Gonzálvez Miguel A, Bernhardt Paul V, Font-Bardia Mercè, Gallen Albert, Jover Jesús, Ferrer Montserrat, Martínez Manuel
School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia.
Secció de Química Inorgànica, Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
Inorg Chem. 2021 Dec 6;60(23):18407-18422. doi: 10.1021/acs.inorgchem.1c03001. Epub 2021 Nov 12.
The preparation of a series of alkali-metal inclusion complexes of the molecular cube [{Co(Me-tacn)}{Fe(CN)}] (Me-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), a mixed-valent Prussian Blue analogue bearing bridging cyanido ligands, has been achieved by following a redox-triggered self-assembly process. The molecular cubes are extremely robust and soluble in aqueous media ranging from 5 M [H] to 2 M [OH]. All the complexes have been characterized by the standard mass spectometry, UV-vis, inductively coupled plasma, multinuclear NMR spectroscopy, and electrochemistry. Furthermore, X-ray diffraction analysis of the sodium and lithium salts has also been achieved, and the inclusion of moieties of the form {M-OH} (M = Li, Na) is confirmed. These inclusion complexes in aqueous solution are rather inert to cation exchange and are characterized by a significant decrease in acidity of the confined water molecule due to hydrogen bonding inside the cubic cage. Exchange of the encapsulated cationic {M-OH} or M units by other alkali metals has also been studied from a kineticomechanistic perspective at different concentrations, temperatures, ionic strengths, and pressures. In all cases, the thermal and pressure activation parameters obtained agree with a process that is dominated by differences in hydration of the cations entering and exiting the cage, although the size of the portal enabling the exchange also plays a determinant role, thus not allowing the large Cs cation to enter. All the exchange substitutions studied follow a thermodynamic sequence that relates with the size and polarizing capability of the different alkali cations; even so, the process can be reversed, allowing the entry of {Li-OH} units upon adsorption of the cube on an anion exchange resin and subsequent washing with a Li solution.
通过氧化还原触发的自组装过程，制备了一系列分子立方体[{Co(Me-tacn)}{Fe(CN)}]（Me-tacn = 1,4,7-三甲基-1,4,7-三氮杂环壬烷）的碱金属包合物，该分子立方体是一种带有桥连氰基配体的混合价态普鲁士蓝类似物。这些分子立方体极其稳定，可溶于5 M [H⁺]至2 M [OH⁻]的水性介质中。所有配合物均通过标准质谱、紫外可见光谱、电感耦合等离子体、多核核磁共振光谱和电化学进行了表征。此外，还对钠盐和锂盐进行了X射线衍射分析，证实了{M-OH}（M = Li，Na）形式的部分被包合。这些水溶液中的包合物对阳离子交换相当惰性，并且由于立方笼内的氢键作用，受限水分子的酸度显著降低。还从动力学机理的角度研究了在不同浓度、温度、离子强度和压力下，用其他碱金属交换包封的阳离子{M-OH}或M单元的情况。在所有情况下，获得的热活化和压力活化参数与一个由进入和离开笼子的阳离子水合差异主导的过程一致，尽管允许交换的通道大小也起着决定性作用，因此不允许大的Cs⁺阳离子进入。所有研究的交换取代都遵循与不同碱金属阳离子的大小和极化能力相关的热力学序列；即便如此，该过程可以逆转，在立方体吸附到阴离子交换树脂上并随后用Li溶液洗涤后，允许{Li-OH}单元进入。
