Isomerism in Coordination Compounds as the name suggests explores the concept of Isomerism in Coordination Compounds i.e., generally compounds formed by d-block elements. Isomerism is the phenomenon of exhibiting different molecular structures by the compounds with same molecular formula. The phenomenon of isomerism is quite significant in hydrocarbons however it is of no less importance in coordination compounds. Coordination Compounds are those chemical compounds in which a group of anions is attached to a central metal atom via covalent bonds. Coordinate compounds are also called coordinate complexes. The coordinate compounds having the same molecular formula but different arrangements of ligands are called isomers of coordination compounds and the phenomenon exhibited is called Isomerism in Coordination Compounds. In this article, we will learn about different types of isomerism exhibited by Coordination Compounds in detail.
Table of Contents
What are Coordination Compounds?
Coordination Compounds are chemical compounds in which the central metal atom or ion is attached to the number of oppositely charged or neutral atoms more than its normal valency. The coordination compounds are formed by the combination of two or more simple and stable compounds that retain their identities. The central atom is usually a transition metal due to its nature of exhibiting variable valency properties as they have the presence of incompletely filled d-orbitals.
The Central Metal Atom has two types of valencies namely primary valency and secondary valency. The primary valency tells the oxidation number and the secondary valency tells about the coordination number. The d-block transition element to which negative or neutral molecules are attached is called the central atom and the neutral atom or the anion attached to the central atom is called ligand. The central atom and the ligand are written inside a square bracket and are often called Coordination Complexes. Coordination Compounds differ from Double Salt in the manner that double salt dissociates on dissolution while Coordination Compounds don’t.
Coordination Compound Examples
Let’s understand more about coordination compounds with the help of a few examples:
In [Co(NH3)6]Cl3 the central atom is Cobalt(Co), to which six neutral molecules of NH3 are attached which is called a ligand. These are attached to Co with primary valency and hence written inside the square bracket and the Cl3 which is written outside is the counter ion attached to the coordination complex that consists of [Co(NH3)6]3+ via secondary valency.
Isomerism in Coordination Compounds
The phenomenon of exhibiting different arrangements of ligands by the coordination compounds with the same molecular formula is called Isomerism in Coordination Compounds. The Coordination Compounds exhibiting isomerism are called isomers. There are two types of isomerism by coordination compounds
Structural Isomerism
Stereoisomerism
Let’s learn them in detail.
Structural Isomerism
The property of coordination compounds having the same number of atoms of each type but showing different bonding patterns is called Structural Isomerism. The Coordination Compounds that have the same number of atoms of each type but show different bonding patterns are called structural isomers. The different types of structural isomerism are:
Ionization Isomerism
Hydrate or Solvate Isomerism
Coordination Isomerism
Linkage Isomerism
Ionization Isomerism
Ionization Isomerism takes place when a ligand that is bound to the central atom exchanges its position with the counter ion which is outside the Coordination Complex. The Coordinate Compounds formed by such exchange of place of the ligand with the counter ion are called Isomers. For Example, [Co(NH3)5Cl]SO4 and [Co(NH3)5(SO4)]Cl are ionization isomers. This is because the ligand Cl which is a part of the Coordination Complex in [Co(NH3)5Cl]SO4 exchanges place with the Counter ion SO4 and hence now Cl becomes the counter ion and SO4 becomes the ligand.
Solvate Isomerism
Solvate Isomerism is a special type of Ionization Isomerism in which the ligand is replaced by a solvent molecule and if the solvent molecule is water then it is called Hydrate Isomerism. For Example, [Cr(H2O)6]Cl3 is a solvate isomer. It is violet in colour. In this, we see that the H2O molecule is directly attached to the central atom Cr. [CrCl(H2O)5]Cl2.H2O is a grey-green coloured hydrate isomer. However, in this case, we see that water molecule is present inside and outside the square bracket. The water molecule inside the square bracket is directly bonded to the central atom while that outside the bracket isn’t attached to the central atom and is called Water of Crystallization.
Water of Crystallization refers to the number of molecules of water attached to the compound but not part of the Coordination Complex. It is usually shown attached to the molecule by a dot(.)
Coordination Isomerism
Coordination Isomerism is exhibited when there is an exchange of ligands between a cationic and an anionic complex bonded together. In this, there is a Cationic Coordinate and an Anionic Coordinate Complex which are bonded together and there is an exchange of one or more ligands between them. For Example are [Co(NH3)6][Cr(C2O4)3] and [Co(C2O4)3][Cr(NH3)6] are Coordinate Isomers. In [Co(NH3)6][Cr(C2O4)3] (NH3)6 is attached to the Co atom and (C2O4)3 is attached to the Cr atom while in [Co(C2O4)3][Cr(NH3)6], Co is attached to C2O4 and Cr is attached to the (NH3)6.
Linkage Isomerism
Linkage Isomerism occurs when the ligand coordinates in more than one way. Such ligands that coordinate in more than one way are called ambidentate ligands. Examples of ambidentate ligands include SCN-/ NCS- and NO2– and ONO–. Examples of linkage isomerism include [Co(NH3)5(NO2)]Cl2 and [Co(NH3)5(ONO)]Cl2. In [Co(NH3)5(NO2)]Cl2, Co is attached to NO2 and called Nitro isomer while in [Co(NH3)5(ONO)]Cl2, the central atom Co is attached to the ONO and called Nitrito isomer.
Stereoisomerism
Stereoisomerism refers to the phenomenon of exhibiting different 3D spatial arrangements of bonds but having the same molecular formula. The compounds exhibiting stereoisomerism are called Stereoisomers. Stereoisomers have even the same set of bonds but they differ in arrangement. There are two types of Stereoisomerism that are:
Geometrical Isomerism
Optical Isomerism
These two types are discussed in detail as follows.
Geometrical Isomerism
There are two types of arrangements possible under Geometrical Isomerism. These are called cis-isomers and trans-isomers. In cis-isomers, the two similar bonds are on the same side of the central atom while in trans-isomer the similar bonds are on the opposite side of the central atom. The image inserted below will give a clear idea of cis and trans-Geometrical Isomerism.
Geometrical isomerism is shown by square planar and octahedral-shaped molecules. Tetrahedral-shaped molecules don’t exhibit cis and trans isomerism. Square-shaped molecules of type MX2L2 exhibit cis and trans isomers. An example of this type is mentioned above i.e. Pt[(NH3)2Cl2]. In this case, the ligands X and L are unidentate. A square planar molecule of type MABXL where M is the central atom and A, B, X, and L are ligands all different then it will exhibit three isomers out of which two will be cis type and one will be trans.
In the case of an Octahedral Coordination Complex of type MA2B4 the cis and trans isomerism is shown below in the attached figure. In this case, the ligand which is two in number is arranged in such a manner as to exhibit cis and trans isomerism.
In the case of a Coordination Complex where the central atom is attached to a didentate ligand i.e. the ligand which has two electron donor atoms, the geometrical isomers are shown below in the picture. The compound is of the type [MX2(L-L)2] where M is the central metal atom, X is the unidentate ligand and L is the didentate ligand. In the picture attached below Co is the central atom, Cl is the unidentate ligand and en is the bidentate ligand which stands for Ethylenediamine whose molecular formula is C2H4(NH2)2.
In the case of an Octahedral Complex of type MA3B3, there two types of isomers formed known as Facial or fac-isomer and Meridional or mer-isomers. For Example, the fac-isomer and mer-isomer for [Co(NH3)3(NO2 )3] are given below. The facial (fac) isomer is formed when three donor atoms of the same ligand occupy adjacent positions at the corners of an octahedral face. The meridional (mer) isomer is obtained when the positions are centred on the octahedron’s meridian.
Optical Isomerism
Optical Isomerism is the phenomenon exhibited by molecules when they have similar bonds, and different arrangements such that their mirror images are non superimposable. The mirror images of molecules that can’t be superimposed on each other are called Optical Isomers. Optical Isomers are also called Enantiomers. These molecules rotate the plane of Polarized light in a Polarimeter. Depending upon the direction of rotation they are classified as Dextrorotatory and Laevorotatory. The Dextrorotatory rotates the plane of light clockwise or in the right-hand direction while Laevorotatory rotates the light rotates the plane of light in Anticlockwise or left-hand direction.
The Optical Isomerism in Coordination Compounds is exhibited by Octahedral and Tetrahedral Coordinate Complexes but not by Square Planar. Hence, we see that Octahedral Coordinate Complexes exhibit both Geometrical and Optical Isomerism. In octahedral complexes containing didentate ligands, optical isomerism is common.
In a coordination entity of the type [PtCl2 (en)2 ]2+, only the cis-isomer shows optical activity.
Isomerism in Coordination Compounds Examples
Example 1: Draw all geometrical isomers of [Fe(NH3 )2 (CN)4 ]–.
Solution:
Example 2: Indicate the types of Isomerism exhibited by the following complexes
Example 3: How many Geometrical Isomers will be possible in [Co(NH3)3(Cl)3]?
Solution:
Two geometrical isomer is possible for [Co(NH3)3(Cl)3]–
Example 4: What are Ligands in Coordination Compounds?
Solution:
Ligands are ions or molecules that are bound to the central atom/ion of the coordination entity. Simple ions like Cl–, small molecules like H2O or NH3, larger molecules like H2NCH2CH2NH2 or N(CH2CH2NH2)3 , and even macromolecules like proteins can fall into this category.
Example 5: Draw the geometrical isomers of [Pt(NH3)(Br)(Cl)(Py)].
Solution:
FAQs on Isomerism in Coordination Compounds
1. What is Coordination Compound?
Coordination Compounds are chemical compounds in which the central atom is a transition metal and negative or neutral ligands are attached more than the normal valency of the central atom.
2. What are Isomers?
Isomers are chemical compounds that have the same molecular formula but different molecular structures.
3. What are the Two different types of Isomers?
The two different types of isomers are Structural Isomers and Stereo Isomers.
4. What are Cis and Trans Isomers?
Cis and Trans isomers are the types of Stereoisomers. In Cis-isomers the two similar bonds with the central atom are on the same side of the central atom while in trans-isomer the two similar bonds are on the different sides of the central atom.
5. What are Ligands?
Ligands are the negative or neutral atoms attached to the central atom in a number more than the usual valency of the central atom.
6. What is Coordination Complex?
The Central Atom together with ligands are called the Coordination Complex.
7. What is Water of Crystallization?
The number of water molecules attached to the crystal of a molecule is called Water of Crystallization. For Example in CuSO4.5H2O, the water number of water molecules attached to the crystal is 5, hence the Water of Crystallization for Copper Sulfate Pentahydrate is 5.
Neeraj Anand, Param Anand
Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations.
In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS".
He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.
Below is the CBSE Class 12 Syllabus along with the marking scheme and time duration of the Chemistry exam.
S.No
Title
No. of Periods
Marks
1
Solutions
10
7
2
Electrochemistry
12
9
3
Chemical Kinetics
10
7
4
d -and f -Block Elements
12
7
5
Coordination Compounds
12
7
6
Haloalkanes and Haloarenes
10
6
7
Alcohols, Phenols and Ethers
10
6
8
Aldehydes, Ketones and Carboxylic Acids
10
8
9
Amines
10
6
10
Biomolecules
12
7
Total
70
CBSE Class 12 Chemistry Practical Syllabus along with Marking Scheme
The following is a breakdown of the marks for practical, project work, class records, and viva. The total number of marks for all parts is 15. The marks for both terms are provided in the table below.
Evaluation Scheme for Examination
Marks
Volumetric Analysis
08
Salt Analysis
08
Content-Based Experiment
06
Project Work and Viva
04
Class record and Viva
04
Total
30
CBSE Class 12 Chemistry Syllabus (Chapter-wise)
Unit -1: Solutions
Raoult's law.
Colligative properties - relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmotic pressure, determination of molecular masses using colligative properties, abnormal molecular mass.
Solutions, Types of solutions, expression of concentration of solutions of solids in liquids, solubility of gases in liquids, solid solutions.
Van't Hoff factor.
Unit -2: Electrochemistry
Redox reactions, EMF of a cell, standard electrode potential
Nernst equation and its application to chemical cells
Relation between Gibbs energy change and EMF of a cell
Kohlrausch's Law
Electrolysis and law of electrolysis (elementary idea)
Dry cell-electrolytic cells and Galvanic cells
Conductance in electrolytic solutions, specific and molar conductivity, variations of conductivity with concentration.
Lead accumulator
Fuel cells
Unit -3: Chemical Kinetics
Rate of a reaction (Average and instantaneous)
Rate law and specific rate constant
Integrated rate equations and half-life (only for zerfirst-order order reactions)
Concept of collision theory (elementary idea, no mathematical treatment)
Factors affecting rate of reaction: concentration, temperature, catalyst;
Order and molecularity of a reaction
Activation energy
Arrhenius equation
Unit -4: d and f Block Elements
Lanthanoids- Electronic configuration, oxidation states, chemical reactivity and lanthanoid contraction and its consequences.
Actinoids- Electronic configuration, oxidation states and comparison with lanthanoids.
General introduction, electronic configuration, occurrence and characteristics of transition metals, general trends in properties of the first-row transition metals – metallic character, ionization enthalpy, oxidation states, ionic radii, color, catalytic property, magnetic properties, interstitial compounds, alloy formation, preparation and properties of K2Cr2O7 and KMnO4.
Unit -5: Coordination Compounds
Coordination compounds - Introduction, ligands, coordination number, color, magnetic properties and shapes
The importance of coordination compounds (in qualitative analysis, extraction of metals and biological system).
IUPAC nomenclature of mononuclear coordination compounds.
Bonding
Werner's theory, VBT, and CFT; structure and stereoisomerism
Unit -6: Haloalkanes and Haloarenes
Haloarenes: Nature of C–X bond, substitution reactions (Directive influence of halogen in monosubstituted compounds only). Uses and environmental effects of - dichloromethane, trichloro methane, tetrachloromethane, iodoform, freons, DDT.
Haloalkanes: Nomenclature, nature of C–X bond, physical and chemical properties, optical rotation mechanism of substitution reactions.
Unit -7: Alcohols, Phenols and Ethers
Phenols: Nomenclature, methods of preparation, physical and chemical properties, acidic nature of phenol, electrophilic substitution reactions, uses of phenols.
Ethers: Nomenclature, methods of preparation, physical and chemical properties, uses.
Alcohols: Nomenclature, methods of preparation, physical and chemical properties (of primary alcohols only), identification of primary, secondary and tertiary alcohols, mechanism of dehydration, and uses with special reference to methanol and ethanol.
Unit -8: Aldehydes, Ketones and Carboxylic Acids
Carboxylic Acids: Nomenclature, acidic nature, methods of preparation, physical and chemical properties; uses.
Aldehydes and Ketones: Nomenclature, nature of carbonyl group, methods of preparation, physical and chemical properties, mechanism of nucleophilic addition, the reactivity of alpha hydrogen in aldehydes, uses.
Unit -9: Amines
Diazonium salts: Preparation, chemical reactions and importance in synthetic organic chemistry.
Amines: Nomenclature, classification, structure, methods of preparation, physical and chemical properties, uses, and identification of primary, secondary and tertiary amines.
Unit -10: Biomolecules
Proteins -Elementary idea of - amino acids, peptide bond, polypeptides, proteins, structure of proteins - primary, secondary, tertiary structure and quaternary structures (qualitative idea only), denaturation of proteins; enzymes. Hormones - Elementary idea excluding structure.
Vitamins - Classification and functions.
Carbohydrates - Classification (aldoses and ketoses), monosaccharides (glucose and fructose), D-L configuration oligosaccharides (sucrose, lactose, maltose), polysaccharides (starch, cellulose, glycogen); Importance of carbohydrates.
Nucleic Acids: DNA and RNA.
The syllabus is divided into three parts: Part A, Part B, and Part C. Part A consist of Basic Concepts of Chemistry, which covers topics such as atomic structure, chemical bonding, states of matter, and thermochemistry. Part B consists of Topics in Physical Chemistry, which includes topics such as chemical kinetics, equilibrium, and electrochemistry. Part C consists of Topics in Organic Chemistry, which covers topics such as alkanes, alkenes, alkynes, and aromatic compounds.
Basic Concepts of Chemistry:
Atomic structure: This section covers the fundamental concepts of atomic structure, including the electronic configuration of atoms, the Bohr model of the atom, and the wave nature of matter.
Chemical bonding: This section covers the different types of chemical bonds, including ionic, covalent, and metallic bonds, as well as the concept of hybridization.
States of the matter: This section covers the three states of matter - solid, liquid, and gas - and the factors that influence their properties.
Thermochemistry: This section covers the principles of thermochemistry, including the laws of thermodynamics and the concept of enthalpy.
Chapters in Physical Chemistry:
Chemical kinetics: This section covers the study of the rate of chemical reactions and the factors that influence it, including the concentration of reactants, temperature, and the presence of catalysts.
Equilibrium: This section covers the principles of chemical equilibrium, including the concept of Le Chatelier's principle and the equilibrium constant.
Electrochemistry: This section covers the principles of electrochemistry, including the concept of half-cell reactions, galvanic cells, and electrolysis.
Chapters in Organic Chemistry:
Alkanes: This section covers the properties and reactions of alkanes, including their structure, isomerism, and combustion.
Alkenes: This section covers the properties and reactions of alkenes, including their structure, isomerism, and addition reactions.
Alkynes: This section covers the properties and reactions of alkynes, including their structure, isomerism, and addition reactions.
Aromatic compounds: This section covers the properties and reactions of aromatic compounds, including their structure, isomerism, and electrophilic substitution reactions.
In addition to the topics covered in the syllabus, the CBSE Class 12 Chemistry exam also tests students on their analytical and problem-solving skills, as well as their ability to apply the concepts learned in the classroom to real-world situations.
Students can also check out the Tips for the Class 12 Chemistry Exam. They can easily access the Class 12 study material in one place by visiting the CBSE Class 12 page at ANAND CLASSES (A School Of Competitions). Moreover, to get interactive lessons and study videos, download the ANAND CLASSES (A School Of Competitions) App.
Frequently Asked Questions on CBSE Class 12 Chemistry Syllabus
Q1
How many chapters are there in the CBSE Class 12 Chemistry as per the syllabus?
There are 10 chapters in the CBSE Class 12 Chemistry as per Syllabus. Students can learn all these chapters efficiently using the study materials provided at ANAND CLASSES (A School Of Competitions).
Q2
What is the marking scheme for CBSE Class 12 Chemistry practical exam according to the syllabus?
The marking scheme for CBSE Class 12 Chemistry practical exam, according to the syllabus, is 8 marks for volumetric analysis, 8 marks for salt analysis, 6 marks for the content-based experiment, 4 marks for the project and viva and 4 marks for class record and viva.
Q3
Which is the scoring chapter in Chemistry as per CBSE Class 12 syllabus?
The chapter Electrochemistry in Chemistry is the scoring chapter as per CBSE Class 12 syllabus.
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