Ch. 4. AQUEOUS COMPLEXES 4-1. A Few Definitions 4-1. A Few Definitions Aqueous complexes Aqueous complexes Association of dissolved (c,a)ions or molecules Association of dissolved (c,a)ions or molecules Ligands Ligands Ions or molecules binding to a central metal to form a complex (by donating electron pair) Ions or molecules binding to a central metal to form a complex (by donating electron pair) Addend Addend Pieces of complexes (either cations or anions) Pieces of complexes (either cations or anions) Monodendate (Cl - ), bidendate (CO 3 2- ), polydendate Monodendate (Cl - ), bidendate (CO 3 2- ), polydendate Chelates Chelates P. 91, Table 3.2 P. 91, Table 3.2

Description: Chemical structure of EDTA chelateEDTAchelate (from wikipedia.org)

4-2. Significance of Complexes 4-2. Significance of Complexes Speciation of metals Speciation of metals Adsorption Adsorption Toxicity Toxicity Solubility Solubility

4-3. Outer vs. Inner Sphere Complexes 4-3. Outer vs. Inner Sphere Complexes Hydration (shell) Hydration (shell) Outer sphere complex (ion pair): ex) CaSO 4 Outer sphere complex (ion pair): ex) CaSO 4 Weak, electrostatic (depending on charges) Weak, electrostatic (depending on charges) Inner sphere coplex: ex) AgS- Inner sphere coplex: ex) AgS- Strong, covalency Strong, covalency Most complexes are in between Most complexes are in between

4-4. Geometry of Common Inorganic Ligands 4-4. Geometry of Common Inorganic Ligands All depends on the radius ratio (p.89) All depends on the radius ratio (p.89) Plan triangular triangle (NO 3 -, CO 3 -, BO 3 - ) Plan triangular triangle (NO 3 -, CO 3 -, BO 3 - ) Regular trigonal low pyramidal (PO 3 3-, AsO 3 3- ) Regular trigonal low pyramidal (PO 3 3-, AsO 3 3- ) Regular tetrahedron (PO 4 3-, SO 4 2-, CrO 4 3- ) Regular tetrahedron (PO 4 3-, SO 4 2-, CrO 4 3- ) Distorted tetrahedron (MoO 4 2- ) Distorted tetrahedron (MoO 4 2- ) Spherical (halogens) Spherical (halogens) Dumbel shape (UO 2 2- ) Dumbel shape (UO 2 2- ) See page 89 & 90 tables See page 89 & 90 tables

4-5. Complexation Mass Balance & Equilibria 4-5. Complexation Mass Balance & Equilibria Extent of complex formation (average ligand number) Extent of complex formation (average ligand number) P. 90, eqn (3.17) P. 90, eqn (3.17) Stepwise formation constant Stepwise formation constant P. 92, eqn (3.18) P. 92, eqn (3.18) Cumulative formation constant Cumulative formation constant P.92, eqn (3.21) P.92, eqn (3.21)

4-6. Hydrolysis of Cations in Water and Ionic Potential 4-6. Hydrolysis of Cations in Water and Ionic Potential Hydrolysis? Hydrolysis? Ionic potential? Ionic potential? How these two factors affect the behavior of the dissolved ions in water? How these two factors affect the behavior of the dissolved ions in water? See p.98, Fig. 3.4; p.99, Table 3.3.; p.100, Fig. 3.5 See p.98, Fig. 3.4; p.99, Table 3.3.; p.100, Fig. 3.5

4-7. Electronegativities & the Stability of Inner-Sphere Complexes 4-7. Electronegativities & the Stability of Inner-Sphere Complexes What is EN? (p.101, Tanle 3.4) What is EN? (p.101, Tanle 3.4) How does EN controls bonding character ? How does EN controls bonding character ? Conseq., the stabilities of complexes? (p.102, Fig. 3.6) Conseq., the stabilities of complexes? (p.102, Fig. 3.6)

4-8. Schwarzenbach’s & Pearson’s Classification of Acids & Bases (forming Complexes) 4-8. Schwarzenbach’s & Pearson’s Classification of Acids & Bases (forming Complexes) Schwarzenbach’s classes A, B, & C Schwarzenbach’s classes A, B, & C A: Those of noble gas configuration (p.103, bottom table) A: Those of noble gas configuration (p.103, bottom table) B: Those of Ni o, Pd o, Pt o electron config. B: Those of Ni o, Pd o, Pt o electron config. C: Transient metals C: Transient metals Pearson’s hard & soft Pearson’s hard & soft Hard: Rigid & nondeformable elctron cloud, tend to form ionic bonding Hard: Rigid & nondeformable elctron cloud, tend to form ionic bonding Soft: Deformable & polarizable electron cloud, tend to form (more) covalent bonding Soft: Deformable & polarizable electron cloud, tend to form (more) covalent bonding See p.104, Table 3.5; p.105, Fig. 3.7; p.106, Fig. 3.8; p.108, Fig See p.104, Table 3.5; p.105, Fig. 3.7; p.106, Fig. 3.8; p.108, Fig. 3.9.

4-9. Thermodynamics of Complexation 4-9. Thermodynamics of Complexation  G o = -RT ln K assoc  G o = -RT ln K assoc  G o =  G o - T  S o  G o =  G o - T  S o Mostly due to entropy change Mostly due to entropy change  S o =  S o net charge +  S o tr +  S o rot +  S o vibr +  S o dehyd  S o =  S o net charge +  S o tr +  S o rot +  S o vibr +  S o dehyd  S o dehyd is probably contributing most  S o dehyd is probably contributing most

4-10. Distribution of Complex Species as a Function of pH Distribution of Complex Species as a Function of pH Write down the association reactions Write down the association reactions Express Kassoc in terms of species Express Kassoc in terms of species Convert them into a function of pH Convert them into a function of pH See p.113, Fig See p.113, Fig. 3.12