Busato Matteo, Tofoni Alessandro, Mannucci Giorgia, Tavani Francesco, Del Giudice Alessandra, Colella Andrea, Giustini Mauro, D'Angelo Paola
Department of Chemistry, University of Rome "La Sapienza", P.le A. Moro 5, Rome 00185, Italy.
Inorg Chem. 2022 Jun 13;61(23):8843-8853. doi: 10.1021/acs.inorgchem.2c00864. Epub 2022 May 26.
The metal-based deep eutectic solvent (MDES) formed by NiCl·6HO and urea in 1:3.5 molar ratio has been prepared for the first time and characterized from a structural point of view. Particular accent has been put on the role of water in the MDES formation, since the eutectic could not be obtained with the anhydrous form of the metal salt. To this end, mixtures at different water/MDES molar ratios () have been studied with a combined approach exploiting molecular dynamics and simulations, UV-vis and near-infra-red spectroscopies, small- and wide-angle X-ray scattering, and X-ray absorption spectroscopy measurements. In the pure MDES, a close packing of Ni ion clusters forming oligomeric agglomerates is present thanks to the mediation of bridging chloride anions and water molecules. Conversely, urea poorly coordinates the metal ion and is mostly found in the interstitial regions among the Ni ion oligomers. This nanostructure is disrupted upon the introduction of additional water, which enlarges the Ni-Ni distances and dilutes the system up to an aqueous solution of the MDES constituents. In the NiCl·6HO 1:3.5 MDES, the Ni ion is coordinated on average by one chloride anion and five water molecules, while water easily saturates the metal solvation sphere to provide a hexa-aquo coordination for increasing values. This multidisciplinary study allowed us to reconstruct the structural arrangement of the MDES and its aqueous mixtures on both short- and intermediate-scale levels, clarifying the fundamental role of water in the eutectic formation and challenging the definition at the base of these complex systems.
首次制备了由氯化镍六水合物（NiCl₂·6H₂O）和尿素以1:3.5摩尔比形成的金属基深共熔溶剂（MDES），并从结构角度对其进行了表征。特别强调了水在MDES形成过程中的作用，因为使用金属盐的无水形式无法获得共熔物。为此，采用分子动力学和模拟、紫外可见光谱和近红外光谱、小角和广角X射线散射以及X射线吸收光谱测量等综合方法，研究了不同水/MDES摩尔比（）的混合物。在纯MDES中，由于桥连氯离子和水分子的介导作用，存在形成低聚团聚体的镍离子簇紧密堆积结构。相反，尿素与金属离子的配位能力较差，主要存在于镍离子低聚物之间的间隙区域。引入额外的水会破坏这种纳米结构，这会增大镍-镍间距并使系统稀释直至形成MDES成分的水溶液。在NiCl₂·6H₂O 1:3.5的MDES中，镍离子平均由一个氯离子阴离子和五个水分子配位，而随着水含量增加，水很容易使金属溶剂化球饱和，从而提供六水配位。这项多学科研究使我们能够在短尺度和中尺度水平上重构MDES及其水性混合物的结构排列，阐明了水在共熔物形成中的基本作用，并对这些复杂体系的基础定义提出了挑战。
