Chapter 09 Coordination Compounds Notes Chemistry Class 12 | Short Notes
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Coordination Compounds are special kind of compounds in which Central Metal atom or ion is surrounded by ions/molecules beyond their normal Valency.
- Haemoglobin ( complex of Fe ) , chlorophyll ( Complex of Mg ) and vitamin B12 ( complex of Co ) are examples of coordination complexes.
- The ions or molecules attached to the central metal atom or ion are called ligands. The ligands must contain atleast one electron pair for donating to the metal.
- Types of ligands : Unidentate ligands, bidentate ligands ( ethane-1,2-diamine ) and Polydentate ligands ( EDTA) . There is special kind of ligands ambidentate ligands which can bind to metal ion through two different donor atoms ( CN- , NO2- )
Gtctuition
- Chelation : When a bidentate or polydentate ligand is attached by two or more donor atoms to the same central metal ion forming ring structure, it is called chelation. It increases the stability of complex.
- Transition metals form coordination compounds because they have (i) empty d-orbitals (ii) large charge/size ratio.
- Werner theory explained the bonding in coordination complexes. According to this theory metal atoms exhibit two types of valencies Primary valency ( oxidation state ) and secondary valency ( coordination number ).
- Coordination Number is the number of ligands attached to the central metal atom or ion.
Isomerism in Coordination Compounds : coordination compounds show structural and stereoisomerism.
- Structural isomerism is of four types : ionisation isomerism, solvate ( hydrate ) isomerism, coordination isomerism and linkage isomerism.
Gtctuition
2. Stereoisomerism is of two types : - Geometrical isomerism is shown by square planar and octahedral complexes. These are cis and trans form.
- Optical isomerism is shown by compounds which have non-superimposable mirror images.
The Valence Bond Theory
- VB theory considers covalent bond between metal and ligand. According to this theory central metal ion in the complex ion makes available a number of empty orbitals for the formation of coordination bonds with suitable ligands. These empty orbitals hybridised to give molecule a definite geometry and the number of hybrid orbitals formed is equal to coordination number of central metal atom.
- Complexes have different geometries depending upon the type of hybridisation.
Gtctuition
Crystal field Splitting Theory
- CF theory consider ionic bond between metal and ligand. The splitting of five d - orbitals of the metal ion into two different sets of orbitals having different energies in the presence of electric field of ligands is called crystal field splitting theory.
- The difference between the two sets of energy levels is called crystal field splitting energy.
- Gtctuition
- Spectrochemical Series : The ligands can be arranged according to the magnitude of the CFSE. Ligands lying above water are strong field ligands and below water are weak field ligands.
The colour of coordination complexes is due to transition of electron from lower d-orbitals to higher d-orbitals.
Metallic Carbonyls are organometallic compounds having both sigma and pi bonds.
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