NEET Study Notes for Coordination Compounds will help candidates to understand important topics like ligands and their formulas, Werner theory, etc. The weightage of this chapter is around 6.70% in the NEET examination that means candidates can expect around 3-4 questions from this chapter. Check NEET Chemistry Pattern

 Coordination compound is one of the most important topics where students appearing for NEET should practice more on this particular topic. We will discuss some important topics and sub-topics under coordination compounds and we will also provide important formulas, sample questions, tips to prepare, etc.

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What are Coordination Compounds?

Coordination compounds are molecules that are coordinated to a transition metal. Coordination compounds consist of substances such as chlorophyll, haemoglobin, vitamin B12, catalyst, and dyes that are used for preparing organic substances. Some of the examples of coordination compounds are [Ni(H2O)6], [Cr(NH3)5(NO2)]2+. Ag(CN)2-, CuCl42-.

Terms and their definitions related to Coordination Compounds:

Complex Ion: It is an electrically charged Ion where the central atom is surrounded by a number of molecules.

Homoleptic and Heteroleptic Complexes

Complexes in which a metal is related to only one type of donor groups are known as homoleptic. Eg.[Co(NH3)6]3+. Complexes in which a metal is related to more than one type of donor groups are known as heteroleptic. Eg.[Co(NH3 ) 4Cl2 ]+.

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What are Ligands and its types?

Ligands are the molecule that is bound to the central ion in the coordination entity.

Types of Ligands

• Unidentate Ligand
• Didentate
• Polydentate 
• Ambidentate Ligands
• Chelate Ligands

Formula and names of some ligands

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Quick Notes on Important Concepts

• Coordination Number: The number of chemical bonds that are formed by the ligands with the central metal atom is called the coordination number.
• Coordination Sphere: The central ion and the ligands attached to it are enclosed with a square bracket which is known as a coordination sphere. The ionisable group which is written outside the bracket is known as counter ions.
• Coordination Polyhedron: The spatial arrangement of the ligands which are directly connected to the central atom is called coordination polyhedron. 
• Oxidation Number of Central Atom: The charge of the complex if all the ligands are removed along with the electron pairs that are connected with the central atom is called the oxidation number of the central atom.
• Shapes: Shapes of coordination compounds depend upon the hybridization present in them.

Chelating Ligands 

• Multidentate ligand simultaneously coordinating to a metal ion through more than one site is called chelating ligand.
• Ex: Ethylenediamine (NH2CH2CH2NH2)
• These ligands produce a ring-like structure called chelate.
• Chelation increases the stability of the complex.

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Sample Questions

1. What is polydentate Ligands?
   1. Donor atoms that bind with coordination centre
   2. Ions which doesn’t bind with coordination
   3. Molecules that are always positive
   4. None of the above

Answer: (A), Donor atoms that bind with the coordination centre is called polydentate Ligands.

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Werner’s Theory

• Metals possess two types of valencies i.e. primary (ionizable) valency and secondary (nonionizable) valency.
• Secondary valency of metal is equal to the number of ligands attached to it i.e. coordination number.
• Primary valencies are satisfied by negative ions, while secondary valencies may be satisfied by neutral, negative or positive ions.

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Isomers and its types

Two or more compounds that have the same chemical formula but a different arrangement of atoms are called isomers.

Types of Isomerism

• Structural isomerism: It is a form of isomerism in which molecules with the same molecular formula have atoms bonded together in different orders.
• Linkage isomerism: This form of isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion.
• Solvate isomerism: It is isomerism in which the solvent is involved as the ligand
• Ionisation isomerism: Linkage isomerism arises in a coordination compound containing an ambidentate ligand
• Coordination isomerism: This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex.
• Stereoisomerism: This type of isomerism arises because of different spatial arrangement.
• Geometrical isomerism: It arises in heteroleptic complexes due to different possible geometrical arrangements of ligands.
• Optical isomerism: Optical isomers are those isomers that are non-superimposable mirror images.

Sample Questions

1. The type of isomerism shown by the complex [CoCl2(en)2] is
   1. Geometrical isomerism
   2. Coordination isomerism
   3. Linkage isomerism
   4. Ionization isomerism

Answer: (A), Geometrical isomerism

2. Which of the following elements do not form a complex with EDTA?
   1. Ca
   2. Mg
   3. Be
   4. Sr

Answer: (C), Be

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Crystal Field Theory

• The attraction between the central metal and ligands in the complexes is considered to be purely electrostatic Thus, bonding in the complex may be ion-ion attraction or ion-dipole attraction.
• Ligands are treated as a point of negative charges
• There is no interaction between metal orbitals and ligand orbitals

Quick Links: 

• Check NEET Month Wise Time Table
• NEET Chemistry Preparation

Oxidation Number of Central Atom

The charge of the complex if all the ligands are removed along with the electron pairs that are shared with the central atom is called the oxidation number of the central atom.

Eg. the Oxidation number of copper in [Cu(Cv)4]3- is + 1 and it is written as Cu(I).

Magnetic Properties

The given complex compound is paramagnetic if one or more unpaired electrons are present in the d-subshell. If the complex does not contain an unpaired electron, is diamagnetic.

Tips for students

• Practice every day: Students should not stop practising. Students should keep on revising the topics which they have learnt earlier. Most importantly they should not study for long hours, taking a break for 15 to 20 minutes is necessary to keep their mind focused.
• Take Mock tests: There are many mock tests available both online and offline. The main purpose of the mock test is to find the strength and weakness of the students, it is required for students to take mock tests more often to get better clarity on every topic.
• Keep revising: After completing a particular topic or lesson students should keep on revising from the next day, they should be in touch with the completed topics so that it gets stored well in their mind.
• Eat Healthy: Try to eat healthy foods which help you to stay healthy and completely avoid junk food which is bad for your health. Stay hydrated, drink plenty of water.

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Previous Year NEET Sample Questions on Coordination Compounds

Ques: The complex compounds which result from the coordination of carbon monoxide are known as

1.  Electronic
2. Carbonyls
3. Carbonates
4. Carbon permono

Answer: 2

Ques: In [Ni(NH3)4]SO4, the valency and coordination number of Ni will be respectively

1.  3 and 6
2.  2 and 4
3. 4 and 2
4. 4 and 4

Answer: 2

Ques: Which of the following represents a chelating ligand?

1.  H2O
2.  OH−
3. DMG
4. Cl−

Answer: 3

Ques: A solution of potassium ferrocyanide would contain...... ions 

1.  2
2.  3
3.  4
4. 5

Answer: 4

Ques: Which kind of isomerism is exhibited by octahedral Co(NH3)4Br2Cl ?

1.  Geometrical and Ionization
2.  Geometrical and Optical
3. Optical and Ionization
4. Geometrical only

Answer: 1

Ques: Which of the following is not true for metal carbonyls 

1.  Oxidation state of the metal in the carbonyls is zero
2. The secondary carbonyls are obtained from photo-decomposition
3. Metal carbonyls are single bonded species
4. \[d\pi -p\pi \] overlap is observed in metal carbonyls

Answer: 4

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