Rasouli Zolaikha, Irani Mehdi, Jafari Sonia, Ghavami Raouf
Chemometrics Laboratory, Chemistry Department, Faculty of Science, University of Kurdistan, P.O. Box 416, 66177-15175, Sanandaj, Iran.
Theoretical Chemistry Laboratory, Chemistry Department, Faculty of Science, University of Kurdistan, P.O. Box 416, 66177-15175, Sanandaj, Iran.
Sci Rep. 2021 Mar 19;11(1):6465. doi: 10.1038/s41598-021-85940-w.
In this study, we determine the acidity constants of methylthymol blue (MTB) and association constants of its complexes with the Zn, Cu, and Fe metal ions (MIs), through theoretical and experimental means. The complexes were characterized using UV-Visible absorption spectroscopy combined with soft/hard chemometrics methods and quantum chemical calculations. Quantum chemical calculations revealed that electronic transitions in the UV-Visible spectra of MTB have mixed n → π* and π → π* characters. The results of molar ratio and multivariate curve resolution alternating least squares (MCR-ALS) revealed the formation of successive 1:2 and 1:1 complexes (MI:MTB) for the Zn and Cu systems. However, the formation of successive 1:1 and 2:1 complexes are suggested for Fe by the molar ratio and MCR-ALS. The majority of transitions observed in the UV-Visible spectra of the Zn(MTB) and Cu(MTB) complexes have ligand-to-ligand charge transfer (LLCT) characters. However, the transitions in the UV-Visible spectrum of the Fe(MTB) complex have LLCT and metal-to-ligand charge transfer (MLCT) characters. For the Fe(MTB) complex, the lowest energy transition of has an LLCT character. However, its higher energy transitions are a mixture of LLCT, MLCT, and metal-to-metal charge transfer (MMCT) characters. The correlation between experimental and computed wavelengths revealed that the 1:1 complexes of Zn and Cu prefer square pyramidal geometries. However, the Fe complexes always show octahedral geometry.
在本研究中，我们通过理论和实验手段测定了甲基百里酚蓝（MTB）的酸度常数及其与锌、铜和铁金属离子（MIs）形成配合物的缔合常数。采用紫外可见吸收光谱结合软/硬化学计量学方法和量子化学计算对配合物进行了表征。量子化学计算表明，MTB紫外可见光谱中的电子跃迁具有混合的n → π和π → π特征。摩尔比和多元曲线分辨交替最小二乘法（MCR-ALS）的结果表明，锌和铜体系形成了连续的1:2和1:1配合物（MI:MTB）。然而，摩尔比和MCR-ALS表明铁形成了连续的1:1和2:1配合物。在Zn(MTB)和Cu(MTB)配合物的紫外可见光谱中观察到的大多数跃迁具有配体间电荷转移（LLCT）特征。然而，Fe(MTB)配合物的紫外可见光谱中的跃迁具有LLCT和金属-配体电荷转移（MLCT）特征。对于Fe(MTB)配合物，最低能量跃迁具有LLCT特征。然而，其较高能量跃迁是LLCT、MLCT和金属-金属电荷转移（MMCT）特征的混合。实验波长与计算波长之间的相关性表明，锌和铜的1:1配合物倾向于四方锥几何构型。然而，铁配合物总是呈现八面体几何构型。
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