Bonding in coordination compound(werners theory)

By Dr. Neelam

1. Shri shankaracharya mahavidyalaya junwani , bhilai Presented by Dr. Neelam Department of chemistry BONDING IN COORDINATION CHEMISTRY

2. BONDING IN COORDINATION COMPOUNDS Werner's Theory : According to Werner's : Each metal in coordination compound possesses two types of valencies primary valency or principal valencies or ionisable valencies (ii) Secondary valency or non ionisable valencies It is satisfied by anions only. It shows oxidation state of the central metal. It is non-directional These are represented by dotted lines (-------) between central metal atom and anion. It is satisfied only by electron pair donor, the ions or the neutral species. secondary valencies also referred as coordination number . It is directional These are represented by thick lines valencies

3. Alfred Werner (considered as the father of coordination chemistry) studied the structure of coordination complexes such as CoCl 3 . 6NH 3 in 1893. According to him-

4. [Co(NH 3 ) 5 Cl]Cl 2 [Co(H 2 O) 5 Cl]Cl 2

5. Effective Atomic Number Rule given by Sidgwick : It can be defined as the resultant number of electrons with the metal atom or ion after gaining electrons from the donor atoms of the ligands . Effective Atomic Number (EAN) = No. of electron present on the metal atom/ion + No. of electrons donated by ligands to it. OR Effective Atomic Number (EAN) = Atomic no. of central metal- Oxidation state of central metal + No. of electrons donated by ligands . EAN = Z- Oxi . No. + no. of e- of ligand The complexes in which the EAN of the central atom equals the atomic number of the next noble gas, are found to be extra stable.

6. [Fe(CN) 6 ] 2+ [Co(H 2 O) 6 ] 3+ EAN = 9 + 2 x 6 -3 = 18 EAN = 27 – 3 + 2 x 6 = 36 EAN = 8 + 2 x 6 -2 = 18 EAN = 26 + 2 x 6 -2 = 36 [Ni(C O) 4 ] EAN = 10 + 2 x 4 = 18 EAN = 28 + 2 x 4 = 36

7. K 4 [Fe(CN) 6 ] Coordination no. Central metal ion Ligand Ionisable sphere Or counter sphere Anionic complex Coordination sphere Various Terms Used in co ordination compounds

8. Valence bond theory The valence bond theory, VBT, was extended to coordination compounds by Linus Pauling in 1931. According to this theory, the formation of a coordinate-covalent (or dative) bonds between metal & ligand . The metal atom or ion under the influence of ligands can use its (n-1) d, ns, np or ns, np , nd orbitals for hybridisation to yield a set of equivalent orbitals of definite geometry such as octahedral, tetrahedral, square planar. M L Empty orbitals Filled orbital of ligand

9. magnetic properties of complexes Paramagnetic : unpaired electrons Diamagnetic : paired electrons magnetic moment : Octahedral complex Inner orbital complex outer orbital complex d 2 sp 3 hybridisation sp 3 d 2 hybridisation Low spin complex high spin complex Tetrahedral complex sp 3 hybridisation Square planer complex dsp 2 hybridisation

10. Thus, the complex has octahedral geometry and is diamagnetic because of the absence of unpaired electron. d 2 sp 3 hybridisation inner orbital or low spin or spin paired complex. Spin magnetic moment = 0 The complex [Co(NH 3 ) 6 ] 3+ , the cobalt ion is in +3 oxidation state and has the electronic configuration represented as shown below.

11. The complex [FeF 6 ] 4– is paramagnetic and uses outer orbital (4d) in hybridisation (sp 3 d 2 ) ; it is thus called as outer orbital or high spin or spin free complex. Thus, the complex has octahedral geometry and is paramagnetic because of the absence of unpaired electron. sp 3 d 2 hybridisation outer orbital or high spin complex. Spin magnetic moment = 4.9 BM

12. Limitations of Valence Bond Theory While the VB theory, to a larger extent, explains the formation, structures and magnetic behaviour of coordination compounds, it suffers from the following shortcomings: ( i ) It involves a number of assumptions. (ii) It does not give quantitative interpretation of magnetic data. (iii) It does not explain the colour exhibited by coordination compounds. (iv) It does not give a quantitative interpretation of the thermodynamic or kinetic stabilities of coordination compounds. (v) It does not make exact predictions regarding the tetrahedral and square planar structures of 4-coordinate complexes. (vi) It does not distinguish between weak and strong ligands .

13. 13 Thank you