Transition metal complexes, such as the low-spin bis (phenylterpyridine) (A) and bis (pyridylterpyrazine)iron (II) (B) complexes, provide didactic chromophore species for demonstrating the Raman, resonance Raman, and the surface-enhanced Raman scattering (SERS) behavior in coordination chemistry, as well as for elucidating the nature of inner-sphere and outer-sphere association with plasmonic nanoparticles. Their electrostatically stabilized ion pairs with citrate–gold nanoparticles have been studied in an aqueous solution, from the pronounced changes in the plasmonic band at 540 nm. Complex A, lacking any coordinating site, can only generate outer-sphere complexes with citrate–gold nanoparticles, but they are stable enough to give a strong SERS response, even at 10⁻⁸ M. At 10⁻⁶ M, agglomeration accompanies the decrease of the electrostatic repulsion, resulting in a sharp decay of the plasmon resonance band at 540 nm. This is followed by the rise of a plasmon coupling band above 700 nm. However, at 10⁻⁴ M, the excess of the complex in the adsorption layer produces a reverse effect, decreasing agglomeration. The observed Raman spectra are essentially similar for the several concentrations employed because the outer-sphere interaction implies a SERS electromagnetic mechanism. In contrast, complex B exhibits several pyridine and pyrazine N-atoms available to form inner-sphere-associated species. A selective enhancement of the SERS signals is observed at 10⁻⁸ M, clearly indicating a chemical mechanism, consistent with a bridging mode. At 10⁻⁶ M and above, the agglomeration leads to a plasmon coupling band at 800 nm, while the SERS response indicates a change in the binding modes dictated by the excess of the complexing molecules.

中文翻译：

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金属配合物和金纳米粒子表面增强拉曼光谱中外球和内球缔合的影响

过渡金属络合物，例如低自旋双（苯基三联吡啶）（A）和双（吡啶三联吡嗪）铁（II）（B）络合物，提供了用于演示拉曼、共振拉曼和表面增强拉曼散射的教学发色团种类（SERS）在配位化学中的行为，以及阐明内球和外球与等离子体纳米颗粒关联的性质。已经在水溶液中研究了它们与柠檬酸盐-金纳米粒子的静电稳定离子对，从 540 nm 等离激元带的显着变化开始。复合物 A 缺乏任何配位位点，只能与柠檬酸盐-金纳米颗粒生成外球复合物，但它们足够稳定，即使在 10 ^-8  M 下也能产生强烈的 SERS 响应。在 10 ^-6  M 下，团聚伴随着浓度的降低静电斥力的影响，导致 540 nm 处的等离激元共振带急剧衰减。随后等离激元耦合带上升到 700 nm 以上。然而，在10 ^-4  M时，吸附层中过量的络合物会产生相反的效果，减少团聚。对于所采用的几种浓度，观察到的拉曼光谱本质上是相似的，因为外层相互作用意味着 SERS 电磁机制。相比之下，配合物 B 具有多个可用于形成内球相关物质的吡啶和吡嗪 N 原子。^{在10 -8} M处观察到SERS信号的选择性增强 ，清楚地表明化学机制，与桥接模式一致。在10 ^-6  M及以上，团聚导致800 nm处的等离激元耦合带，而SERS响应表明由过量络合分子决定的结合模式的变化。