Triple-stranded helicates of zinc(II) and cadmium(II) involving a new redox-active multiring nitrogenous heterocyclic ligand: synthesis, structure, and electrochemical and photophysical properties.
Triple-stranded helicates of zinc(II) and cadmium(II) involving a new redox-active multiring nitrogenous heterocyclic ligand: synthesis, structure, and electrochemical and photophysical properties.
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DOI：
10.1021/ic202595p
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发表时间：
2012-01
影响因子：
4.6
通讯作者：
Nabanita Kundu;Sk Md Towsif Abtab;Sanchita Kundu;A. Endo;S. Teat;M. Chaudhury
中科院分区：
文献类型：
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作者：
Nabanita Kundu;Sk Md Towsif Abtab;Sanchita Kundu;A. Endo;S. Teat;M. Chaudhury
本文报道了一种新的双齿含氮杂环配体的质子化形式[H（2）（L）]（CF（3）SO（3））（2）（1），合成了3，3 ′-二吡啶-2-基[1，1 ′]二[咪唑并[1，5-a]吡啶]（L）及其锌（II）和镉（II）配合物（2和3），并通过单晶X-射线衍射进行了表征。在固态下，2和3都具有三链螺旋结构，其涉及经历扭曲和弯曲到中心金属离子的立体电子需求所需的程度的配体。锌（II）配合物[Zn（2）（L）（3）]（ClO（4））（4）（2）中的金属中心是等价的，每个中心具有扭曲的八面体几何形状，沿C（3）轴沿着变平，Zn 1··Zn 1 #间距为4.8655（13）π。另一方面，镉配合物[Cd（2）（L）（3）（H（2）O）]（ClO（4））（4）（3）具有罕见的螺旋结构，显示出金属中心周围的配位不对称性，Cd 1···Cd 2分离大大降低，为4.070 Ω。Cd 1周围的配位环境是一个扭曲的五角双锥，涉及一个N（6）O供体与来自配位水的氧原子，剩下的金属中心Cd 2与扭曲的八面体几何形状。2和3的结构还涉及阴离子-π-和CH-π-型非共价相互作用，这些非共价相互作用在形成这些分子在固态下的延伸结构中起主导作用。在溶液中，这些化合物表现出强烈的流动行为，使得各个配体链彼此无法区分，如从它们的（1）H NMR光谱所揭示的，这也提供了关于这些分子在溶液中保留其螺旋结构的指示。在电化学上，这些化合物是非常有趣的，在两个连续的单电子步骤中在约1/2的E（1/2）处经历基于配体的氧化。0.65和0.90 V相对于Ag/AgCl（3 M NaCl）参比。这些分子在红色和蓝色区域都是有效的发射体，因为基于配体的π*-π荧光发射，通过连接的刘易斯酸中心适当地调节。
The protonated form [H(2)(L)](CF(3)SO(3))(2) (1) of a new redox-active bis-bidentate nitrogenous heterocyclic ligand, viz., 3,3'-dipyridin-2-yl[1,1']bi[imidazo[1,5-a]pyridinyl] (L), and its zinc(II) and cadmium(II) complexes (2 and 3) have been synthesized and characterized by single-crystal X-ray diffraction analysis. In the solid state, both 2 and 3 have triple-stranded helical structures involving ligands that experience twisting and bending to the extent needed by the stereoelectronic demand of the central metal ion. The metal centers in the zinc(II) complex [Zn(2)(L)(3)](ClO(4))(4) (2) are equivalent, each having a distorted octahedral geometry, flattened along the C(3) axis with a Zn1···Zn1# separation of 4.8655(13) Å. The cadmium complex [Cd(2)(L)(3)(H(2)O)](ClO(4))(4) (3), on the other hand, has a rare type of helical structure, showing coordination asymmetry around the metal centers with a drastically reduced Cd1···Cd2 separation of 4.070 Å. The coordination environment around Cd1 is a distorted pentagonal bipyramid involving a N(6)O donor set with the oxygen atom coming from a coordinated water, leaving the remaining metal center Cd2 with a distorted octahedral geometry. The structures of 2 and 3 also involve anion-π- and CH-π-type noncovalent interactions that play dominant roles in shaping the extended structures of these molecules in the solid state. In solution, these compounds exhibit strong fluxional behavior, making the individual ligand strands indistinguishable from one another, as revealed from their (1)H NMR spectra, which also provide indications about these molecules retaining their helical structures in solution. Electrochemically, these compounds are quite interesting, undergoing ligand-based oxidations in two successive one-electron steps at E(1/2) of ca. 0.65 and 0.90 V versus a Ag/AgCl (3 M NaCl) reference. These molecules are all efficient emitters in the red and blue regions because of ligand-based π*-π fluorescent emissions, tuned appropriately by the attached Lewis acid centers.