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Unveiling Anomalous Surface-Enhanced Resonance Raman Scattering on an Oxo–Triruthenium Acetate Cluster Complex by a Theoretical–Experimental Approach
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-09-09 , DOI: 10.1021/acs.jpcc.0c05560 Jonnatan J. Santos 1 , Sergio H. Toma 1 , Romulo A. Ando 1 , Paola Corio 1 , Koiti Araki 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-09-09 , DOI: 10.1021/acs.jpcc.0c05560 Jonnatan J. Santos 1 , Sergio H. Toma 1 , Romulo A. Ando 1 , Paola Corio 1 , Koiti Araki 1
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Surface-enhanced Raman spectroscopy (SERS) has been explored by the most diverse areas of research over the past 40 years, with more special attention from analytical chemistry. Although there is a great consensus that there are two mechanisms that contribute most to the observation of the phenomenon (electromagnetic (EM) and charge transfer (CT)), several anomalies are observed, especially when studying complexes of transition metals. In this article, we present a theoretical and experimental study of Raman and SERS of an oxo–triruthenium acetate cluster ([Ru3O (CH3COO)6(py)2(pytpy)]), where it was possible to observe one of these “anomalies” of the SERS effect, in this case, an unexpected enhancement of the vibrational stretching mode of the oxo group. This cluster had its electrochemical and spectroelectrochemical properties studied by cyclic voltammetry and electronic spectroscopy in the visible and near-infrared, where it was possible to observe the fully reversible waves of the ruthenium sites (separated by 1.00 V) and the terpyridinic ligand and how the absorption of this complex varies drastically when reduced electrochemically. The molecular orbitals and electronic transitions of this cluster were calculated by time-dependent density-functional theory (TDDFT), where it can be noted that the HOMO orbitals are almost exclusively composed of the atomic orbitals of ruthenium and the LUMO orbitals can be composed of a mixture of ruthenium orbitals and acetate ligands, as well as terpyridine. From the TDDFT calculations and the transitions energies obtained, the complex resonant Raman and Raman spectra were simulated using different excitation wavelengths (696, 785, and 1064 nm), where an unexpected intensification of oxygen stretching at the Ru3O center at 700 cm–1 was observed considering the excitation at 785 nm, even though there was no expected transition. The experimental SERS spectra of the complex in two redox states (Ru3III, III, III and Ru3III, III, II) were obtained experimentally using gold and silver nanoparticles with an excitation wavelength laser at 785 nm, where a very intense signal at 700 cm–1, for the Ru3III, III, II redox state, was observed. The simulation of electronic states by TDDFT and SERS spectra by DFT, considering an Au20 cluster adduct, showed an intensification of the entire complex, with great emphasis on the Ru3O center and the 700 cm–1 mode that, however, was not as intense as the results obtained experimentally, indicating an anomalous intensification.
中文翻译：
通过理论-实验方法揭示乙酸三钌乙酸酯簇复合物上的异常表面增强共振拉曼散射
在过去40年中，表面增强拉曼光谱（SERS）已被最广泛的研究领域所探索，其中分析化学引起了更多关注。尽管已达成共识，即有两种机制对现象的观察贡献最大（电磁（EM）和电荷转移（CT）），但仍观察到一些异常现象，尤其是在研究过渡金属配合物时。在本文中，我们介绍了氧代-三钌乙酸酯簇（[Ru 3 O（CH 3 COO）6（py）2（pytpy）]），可以观察到SERS效应的这些“异常”之一，在这种情况下，羰基的振动拉伸模式意外增强。该团簇在可见光和近红外光下通过循环伏安法和电子光谱学研究了其电化学和光谱电化学性质，可以观察到钌位点（以1.00 V隔开）和吡啶鎓配体的完全可逆波，以及如何当电化学还原时，该络合物的吸收变化很大。该团簇的分子轨道和电子跃迁是根据时间依赖性密度泛函理论（TDDFT）计算的，可以注意到，HOMO轨道几乎完全由钌的原子轨道组成，而LUMO轨道可以由钌轨道和乙酸盐配体以及三联吡啶的混合物组成。根据TDDFT计算和获得的跃迁能量，使用不同的激发波长（696、785和1064 nm）模拟了复杂的共振拉曼光谱和拉曼光谱，其中Ru处的氧气拉伸意外增强考虑到在785 nm处的激发，观察到700 cm –1处的3 O中心，即使没有预期的跃迁。使用金和银纳米颗粒，通过激发波长为785 nm的激光，通过实验获得了在两种氧化还原状态（Ru 3 III，III，III和Ru 3 III，III，II）下的配合物的实验SERS光谱在700 cm –1处，观察到Ru 3 III，III，II的氧化还原状态。考虑了Au 20团簇加合物，通过TDDFT和SERS光谱对电子态进行模拟，显示出整个复合物的强化，特别是Ru 3O中心和700 cm –1模式的强度不如实验结果强，表明异常增强。
更新日期：2020-10-02
中文翻译：
通过理论-实验方法揭示乙酸三钌乙酸酯簇复合物上的异常表面增强共振拉曼散射
在过去40年中，表面增强拉曼光谱（SERS）已被最广泛的研究领域所探索，其中分析化学引起了更多关注。尽管已达成共识，即有两种机制对现象的观察贡献最大（电磁（EM）和电荷转移（CT）），但仍观察到一些异常现象，尤其是在研究过渡金属配合物时。在本文中，我们介绍了氧代-三钌乙酸酯簇（[Ru 3 O（CH 3 COO）6（py）2（pytpy）]），可以观察到SERS效应的这些“异常”之一，在这种情况下，羰基的振动拉伸模式意外增强。该团簇在可见光和近红外光下通过循环伏安法和电子光谱学研究了其电化学和光谱电化学性质，可以观察到钌位点（以1.00 V隔开）和吡啶鎓配体的完全可逆波，以及如何当电化学还原时，该络合物的吸收变化很大。该团簇的分子轨道和电子跃迁是根据时间依赖性密度泛函理论（TDDFT）计算的，可以注意到，HOMO轨道几乎完全由钌的原子轨道组成，而LUMO轨道可以由钌轨道和乙酸盐配体以及三联吡啶的混合物组成。根据TDDFT计算和获得的跃迁能量，使用不同的激发波长（696、785和1064 nm）模拟了复杂的共振拉曼光谱和拉曼光谱，其中Ru处的氧气拉伸意外增强考虑到在785 nm处的激发，观察到700 cm –1处的3 O中心，即使没有预期的跃迁。使用金和银纳米颗粒，通过激发波长为785 nm的激光，通过实验获得了在两种氧化还原状态（Ru 3 III，III，III和Ru 3 III，III，II）下的配合物的实验SERS光谱在700 cm –1处，观察到Ru 3 III，III，II的氧化还原状态。考虑了Au 20团簇加合物，通过TDDFT和SERS光谱对电子态进行模拟，显示出整个复合物的强化，特别是Ru 3O中心和700 cm –1模式的强度不如实验结果强，表明异常增强。
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