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23 Transition Metals and Solutions to Exercises Coordination Chemistry 23.31 (a) The term chelate effect means there is a special stability associated with formation of a metal complex containing a polydentate (chelate) ligand relative to a complex containing only monodentate ligands. (b) When a single chelating ligand replaces two or more monodendate ligands, the number of free molecules in the system increases and the entropy of the system increases. Chemical reactions with tend to be spontaneous, have negative G, and large positive values of K. (c) Polydentate ligands can be used to bind metal ions and prevent them from undergoing unwanted chemical reactions without removing them from solution. The polydentate ligand thus hides or sequesters the metal ion. 23.32 (a) Pyridine is a monodentate ligand because it has one N donor atom and therefore occupies one coordination site in a metal complex. (b) K for this reaction will be less than one. Two free pyridine molecules are replaced by one free bipy molecule. There are more moles of particles in the reactants than products, so is predicted to be negative. Processes with a net decrease in entropy are usually nonspontaneous, have positive G, and values of K less than one. This equilibrium is likely to be spontaneous in the reverse direction. 23.33 Analyze/Plan. Consider the structural or steric requirements for chelating ligands. Analyze the structure of the ligand in the figure to determine whether it meets these requirements. Solve. The ligand shown in the figure is not typically a chelate. The entire molecule is planar; there is no "bend" in the central 6-membered ring that includes the two N atoms. The benzene rings on either side of the two N atoms inhibit their approach in the correct orientation for chelation. 23.34 The complex in the figure has tetrahedral geometry about the metal. The ligands are neutral molecules and the metal is a cation, so the complex will have a positive charge and there will be negatively charged counterions. Nomenclature and Isomerism in Coordination Chemistry (section 23.4) 23.35 Analyze/Plan. Given the name of a coordination compound, write the chemical formula. Refer to Tables 23.4 and 23.5 to find ligand formulas. Place the metal complex (metal ion + ligands) inside square brackets and the counter ion (if there is one) outside the brackets. Solve. (a) [Cr(NH₃)₆](NO₃)₃ (b) [Co(NH₃)₄CO₃]₂SO₄ (c) [Pt(en)₂Cl₂]Br₂ (d) K[V(H₂O)₂Br₄] (e) 23.36 (a) (b) (c) (d) Cs[Cr(NH₃)₂(CN)₄] (e) [Rh(en)₃][Co(ox)₃] 700