Investigation of the extraction complexes of palladium(ii) with novel thiodiglycolamide and dithiodiglycolamide ligands by EXAFS and computational methods
作者:R. Ruhela、B. S. Tomar、A. K. Singh、R. C. Hubli、A. K. Suri
DOI:10.1039/c3dt32417f
日期:——
The structure of the extraction complexes of palladium(II) with novel ligands, namely, N,N,N′,N′-tetra-(2-ethylhexyl) thiodiglycolamide (T(2EH)TDGA) and N,N,N′,N′-tetra-(2-ethylhexyl) dithiodiglycolamide (DTDGA), have been determined by extended X-ray absorption fine structure spectroscopy (EXAFS). The interpretation of the EXAFS data is well supported by theoretical calculations of the complex geometry based on density functional theory (DFT). T(2EH)TDGA, having one thioetheric ‘S’ atom, forms a square planar complex with the Pd(II) ion, exhibiting 2 : 1 stoichiometry with one sulphur atom and one carbonyl oxygen atom from each T(2EH)TDGA molecule interacting with Pd(II) at distances of 2.24 and 2.04 Å, respectively. On the other hand, DTDGA, having two ‘S’ atoms in addition to two carbonyl groups, forms a square planar complex with Pd(II), exhibiting 1 : 1 stoichiometry, wherein both the sulphur atoms and the carbonyl oxygen of DTDGA interact with Pd(II) at distances of 2.29 and 2.05 Å, respectively. The slight distortion from the perfect square planar geometry could be attributed to the steric hindrance imposed by the bulky alkyl group of the amidic moieties. DFT calculations for the Pd–ligand complexes show that the Pd(II)–DTDGA complex with 1 : 1 stoichiometry is energetically more stable than the Pd(II)–T(2EH)TDGA complex with 1 : 2 stoichiometry. Among the two possible Pd(II)–T(2EH)TDGA complex geometries, the cis configuration appears more favorable. The methodology of fitting the EXAFS data has been validated by fitting the EXAFS data of a Pd(II)–aquo complex which showed square planar geometry with two axial water molecules constituting the secondary hydration sphere.
扩展 X 射线吸收精细结构光谱(EXAFS)测定了钯(II)与新型配体,即 N,N,N′,N′-四(2-乙基己基)硫代二甘醇酰胺(T(2EH)TDGA)和 N,N,N′,N′-四(2-乙基己基)二硫代二甘醇酰胺(DTDGA)的萃取配合物的结构。基于密度泛函理论(DFT)对复合物几何形状进行的理论计算为 EXAFS 数据的解释提供了有力支持。T(2EH)TDGA 具有一个硫醚 "S "原子,与钯(II)离子形成方形平面配合物,呈现出 2 :每个 T(2EH)TDGA 分子中的一个硫原子和一个羰基氧原子与钯(II)的相互作用距离分别为 2.24 Å 和 2.04 Å。另一方面,DTDGA 除了两个羰基外,还具有两个 "S "原子,与钯(II)形成方形平面配合物,显示出 1 :1 的比例,其中 DTDGA 的硫原子和羰基氧与钯(II)的相互作用距离分别为 2.29 Å 和 2.05 Å。与完美的正方形几何形状相比,DTDGA 稍有变形,这可能是由于酰胺分子中的大块烷基造成的立体阻碍。钯配体复合物的 DFT 计算表明,配比为 1 :1 的 Pd(II)-T(2EH)TDGA 复合物比 1:2 的 Pd(II)-T(2EH)TDGA 复合物能量更稳定。在两种可能的 Pd(II)-T(2EH)TDGA 复合物几何结构中,顺式构型似乎更有利。拟合 Pd(II)-aquo 复合物的 EXAFS 数据验证了拟合 EXAFS 数据的方法。