Department of Chemistry, University of Calgary, Calgary, AB, Canada T2N 1N4.
Inorg Chem. 2012 Oct 15;51(20):10619-30. doi: 10.1021/ic300852t. Epub 2012 Sep 27.
The complexes formed in methanol solutions of Cd(CF(3)SO(3))(2) with selenourea (SeU) or thiourea (TU), for thiourea also in aqueous solution, were studied by combining (113)Cd NMR and X-ray absorption spectroscopy. At low temperature (~200 K), distinct (113)Cd NMR signals were observed, corresponding to CdL(n)(2+) species (n = 0-4, L = TU or SeU) in slow ligand exchange. Peak integrals were used to obtain the speciation in the methanol solutions, allowing stability constants to be estimated. For cadmium(II) complexes with thione (C═S) or selone (C═Se) groups coordinated in Cd(S/Se)O(5) or Cd(S/Se)(2)O(4) (O from MeOH or CF(3)SO(3)(-)) environments, the (113)Cd chemical shifts were quite similar, within 93-97 ppm and 189-193 ppm, respectively. However, the difference in the chemical shift for the Cd(SeU)(4)(2+) (578 pm) and Cd(TU)(4)(2+) (526 ppm) species, with CdSe(4) and CdS(4) coordination, respectively, shows less chemical shielding for the coordinated Se atoms than for S, in contrast to the common trend with increasing shielding in the following order: O > N > Se > S. In solutions dominated by mono- and tetra-thiourea/selenourea complexes, their coordination and bond distances could be evaluated by Cd K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. At ~200 K and high excess of thiourea, a minor amount (up to ~30%) of Cd(TU)(5-6) species was detected by an upfield shift of the (113)Cd NMR signal (up to 423 ppm) and an amplitude reduction of the EXAFS oscillation. The amount was estimated by fitting linear combinations of simulated EXAFS spectra for Cd(TU)(4) and Cd(TU)(6) complexes. At room temperature, Cd(TU)(4) was the highest complex formed, also in aqueous solution. Cd L(3)-edge X-ray absorption near edge structure (XANES) spectra of cadmium(II) thiourea solutions in methanol were used to follow changes in the CdS(x)O(y) coordination. The correlations found from the current and previous studies between (113)Cd NMR chemical shifts and different Cd(II) coordination environments are generally useful for evaluating cadmium coordination to thione-containing or Se-donor ligands in biochemical systems or for monitoring speciation in solution.
在甲醇溶液中，研究了 Cd(CF3SO3)2与硒脲（SeU）或硫脲（TU）形成的配合物，对于 TU 也在水溶液中进行了研究，结合113Cd NMR 和 X 射线吸收光谱。在低温（200 K）下，观察到明显的113Cd NMR 信号，对应于缓慢配体交换中的 CdL(n)(2+)物种（n = 0-4，L = TU 或 SeU）。通过峰积分获得甲醇溶液中的形态，从而估算稳定常数。对于具有配位在 Cd(S/Se)O(5)或 Cd(S/Se)(2)O(4)（来自 MeOH 或 CF3SO3-的 O）环境中的硫酮（C═S）或硒酮（C═Se）基团的 Cd(II)配合物，113Cd 化学位移非常相似，分别在 93-97 ppm 和 189-193 ppm 范围内。然而，Cd(SeU)(4)(2+)（578 pm）和 Cd(TU)(4)(2+)（526 ppm）物种的 Cd 化学位移差异表明，与 S 相比，配位的 Se 原子的化学屏蔽较小，与以下常见趋势相反：O > N > Se > S，随着屏蔽的增加而增加。在以单和四硫脲/硒脲配合物为主的溶液中，通过 Cd K 边扩展 X 射线吸收精细结构（EXAFS）光谱可以评估它们的配位和键距离。在200 K 和硫脲过量的情况下，通过（113）Cd NMR 信号的向上位移（高达 423 ppm）和 EXAFS 振荡的幅度降低，检测到少量（高达~30%）Cd(TU)(5-6)物种。通过拟合Cd(TU)(4)和Cd(TU)(6)配合物的模拟 EXAFS 光谱的线性组合来估计数量。在室温下，Cd(TU)(4)是形成的最高配合物，在水溶液中也是如此。甲醇中 Cd(II)硫脲溶液的 Cd L(3)-边 X 射线吸收近边结构（XANES）光谱用于跟踪 CdS(x)O(y)配位的变化。当前和以前的研究之间发现的113Cd NMR 化学位移与不同的 Cd(II)配位环境之间的相关性通常可用于评估生物化学系统中含硫酮或 Se 供体配体的 Cd 配位，或用于监测溶液中的形态。
