for the same metal. For example, [Fe(CN) ] - is diamagnetic (low spin) whereas [FeF ] - is paramagnetic (high spin). Evaluate yourself : i. The spin only magnetic moment of Tetrachloridomanganate(II)ion is .
BM. On the basis of VBT, predict the type of hybridisation and geometry of the compound. ii. Predict the number of unpaired electrons in [CoCl ] - ion on the basis of VBT.
iii. A metal complex having composition Co(en) Cl Br has been isolated in two forms A and B. (B) reacted with silver nitrate to give a white precipitate readily soluble in ammonium hydroxide. Whereas A gives a pale yellow precipitate.
Write the formula of A and B. state the hybridization of Co in each and calculate their spin only magnetic moment. XII U5 Coordination XII U5 Coordination - - - - . .
Crystal Field Theory Valence bond theory helps us to visualise the bonding in complexes. However, it has limitations as mentioned above. Hence Crystal Field Theory to explain some of the properties like colour, magnetic behaviour etc.,This theory was originally used to explain the nature of bonding in ionic crystals. Later on, it is used to explain the properties of transition metals and their complexes.
The salient features of this theory are as follows. . Crystal Field Theory (CFT) assumes that the bond between the ligand and the central metal atom is purely ionic. i.e.
the bond is formed due to the electrostatic attraction between the electron rich ligand and the electron deficient metal. . In the coordination compounds, the central metal atom/ion and the ligands are considered as point charges (in case of charged metal ions or ligands) or electric dipoles (in case of metal atoms or neutral ligands). .
According to crystal field theory, the complex formation is considered as the following series of hypothetical steps. Step : In an isolated gaseous state, all the five d orbitals of the central metal ion are degenerate. Initially, the ligands form a spherical field of negative charge around the metal.