Distinguishing between aquo and hydroxo coordination in molecular copper complexes by 1H and 17O ENDOR spectroscopy

IF 3.5 3区化学 Q2 CHEMISTRY, INORGANIC & NUCLEAR

Dalton Transactions Pub Date : 2024-11-21 DOI:10.1039/d4dt02708f

Julia Haak, George E. Cutsail

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Abstract

Aquo and hydroxo ligands play an essential role in the chemistry of many copper enzymes and small molecule catalysts. The formation of a series of copper complexes with H₂O and OH⁻ ligands in various positions, including [Cu(bpy)(OAc)(H₂O)_2,ax]⁺ (Cu-I), [Cu(bpy)(OH)_2,eq(H_xO)_2,ax] (Cu-III), [Cu(OH)_4,eq(H_xO)_2,ax]²⁻ (Cu-IV), [Cu(bpy)(H₂O)_2,eq(H₂O)_2,ax]²⁺ (Cu-V) and [Cu(bpy)₂(H₂O)_ax]²⁺ (Cu-VI), were investigated through Electron Paramagnetic Resonance (EPR) and UV-Vis spectroscopy in aqueous copper bipyridine solutions in the dependence of the pH and the copper-to-bipyridine ratio (bpy = 2,2′-bipyridine). ²H- and ¹⁷O-enrichment of the copper complexes allowed us to determine the ¹H and ¹⁷O nuclear hyperfine interactions of their H_xO ligands via Q-band Electron Nuclear Double Resonance (ENDOR) spectroscopy. These techniques gave direct insight into the metal–ligand covalencies and geometries and were further supported by Density Functional Theory (DFT) calculations. It is shown that ¹H and ¹⁷O ENDOR spectroscopy can aid in (1) determining the coordination position, thereby differentiating between equatorial and axial H_xO ligands and (2) distinguishing equatorial aqua and hydroxo ligands, particularly through their anisotropic dipolar components. We further studied the influence of trans coordinating ligands on the hyperfine parameters of aquo and hydroxo ligands, enabled through contrasting the coordination environments in the examined complexes, supported by quantum chemical computations.

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通过 1H 和 17O ENDOR 光谱区分分子铜络合物中的水配位和羟配位

水氧配体和羟基配体在许多铜酶和小分子催化剂的化学过程中发挥着重要作用。在不同位置与 H2O 和 OH- 配体形成一系列铜配合物，包括 [Cu(bpy)(OAc)(H2O)2,ax]+ (Cu-I)、[Cu(bpy)(OH)2,eq(HxO)2,ax] (Cu-III)、[Cu(OH)4,eq(HxO)2,ax]2- (Cu-IV)、[Cu(bpy)(H2O)2,eq(H2O)2、ax]2+（Cu-V）和[Cu(bpy)2(H2O)ax]2+（Cu-VI），通过电子顺磁共振（EPR）和紫外可见光谱研究了双吡啶铜水溶液中 pH 值和铜与双吡啶比率（bpy = 2,2′-双吡啶）的变化。铜络合物的 2H 和 17O 富集使我们能够通过 Q 波段电子核双共振（ENDOR）光谱测定其 HxO 配体的 1H 和 17O 核超频相互作用。这些技术直接揭示了金属配体的共价关系和几何结构，并得到了密度泛函理论（DFT）计算的进一步支持。研究表明，1H 和 17O ENDOR 光谱有助于 (1) 确定配位位置，从而区分赤道和轴向 HxO 配体，以及 (2) 区分赤道水配体和羟配体，特别是通过其各向异性的偶极成分。我们进一步研究了反式配位体对水氧配位体和羟基配位体超频参数的影响，通过量子化学计算的支持，对比了所研究配合物中的配位环境。

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

Dalton Transactions 化学-无机化学与核化学

CiteScore

6.60

自引率

7.50%

发文量

1832

审稿时长

1.5 months

期刊介绍： Dalton Transactions is a journal for all areas of inorganic chemistry, which encompasses the organometallic, bioinorganic and materials chemistry of the elements, with applications including synthesis, catalysis, energy conversion/storage, electrical devices and medicine. Dalton Transactions welcomes high-quality, original submissions in all of these areas and more, where the advancement of knowledge in inorganic chemistry is significant.