Important questions based on NCERT syllabus for Chapter 9 - Coordination Compounds:
Question-1: Explain with two examples each of the following: coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic.
Solution: Coordination entity: It constitutes of a central atom/ion bonded to fixed number of ions or molecules by coordinate bonds e.g. [COCl3(NH3)3], [Ni (CO)4] etc.
Ligand : The ions/molecules bound to central atom/ion in coordination entity are called ligands. Ligands in above examples are CL, NH3, CO Coordination number : This is the number of bond formed by central atom/ion with ligands. Coordination polyhedron : Spatial arrangement of ligands defining the shape of complex. In above cases Co and Ni polyhedron are octahedral and tetrahedral in [CoCl3 (NH3)3] and [Ni(CO)4] respectively.
Homoleptic : Metal is bound to only one kind of ligands eg Ni in[Ni(CO)4]
Heteroletric Metal is bound to more than one kind of ligandseg Coin [CoCl3(NH3)3]
Question-2: What is spectrochemical series? Explain the difference between a weak field ligand and a strong field ligand.
Solution: The arrangement of ligands in order of their increasing field strengths, i.e., increasing crystal field splitting energy (CFSE) values is called spertrochemical series.
The ligands with small value of CFSE (Δ0) are called weak field ligands whereas those with large value of CFSE (Δ0) are called strong field ligands.
Question-3: What is crystal field splitting energy? How does the magnitude of Δ0 decide the actual configuration of d-orbitals in a coordination entity?
Solution: When the ligands approach a transition metal ion, the d-orbitals split into two sets, one with lower energy and the other with higher energy. The difference of energy between the two sets of orbitals is called crystal field splitting energy (Δ0 for octahedral field). If Δ0 < P (pairing energy), the fourth electron enters one of the e°g, orbitals giving the configuration t32ge1g, thus forming high spin complexes. Such ligands for which Δ0 < P are called weak field ligands. If Δ0 > P, the fourth electron pairs up in one of the t2g orbitals giving the configuration t42ge1g thereby forming low spin complexes. Such ligands for which Δ0> P are called strong field ligands.