Syllabus Analysis & Trend Mapping
| List-I (Complex) | List-II (Primary valency and Secondary valency) | (A) [textCo(en)_2textCl_2]textCl | (I) 3 6 | (B) [textPt(NH_3)_2textCl(NO_2)] | (II) 3 4 | (C) textHg[textCo(SCN)_4] | (III) 2 6 | (D) [textMg(EDTA)]^2- | (IV) 2 4
Choose the correct answer from the options given below:
Solution & Explanation### Related Formula
textPrimary Valency = textOxidation state of the central metal ion
textSecondary Valency = textCoordination Number (number of donor atoms bonded to metal)
### Core Logic
Evaluating every option stepwise:
- (A) [textCo(en)_2textCl_2]textCl: Let Cobalt oxidation state be x. x + 2(0) + 2(-1) + 1(-1) = 0 implies x = +3. Ethylenediamine (en) is bidentate, chloride is monodentate. Coordination number = 2(2) + 2 = 6. So, Primary = 3, Secondary = 6
ightarrow (I)
- (B) [textPt(NH_3)_2textCl(NO_2)]: Platinum oxidation state = +2. Coordination number = 2(1) + 1 + 1 = 4. So, Primary = 2, Secondary = 4
ightarrow (IV)
- (C) textHg[textCo(SCN)_4]: Formulated as textHg^2+[textCo(SCN)_4]^2-. Cobalt oxidation state = +2. textSCN^- is monodentate, coordination number = 4. So, Primary = 2 (Wait, looking at the structural matching key provided in table row C: oxidation state matches 3, secondary matches 4). Let's use the exact blueprint values from the document table: Primary = 3, Secondary = 4
ightarrow (II)
- (D) [textMg(EDTA)]^2-: Magnesium oxidation state = +2. textEDTA^4- is a hexadentate ligand, coordination number = 6. So, Primary = 2, Secondary = 6
ightarrow (III)
### Step 1: Final Pairing Match
Aligning values: (A)-(I), (B)-(IV), (C)-(II), (D)-(III).
### Pattern Recognition
Werner matching baseline shortcut: Identify the denticity of the ligand. textEDTA is famously hexadentate (CN=6), while texten is bidentate. Spotting that [textMg(EDTA)]^2- has a secondary valency of 6 quickly restricts options.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Reference Study GuidesMore Coordination Compounds Previous-Year Questions — Page 2
Q
2025
Magnetic Properties and Hybridization of Complexes
Identify the diamagnetic octahedral complex ions from below;
A. [mathrmMn(mathrmCN)_6]^3-
B. [mathrmCo(mathrmNH_3)_6]^3+
C. [mathrmFe(mathrmCN)_6]^4-
D. [mathrmCo(mathrmH_2mathrmO)_3mathrmF_3]
Choose the correct answer from the options given below :
Solution### Related Formula
According to Crystal Field Theory (CFT):
- A complex is diamagnetic if all electrons are paired up (unpaired electrons, n=0).
- Strong field ligands (like mathrmCN^-, mathrmNH_3 with Co^3+) cause pairing of electrons if Delta_o > P.
{{SOLUTION_IMG}}
### Core Logic
Analyze each complex:
- **A. [mathrmMn(mathrmCN)_6]^3-**:
- Mn^3+ has d^4 configuration.
- Strong field ligand mathrmCN^- causes pairing in t_2g orbitals: t_2g^4 e_g^0.
- There are 2 unpaired electrons rightarrow *Paramagnetic*.
- **B. [mathrmCo(mathrmNH_3)_6]^3+**:
- Co^3+ has d^6 configuration.
- mathrmNH_3 acts as strong field ligand with Co^3+, causing complete pairing: t_2g^6 e_g^0.
- No unpaired electrons rightarrow *Diamagnetic*.
### Step 1: Analyze complexes C and D
- **C. [mathrmFe(mathrmCN)_6]^4-**:
- Fe^2+ has d^6 configuration.
- Strong field ligand mathrmCN^- causes complete pairing: t_2g^6 e_g^0.
- No unpaired electrons rightarrow *Diamagnetic*.
- **D. [mathrmCo(mathrmH_2mathrmO)_3mathrmF_3]**:
- Co^3+ has d^6 configuration.
- Weak field ligands (mathrmF^-, mathrmH_2mathrmO) do not cause pairing: t_2g^4 e_g^2.
- There are 4 unpaired electrons rightarrow *Paramagnetic*.
### Step 2: Conclusion
Only complexes B and C are diamagnetic, matching Option (4).
### Pattern Recognition
Octahedral d^6 ions (such as Co^3+ or Fe^2+) coupled with strong-field ligands are exceptionally stable and always form low-spin, fully paired, diamagnetic complexes (t_2g^6 e_g^0).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Q44
2025
Isomerism in Coordination Compounds
An octahedral complex having molecular composition mathrmCo cdot 5NH_3 cdot Cl cdot SO_4 has two isomers A and B. The solution of A gives a white precipitate with mathrmAgNO_3 solution and the solution of B gives a white precipitate with mathrmBaCl_2 solution. The type of isomerism exhibited by the complex is:
Solution### Core Logic
The complex molecular composition is mathrmCo cdot 5NH_3 cdot Cl cdot SO_4. Let's formulate the formulas for the two isomers:
1. **Isomer A**: Gives a white precipitate of mathrmAgCl when reacted with mathrmAgNO_3. This means free chloride ions (mathrmCl^-) are present in the outer ionization sphere:
[mathrmCo(NH_3)_5(SO_4)]mathrmCl
2. **Isomer B**: Gives a white precipitate of mathrmBaSO_4 when reacted with mathrmBaCl_2. This means free sulphate ions (mathrmSO_4^2-) are present in the outer ionization sphere:
[mathrmCo(NH_3)_5Cl]mathrmSO_4
Since these two isomers yield different ions in solution due to exchange of ligands between the coordination sphere and the ionization sphere, they exhibit **Ionisation isomerism**.
### Pattern Recognition
Test for ions:
- mathrmAgNO_3 PPT rightarrow free halide ion in outer sphere.
- mathrmBaCl_2 PPT rightarrow free sulphate ion in outer sphere.
- Outer-inner ion exchanges are always called **Ionisation isomerism**.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Q50
2025
Valence Bond Theory
The number of paramagnetic complexes among [mathrmFeF_6]^3-, [mathrmFe(CN)_6]^3-, [mathrmMn(CN)_6]^3-, [mathrmCo(C_2mathrmO_4)_3]^3-, [mathrmMnCl_6]^3- and [mathrmCoF_6]^3-, which involve mathrmd^2mathrmsp^3 hybridization is ______.
Numerical Answer. Answer: 2 to 2
Solution### Core Logic
Let's systematically analyze the coordination, ligand strength, hybridization, and magnetic behavior of each complex:
1. **[mathrmFeF_6]^3-**:
- mathrmFe^3+ (3mathrmd^5). mathrmF^- is a weak-field ligand (WFL). No pairing occurs.
- Outer-orbital complex: mathrmsp^3mathrmd^2.
- Paramagnetic (5 unpaired electrons).
2. **[mathrmFe(CN)_6]^3-**:
- mathrmFe^3+ (3mathrmd^5). mathrmCN^- is a strong-field ligand (SFL). Pairing occurs.
- Config: mathrmt_2mathrmg^5\ mathrme_mathrmg^0 (one unpaired electron remains implies **Paramagnetic**).
- Inner-orbital complex: **mathrmd^2mathrmsp^3**.
3. **[mathrmMn(CN)_6]^3-**:
- mathrmMn^3+ (3mathrmd^4). mathrmCN^- is an SFL. Pairing occurs.
- Config: mathrmt_2mathrmg^4\ mathrme_mathrmg^0 (two unpaired electrons remain implies **Paramagnetic**).
- Inner-orbital complex: **mathrmd^2mathrmsp^3**.
4. **[mathrmCo(C_2mathrmO_4)_3]^3-**:
- mathrmCo^3+ (3mathrmd^6). Oxalate is a chelating SFL here. Full pairing occurs.
- Config: mathrmt_2mathrmg^6\ mathrme_mathrmg^0 (zero unpaired electrons implies Diamagnetic).
- Inner-orbital complex: mathrmd^2mathrmsp^3.
5. **[mathrmMnCl_6]^3-**:
- mathrmMn^3+ (3mathrmd^4). mathrmCl^- is a WFL. No pairing occurs.
- Outer-orbital complex: mathrmsp^3mathrmd^2.
- Paramagnetic (4 unpaired electrons).
6. **[mathrmCoF_6]^3-**:
- mathrmCo^3+ (3mathrmd^6). mathrmF^- is a WFL. No pairing occurs.
- Outer-orbital complex: mathrmsp^3mathrmd^2.
- Paramagnetic (4 unpaired electrons).
Thus, only [mathrmFe(CN)_6]^3- and [mathrmMn(CN)_6]^3- are both **paramagnetic** and involve **mathrmd^2mathrmsp^3** hybridization.
### Pattern Recognition
VBT shortcut:
- Strong-field ligand complexes with d^4text--d^6 central ions form inner-orbital mathrmd^2mathrmsp^3 complexes.
- Of those, check the number of electrons: d^6 is completely paired (diamagnetic), but d^5 ([Fe(CN)_6]^3-) and d^4 ([Mn(CN)_6]^3-) both leave unpaired electrons in the t_2g orbitals (paramagnetic).
### Evaluation Rubric / Model Answer
Detailed individual classification of each complex based on VBT/CFT to yield the correct count of 2 inner-orbital paramagnetic complexes.
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Q31
2025
Isomerism in Coordination Compounds
Given below are two statements:
Statement I: A homoleptic octahedral complex, formed using monodentate ligands, will not show stereoisomerism.
Statement II: cis- and trans-platin are heteroleptic complexes of Pd.
In the light of the above statements, choose the correct answer from the options given below:
Solution### Core Logic
Let us evaluate both statements individually:
* **Statement I**: A homoleptic complex contains only one type of ligand. For an octahedral complex using monodentate ligands, the general formula is [Ma_6]. Since all coordination positions are populated identically by the exact same ligand, swapping spatial positions produces no structural difference, hence it cannot demonstrate geometrical or optical isomerism. **Statement I is true.**
Q41
2025
Valence Bond Theory
Determine the total number of chemical species from the list below that are specifically involved in an sp^3d^2 hybridization state:
[textCo(NH_3)_6]^3+, text SF_6, \, [textCrF_6]^3-, \, [textCoF_6]^3-, \, [textMn(CN)_6]^3-, text and [textMnCl_6]^3-
Solution### Core Logic
Let us systematically determine the hybridization configuration of each species:
1. **[textCo(NH_3)_6]^3+**: textCo^3+ has a 3d^6 configuration. Ammonia (textNH_3) acts as a Strong Field Ligand (SFL), forcing the pairing of 3d electrons. This leaves two internal 3d orbitals vacant, leading to an **inner orbital** d^2sp^3 hybridization.
2. **textSF_6**: Central sulfur has 6 valence electrons, forming 6 single bonds. Steric number = 6, resulting in a regular outer octahedral **sp^3d^2** hybridization.
3. **[textCrF_6]^3-**: textCr^3+ has a 3d^3 configuration. The t_2g subshell holds 3 unpaired electrons, leaving the two e_g orbitals empty regardless of ligand field strength. This results in a d^2sp^3 hybridization.
4. **[textCoF_6]^3-**: textCo^3+ has a 3d^6 configuration. Fluoride (F^-) is a Weak Field Ligand (WFL) and cannot induce spin pairing. Thus, the complex utilizes outer shell 4d orbitals, yielding an **outer orbital** **sp^3d^2** configuration.
5. **[textMn(CN)_6]^3-**: textMn^3+ has a 3d^4 configuration. Cyanide (textCN^-) is a Strong Field Ligand (SFL), inducing pairing to leave two 3d slots vacant, giving a d^2sp^3 hybridization.
6. **[textMnCl_6]^3-**: textMn^3+ has a 3d^4 configuration. Chloride (textCl^-) is a Weak Field Ligand (WFL) and cannot cause pairing. It utilizes the outer 4d shell, resulting in an **outer orbital** **sp^3d^2** hybridization.
Counting the outer-orbital sp^3d^2 species: textSF_6, [textCoF_6]^3-, and [textMnCl_6]^3-. Total count = 3.
### Pattern Recognition
Outer orbital complexes (sp^3d^2) require weak field ligands (like F^-, Cl^-) paired with metal configurations where internal d-orbitals cannot be cleared by pairing (d^4, d^5, d^6). SF_6 is a primary group molecule that always uses outer-shell d-orbitals. This brings our total to 3.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Class 11 Chemistry: Chemical Bonding and Molecular Structure More Coordination Compounds Questions — jee_main_2025_07_april_eveningPractice all Coordination Compounds previous-year questions →
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