Gasser Gilles, Belousoff Matthew J, Bond Alan M, Spiccia Leone
School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
Inorg Chem. 2007 May 14;46(10):3876-88. doi: 10.1021/ic061622+. Epub 2007 Apr 17.
The reaction of Cu(NO3)2.3H2O with the ligand 1-(ferrocenemethyl)-1,4,7,10-tetraazacyclododecane (L) in acetonitrile leads to the formation of a blue complex, [Cu(L)(NO3)][NO3] (C1). The X-ray structure determination shows an unexpected binding of a nitrate anion in that the CuII center is surrounded by four N atoms of the 1,4,7,10-tetraazacyclododecane (cyclen) macrocycle and two O atoms from a chelating nitrate anion, both Cu-O distances being below the sums of the van de Waals radii. Hydrogen-bonding interactions in the crystal lattice and a weak interaction between a second nitrate O and the CuII center in C1 give rise to a highly distorted CuII geometry relative to that found in the known structure of [Cu(cyclen)(NO3)][NO3] (C5). Electrochemical studies in acetonitrile containing 0.1 M [Bu4N][NO3] as the supporting electrolyte showed that oxidation of C1 in this medium exhibits a single reversible one-electron step with a formal potential E degrees f of +85 mV vs Fc0/+ (Fc = ferrocene). This process is associated with oxidation of the ferrocenyl pendant group. Additionally, a reversible one-electron reduction reaction with an E degrees f value of -932 mV vs Fc0/+, attributed to the CuII/I redox couple, is detected. Gradual change of the supporting electrolyte from 0.1 M [Bu4N][NO3] to the poorly coordinating [Bu4N][PF6] electrolyte, at constant ionic strength, led to a positive potential shift in E degrees f values by +107 and +39 mV for the CuII/I(C1) and Fc0/+(C1) redox couples, respectively. Analysis of these electrochemical data and UV-vis spectra is consistent with the probable presence of the complexes C1, [Cu(L)(CH3CN)2]2+ (C2), [Cu(L)(CH3CN)(NO3)]+ (C3), and [Cu(L)(NO3)2] (C4) as the major species in nitrate-containing acetonitrile solutions. In weakly solvating nitromethane, the extent of nitrate complexation remains significant even at low nitrate concentrations, due to the lack of solvent competition.
硝酸铜三水合物（Cu(NO₃)₂·3H₂O）与配体1-(二茂铁甲基)-1,4,7,10-四氮杂环十二烷（L）在乙腈中反应生成蓝色配合物[Cu(L)(NO₃)][NO₃]（C1）。X射线结构测定显示出一种意想不到的硝酸根阴离子配位情况，即CuII中心被1,4,7,10-四氮杂环十二烷（环壬四胺）大环的四个N原子以及来自螯合硝酸根阴离子的两个O原子所包围，两个Cu - O距离均低于范德华半径之和。晶格中的氢键相互作用以及C1中第二个硝酸根O与CuII中心之间的弱相互作用导致相对于已知结构的[Cu(环壬四胺)(NO₃)][NO₃]（C5），CuII的几何结构发生了高度扭曲。在含有0.1 M [Bu₄N][NO₃]作为支持电解质的乙腈中的电化学研究表明，在该介质中C1的氧化表现出一个单一的可逆单电子步骤，相对于Fc⁰/⁺（Fc = 二茂铁）的形式电位E⁰f为 +85 mV。这个过程与二茂铁基侧链的氧化有关。此外，检测到一个可逆的单电子还原反应，相对于Fc⁰/⁺的E⁰f值为 -932 mV，归因于CuII/I氧化还原对。在恒定离子强度下，将支持电解质从0.1 M [Bu₄N][NO₃]逐渐变为配位能力较弱的[Bu₄N][PF₆]电解质，导致CuII/I（C1）和Fc⁰/⁺（C1）氧化还原对的E⁰f值分别正向电位偏移 +107 mV和 +39 mV。对这些电化学数据和紫外可见光谱的分析与在含硝酸盐的乙腈溶液中可能存在配合物C1、[Cu(L)(CH₃CN)₂]²⁺（C2）、[Cu(L)(CH₃CN)(NO₃)]⁺（C3）和[Cu(L)(NO₃)₂]（C4）作为主要物种一致。在弱溶剂化的硝基甲烷中，由于缺乏溶剂竞争，即使在低硝酸盐浓度下，硝酸盐络合程度仍然很高。
