Martin Noreen, Bünzli Jean-Claude G., McKee Vickie, Piguet Claude, Hopfgartner Gérard
Institute of Inorganic and Analytical Chemistry, University of Lausanne, CH-1015 Lausanne, Switzerland, Department of Inorganic Chemistry, Queen's University, BT9 5AG, Belfast, N. Ireland, Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, CH-1211 Geneva 4, Switzerland, and Pharma Division, F. Hoffmann-La Roche Ltd., CH-4070 Basle, Switzerland.
Inorg Chem. 1998 Feb 9;37(3):577-589. doi: 10.1021/ic971401r.
The segmental ligands bis{1-alkyl-2-[6'-(N,N-diethylcarbamoyl)pyridin-2'-yl]benzimidazol-5-yl}methane (alkyl = methyl (L(5)), ethyl (L(6))) react with lanthanide perchlorates (Ln = La, Eu, Gd, Tb) in acetonitrile to yield the f-f dinuclear homotopic triple-stranded helicates Ln(2)(L(i)())(3) (i = 5, 6) under thermodynamic control. The crystal structure of Tb(2)(L(6))(3)(3)(MeCN)(2)(THF)(0.5)(EtOH)(0.5) (11a, C(124)H(145)N(26)O(31)Cl(6)Tb(2), triclinic, P&onemacr;, Z = 2) shows the wrapping of the ligands about a pseudo-C(3) axis passing through the metal ions. The Tb ions are 9-coordinate in facial pseudo-tricapped trigonal prismatic sites and are separated by 9.06 Å. (1)H-NMR and ES-MS data establish that the triple helical structure is maintained in solution. Spectrophotometric titrations (Ln = La, Eu) indicate log beta(23) = 24-25 and the formation of a 2:2 complex Ln(2)(L(5))(2) (log beta(22) = 19-20). Quantum yield determination in acetonitrile shows that the terminal N,N-diethylcarboxamide groups in L(5) favor efficient intramolecular L(5) --> Eu(III) energy transfers leading to strong Eu-centered red luminescence, 50 times as intense as the luminescence observed when the carboxamide groups are replaced by substituted benzimidazole units in Eu(2)(L(4))(3). Resistance toward hydrolysis also results from the use of carboxamide groups, and no quenching of luminescence is observed for Eu(2)(L(5))(3) in moist acetonitrile up to 2.5 M water. The crucial role played by carboxamide groups for the control of structural, electronic, and photophysical properties is discussed. Replacing perchlorates by triflates allows the isolation of the dinuclear double-stranded helicate Eu(2)(L(6))(2)(CF(3)SO(3))(4)(H(2)O(2))(2)(2)(MeOH)(2)(H(2)O)(5)(.5), whose crystal structure (13a, C(85)H(106)Eu(2)F(18)N(16)O(30)S(6), monoclinic, C2/m, Z = 2) reveals a side-by-side arrangement of the two strands and 9-coordinate Eu ions linked through hydrogen-bonded water molecules.
链段配体双{1-烷基-2-[6'-(N,N-二乙基氨基甲酰基)吡啶-2'-基]苯并咪唑-5-基}甲烷（烷基 = 甲基 (L(5))，乙基 (L(6))）在乙腈中与高氯酸镧系元素（Ln = La、Eu、Gd、Tb）反应，在热力学控制下生成f-f双核同核三链螺旋配合物[Ln₂(Lᵢ)₃]⁶⁺（i = 5, 6）。Tb₂(L(6))₃₃(MeCN)₂(THF)₀.₅(EtOH)₀.₅（11a，C₁₂₄H₁₄₅N₂₆O₃₁Cl₆Tb₂，三斜晶系，P&onemacr;，Z = 2）的晶体结构显示配体围绕一条穿过金属离子的伪C₃轴缠绕。Tb离子在面式伪三帽三棱柱位点中为九配位，且相距9.06 Å。¹H-NMR和ES-MS数据表明三螺旋结构在溶液中得以保持。分光光度滴定（Ln = La、Eu）表明logβ₂₃ = 24 - 2；5以及形成了2:2配合物[Ln₂(L(5))₂]⁶⁺（logβ₂₂ = 19 - 20）。在乙腈中进行的量子产率测定表明，L(5)中的末端N,N-二乙基甲酰胺基团有利于高效的分子内L(5)→Eu(III)能量转移，从而产生强烈的以Eu为中心的红色发光，其强度是[Eu₂(L(4))₃]⁶⁺中羧酰胺基团被取代苯并咪唑单元取代时所观察到的发光强度的50倍。使用羧酰胺基团还导致了对水解的抗性，并且在高达2.5 M水的潮湿乙腈中，[Eu₂(L(⁵))₃]⁶⁺未观察到发光猝灭。讨论了羧酰胺基团在控制结构、电子和光物理性质方面所起的关键作用。用三氟甲磺酸盐取代高氯酸盐可分离出双核双链螺旋配合物Eu₂(L(6))₂(CF₃SO₃)₄(H₂O₂)₂₂(MeOH)₂(H₂O)₅·₅，其晶体结构（13a，C₈₅H₁₀₆Eu₂F₁₈N₁₆O₃₀S₆，单斜晶系，C2/m，Z = 2）揭示了两条链并排排列以及通过氢键连接的水分子相连的九配位Eu离子。
