Q4. Specify the oxidation number of the metal in [Co(H2O)(CN)(en)2]2+ and [Cr(NH3)3Cl3]. (The rest of NCERT Exercise 5.5.)
[Co(H2O)(CN)(en)2]2+: H2O and en are neutral and CN− is −1, so x − 1 = +2 and cobalt is +3. [Cr(NH3)3Cl3]: x − 3 = 0, chromium +3 (reasoned).
Q5. Explain, with two examples each, coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic. (NCERT Exercise 5.3.)
Coordination entity: a central metal atom or ion bonded to a fixed number of ions or molecules, [Ni(CO)4], [Co(NH3)6]3+. Ligand: an ion or molecule bound to the central atom, Cl−, NH3. Coordination number: donor atoms bonded to the metal, 6 in [PtCl6]2−, 4 in [Ni(NH3)4]2+. Coordination polyhedron: the shape of the ligand atoms round the metal, octahedral [Co(NH3)6]3+, square planar [PtCl4]2−. Homoleptic: one kind of ligand, [Co(NH3)6]3+, [Fe(CN)6]4−. Heteroleptic: more than one kind, [Co(NH3)4Cl2]+, [PtCl2(NH3)2] (NCERT pages 121–122).
Q6. In [Ni(NH3)6]Cl2, name the coordination sphere, the counter ions, the central ion and its oxidation number.
The coordination sphere is [Ni(NH3)6]2+, a complex cation, so the counter ions are the two Cl− (compare K+ in K4[Fe(CN)6], NCERT page 122). NH3 is neutral, so x + 0 = +2: the central ion is Ni2+, oxidation number +2.
Q7. What is meant by the chelate effect? Give an example. (NCERT Exercise 5.26.)
A chelate complex tends to be more stable than a similar complex of unidentate ligands (NCERT page 121); this is the chelate effect. For example, [Co(en)3]3+ tends to be more stable than [Co(NH3)6]3+ (reasoned).