Ansari Mohd Asif, Mondal Sudipta, Kaim Wolfgang, Lahiri Goutam Kumar
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai400076, India.
Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
Inorg Chem. 2020 Apr 6;59(7):4397-4405. doi: 10.1021/acs.inorgchem.9b03543. Epub 2020 Mar 9.
π-Conjugated bridged isomeric diruthenium(II) complexes [(acac)Ru(μ-DIPQD)Ru(acac)], () and () (acac = acetylacetonate, (8,16)-,-diphenylindeno[1,2-]indeno[2',1':5,6]pyrazino[2,3-]quinoxaline-8,16-diimine (-DIPQD), and (12,16)-,-diphenylindeno[1,2-]indeno[1',2':5,6]pyrazino[2,3-]quinoxaline-12,16-diimine (-DIPQD) were separated and structurally characterized. The structures of the (ΔΔ/ΛΛ) forms of and exhibit two units of {Ru(acac)}, linked to adjacent pyrazine and imine nitrogen donors of the bridge (DIPQD) in and modes, with metal-metal separations of 9.050 and 6.330 Å, respectively. The packing diagrams of and revealed an intermolecular π···π stacking interaction (3.202-3.398 Å) involving the face-to-face arrangement of the aromatic rings of DIPQD in adjacent molecules and varying solid-state packing modes, slipped stacking in the former versus brick-layer stacking in the latter. The electronic forms associated with multiple reversible one-electron redox steps of and were addressed by DFT (MO composition, Mulliken spin density distribution), supported by EPR of intermediate paramagnetic states and by UV-vis-NIR spectroelectrochemistry in all redox states. The results reveal similar electronic forms along the redox series irrespective of their isomeric identities in and , viz., primarily metal-based oxidations ([(acac)Ru(μ-DIPQD)Ru(acac)], /, = 1/2; [(acac)Ru(μ-DIPQD)Ru(acac)], /, = 1) and bridge-based reductions ([(acac)Ru(μ-DIPQD)Ru(acac)], /, = 1/2; [(acac)Ru(μ-DIPQD)Ru(acac)], /, = 1). TD-DFT analysis of the electronic transitions in the complexes suggests bridge-targeted mixed metal/ligand-based multiple charge transfer transitions over the visible to NIR region in all redox states, while a weak band involving the radical bridge appeared in the long-wavelength region (∼2000 nm) in /.
π共轭桥连异构二钌（II）配合物[(acac)Ru(μ-DIPQD)Ru(acac)]，（）和（）（acac = 乙酰丙酮，(8,16)-,-二苯基茚并[1,2-]茚并[2',1':5,6]吡嗪并[2,3-]喹喔啉-8,16-二亚胺（-DIPQD），以及(12,16)-,-二苯基茚并[1,2-]茚并[1',2':5,6]吡嗪并[2,3-]喹喔啉-12,16-二亚胺（-DIPQD））被分离并进行了结构表征。和的（ΔΔ/ΛΛ）形式的结构显示出两个{Ru(acac)}单元，分别以和模式与桥连（DIPQD）的相邻吡嗪和亚胺氮供体相连，金属-金属间距分别为9.050 Å和6.330 Å。和的堆积图显示存在分子间π···π堆积相互作用（3.202 - 3.398 Å），涉及相邻分子中DIPQD芳环的面对面排列以及不同的固态堆积模式，前者为错位堆积，后者为砖层堆积。通过DFT（分子轨道组成、 Mulliken自旋密度分布）研究了与和的多个可逆单电子氧化还原步骤相关的电子形式，并得到中间顺磁态的EPR以及所有氧化还原态的紫外-可见-近红外光谱电化学的支持。结果表明，无论和中的异构身份如何，沿着氧化还原系列的电子形式相似，即主要是基于金属的氧化（[(acac)Ru(μ-DIPQD)Ru(acac)]，/， = 1/2；[(acac)Ru(μ-DIPQD)Ru(acac)]，/， = 1）和基于桥连的还原（[(acac)Ru(μ-DIPQD)Ru(acac)]，/， = 1/2；[(acac)Ru(μ-DIPQD)Ru(acac)]，/， = 1）。配合物中电子跃迁的TD-DFT分析表明，在所有氧化还原态下，在可见光到近红外区域存在以桥连为目标的混合金属/配体基多电荷转移跃迁，而在/的长波长区域（约2000 nm）出现了一个涉及自由基桥连的弱带。
