Complex formation (1:1) between lanthanoids(III) and 2-(5-bromo-2-pyridylazo)-5-(N-propyl-3-sulfopropylamino)phenol (5-Br-PAPS, HL) has been studied by spectrophotometry at 25 °C and at I=0.1 (NaNO3). The protonated complex MHL is found to exist in equilibrium with the normal complex ML at pH 5–6. The formation constants KML and KMHL are obtained by a graphical analysis. The KML values uniformly increase with increasing atomic number except for those in the Gd–Ho region where a distinct decrease is observed. However, there is little variation in the KMHL values with atomic number. A linear relation holds well between log KML values of 5-Br-PAPS and 4-(2-pyridylazo)resorcinol (PAR) complexes for the elements up to Eu(III), the intercept of which reflects the difference in the basicity of the oxygen atom ortho to the azo group between the two ligands. This is not the case for log KMHL of the two systems.
研究了
镧系元素 (III) 和 2-(5-
溴-2-
吡啶偶氮)-5-(N-丙基-3-磺基丙
氨基)
苯酚 (5-Br-P
APS, HL) 之间的络合物形成 (1:1)在 25 °C 和 I=0.1 (NaNO3) 下进行分光光度测定。发现质子化复合物
MHL 在 pH 5-6 时与正常复合物 ML 处于平衡状态。形成常数KML和K
MHL通过图形分析获得。 KML 值随着原子序数的增加而均匀增加,除了在 Gd-Ho 区域中观察到明显下降的值。然而,K
MHL 值随原子序数的变化很小。对于Eu(III)以下的元素,5-Br-P
APS和4-(2-
吡啶偶氮)
间苯二酚(PAR)络合物的log KML值之间存在良好的线性关系,其截距反映了元素碱度的差异。氧原子位于两个
配体之间的偶氮基团的邻位。两个系统的 log K
MHL 的情况并非如此。