Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store
NEET 2022 | Class 12

NEET Chapter- Coordination Compounds

Get plus subscription and access unlimited live and recorded courses
Introduction to Coordination Compounds

Introduction to Coordination Compounds


Last updated date: 22nd Mar 2024
Total views: 203.1k
Views today: 8.57k

Chemical compounds made up of complex anion and simple cation or complex cation and simple anion, or complex anion and complex cation are known as coordination compounds. The central metal in the complex ions is connected to the ligands via coordinate covalent bonds formed by the electron pairs donated by the ligands. Chlorophyll, hemoglobin,  vitamin B12 are some of the naturally occurring coordination compounds. Hence, we can say life would have been impossible without coordination compounds.


Coordination compounds are the colorful stable compounds that show specific magnetic properties, due to which they are widely used in biochemistry, extraction of metals, dyes and pigments industry, medines, as catalysts etc.


Important Topics of Co-ordination Compounds:

  • Double salts and Coordination compounds

  • IUPAC nomenclature of coordination compounds

  • Werner’s Theory

  • Valence Bond Theory (VBT)

  • Crystal Field Theory (CFT)

  • Magnetic Properties of coordination compounds

  • Isomerism in coordination compounds

  • Ambident ligand

  • Homoleptic and heteroleptic complex

  • chelating effect

  • Denticity


Important Definitions of Coordination Compounds

Important Topics

Explanation

Complex ion

Complex ions are the ions (cations or anions) which have a central metal ion attached to ligand(s) through coordinate bond, which is  formed by electron pairs donated by ligand.  

Coordination compounds

Coordination compounds are the compounds which have complex ion(s) (complex anion and simple cation or complex cation and simple anion or both complex cation and complex anion) in which the central metal is bonded to ligand(s) by coordinate covalent bond.

Double salts

Double salts are the salts formed by the combination of two or more simple salts in some specific stoichiometric ratios which retain their composition in solid state by dissociating into simple ions in solutions.

Homoleptic complex 

The complex in which all the ligands, attached to the central atom/ ion are identical.

Heteroleptic complex 

The complex in which the ligands attached to the central atom/ ion are more than one kind.

Spectrochemical Series

It is the arrangement of ligands on the basis of their increasing order of crystal field splitting strength.


Some Important Terms Pertaining to Coordination Compounds:

Some Important Terms Pertaining to Coordination Compounds:  

1. Coordination Entity: 

Coordination entity constitutes the central metal ion bonded to a fixed number of molecules or ions.


2. Central Atom or Ion:

In coordination sphere, the fixed number of molecules or ions are bound to the atom or 

ion in a definite geometrical arrangement. In complex K4[Fe(CN)6], the central ion is Fe2+.


3. Ligand:

Ions or molecules which are bound to a central metal or ion by coordinate bond which is  formed by donated electron pairs by the atom of a molecule or ion known as ligand.

  • Unidentate Ligand:

In coordination chemistry, the donor atom of a ligand of coordinate compounds  is bound to central metal through the single donor atom, the ligand is known as unidentate. For example- Cl, H2O, NH3.


  • Bidentate Ligand:

In coordination chemistry, the donor atom of a ligand of coordinate compounds  is bound to central metal through the two donor atoms, the ligand is known as bidentate. For example - ethane-1,2-diamine (H2NCH2CH2NH2), oxalate ion (C2O4–2-).


  • Polydentate Ligand:

When the ligand ion or molecule is bound to central metal through the two or more than two donor atoms, for example -EDTA–4.


  • EDTA–4: It is a hexadentate ligand, has 6 atoms of ligand molecule to form bonds with central metal. The O atom of 4 carboxylic group and 2 N atoms of amine group acts as donon atom as shown below:

EDTA–4 :  A hexadentate (polydentate) ligand


EDTA  is a chelating agent which forms four or six bonds with the central metal ion to show  chelates.

4. Coordination Number: 

Coordination number of the complex ion is the number of donor atoms of the ligand bonded to the central metal ion. In complex K4[Fe(CN)6], 6 atoms of cyanide ligand are attached to Fe2+ ion hence, the coordination number for the complex is 6.


Isomerism in Coordination Compounds:

Isomers are the compounds which have the same molecular formula but different chemical formula. Let's discuss the isomerism of coordination compounds with examples.


1. Structural Isomerism:

  • Ionisation Isomerism:

Ionisation isomerism occurs when the compounds have different counter ions to produce different ions in the solution.


The examples of coordination compounds showing ionisation isomerism: [Co(NH3)5(Br)]SO4  and [Co(NH3)5(SO4)]Br are ionisation isomers that have SO4 2–  and Br counter ions. 


  • Linkage Isomerism:

This isomerism occurs in the compound containing ambident ligands such as SCN, CN, NO2 as they have two donor atoms and can be bonded to metal form either of atoms of ligand.   


The examples  of coordination compounds showing linkage isomerism:  [Co(NH3)5(NO2)]Cl2  and [Co(NH3)5(ONO)]Cl2. Ligand is linked through N or O atoms in the isomers.


  • Coordination Isomerism

The isomerism occurs in complex cation and complex anion in which the central metal ions of cation and anion exchanges.


The examples  of coordination compounds showing coordination isomerism:   [Co(NH3)6][Cr(CN)6]  and [Cr(NH3)6][Co(CN)6]    


  • Hydrate or Solvate Isomerism:

This isomerism occurs in the compound containing water molecule . The water molecule in the isomers can be present as ligand or present as free molecule.


The examples  of coordination compounds showing hydrate or solvate isomerism: [Cr(H2O)6]Cl3]  and [Cr(H2O)5Cl]Cl2,H2


2. Stereoisomerism:

  • Geometrical Isomerism: 

This isomerism occurs in  the compounds which have 4 and 6 coordination number. 

  • (MA2B2) type of complex is a square planar complex which exhibits geometrical isomerism where A and B are unidentate ligands.


[MA2B2] type of complex is a square planar complex which exhibits geometrical isomerism where A and B are unidentate ligands.


  • (MA2B4) type complex is an octahedral complex  which exhibits geometrical isomerism where A and B are unidentate ligands.


[MA2B4] type complex is an octahedral complex  which exhibits geometrical isomerism where A and B are unidentate ligands.


  • ((AA)2B2) type complex is an octahedral complex  which exhibits geometrical isomerism where AA is bidentate ligand  and B is unidentate ligand.


[M(AA)2B2] type complex is an octahedral complex  which exhibits geometrical isomerism where AA is bidentate ligand  and B is unidentate ligand.


  • (MA3B3) type complex is an octahedral complex which exhibits geometrical isomerism where A and B are unidentate ligands.


[MA3B3] type complex is an octahedral complex which exhibits geometrical isomerism where A and B are unidentate ligands.


Optical Isomerism:

This isomerism occurs due to non-superimposable mirror images formed due to chirality and no plane of symmetry in the compound.  Chirality in the molecule generally  occurs due to attachment of different groups to the carbon atom. The plane of symmetry is the imaginary line that bisects the molecule. The two forms of isomerism are dextro(d) and leavo(l).

  • (M(AA)3) type complex is an octahedral complex  which exhibits optical isomerism where AA is bidentate ligand due to no plane of symmetry. 


[M(AA)3] type complex is an octahedral complex  which exhibits optical isomerism where AA is bidentate ligand due to no plane of symmetry.


  • (M(AA)2B2) type complex is an octahedral complex  which exhibits optical isomerism where AA is a bidentate ligand  and B is a unidentate ligand.

[M(AA)2B2] type complex is an octahedral complex  which exhibits optical isomerism where AA is a bidentate ligand  and B is a unidentate ligand.


Valence Bond Theory(VBT):

This theory explained the orbital hybridisation in the complex as the penultimate d orbital close to s and p orbital hybridized to form the complex when the ligand approaches the central metal ion. This theory helps to predict the geometry of the complex.

  • Inner Orbital or Low Spin Complex: When the inner d orbitals are used in hybridisation of the complex inner orbital or low spin complex are formed . 

In complex [Co(NH3)6]3+, Co metal has +3 oxidation state, so the electronic configuration is 3d6, when the NH3 ligand approaches the central metal ion, inner 3d orbital hybridisation to form the complex. As all the electrons are paired in the complex, it is a diamagnetic complex.


Inner orbital or low spin complex


  • Outer Orbital Complex or High Spin Complex: When the outer d orbitals are used in hybridisation of the complex outer orbital or high spin complex are formed.  In complex [CoF6]3–, Co metal has +3 oxidation state, so the electronic configuration is 3d6, when the Fligand approaches the central metal ion, outer 3d orbital hybridisation to form complex. As the complex has  unpaired  electrons, it is a paramagnetic in nature.

Outer orbital complex or high spin complex:


  • Magnetic Properties of Coordination Compounds:

  • The coordinate compound can be characterized as diamagnetic and paramagnetic compounds.

  • Diamagnetic compounds have all the electrons paired in the complex.

  • Paramagnetic compounds have at least one unpaired electron in the complex.

  • Spin only magnetic moment is given by $\sqrt{n(n+1)}$, where n is the number of unpaired electrons.


  • Postulates of VBT:

  • Theory could not explain the inner orbital and outer orbital complex on the basis of strong and weak ligands.

  • It could not explain the color exhibited by the complex.

  • It has many assumptions.

  • It could not distinguish between the tetrahedral and square planar geometry existed by the complex.

  • It could not explain the thermal or kinetic stability of the complex.


Crystal Field Theory (CFT):

  • Theory is based on the electrostatic bonding model between metal- ligands.

  • According to CFT, the d orbital in the complex in the presence of ligands degenerate.

  • In octahedral crystal field, d orbital degenerate to yield three orbitals of lower energy, t2g and two orbitals of higher energy, eg.

d-orbital splitting in an octahedral crystal field


  • In the tetrahedral crystal field, d orbital degenerates to yield two orbitals of lower energy, eg and three orbital of higher energy, t2g.

    (image will be uploaded soon)

                        

  • Spectrochemical Series:

(Weak field ligand)  I< Br < Cl < NO2 < F < OH < C2O42–< H2O  < EDTA4– < NH3  <       ethylenediamine (en) <NO2  < CN < CO  (Strong field ligand).


Effective Atomic Number (EAN):

EAN is the total number of electrons present in the central atom along with the electrons gained from the ligands. It represents the electronic configuration of the nearest noble gas.

EAN = Z - O.N. + 2 (C.N.)

Z      :  Atomic number of of the central atom

O     :  Oxidation number of the central atom

C.N. : Coordination number of the central atom


Solved Examples From the Chapter

Example 1: Co-ordination number of Co in [Co(NH3)6]2+ is:

(a) 4

(b) 5

(c) 6

(d) 8

Solution (b) The compound,  [Co(NH3)6]2+ which is a coordination compound has 6 NH3 ligands attached to the Cobalt (Co) metal , therefore, the coordination number of Co is 6.

Trick: Co-ordination number is equal to total number of ligands in a complex. 


Example 2: Which of the following complexes will show geometrical as well as optical isomerism? en = ethylenediamine 

(A) [Pt(NH3)2Cl2

(B) [Pt(NH3)Cl4

(C) [Pt(en)3}4+ 

(D) [Pt(en)2Cl2

Solution: en is a bidentate ligand and Cl is a unidentate ligand. [Pt(en)2Cl2]  which is a coordination compound of type  [M(AA)2B2]  complex that will show geometrical as well as optical isomerism. 


Solved Questions from the Previous Year Question Papers

Question 1: The geometry and magnetic behavior of the complex [Ni(CO)4]

(a) Square planar geometry and paramagnetic 

(b) Tetrahedral geometry and diamagnetic 

(c) Square planar geometry and diamagnetic 

(d) Tetrahedral geometry and paramagnetic 

Solution:  (b) In [Ni(CO)4], which is a coordination compound, the Ni is in zero oxidation state and  CO is a strong field ligand, so it forms inner orbital complex as shown below:


(image will be uploaded soon)


Hybridisation of [Ni(CO)4] is sp3 and hence, it has tetrahedral geometry and all the electrons are paired hence, it is a diamagnetic complex.


Question 2: The type of isomerism shown by the complex [CoCl2(en)2] is- 

(a) Ionization isomerism 

(b) Coordination isomerism 

(c) Geometrical isomerism 

(d) Linkage isomerism 

Solution: The type of isomerism shown by the complex [CoCl2(en)2] is geometrical isomerism as shown below:

The type of isomerism shown by the complex [CoCl2(en)2] is geometrical isomerism


Question 3: Ethylene diaminetetraacetate (EDTA) ion is : 

  1. Tridentate ligand with three "N" donor atoms

  2. hexadentate ligand with four "O" and two "N" donor atoms  

  3. Unidentate ligand 

  4. Bidentate ligand with two "N" donor atoms 

Solution:(b)  EDTA ion is a hexadentate ligand, has 6 atoms of ligand molecule to form bonds with central metal. The O atom of 4 carboxylic group and 2 N atoms of amine group acts as donon atom


Practice Questions

Question 1: The complex [Co(NH3)6][Cr(CN)6] and [Cr(NH3)6] [Co(CN)6] are the examples of which type of isomerism ?  

(a) Linkage isomerism 

(b) Ionization isomerism 

(c) Coordination isomersim 

(d) Geometrical isomerism 

Answer:  (a) Coordination isomerism 


Question 2: Considering H2O as a weak field ligand, the number of unpaired electrons in [Mn(H2O)62+ will be (At. no. of Mn = 25) :- 

(a) Four 

(b) Three 

(c) Five 

(d) Two 

Answer:  (c) Five 

 

Conclusion:

In coordination compounds, the central atom or ion is connected to the ligands, and the ligands give electron pairs to create coordinate covalent bonds.. Coordinate compounds on the basis of the number and type of ligand and counter ions attached to the central atom or ion shows isomerism.  There were many theories to explain the structure, shape, geometry, magnetic property, color and stability of compounds.

In the NEET competitive exam, coordination compound is one of the important topics of inorganic chemistry, which is of moderate to easy level in terms of difficulty level.

See More
NEET 2024 Important Dates

NEET 2024 Important Dates

View All Dates
NEET 2024 exam date and revised schedule have been announced by the NTA. NEET 2024 will now be conducted on 5 May 2024, and the exam registration starts on 9 February 2024 and closes on 9 March 2024. You can check the complete schedule on our site. Furthermore, you can check NEET 2024 dates for application, admit card, exam, answer key, result, counselling, etc along with other relevant information.
See More
View All Dates
NEET Information

NEET Information

Application Form
Eligibility Criteria
Reservation Policy
Admit Card
NTA has announced the NEET 2024 application form release date on the official website https://neet.nta.nic.in/. The NEET 2024 Application Form is available on the official website for online registration from 9 February 2024 to 9 March 2024. Besides the NEET 2024 application form release date, learn about the application process, steps to fill out the form, how to submit it, the exam date sheet, etc online. Check our website for more details.
NEET 2024 applicants should be aware of the eligibility criteria before applying for the exam. NTA has released all the relevant information on the official website, i.e. https://neet.nta.nic.in/. NEET 2024 aspirants should have passed Class 12th or any other equivalent qualifying examination in 2023, or 2022, or students appearing in the Class 12th final exam in 2024 can also apply. For further details, visit our website.
As per the union government’s norms, NTA has released the NEET 2024 reservation criteria for different candidates’ categories (SC/ST/OBC/PwD), All India Quota, State Government Quota, Deemed Universities, and more. You can check more details on the Vedantu website.
NEET 2024 Admit Card will be released by the NTA in the 4th week of April 2024. Candidates can download the NEET admit card and hall ticket from the NEET official website i.e. https://neet.nta.nic.in/. For more details on the NEET admit card 2024, candidates can check Vedantu's official website.
NEET 2024 Study Material

NEET 2024 Study Material

View NEET Syllabus in Detail
Download full syllabus
Download full syllabus
View NEET Syllabus in Detail
NEET 2024 Study Material

NEET 2024 Study Material

View all study material for NEET
All
Physics
Chemistry
Biology
See All
NEET Question Papers

NEET Question Papers

NEET 2024 Book Solutions and PDF Download

NEET 2024 Book Solutions and PDF Download

View all NEET Important Books
Biology
NCERT Book for Class 12 Biology
Physics
NCERT Book for Class 12 Physics
Chemistry
NCERT Book for Class 12 Chemistry
Physics
H. C. Verma Solutions
See All
NEET 2024 Mock Tests

NEET 2024 Mock Tests

View all mock tests
NEET 2024 free online mock test series for exam preparation are available on the Vedantu website for free download. Practising these mock test papers of Physics, Chemistry and Biology prepared by expert teachers at Vedantu will help you to boost your confidence to face the NEET 2024 examination without any worries. The NEET test series for Physics, Chemistry and Biology that is based on the latest syllabus of NEET and also the Previous Year Question Papers.
See More
NEET 2024 Cut Off

NEET 2024 Cut Off

NEET Cut Off
NTA is responsible for the release of the NEET 2024 cut off score. The qualifying percentile score might remain the same for different categories. According to the latest trends, the expected cut-off mark for NEET 2024 is 50% for general category candidates, 45% for physically challenged candidates, and 40% for candidates from reserved categories. For the general category, NEET qualifying marks for 2024 ranged from 715-117 general category, while for OBC/SC/ST categories, they ranged from 116-93 for OBC, 116-93 for SC and 116-93 for ST category.
See More
NEET 2024 Results

NEET 2024 Results

The NEET 2024 result will be published by NTA on https://neet.nta.nic.in/ in the form of a scorecard on 14 June 2024. The scorecard will include the roll number, application number, candidate's personal details, and the percentile, marks, and rank of the candidate. Only those candidates who achieve the NEET cut-off will be considered qualified for the exam.
See More
Rank List
Counselling
Marks and Rank
NEET 2024 state rank lists will be released by the Medical Counselling Committee (MCC) for admissions to the 85% state quota and to all seats in private medical and dental colleges. NEET 2024 state rank lists are based on the marks obtained in medical entrance exams. Candidates can check the NEET 2024 state rank list on the official website or our site.
The Medical Counselling Committee (MCC) will conduct NEET 2024 counselling at www.mcc.nic.in. There will be two rounds of counselling for admission under 15% All India Quota (AIQ), deemed and central universities, AIIMS, JIPMER, ESIC, and AFMC. A mop-up round of NEET counselling will be conducted excluding 15% AIQ seats, while the dates of NEET counselling for 85% state quota seats will be announced by the respective state authorities.
As per the union government’s norms, NTA has released the NEET 2024 reservation criteria for different candidates’ categories (SC/ST/OBC/PwD), All India Quota, State Government Quota, Deemed Universities, and more. Previously, the Indian Government has provided NEET reservations to OBC (27%) and EWS (10%) candidates under All India Quota (AIQ). You can check more details on the Vedantu website.
NEET 2024 Top Colleges

NEET 2024 Top Colleges

View all NEET 2024 Top Colleges
Want to know which Engineering colleges in India accept the NEET 2024 scores for admission to Engineering? Find the list of Engineering colleges accepting NEET scores in India, compiled by Vedantu. 1990 Colleges are accepting NEET Score. It includes 706 Medical, 323 Dental, 914 AYUSH, and 47 BVSc & AH colleges. Also find more details on Fees, Ranking, Admission, and Placement.
See More
question-image

FAQs on NEET Chapter- Coordination Compounds

FAQ

1. What is coordination compound with example?

Coordination compounds are the compounds that contain a central atom or ion attached to ligand molecule or ion by coordinate covalent bond, formed by electron pair donation by the ligand. Coordinate compounds give complex ions in solution.

Example: [Pt(NH3)2Cl2], K3[Fe(CN)6] and [Fe(CO)5]

2. What are the important topics in coordination compounds?

Important topics of coordination compounds are:

  • Coordination number

  • Oxidation

  • Magnetic moment and magnetic properties of compound

  • Color of compound

  • Homoleptic and heteroleptic compound

  • Types of ligands

  • Nomenclature of coordination compounds

  • Isomerism in coordination compounds

3. Is coordination compounds important for NEET? 

Yes, coordination chemistry is one of the important topics of chemistry, also for NEET exam. 3 questions of coordination compounds are asked in the paper, which in total is of 12 marks, so it is an important topic for NEET exam.