01Introduction to Coordination Compounds
Are you searching for a definitive coordination compounds class 12 pdf resource for your NEET 2026 preparation? You are in the right place. Coordination chemistry is a fascinating branch of Inorganic Chemistry that explores complex molecules where a central metal atom is surrounded by ligands. For medical aspirants, this chapter is high-yield, consistently accounting for 3-4 questions in the chemistry section. Mastering the IUPAC naming, isomerism, and bonding theories is the secret to securing a top rank.
Historically, the study of these complexes began with Alfred Werner, who is known as the father of coordination chemistry. His pioneering work explains how metals exhibit two types of valencies—primary and secondary—which dictates the structure and properties of these compounds. From the hemoglobin in our blood to industrial catalysts, coordination complexes are everywhere.
02Werner’s Coordination Theory
Mastering the coordination compounds class 12 pdf notes requires a deep understanding of Werner’s postulates. He proposed that in a coordination compound, the central metal atom exhibits two types of linkages (valencies).
03Key Terminology in Coordination Chemistry
Before diving into naming rules, you must be comfortable with the jargon used in any coordination compounds class 12 pdf guide. The central metal atom acts as a Lewis acid, while ligands act as Lewis bases.
| Term | Definition | Example |
|---|---|---|
| Ligand | An ion or molecule capable of donating a pair of electrons to the metal. | Cl−, H2O, NH3 |
| Chelation | When a polydentate ligand binds to a metal ion through two or more donor atoms. | EDTA, Ethane-1,2-diamine (en) |
| Coordination No. | Total number of ligand donor atoms to which the metal is directly bonded. | 6 in [Fe(CN)6]4− |
| Homoleptic | Complexes in which a metal is bound to only one kind of donor groups. | [Co(NH3)6]3+ |
04Nomenclature of Coordination Compounds
IUPAC naming is a cornerstone of this chapter. Most coordination compounds class 12 pdf materials emphasize these rules for quick scoring. The standard format is: Prefix-Ligand(s) + Metal + (Oxidation State in Roman numerals).
2. Ligands are named in alphabetical order.
3. For anionic complexes, metal name ends in ‘-ate’ (e.g., Ferrate, Platinate).
05Isomerism: Structural and Stereo
Isomerism is the property where compounds have the same molecular formula but different arrangements. In your coordination compounds class 12 pdf study, focus heavily on Geometrical and Optical isomerism as they are frequently tested.
1. Structural Isomerism
- Linkage: Occurs with ambidentate ligands like SCN/NCS.
- Ionisation: Different ions produced in solution (e.g., [Co(NH3)5Br]SO4).
- Solvate: Difference in the number of water molecules as ligands.
2. Stereoisomerism
Stereoisomers have the same chemical bonds but different spatial arrangements. Octahedral complexes of type [MA2B4] show cis-trans isomerism, while [MA3B3] show fac-mer (facial-meridional) isomerism.
06Bonding in Complexes: VBT and CFT
How do metals bond with ligands? This is the most conceptual part of any coordination compounds class 12 pdf. Two major theories dominate: Valence Bond Theory (VBT) and Crystal Field Theory (CFT).
07Colour and Magnetic Properties
The striking colours of transition metal complexes are due to d-d transitions. When a complex absorbs light, an electron is excited from a lower energy d-orbital to a higher one. The complementary colour is observed by the human eye.
(Where n = number of unpaired electrons)
08Applications of Coordination Compounds
This section of the coordination compounds class 12 pdf highlights the practical significance of these molecules in biology and industry.
| Complex | Significance / Use |
|---|---|
| Chlorophyll | Magnesium complex; vital for photosynthesis. |
| Hemoglobin | Iron complex; oxygen carrier in blood. |
| Cisplatin | Platinum complex; used as an effective anti-cancer drug. |
| Vitamin B12 | Cobalt complex; prevents pernicious anemia. |
Quick Revision Formula Sheet
- Effective Atomic Number (EAN): Z − Oxidation State + 2(Coordination Number).
- Magnetic Moment: μ = √[n(n+2)] BM.
- CFSE for Octahedral: −0.4 x n(t2g) + 0.6 x n(eg).
- CFSE for Tetrahedral: −0.6 x n(e) + 0.4 x n(t2).
- Δt = (4/9) Δo.
- Ambidentate ligands: SCN−/NCS−, NO2−/ONO−, CN−/NC−.
- Optical isomerism is common in octahedral complexes with bidentate ligands like [Co(en)3]3+.
- Wilkinson’s catalyst is used for hydrogenation of alkenes.
- EDTA is a hexadentate ligand used to estimate water hardness.
09Frequently Asked Questions
What is the difference between a double salt and a coordination compound?
Why is [Ni(CN)4]2− diamagnetic while [NiCl4]2− is paramagnetic?
What does the term “chelate effect” mean?
Explain linkage isomerism with an example.
Why do tetrahedral complexes not show geometrical isomerism?
What is the geometry of a complex with dsp2 hybridization?
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Table of Contents
Chemistry — Class 12
| 01 | Solutions | Go to page |
| 02 | Electrochemistry | Go to page |
| 03 | Chemical Kinetics | Go to page |
| 04 | d- and f-Block Elements | Go to page |
| 05 | Coordination Compounds | Go to page |
| 06 | Haloalkanes and Haloarenes | Go to page |
| 07 | Alcohols, Phenols and Ethers | Go to page |
| 08 | Aldehydes, Ketones and Carboxylic Acids | Go to page |
| 09 | Amines | Go to page |
| 10 | Biomolecules | Go to page |