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1. TUMKUR UNIVERSITY TUMAKURU DEPARTMENT OF STUDIES AND RESEARCH IN ORGANIC CHEMISTRY Seminar topic: “SPLITTING OF d-ORBITALS IN TETRAGONAL, SQUARE PLANAR” Submitted By M ANJUNATHA R Reg. No.:P11AZ23S10401 5 I M.Sc. I Semester Under the guidance Dr. PRIYARANI R S F aculty Submitted to Dr. SURESH D The co-ordinator 2023-2024 1

2. CONTENTS Introduction Crystal field splitting in square planar complexes Tetragonal distortion consequences of tetragonal distortion Conclusion References 2

3. INTRODUCTION : The crystal field theory was proposed a little earlier than the valence bond theory . But it took about twenty years for this theory to be used by chemists. In 1951 many theoretical Chemists working independently. This theory involves an electrostatic approach to the bonding in complexes. It was first applied to ionic type crystalline Substances. Therefore, it is very often called the CFT. This theory considers the metal ion as being placed in an electrostatic field Crated by the surrounding molecules or ions. This electric field changes the energies of the d-electrons in the case of the transition metal ions. Many of the properties of the complexes are related to these energy changes. This theory considers the bonding in complexes to be entirely electrostatic. Crystal field splitting: It refers to the process by which degenerate d-orbitals of a transition metal ion split into different energy levels when subjected to the electric field created by surrounding ligands in a coordination complex. 3

4. CRYSTAL FIELD SPLITTING in Square- planar COMPLEXES The splitting of the energy levels in square planar complexes may be justified in the same manner as discussed for the octahedral geometry. Generally, we speak of the xy plane as the square plane. If the two trans ligands, lying on the z-axis of an octahedron are moved away from the central cation , then their distance from the metal cation is slightly greater than it is for the other four ligands lying in the xy plane. In a tetragonal structure, the distance of the two ligands on z-axis is increased by moving these ligands away from the central metal ion. d-orbitals such as d z 2 , d xz and d yz experience less repulsion from the ligands than they do in an octahedral geometry. The other two orbitals d xy and d x2-y2 experience grater repulsion from the ligands than they do in an octahedral environment. As a result , the energy of the orbitals experiencing greater repulsion increases whereas the energy of the orbitals experiencing lesser repulsion decreases. The d xz and d yz orbitals are degenerate. Thus under the influence of ligands in a tetragonal complex, the order of increasing energy of various d-orbitals is, d xz = d yz < d xy < d z 2 < d x 2 -y 2 4

5. If the two ligands on the z-axis are completely removed ,we get a square-planar complex .this is accompanied by a further d ecrease in energies of d z 2 , d xz and d yz orbitals and a further increase in the energies of d xy and d x 2 -y 2 orbitals. Thus order of increasing energies of d-orbitals in a square-planar complex it has been found that is, d xz = d yz < d z 2 < d xy < d x 2 -y 2 The difference in energy between the lowest d xz , d yz pair and the highest d x 2 -y 2 is called the square planar splitting energy and it is denoted by sp . the value of sp is larger than . it has been found that sp is about 1.3 times . CFSE=(-0.51)(#e)+(-0.42)(#e)+(0.23)(#e)+(1.23)(#e)*1.74 +m*p; #e = number of electron present in each orbital respectively 5

6. d x 2 -y 2 d z 2 d xy d yz d zx d x 2 -y 2 d xy d z 2 d yz d xz 1 2 3 1.23 o 0.23 o -0.43 o -0.51 o sp = 1 + 2 + 3 = 17.46 Dq 6

7. Tetragonal Distortion: The six coordinated complexes in which all the six distances between metal cation and the ligands are same and said to be regular octahedral complexes. A complex will be regular octahedral when the electronic arrangement in t 2g and e g orbitals is symmetric. It is because of the fact that symmetrically arranged electrons will repell all the six ligands equally. When either t 2g or e g orbitals are asymmetrically filled i.e , either t 2g or e g orbitals are electronically degenerate the regular octahedral geometry is not the stable but it transforms into a distorted octahedral geometry. 7

8. A tetragonal distortion occurs when the two trans ligands on the z-axis in an octahedral complex say ML 6 , are moved either towards the metal ion or away from the metal ion or atom. Motion of the trans-ligands along the z-axis towards the metal cation produces a tetragonal Compression and motion of these ligands away from the metal cation produces a tetragonal elongation. The term tetragonal distorted is derived from the fact that when viewed along the z-axis , an octahedral complex looks like a tetragon. The condition which cause such type of distortion was described by the Jahn -Teller theorem This theorem states that -“ any non-linear molecules in an electronically degenerate state is unstable and the molecules becomes distorted in such a way as to remove degeneracy ,lower is symmetry and lower the energy” Regular octahedral Tetragonal compression Tetragonal elongation 8

9. d x 2 - y 2 d z 2 d x 2 - y 2 d z 2 d z 2 d x 2 - y 2 d xy d yz d xz d xy d yz d zx d yz d xz d xy e g t 2g Octahedral Z-out or tetragonal elongation Z-in or tetragonal compression 9

10. Consequences of Jahn -Teller Distortion : Stability of Cu 2+ complexes: For a given ligand , the relative stability of complexes with dipositive metal ions of first transition series follow the order Ba +2 < Sr +2 < Ca +2 < Mg +2 < Fe +2 < Co +2 <Ni +2 <Cu +2 >Zn +2 This series is called Irving – William series. The extra stability of Cu(II) complexes is due to Jahn – Teller distortion. 2 . The absorption spectra of complexes having this distortion are different from the spectra of complexes having no distortion; instead of getting a single Gaussian curve, a curve with a shoulder as shown in fig. is obtain in the spectrum due to distortion. Wavelength 1.Without distortion Wavelength 2.With distortion 10

11. 3. In the crystalline KCuF 3 , the two Cu-F distances on Z-axis are 1.96A and the remaining four Cu-F distances in xy -plane are at 2.07 A it is due to Jahn -Teller distortion. 11

12. Conclusion : The crystal field theory and the resulting splitting patterns for square planar complexes and tetragonal distortions are crucial for predicting the behavior of metal complexes in coordination chemistry . Explain the stability and properties of transition metal complexes 12

13. REFERENCE Concise coordination chemistry - R Gopalan V Ramalingam Coordination chemistry - AJAI KUMAR page no; (25-31) 13

14. THANK YOU 14