Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles. Chemistry and excited-state behavior of 1,4-C2-cyclam complexes.
Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles. Chemistry and excited-state behavior of 1,4-C2-cyclam complexes.
复制标题
空间约束对四氮杂大环铬(III)配合物的影响。
DOI：
10.1021/ic030037v
复制
发表时间：
2003
影响因子：
4.6
通讯作者：
Nathan,LawrenceC
中科院分区：
文献类型：
--
作者：
Wright-Garcia,Kimberley;Basinger,Jillian;Williams,Sarah;Hu,Chuanjiang;Wagenknecht,PaulS;Nathan,LawrenceC
报道了约束大环配体1,4- c2 -cyclam = 1,4,8,11-tetraazabicyclo[10.2.2]十六烷的几种Cr（III）配合物的合成和表征。该配体似乎只形成反式配合物，并提出了反式-[Cr(1,4- c2 -cyclam)Cl2] pf6的结构。额外的c2键所施加的约束使键角明显偏离理想值90°和180°。畸变的作用是使trans-[Cr(1,4- c2 -cyclam)Cl2]+(trans-[Cr（1,4- c2 -cyclam)(H2O)2] + = 6.5 × 10-2s- 1,0.01 m HNO3, 25℃）的水化速率比trans-[Cr(cyclam)Cl2]+提高了5个数量级以上。配合物-[Cr(1,4- c2 -cyclam)Cl2]+和反式-[Cr(1,4- c2 -cyclam)(CN)2]+的消光系数比它们的cyclam类似物高4到5倍，这是由于空间约束导致的中心对称性的缺乏。该反式-[Cr(1,4- c2 -cyclam)(CN)2]+配合物在水溶液中是一个非常弱的发射体，其发射中心为735 nm （τ = 0.24 μs）。反式-[Cr（1,4- c2 -环环烷）（CN）2]+在水溶液中的长时间光解（350 nm, 15 h）导致CN配体损失。这与不受约束的cyclam类似物形成鲜明对比，后者具有光惰性，室温发射寿命为335 μs。
The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,4-C2-cyclam = 1,4,8,11-tetraazabicyclo[10.2.2]hexadecane is reported. The ligand appears to form only trans complexes, and the structure oftrans-[Cr(1,4-C2-cyclam)Cl2]PF6is presented. The constraint imposed by the additional C2linkage distorts the bond angles significantly away from the ideal values of 90 and 180°. The effect of the distortion is to enhance the aquation rate oftrans-[Cr(1,4-C2-cyclam)Cl2]+(kobsfortrans-[Cr(1,4-C2-cyclam)(H2O)2]3+formation = 6.5 × 10-2s-1, 0.01M HNO3, 25 °C) by over 5 orders of magnitude relative totrans-[Cr(cyclam)Cl2]+. The complexestrans-[Cr(1,4-C2-cyclam)Cl2]+andtrans-[Cr(1,4-C2-cyclam)(CN)2]+are found to have extinction coefficients four to five times higher than their cyclam analogues, owed to the lack of centrosymmetry caused by the steric constraint. Thetrans-[Cr(1,4-C2-cyclam)(CN)2]+complex is a very weak emitter in aqueous solution with a broad room-temperature emission centered at 735 nm (τ = 0.24 μs). Extended photolysis (350 nm, 15 h) oftrans-[Cr(1,4-C2-cyclam)(CN)2]+in aqueous solution results in CN-ligand loss. This is in stark contrast to its unconstrained cyclam analogue, which is photoinert and has a room-temperature emission lifetime of 335 μs.