Inorganic chemistry.pptx

Inorganic chemistry.pptx

• 1.
  UNIT-3 INORGANIC CHEMISTRY-І THEORIES OFMETAL-LIGAND BOND
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  INORGANIC CHEMISTRY CRYSTAL FIELDTHEORY:- It mainly concerned with the interaction of d orbitals of central metal with the surrounding ligands IMPORTANT FEATURES OF CFT:- The inter reaction between electrons of cation and those of the ligands is entirely repulsive. the repulsive force 1)CFT regards a complex as a combination of a central ion surrounded by other ions or molecules with electrical dipoles are responsible of are causing the splitting of the d orbitals of the metal cation. The bonds between the metal and the surrounding ligands are thus purely ionic. 2)It does not consider any orbital overlap. CFT gives a representation of bonding that is purely and electrostatic or columbic inter reaction between positively charged and negatively charged species.
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  4)The number ofligand and the arrangement around the metal ion will determine the crystal field. 5)Different crystal fields will have different effect on the relative energies of the five d orbitals. SPLITTING OF d ORBITALS UNDER VARIOUS GEOMETRIES:- SPLITTING OF d ORBITALS IN OCTAHEDRAL COMPLEXES:
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  On the basisof the orientation of the lobes of the five d-orbitals with respect to coordination these have been divided into two groups. i. One group has the orbitals, which have their lobes along the axes and hence are called axial orbitals. These are called eg orbitals in which e refers to doubly degenerate set. ii.Second group includes the orbitals whose lobes lie between the axes and are called non-axial orbitals. These are referred to t2g ,degenerate set. CRYSTAL FIELD SPLITTING IN OCTAHEDRAL COMPLEXES: • In the octahedral complex, the six ligands are arranged octahedrally around a central metal ion. In this arrangement the dx 2 -y 2 and dz 2 orbitals lie along the x, y and z axes and point towards ligands. • So they experience much more repulsion then the remaining d orbitals (dxy, dyz and dZX) which are directed in between x, y and z axes. Consequently the energies of dx 2 -y 2 and dz 2 orbitals are increased much more than the other orbitals.
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  • Under theinfluence of approaching ligands, the five d orbitals which were originally degenerate in the free metallic cation are now split into two levels. t2g levels is of lower energy eg levels of higher energy. • The separation of five d-orbitals of metal into two sets having different energies is called crystal field splitting or energy levels splitting. • The energy gap between t2g and eg sets is donated by ∆o or 10 Dq. This energy difference arise because of the difference in electrostatic field exerted by the ligandson t2g and eg sets of orbitals of the metal ion. ∆o is called crystal field splitting energy(CFSE).
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  • Electrons willtend to occupy the lower energy t2g orbitals to achieve stability. Each electron entering the t2g orbitals stabilizes the complex by 0.4∆o units and each electron entering the higher energy orbital (eg) introduces an instability unit of 0.6∆o. The greater amount of CFSE of the complex, the greater is its stability. Splitting of d-orbitals in tetragonal geometry: • Since the distance of the two ligands Z-axis is increased from the central metal by removing them away, d-orbitals along the z-axis and in xz and yz planes experience less repulsion from the ligands and those in the xy plane experience relatively greater repulsion. • Consequently the energy of the orbitals experiencing less repulsion decreases while that of the orbitals experiencing greater repulsion increases.
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  Splitting of dorbitals in square planer geometry: • If the two trans ligands on the z-axis are completely removed , we get a square planer geometry. This is accompanied by a further rise in energies of dx 2 -y 2 and dxy orbitals and a further fall in energies of dz 2,dxzand dyz orbitals as shown in the diagram. Thus in square planer geometry the order of energy of different d-orbitals is dyz=dzx<dz2<dxy<dx2-y2. The crystal field splitting in square planar complex is given by ∆sp=∆1+∆2+∆3. • The value of ∆sp has been found to be larger than ∆o because of the reason that dxz and dyz orbitals interact with only two ligands in the square planar complexes while in octehedral complexes the interaction takes place with four ligands. Therefore, ∆sp=1 Splitting of d-orbitals in tetrahedral complexes: • In a tetrahedral field, the t2g orbitals experience greater force of repulsion from
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  • the ligandsthan those of eg orbitals whose lobes are lying along the axis. Thus the energy of t2g orbitals is increased while that of eg orbitals is decreased. The order of the energy of t2g and eg sets is the reverse of that seen in octahedral complexes. The energy difference between t2g and eg sets for tetrahedral complex is represented as ∆t. • It has been shown that ∆t<∆o and ∆t=0.45∆o.thus the energy levels of the t2g set is raised by 0.4 ∆t while that of eg set is lowered by 0.6 ∆ since ∆t<∆ crystal field splitting favours the formation of octahedral complex. FACTORS AFFECTING SPLITTING:- • Nature of ligands: Small ligands approach the ligands easily, so they can cause great crystal field splitting. Ligands containing easily polarisable electron pair will be drawn more easily to the metal ion.