Advanced Geochemistry of Natural Waters: Lesson 5 - Aqueous Complexes and Chelation, Study notes of Hydrogeology

Download Advanced Geochemistry of Natural Waters: Lesson 5 - Aqueous Complexes and Chelation and more Study notes Hydrogeology in PDF only on Docsity! 1 GEOL578 Advanced Geochemistry of Natural Waters Start Audio Lecture! LESSON 5 Aqueous Complexes (Coordination Chemistry) MODULE 1 Definitions and General Concepts 2 GEOL578: Advanced Geochemistry of Natural Waters WHY IS CHEMICAL SPECIATION SO IMPORTANT? • The biological availability (bioavailability) of metals and their physiological and toxicological effects depend on the actual species present. • Example: CuCO30, Cu(en)20, and Cu2+ all affect the growth of algae differently • Example: Methylmercury (CH3Hg+) is readily formed in biological processes, kinetically inert, and readily passes through cell walls. It is far more toxic than inorganic forms. • Solubility and mobility depend on speciation. 3 GEOL578: Advanced Geochemistry of Natural Waters Figure 6-20 from Stumm & Morgan: Effect of free Cu2+ on growth of algae in seawater. 2 4 GEOL578: Advanced Geochemistry of Natural Waters DEFINITIONS - I Coordination (complex formation) - any combination of cations with molecules or anions containing free pairs of electrons. Bonding may be electrostatic, covalent or a mix. Central atom (nucleus) - the metal cation. Ligand - anion or molecule with which a cation forms complexes. Multidentate ligand - a ligand with more than one possible binding site. Chelation - complex formation with multidentate ligands. Multi- or poly-nuclear complexes - complexes with more than one central atom or nucleus. 5 GEOL578: Advanced Geochemistry of Natural Waters NH2 NH2 M N N HO O OH O OH O HO O Oxalate (bidentate) Ethylendiamine (bidentate) Ethylendiaminetetraacetic acid or EDTA (hexadentate) O O O O M MULTIDENTATE LIGANDS 6 GEOL578: Advanced Geochemistry of Natural Waters Chelation NH2 NH2 Ni H2N H2N Polynuclear complexes Sb2S42- OH Hg OH Hg OH OH Hg 2+ Hg3(OH)42+ Sb Sb S SS S 2-