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23 Transition Metals and Solutions to Exercises Coordination Chemistry (d) In Co(NH₃)₆Cl₃, there are two types of chemical bonds. The bonds formed between Co³+ and :NH₃ are covalent. They are the result of Lewis acid-Lewis base interactions, where :NH₃ is the electron pair donor (Lewis base) and is the electron pair acceptor (Lewis acid). The interactions between the complex cation and the three anions are ionic bonds. (e) The most common coordination numbers for metal complexes are six and four. (Coordination numbers of two, three and five are less common, but not unknown.) 23.23 Analyze/Plan. Follow the logic in Sample Exercises 23.1 and 23.2. Solve. (a) This compound is electrically neutral, and the NH₃ ligands carry no charge, so the charge on Ni must balance the -2 charge of the 2 ions. The charge and oxidation state of Ni is +2. (b) Since there are 6 NH₃ molecules in the complex, the likely coordination number is 6. In some cases Br- acts as a ligand, so the coordination number could be other than 6. (c) Assuming that the 6 NH₃ molecules are the ligands, 2 ions are not coordinated to the Ni²⁺, so 2 mol AgBr(s) will precipitate. (If one or both of the Br- act as a ligand, the mol AgBr(s) would be different.) 23.24 (a) Yes. Conductivity is directly related to the number of ions in a solution. The lower the conductivity, the more Cl⁻ ions that act as ligands. Conductivity measurements on a set of standard solutions with various moles of ions per mole of complex would provide a comparative method for quantitative determination of the number of free and bound ions. (b) In using conductivity measurements to test which ligands are bound to the metal atom, the assumption is that the total number of ions in solution is constant. This requires that either the in the coordination sphere are so tightly bound that exchange with ions in solution is extremely slow, or that the rates at which they leave and enter are equal. (c) For coordination number 6, an octahedral complex with 3 and 3 ligands; all ligands are monodentate. For coordination number 4, a tetrahedral complex with varying amounts of and ligands are possible. Since there is a single species in solution, the octahedral complex is more likely. 23.25 Analyze/Plan. Count the number of donor atoms in each complex, taking the identity of polydentate ligands into account. Follow the logic in Sample Exercise 23.2 to obtain oxidation numbers of the metals. Use Tables 23.4 and 23.5 to determine the number and kinds of donor atoms in the ligands of the complexes. (a) Coordination number = 4, oxidation number = +2; 4 Cl⁻ (b) 5, +4; 4 1 O²⁻ (c) 6, +3; 4 N, 2 Cl⁻ (d) 5, +2; 5 C. In both C and N have an unshared electron pair. C is less electronegative and more likely to donate its unshared pair. 698