现出强的圆偏振发光。使用超瑞利光散射方法，在溶液中测量了整个镧系元素配合物系列中一种配体的分子二次超极化率〈β(HLS)〉。〈β(HLS)〉的值在系列的中心附近达到最大值，并不简单地取决于 f 电子的数量，这表明主要贡献来自于八极而不是偶极项。
