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Introduction to Organometallics
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Samir H. Chikkali, Sandeep Netalkar
In a single ligand, there can be a number of sites (donor atoms) that can bind to the same central metal atom, which is described by the term called denticity. If the coordination of a single ligand to the central metal atom is through a single site, then the ligands are referred as monodentate ligands. Similarly, bidentate ligand binds to metal through its two different donor sites: tridentate ligand through three sites and polydentate ligand through many sites. Table 1.3 lists types of ligands based on their coordination ability with examples of each type.
A critical review of bioleaching of rare earth elements: The mechanisms and effect of process parameters
Published in Critical Reviews in Environmental Science and Technology, 2021
Payam Rasoulnia, Robert Barthen, Aino-Maija Lakaniemi
In bioleaching environments, organic molecules can also induce metal solubilization processes. Such molecules can create a low pH environment, promoting acidolysis, but can also promote mineral dissolution via complexolysis. Thus, their effectiveness in furthering mineral dissolution depends on their complex formation abilities either on whether they can generate protons (Table 1) (Ilyas & Lee, 2014; Shin, Kim, Kim, Jeong, & Lee, 2015). In general, complex stability increases with the denticity of the (in)organic ligand (chelate effect) (Janiak, Meyer, Gudat, Alsfasser, & Meyer, 2012). Additional stability can result from the so-called macrocyclic effect i.e., that cyclic ligands form more stable complexes than their open chain analogs (Cabbiness & Margerum, 1969; Hinz & Margerum, 1974). This can be observed e.g., when comparing stabilities of Fe3+-desferrioxamine E (DFOE) and Fe3+-desferrioxamine B (DFOB) complexes (Hider & Kong, 2010). Whether acidolysis or complexolysis dominates, depends on solution pH, acid dissociation constant (pKa) of the functional groups and stability of the formed complexes (expressed as the respective complex stability constant logK). At pH values below the pKa of the acids, protonation of the acid reduces the stability of the formed (surface)-complexes (Furrer & Stumm, 1986) and acidolysis is expected to dominate, whereas at higher pH, complexolysis dominates.
Solution processible Co(III) quinoline-thiosemicarbazone complexes: synthesis, structure extension, and Langmuir-Blodgett deposition studies
Published in Journal of Coordination Chemistry, 2021
Robert J. Laverick, Ningjin Zhang, Eleanor Reid, Jaehwan Kim, Kelly J. Kilpin, Jonathan A. Kitchen
When designing supramolecular materials containing transition metals, the ligand coordination pocket must be considered in addition to the functional and structure directing groups. The correct donor atoms and denticity must be chosen to give a stable complex, with the metal binding at the desired site rather than interacting with the structure directing group. The binding pocket should also be remote enough from the structure directing group to ensure intermolecular interactions are enhanced. Additionally, the field strength of the ligands must also be carefully considered so that the desired metal-based functionality is achieved. Ideally, ligand synthesis should be modular so that a variety of structure directing groups can be introduced to the ligand scaffold with minimal synthetic effort.