Estimation of the acceptor numbers of cations by means of an acid-base indicator
Estimation of the acceptor numbers of cations by means of an acid-base indicator
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DOI：
10.1080/00958979708230435
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发表时间：
1997-01-01
影响因子：
1.9
通讯作者：
Taha, A
中科院分区：
文献类型：
--
作者：
Linert, W;Jameson, RF;Taha, A
本文研究了Fe(Phen)(2)(CN)(2)在不同溶剂中由于溶剂分子或阳离子物种与-CN基团(S)上的自由电子对相互作用而引起的可见电荷转移吸收带的移动，并用这些结果建立了阳离子，Mn+在低给体度溶剂中的受主数目(An(M，NM))。硝基甲烷(NM)既是一种非常弱的供体溶剂，又是一种相对弱的受体溶剂，因此一直被用作参考溶剂。(为了确保阳离子物种和Fe(Phen)(2)(CN)(2)指示剂的溶解性，溶剂必须表现出一定的给体和接受体性质。)还给出了阳离子在不同溶剂中的表观受主数(An(M，solv))，并用它来说明阳离子的受主性质与溶剂的给体数目直接相关(即，阳离子的有效受主数目随DNSolv的增加而减少。这是由于溶剂和受体离子对用作Lewis酸指示剂的Fe(Phen)(2)(CN)(2)的竞争所致。并与类似络合物Ru(Phen)(2)(CN)(2)的光谱位移进行了比较。讨论了所提出的阳离子标度与其他阳离子Lewis酸度的实际测量和理论测量之间的关系。
The shift of the visible charge-transfer absorption bands of Fe(phen)(2)(CN)(2) in various solvents resulting from the interaction of solvent molecules or of cationic species with the free electron pair on the -CN group(s) has been investigated and the results have been used to establish Acceptor Numbers (AN(M,NM)) for cations, Mn+, dissolved in solvents of low donicity. Nitromethane (NM) has been used as a reference solvent because it is both a very weak donor and a relatively weak acceptor solvent. (The solvent must exhibit some donor and acceptor properties in order to ensure solubility of the cationic species and the Fe(phen)(2)(CN)(2) indicator.) Apparent Acceptor Numbers (AN(M,solv)) for cations dissolved in various solvents other than nitromethane are also given and used to show that the acceptor properties of cations vary in a way directly related to the Donor Number of the solvent (i.e., a decrease in the effective Acceptor Number of the cations is observed with increasing DNSolv. This arises from competition between solvent and acceptor ion for the Fe(phen)(2)(CN)(2) used as the Lewis-acid indicator). Results are compared with the spectroscopic shift of the analogous complex Ru(phen)(2)(CN)(2). The relationship between the proposed AN scale for cations and other practical and theoretical measurements of the Lewis acidity of cations is discussed.