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Complexation of Metal Ions by Ligands
Published in James F. Pankow, Aquatic Chemistry Concepts, 2018
When a ligand has one electron pair available for binding to a metal, it is said to be “monodentate” or “unidentate” (i.e., “single-toothed”). Ligands with two, three, four, etc. available electron pairs that are located geometrically on the ligand such that they are capable of binding simultaneously with a metal ion are referred to as being “bidentate,” “tridentate,” “tetradentate,” etc., respectively. Generically, the terms “multidentate” and “polydentate” are used to refer to any ligand with two or more binding sites.
Orbital Tuning of Ruthenium Polyimine Complexes by Ligand Design: From Basic Principles to Applications
Published in Ajay Kumar Mishra, Lallan Mishra, Ruthenium Chemistry, 2018
Joe Otsuki, Guohua Wu, Ryuji Kaneko, Yayoi Ebata
We prepared a set of three complexes, PYZ, TRZ, and TEZ dyes (Wu et al., 2016a). The tridentate anchoring ligand of these complexes are common terpyridine tricarboxylic acid. The tridentate ancillary ligand has a pyridine and an azole as well as a cyclometalating moieties. The azole group is deprotonated in the complexes, coordinating to ruthenium as an azolate anion. The ancillary ligand is thus a dianionic and the overall charge of the complex is neutral. The asymmetric nature of the ancillary ligand lifts the degeneracy of transitions and would help broaden the absorption range in the spectrum. On going from TRZ dye to TEZ dye, the number of an electron-withdrawing nitrogen atom increases but at the same time an electron-withdrawing CF3 group is removed. It is not obvious from inspection of the structure which one is more electron withdrawing. Electrochemical and spectroscopic investigation revealed the HOMO and LUMO levels for these complexes, which are shown in Fig. 6.22. The HOMO and LUMO of TEZ are slightly more stabilized than those of TRZ dye. This observation reveals that the additional nitrogen atom in the azole ring is slightly more electron withdrawing than the CF3 group. These dyes exhibit similar absorption feature and panchromatic absorption covering the visible and near-IR region. The efficiencies of DSSCs using PYZ, TRZ, and TEZ dyes as the sensitizer dye recorded 3.09%, 4.16%, and 6.44%, respectively, compared to 8.46% by N719 under the same experimental set up. TEZ dye has the smallest driving force for electron injection to the conduction band of TiO2, but it has the largest driving force for regeneration by the iodide ions in the electrolyte solution. Time-resolved measurement indicated that the rates of charge injection from these complexes are similarly fast in tens of picoseconds, while the regeneration rates are in the order of TEZ dye > TRZ dye > PYZ dye. We concluded from these observations that the regeneration of the dye is the determining factor for the performance of the set of dyes. Finally, the efficiency of TEZ DSSCs remained to be over 90% of the initial value over 1000 h light irradiation. The tridentate ligands are apparently beneficial for the long term stability of the complexes.
The Coordination Chemistry and Stoichiometry of Extracted Diglycolamide Complexes of Lanthanides in Extraction Chromatography Materials
Published in Solvent Extraction and Ion Exchange, 2022
Ramedy Flores, M. Abdul Momen, Mary R. Healy, Santa Jansone-Popova, Kevin L. Lyon, Benjamin Reinhart, Michael C. Cheshire, Bruce A. Moyer, Vyacheslav S. Bryantsev
Despite the uncertainties associated with characterization of the local structure of amorphous solids, a reasonable structural model of Dy coordination at high loading emerges from the combination of EXAFS and DFT modeling studies. Whenever the DGA loading based on 2:1 ligand-to-metal ratio is close to 100%, there is a drop in the intensities of the FT-EXAFS correlation peaks indicating that on average there are less than three DGA ligands around each Dy3+. In the most informative case involving extraction by the DMDODGA resin from the nitric acid, the coordination number is very close to six, exactly what is expected for coordination with two tridentate DGA ligands. Since this is an unusually low coordination number for Ln(III) involving only neutral ligands, we expect that under an abundance of water, these complexes would add several inner-sphere water molecules. This assertion is supported by changes in the bond distances for high and low Dy loading observed by EXAFS and DFT calculations for several plausible 2:1 models with different numbers of water molecules. As can be seen from Tables 4 and 5, the largest contraction of the bond distances is for DMDODGA that is at most 0.03 Å for Dy–Oe bond lengths and Dy–Ca/e interatomic distances. Relatively minor changes in the distance metrics found from the EXAFS analysis are more consistent with the initial complex containing three water molecules. Here, we surmise that the changes in the inner-sphere coordination upon removal of water are relatively minor, likely due to strong intermolecular forces and steric constraints preventing ligands to fully relax at the coordination site. Complexes with fewer water molecules are less plausible, because they would result in much larger bond distance contractions, which is not supported by EXAFS.
Metal(II) chloride complexes containing a tridentate N-donor Schiff base ligand: syntheses, structures and antimicrobial activity
Published in Journal of Coordination Chemistry, 2021
Sadeka J. Munshi, Jaswinder Kaur Saini, Sanjay Ingle, Sujit Baran Kumar
The Schiff base ligand (L) was synthesized as a light yellow solid by the condensation of 2-benzoylpyridine and N-phenyl-ethylenediamine in ethanol (Scheme 1). The ligand was characterized by 1H NMR and FT-IR spectroscopies and by single-crystal X-ray diffraction studies (Figure 1). The ligand is tridentate with N3-coordination sites.