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首页> 外文期刊>Chemistry: A European journal >Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy
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Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

机译：NMR和光谱显示溶剂和抗衡阴离子相互作用引起的质子化海绵阳离子氢桥的对称性

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The properties of the intramolecular hydrogen bonds of doubly 15N-labeled protonated sponges of the 1,8-bis(dimethylamino)naphthalene (DMANH+) type have been studied as a function of the solvent, counteranion, and temperature using low-temperature NMR spectroscopy. Information about the hydrogen-bond symmetries was obtained by the analysis of the chemical shifts dH and dN and the scalar coupling constants JACHTUNGTRENUNG(N,N), JACHTUNGTRENUNG( N,H), JACHTUNGTRENUNG(H,N) of the 15NH15N hydrogen bonds. Whereas the individual couplings JACHTUNGTRENUNG(N,H) and JACHTUNGTRENUNG(H,N) were averaged by a fast intramolecular proton tautomerism between two forms, it is shown that the sum j JACHTUNGTRENUNG(N,H)+JACHTUNGTRENUNG(H,N)j generally represents a measure of the hydrogen-bond strength in a similar way to dH and JACHTUNGTRENUNG(N,N). The NMR spectroscopic parameters of DMANH+ and of 4-nitro-DMANH+ are independent of the anion in the case of CD3CN, which indicates ion-pair dissociation in this solvent. By contrast, studies using CD2Cl2, [D8]toluene as well as the freon mixture CDF3/ CDF2Cl, which is liquid down to 100 K, revealed an influence of temperature and of the counteranions. Whereas a small counteranion such as trifluoroacetate perturbed the hydrogen bond, the large noncoordinating anion tetrakisACHTUNGTRENUNG[3,5-bis(trifluoromethyl)phenyl] borate BACHTUNGTRENUNG[{C6H3ACHTUNGTRENUNG(CF3)2}4] (BARF), which exhibits a delocalized charge, made the hydrogen bond more symmetric. Lowering the temperature led to a similar symmetrization, an effect that is discussed in terms of solvent ordering at low temperature and differential solvent order/disorder at high temperatures. By contrast, toluene molecules that are ordered around the cation led to typical high-field shifts of the hydrogen-bonded proton as well as of those bound to carbon, an effect that is absent in the case of neutral NHN chelates.
机译：使用低温NMR光谱研究了1,8-双（二​​甲基氨基）萘（DMANH +）类型的15N标记的双15N标记质子化海绵的分子内氢键的性质与溶剂，抗衡阴离子和温度的关系。通过分析化学位移dH和dN以及标量耦合常数JACHTUNGTRENUNG（N，N），JACHTUNGTRENUNG（N，H），JACHTUNGTRENUNG（H，N）的15NH15N氢键获得有关氢键对称性的信息。个别耦合JACHTUNGTRENUNG（N，H）和JACHTUNGTRENUNG（H，N）是由两种形式之间的快速分子内质子互变异构平均得出的，显示总和j JACHTUNGTRENUNG（N，H）+ JACHTUNGTRENUNG（H，N）j通常以类似于dH和JACHTUNGTRENUNG（N，N）的方式表示氢键强度的量度。在CD3CN的情况下，DMANH +和4-硝基-DMANH +的NMR光谱参数与阴离子无关，这表明在该溶剂中离子对解离。相比之下，使用CD2Cl2，[D8]甲苯以及低至100 K的液态氟利昂混合物CDF3 / CDF2Cl进行的研究揭示了温度和抗衡阴离子的影响。较小的抗衡阴离子（例如三氟乙酸根）会扰动氢键，而大的非配位阴离子四（CHS）TUNGTRENUNG [3,5-双（三氟甲基）苯基]硼酸钡BACHTUNGTRENUNG [{C6H3ACHTUNGTRENUNG（CF3）2} 4]（BARF）则表现出离域电荷，使氢键更加对称。降低温度会导致类似的对称化，这种效应在低温下的溶剂有序性和高温下的不同溶剂有序/无序性方面进行了讨论。相比之下，在阳离子周围排列的甲苯分子会导致氢键质子以及与碳键合的质子发生典型的高场位移，这在中性NHN螯合物中是不存在的。

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