question_answer

  Explain the following terms giving a suitable example in each case. (i)Ambident ligand                          (ii) Denticity of a ligand (iii) Crystal field splitting in an octahedral field                                                                                                     [3 x 1]

Answer:

(i) Ambident ligand Some ligands can be coordinated to the metal or metal ion through either of the sides. They are called ambident ligands. Examples (a)  (b) CN (a) If the nitrite ion is attached through N-atom it is nitro ; if it is attached through 0-atom. (?ONO), then it is nitrito pent amine-N-nitro cobalt (III) ion ?N? indicates that ligand joined to metal ion through N-side. (b) Cyano ?CN if jointed to metal through carbon. Isocyano (?NC) if jointed to metal through nitrogen.                                                           [1] (ii) Denticity of ligand donate one pair of electrons in complex formation and are called unidentate ligands. etc. donate two electron pairs in complex formation and are called bidentate. When a di-or polydentate ligand uses its two or more donar atoms to bind a single metal ion, it is said to be a chelate ligand. The number of such ligating groups is called denticity of the ligands. Such complexes are called chelate complexes. They are more stable as compared to complexes containing unidentate ligand. Nickel dimethyl glyoximate chelate         [1] (iii) Octahedral field splitting in an octahedral field Five d-orbitals (and) are of equal energy and thus are degenerate. The  and  orbitals are directed along a set of mutually perpendicular x, y and z-axis. As a group, these orbitals are called e, orbitals. Theeand  orbitals, I ie between the axis and collectively called  orbitals. The ligand donor atoms approach the metal ion along the axes to from octahedral complexes. Crystal field theory proposes that the approach of the six donor atoms along the axes sets up an electric field (crystal field). Electrons on the ligand repel electrons in eg orbitals on the metal ion more strongly than they repel those in  orbitals. This removes the degeneracy of the set of d-orbitals and splits them into two sets, the eg set at higher energy and the  set at lower energy. Free metal ion (into crystal field) The energy separation between the two sets is called orproportional to the crystal field of the strength of the ligands. The d-electrons on a metal ion occupy the  set in preference to the higher energy, eg set. Electrons that occupy the eg orbitals are strongly repelled by the relatively close approach of ligands. Electron in eg set tends to destabilise octahedral complexes.