Solution structure of chiral lanthanide complexes

The determination of solution structure of small to medium size chiral lanthanide complexes through paramagnetic NMR and circular dichroism is briefly reviewed. The main focus is on ytterbium as the rare earth, because of its negligible contact contribution to the hyperfine shift and of its intense CD spectrum in the near IR. The structures discussed contain various stereogenic elements: classical chiral centres, atropisomeric axes, slowly interconverting conformations, which gives rise to a manifold of situations to be identified, classified, and characterised through spectroscopic tools. The fallout of these structural properties are in enantioselective catalysis, in molecular recognition, or even in biomedicine, on account of the role of Gd³⁺ complexes as MRI contrast agents. Moreover, the information encoded in the NMR and CD spectra of Ln³⁺ complexes may be used to extract original data on the solution stereochemistry of organic molecules used as ligands. The first part summarises some basic theoretical aspects, with special emphasis onto those which have practical consequences in the experimental design. A discussion of selected applications can be found in the second part.     

Crystal Structure of Di[(μ‐benzoato‐O,O′)bis(η5‐methylcylopentadienyl)ytterbium(III)]

Transparent orange‐red crystals of [Yb(MeCp)₂(O₂CPh)]₂ obtained by oxidation of Yb(MeCp)₂ with Tl(O₂CPh) in tetrahydrofuran have a dimeric structure with bridging bidentate (O,O′)‐benzoate groups and eight‐coordinate ytterbium.     

表面活性剂-磺基水扬酸对镱原子吸收光谱的高增敏作用研究

本文就表面活性剂-磺基水杨酸对镱在乙炔-空气火焰中的高增敏作用进行了研究,结果表明,在十二烷基硫酸钠(SDS)与磺基水杨酸(SSA)共存时。镱的灵敏度增高50倍,其它稀土元素和一些阴离子对Yb的干扰得到了有效的抑制,对硫酸根和磷酸根尤其明显,同时也研究了该体系的增敏机理。在Yb-SDS-SSA体系中,镱的检出限为0.031μg/mL,在0.050～2.0μg/mL镱的浓度范围内,其相对标准偏差为3.0％。     

Dinuclear Dysprosium and Ytterbium Complexes Incorporating N,N‐Bis(pyrrolyl‐α‐methyl)‐N‐methylamine Ligand: Syntheses and Structures

Reaction of DyCl₃ with two equivalents of NaN(SiMe₃)₂ in THF yielded {Dy(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 1 ). X‐ray crystal structure analysis revealed that 1 is a centrosymmetric dimer with asymmetrically bridging chloride ligands. The metal coordination arrangement can be best described as distorted trigonal bipyramid. The bond lengths of Ln–Cl and Ln–N showed a decreasing trend with the contraction of the size of Ln³⁺. Treatment of N,N‐bis(pyrrolyl‐α‐methyl)‐N‐methylamine (H₂dpma) with 1 and known compound {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂, respectively, led to the formations of [Dy(μ‐Cl)(dpma)(THF)₂]₂ ( 2 ) and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 3 ). Compounds 2 and 3 were fully characterized by single‐crystal X‐ray crystallography, elemental analysis, and ¹H NMR spectroscopy. Structure determination indicated that 2 and 3 exhibit as centrosymmetric dimers with asymmetrically bridging chloride ligands. One pot reactions involving LnCl₃ (Ln = Dy and Yb), LiN(SiMe₃)₂, and H₂dpma were explored and desired products 2 and 3 were not yielded, which indicated that 1 and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ are the demanding precursors to synthesize Dysprosium and Ytterbium complexes supported by dpma^2– ligand. Compounds 2 and 3 are the first reported lanthanide complexes chelated by dpma^2– ligand.     

Synthesis and crystal structure of the monoclinic modification of Yb(ReO4)3(H2O)4

Ytterbium(III) tetraaquatris(tetraoxorhenate(VII)), Yb(ReO₄)₃(H₂O)₄, was prepared by the reaction of Yb₂O₃ with concentrated HReO₄ at room temperature. The colorless compound crystallizes in the monoclinic space group P2₁/n (No. 14) with four formula units per unit cell (a=730.5(1) pm, b=1484.1(5) pm, c=1311.7(2) pm, β=93.69(1)). The main feature of the crystal structure is the formation of chains _∞¹[Yb(H₂O)₄(ReO₄)₂(ReO₄)_2/2] running along [100]. This arrangement shows distorted cubic antiprisms of [Yb(H₂O)₄(ReO₄)₂(ReO₄)_2/2] interconnected via the ReO₄⁻ ligands. The chains are held together in the solid by hydrogen bonding. The compound is paramagnetic and follows the Curie-Weiss law with a magnetic moment of 4.0 μ_B at room temperature and θ=−42 K. It loses hydration water in two steps at temperatures below 400 K; decomposition begins at 850 K, forming Yb₂O₃(Re₂O₇)₂ and is complete at 1350 K leading to Yb₂O₃ as final product.     

OH-对磷酸盐铒玻璃光谱性质的影响

本文系统研究了Yb³⁺、Er³⁺共掺磷酸盐铒玻璃中OH^-含量与铒玻璃荧光寿命和光谱性质的关系.结果表明OH^-基团的存在使得Er³⁺离子的荧光强度显著降低,荧光寿命大大缩短.比较了三种不同Al₂O₃含量(5mol%,8mol%和13mol%)的铒玻璃在2.9μm波长处的红外吸收系数与铒离子荧光寿命的关系,发现玻璃中OH^-在2.9μm的吸收系数和Er³⁺的⁴Ⅰ_13/2能级离子衰减速率成线性关系,不同Al₂O₃含量的玻璃具有不同Er³⁺和OH^-基团的相互作用参量和不同的荧光寿命值及量子效率.并从玻璃结构上解释了Al₂O₃含量对除水机制和光谱性质的影响.经过充分除水后的铒玻璃荧光寿命可达到9.1ms.     

用波导结构的周期极化铌酸锂产生507nm的连续倍频输出

稀土金属镱原子的3P2态是镱原子的一个很重要的长寿命亚稳态,为了研究将跃迁1S0→3 P2作为镱原子钟跃迁的可能性,通过507nm的激光场进行激发而实现态制备.实验中利用波导型周期极化铌酸锂作为倍频晶体的单次倍频方式,采用了一种简单的短焦距单透镜耦合方式,获得了507nm的连续光输出.结果表明,采用焦距为20mm的单透镜将58mW的1 014nm基频光直接耦合到波导结构的周期极化铌酸锂,得到了86.5μW的507nm倍频光.同时,给出了倍频输出光的输出功率与温度的关系曲线.对比传统的裸光纤直接耦合方式,单透镜直接耦合方式优于光纤耦合的倍频效率.     

稀土Yb(Ⅲ)对Luminol－H2O2－Cr（Ⅲ) 体系的化学发光熄灭效应

研究了稀土Yb(Ⅲ) 对Luminol－H