Break-Junction Studies on Paddle-Wheel Complexes with Four Lateral Anchor Groups: Small Influence of Metal-Metal Bond Order

IF 5.1 3区材料科学 Q1 CHEMISTRY, MULTIDISCIPLINARY

Nanoscale Pub Date : 2025-09-30 DOI:10.1039/d5nr01695a

André Mang, Katawoura Beltako, Besa Kadriu, Michael Linseis, Fabian Pauly, Rainer R.F. Winter

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Abstract

This contribution investigates the role of the metal-metal bond in paddle-wheel complexes for molecular conductance. To these ends, we compare two pairs of Mo and Rh paddle-wheel complexes M2(LN)4 and M2(LSMe)4 (M = Rh, Mo), each with four lateral 4-pyridyl- (LN-) or 4-(methylthio)- (LSMe-) functionalized benzamidinate ligands mutually disposed at 90° angles. These complexes represent bond orders of 4 (Mo) and 1 (Rh), while offering metal-based highest occupied frontier orbitals of the same δ symmetry. The structural features of the complexes were established by X-ray diffraction on single crystals. Molecular conductance measurements were performed with the aid of a scanning-tunnelling microscopy break-junction setup and revealed that the Mo complexes surpass their Rh congeners. Decoration of the paddle-wheel complexes with four laterally disposed anchor groups results in four different possible modes of molecule attachment to the Au electrodes with two, three or even four anchoring points. The conductances of possible junction geometries were assessed quantum chemically with the DFT+Σ approach using Au slab electrodes. Calculated variations by about one order of magnitude for the different anchoring geometries can explain the rather broad conductance distributions observed in our experiments. Further transport calculations considered two-point molecule attachment to sharp or blunt nanoelectrodes for mutual cis and trans dispositions of the anchor groups. Our computational results indicate that the better performance of the Mo complexes originates from superior conjugation between the Mo2 δ-binding and the ligand π orbitals as compared to the Rh2 δ* orbital, rather than from the larger metal-metal bond order. Upon increasing the bias voltage, we observed a new conductance feature associated with a nearly 100 times higher G value, which we ascribe tentatively to oxidation of the molecule inside the junction

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具有四个横向锚基的桨轮配合物的断结研究：金属-金属键序的小影响

这篇文章研究了金属-金属键在桨轮配合物中对分子电导的作用。为此，我们比较了两对Mo和Rh桨轮配合物M2(LN)4和M2(LSMe)4 (M = Rh, Mo)，每个配合物都有四个横向4-吡啶基-(LN-)或4-（甲基硫代）- (LSMe-)功能化的苯甲酰胺配体，它们以90°角相互配置。这些配合物的键序为4 （Mo）和1 (Rh)，同时提供相同δ对称的金属基最高已占边界轨道。通过单晶x射线衍射确定了配合物的结构特征。分子电导测量是在扫描隧道显微镜的帮助下进行的，发现Mo配合物超过了它们的Rh同系物。用四个横向定位的锚基团修饰桨轮配合物，导致分子以四种不同的模式附着在具有两个、三个甚至四个锚点的Au电极上。使用Au板电极，用DFT+Σ方法对可能的结几何形状的电导进行量子化学评估。计算出的不同锚固几何形状的变化约为一个数量级，可以解释我们在实验中观察到的相当广泛的电导分布。进一步的输运计算考虑两点分子附着在锋利或钝的纳米电极上，以实现锚基团的相互顺式和反式配置。我们的计算结果表明，Mo配合物的更好的性能来自于Mo2 δ键与配体π轨道之间比Rh2 δ*轨道更优越的共轭关系，而不是来自于更大的金属-金属键序。在增加偏置电压后，我们观察到一个新的电导特征，与近100倍的高G值相关，我们暂时将其归因于结内分子的氧化

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Nanoscale CHEMISTRY, MULTIDISCIPLINARY-NANOSCIENCE & NANOTECHNOLOGY

CiteScore

12.10

自引率

3.00%

发文量

1628

审稿时长

1.6 months

期刊介绍： Nanoscale is a high-impact international journal, publishing high-quality research across nanoscience and nanotechnology. Nanoscale publishes a full mix of research articles on experimental and theoretical work, including reviews, communications, and full papers.Highly interdisciplinary, this journal appeals to scientists, researchers and professionals interested in nanoscience and nanotechnology, quantum materials and quantum technology, including the areas of physics, chemistry, biology, medicine, materials, energy/environment, information technology, detection science, healthcare and drug discovery, and electronics.