New [2 × 2] Copper(I) Grids as Anion Receptors. Effect of Ligand Functionalization on the Ability to Host Counteranions by Hydrogen Bonds

Several complexes with a [2 × 2] grid structure have been obtained by the self-assembly of different copper(I) salts and ligands of the type 4,6-bis(pyrazol-1-yl)pyrimidine containing different substituents on the heterocycles. The main goal has been to evaluate the influence over the solid state and solution behavior of the functionalization of the pyrimidine ring with a primary amino substituent. The molecular and crystalline structures of some derivatives have been determined by X-ray diffraction. The grids contain two open voids formed by pairs of ligands facing one another on opposite sides of the grid in a somewhat divergent manner. One counteranion is hosted in each void interacting through hydrogen bonds and anion−π interactions. The presence of the amino group that points toward the inside of the cavity dominates the interactions in the void and apparently determines the orientation of the hosted counteranion and that of the ligands. With the exception of the derivative with chloride as the anion, the grid structure is preserved in solution (NMR and UV−vis) and some cation−anion interaction, increased by the presence of the amino group, exists also in solution (DOSY experiments). The experiments of anion interchange performed in solution indicate that a higher stability is found for the host−guest aggregates with OTs− (p-Me-C6H4SO3) and NO3−. While for these anions a 1:2 stoichiometry is reached, for the rest of the anions tested (ReO4−, OTf−, and PF6−), only weaker 1:1 complexes are formed. Computational studies support the presence of anion−π interactions.

通过不同铜(I)盐与杂环上带有不同取代基的4,6-双(1-吡唑基)嘧啶(4,6-bis(pyrazol-1-yl)pyrimidine)类配体的自组装，成功构建了一系列具有[2×2]网格结构的铜(I)配合物。本研究的核心目标为考察伯氨基取代基对嘧啶环进行官能化后，配合物在固态与溶液中的行为变化规律。部分衍生物的分子结构与晶体结构通过X射线衍射(X-ray diffraction)法得以解析。该网格结构包含两个开放式空腔：成对配体以略微发散的姿态分别位于网格两侧并相互对置，从而形成上述空腔。每个空腔内均容纳一个抗衡阴离子，该阴离子通过氢键与阴离子-π相互作用(anion−π interactions)与空腔主体结合。指向空腔内部的氨基基团主导了空腔内的所有相互作用，并显著决定了所容纳的抗衡阴离子以及配体的空间取向。除抗衡阴离子为氯离子的衍生物外，其余配合物的网格结构在溶液中（核磁共振(NMR)与紫外-可见(UV−vis)光谱测试）均得以保持；且溶液中还存在受氨基作用增强的阳离子-阴离子相互作用，该现象可通过扩散序谱(DOSY)实验得以证实。溶液中的阴离子交换实验表明，以OTs⁻(p-Me-C₆H₄SO₃，对甲基苯磺酸根)与NO₃⁻(硝酸根)为客体的主客体聚集体(host−guest aggregates)具有更高的稳定性。对于上述两种阴离子，主客体聚集体的化学计量比为1:2；而对于其余测试阴离子（ReO₄⁻，高铼酸根；OTf⁻，三氟甲磺酸根；PF₆⁻，六氟磷酸根），仅能形成结合力较弱的1:1型配合物。计算化学研究结果进一步证实了阴离子-π相互作用的存在。