• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Chemistry: A European journal >Coordination-induced spin crossover (CISCO) through axial bonding of substituted pyridines to nickel-porphyrins: σ-Donor versus π-acceptor effects
【24h】

Coordination-induced spin crossover (CISCO) through axial bonding of substituted pyridines to nickel-porphyrins: σ-Donor versus π-acceptor effects

机译：通过取代吡啶与镍-卟啉的轴向键合而引起的配位诱导的自旋交叉（CISCO）：σ-给体与π-受体效应

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Nickel-porphyrins, with their rigid quadratic planar coordination framework, provide an excellent model to study the coordination-induced spin crossover (CISCO) effect because bonding of one or two axial ligands to the metal center leads to a spin transition from S=0 to S=1. Herein, both equilibrium constants K_(1S) and K_2, and for the first time also the corresponding thermodynamic parameters ΔH_(1S), ΔH_2, ΔS_(1S), and ΔS_2, are determined for the reaction of a nickel-porphyrin (Nitetrakis(pentafluorophenyl) porphyrin) with different 4-substituted pyridines by temperature-dependent NMR spectroscopy. The association constants K_(1S) and K_2 are correlated with the basicity of the 4-substituted pyridines (R: OMe>H>CO_2Et-NO_2) whereas the ΔH_(1S) values exhibit a completely different order (OMeCO_2Et> NO_2). 4-Nitropyridine exhibits the largest binding enthalpy, which, however, is overcompensated by a large negative binding entropy. We attribute the large association enthalpy of nitropyridine with porphyrin to the back donation of electrons from the Ni d_(xz) and d_(yz) orbitals into the π orbitals of pyridine, and the negative association entropy to a decrease in vibrational and internal rotation entropy of the more rigid porphyrin-pyridine complex. Back donation for the nitro-and cyanopyridine complexes is also confirmed by IR spectroscopy, and shows a shift of the N-O and C-N vibrations, respectively, to lower wave numbers. X-ray structures of 2:1 complexes with nitro-, cyano-, and dimethylaminopyridine provide further indication of a back donation. A further trend has been observed: the more basic the pyridine the larger is K_(1S) relative to K_(2.) For nitropyridine K_2 is 17 times larger than K_(1S) and in the case of methoxypyridine K_2 and K_(1S) are almost equal.
机译：镍卟啉及其刚性的二次平面配位框架，为研究配位诱导的自旋交叉（CISCO）效应提供了一个极好的模型，因为一个或两个轴向配体键合到金属中心会导致从S = 0到自旋转变S = 1。在此，对于镍-卟啉（Nitetrakis（Nitetrakis（，））的反应，首先确定了平衡常数K_（1S）和K_2，还首次确定了相应的热力学参数ΔH_（1S），ΔH_2，ΔS_（1S）和ΔS_2。五氟苯基）卟啉）与不同的4-取代的吡啶通过温度依赖性NMR光谱分析。缔合常数K_（1S）和K_2与4-取代吡啶的碱度相关（R：OMe> H> CO_2Et-NO_2），而ΔH_（1S）值表现出完全不同的阶数（OMe CO_2Et> NO_2）。 4-硝基吡啶具有最大的结合焓，但是，其被较大的负结合熵过度补偿。我们将硝基吡啶与卟啉的大缔合焓归因于电子从Ni d_（xz）和d_（yz）轨道向吡啶的π轨道的反向捐赠，而负缔合熵则归因于振动和内旋转熵的降低刚性较高的卟啉-吡啶配合物红外光谱也证实了硝基-和氰基吡啶配合物的反向捐赠，表明N-O和C-N振动分别向较低波数移动。具有硝基，氰基和二甲基氨基吡啶的2：1配合物的X射线结构进一步表明了回馈。观察到进一步的趋势：吡啶越碱性，相对于K_（2）K_（1S）越大。对于硝基吡啶，K_2比K_（1S）大17倍;对于甲氧吡啶K_2和K_（1S）几乎相等。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号