Coordination Chemistry

Step 1: Rules of IUPAC nomenclature.
The IUPAC system provides a standard way of naming coordination compounds. The rules include: \begin{enumerate} \item
Name of cation is written before anion.
For example: [Co(NH ) ]Cl is named as hexaamminecobalt(III) chloride. \item
Ligands are named first, followed by the central atom.
Ligands are named in alphabetical order irrespective of charge. \item
Prefixes are used for number of ligands.
Mono-, di-, tri-, etc. are used. For complex ligands, bis-, tris-, tetrakis- are used. \item
Oxidation state of the central metal ion is shown in Roman numerals.
Example: [Fe(CN) ] → hexacyanoferrate(II). \item
Anionic complexes end with -ate.
Example: [PtCl ] → hexachloroplatinate(IV). \end{enumerate} Step 2: Example.
For [Cr(H O) Cl ]Cl: Name is tetraaquadichlorochromium(III) chloride. Conclusion:
The IUPAC nomenclature system ensures clarity and uniformity in naming coordination compounds by following systematic rules.

Step 1: Definition.
Coordination number is defined as the number of ligand donor atoms that are directly bonded to the central metal atom or ion in a coordination compound.
Step 2: Explanation.
It tells us how many atoms, ions, or molecules are attached to the central atom in a complex. This depends on the size, charge, and electronic configuration of the central atom.
Step 3: Example.
In the complex :
- The central metal ion is .
- Six ammonia molecules ( ) are bonded directly to cobalt.
Thus, the coordination number of cobalt is 6. Conclusion:
The coordination number represents the total number of bonds formed between the central metal ion and the surrounding ligands.

Step 1: Introduction.
Crystal Field Theory (CFT) explains the bonding in coordination compounds in terms of the effect of the electric field produced by ligands on the -orbitals of the central metal ion. Step 2: Splitting of d-orbitals.
In a free metal ion, all five -orbitals are degenerate (equal energy).
When ligands approach the central metal ion: - In an octahedral field, the -orbitals split into two sets: - The energy difference is called the
crystal field splitting energy ( ). Step 3: Consequences.
\begin{enumerate} \item Explains colour of complexes due to transitions. \item Explains magnetic properties (high spin or low spin) based on pairing of electrons and magnitude of . \end{enumerate} Step 4: Limitations of CFT.
\begin{enumerate} \item It treats metal-ligand bonds as purely ionic and ignores covalent character. \item Cannot explain the spectra of some complexes accurately. \item Does not account for ligand-metal orbital overlap or back bonding. \end{enumerate} Conclusion:
Crystal Field Theory successfully explains splitting of -orbitals, colour, and magnetic properties of coordination compounds, but fails to explain covalent interactions and detailed spectra.

- In aqueous solution, dissociates as: - Oxidation number of in is :

Step 1: Definition of Ambidentate Ligand:
Ambidentate ligands can coordinate through two different donor atoms. Step 2: Why is ambidentate?
- It can bind via Nitrogen ( as Nitro) or Oxygen ( as Nitrito).

Valence Bond Theory explains bonding in coordination compounds by hybridization of atomic orbitals on the central metal ion:
1. Ligands donate lone pairs to vacant orbitals of the metal ion.
2. Hybrid orbitals form sigma bonds with the ligands.
3. Example: In , undergoes hybridization, forming a square planar structure.

The co-ordination number is the number of ligand atoms directly bonded to the central atom in a coordination compound. Example: where the co-ordination number of cobalt is 6.

Step 1: Ionisation Isomerism:
Occurs when compounds produce different ions in solution. Example: Step 2: Coordination Isomerism:
Occurs when the ligands exchange between cation and anion parts. Example:

Step 1: Main Postulates of Werner’s Theory: 1. Metals exhibit primary valency (oxidation state) and secondary valency (coordination number).
2. Secondary valency is directed towards specific ligands in a fixed geometry.
3. Example: In , Co has:
- Primary valency: +3 (satisfied by Cl )
- Secondary valency: 6 (satisfied by NH )

Step 1: Identify the Isomers
The given compounds are coordination compounds of cobalt. They have the same molecular formula but differ in the position of the ligands, so they are a type of **linkage isomers**.
Step 2: Explanation of Linkage Isomerism
In linkage isomerism, a ligand can coordinate to the metal center through different atoms. For example, in , the chloride ion ( ) is coordinating to the cobalt center, while in , the sulfate ion ( ) is coordinating. Final Answer: The compounds and are linkage isomers. Correct Answer: Linkage isomers.

Step 1: Double salt.
- Double salts are crystalline salts formed by the combination of two simple salts in a fixed ratio.
- They dissociate completely into their constituent ions when dissolved in water.
- Examples: \cdot (NH ) SO \cdot 6H O)}\) , \cdot 6H O)}\) .
Step 2: Complex salt.
- Complex salts consist of a central metal ion bonded to ligands through coordinate bonds.
- They do not dissociate completely into simple ions; instead, they give a complex ion in solution.
- Examples: )_4]SO_4\) , . Final Answer:

Step 1: Apply oxidation number rule.
Let oxidation number of Cu = .
Charge on cyanide (CN ) = –1 each.
There are 4 CN ligands total = –4.
Step 2: Write equation.



Step 3: Conclude.
Oxidation number of Cu is +1. Final Answer: % Quciktip

(x) :
- Oxidation state of Co: +3 (since each oxalate contributes -2 charge, and there are three oxalates, the net charge is -6. The overall charge of the complex is -3, so Co must be +3 to balance this).
- Distribution of d-orbitals: Co (d⁶ configuration) will have 6 electrons in its d-orbitals.
- Coordination number of Co: 6 (since there are three oxalate ions, each of which is a bidentate ligand, contributing 2 donor atoms per ligand, for a total coordination of 6).
(y) :
- Oxidation state of Mn: +2 (the complex ion is neutralized by the sulfate ion , indicating Mn is in the +2 oxidation state).
- Distribution of d-orbitals: Mn (d⁵ configuration) will have 5 electrons in its d-orbitals.
- Coordination number of Mn: 6 (since there are six water molecules, each contributing one donor atom, making the coordination number 6).

(x) Tetraammine diaqua cobalt (III) chloride
Ligands: 4 ammine (NH ; neutral) and 2 aqua (H O; neutral). Central metal: Co(III) complex cation charge . Chloride is the counter anion ( each), hence three Cl are required.
[2pt] (y) Potassium trioxalato chromate (III)
Oxalato (oxalate) ligand = C O (bidentate). Three such ligands: total charge . Central metal: Cr(III) complex-anion charge . Balance with three K .
[2pt]

Paramagnetism arises from the presence of unpaired electrons. Transition elements have their valence electrons in the and subshells. Because the -subshell can accommodate ten electrons and is partially filled across the series, most transition-metal atoms and many of their ions retain one or more unpaired -electrons.
These unpaired electrons give a net magnetic moment ( , where is the number of unpaired electrons), hence paramagnetism.
Further, transition metals exhibit variable oxidation states; during oxidation or complex formation, electrons are removed from and levels, often leaving unpaired -electrons in the cations/complexes.
Notes/Exceptions: Closed-shell cases like , , are diamagnetic. Some strong-field, low-spin complexes can also become diamagnetic if all electrons pair.

Step 1: Find number of unpaired electrons from .
Spin-only formula: . Given . The nearest integer solution is (since ).
Step 2: Determine metal oxidation state and -count.
Let oxidation state of Mn be : . Thus is .
Step 3: Decide geometry.
is a weak-field ligand, so pairing is unfavorable; a ion remains high spin with 5 unpaired electrons—consistent with the observed . Four-coordinate with weak-field ligands prefers tetrahedral over square planar (which is typical for ions and would require strong-field stabilization).

To calculate the oxidation number of cobalt in the given complex :
Step 1: Assign charges of known species.
- Potassium (K) has an oxidation state of .
- Carbonyl (CO) is a neutral ligand, so each CO contributes charge.
Step 2: Write the overall charge balance equation.
Let the oxidation number of cobalt be . The complex ion is , since K is outside with .
Step 3: Solve for .
Thus, the oxidation number of cobalt in is .

In this question, we are dealing with the complex , which is an octahedral coordination complex. The central metal ion is iron (Fe), surrounded by two ammonia (NH ) molecules and four cyanide (CN ) ions. The coordination number of the metal ion is 6, forming an octahedral geometry. Geometrical Isomerism in Octahedral Complexes:
Geometrical isomerism arises in octahedral complexes when there are different possible spatial arrangements of ligands. In this case, the complex can have cis and trans isomers based on the arrangement of the ligands. 1. Cis-Isomer: In the cis configuration, the two NH molecules are placed next to each other, i.e., they occupy adjacent positions (90° apart) in the octahedral arrangement. The four cyanide ions are placed at the remaining positions, opposite each other. This creates a symmetrical arrangement of the ligands in the octahedral complex. The formula for this isomer can be represented as: 2. Trans-Isomer: In the trans configuration, the two NH molecules are placed opposite each other, i.e., they occupy opposite positions (180° apart) in the octahedral arrangement. The four cyanide ions occupy the remaining positions. This arrangement is different from the cis-isomer and results in a distinct geometric shape. The formula for this isomer is: Conclusion: - The cis-isomer has the two NH molecules adjacent to each other, while in the trans-isomer, the NH molecules are opposite each other. These two different spatial arrangements of the ligands lead to geometrical isomerism in the complex.

The complex consists of a coordination sphere and 2 chloride ions outside the coordination sphere. When this complex dissolves in water, it dissociates as follows:
Thus, the total number of ions generated is: - 1 ion of ,
- 2 ions of .
The total number of ions = 1 + 2 = 3 ions. Therefore, the correct answer is option (C) 3.