Organometallic Compounds MCQ Quiz in मराठी - Objective Question with Answer for Organometallic Compounds - मोफत PDF डाउनलोड करा

CONCEPT:

Bond Polarity in Zn–C Bonds

• The polarity of a bond between two atoms depends on the difference in electronegativity between them. In this case, the polarity of the Zn–C bond is influenced by the nature of the carbon species attached to the zinc atom.
• Carbon in different hybridizations (sp, sp², sp³) will have different electronegativities due to varying s-character. Higher s-character increases electronegativity.
• For sp-hybridized carbon (as in alkynes), the s-character is 50%, making it more electronegative compared to sp² (33% s-character, as in alkenes) and sp³ (25% s-character, as in alkanes) carbons.
• As a result, a Zn–C bond with an sp-hybridized carbon will be more polarized than a Zn–C bond with an sp² or sp³ hybridized carbon.

EXPLANATION:

• Compound I: Here, the Zn is bonded to an sp-hybridized carbon (triple bond), which has the highest electronegativity among the three compounds due to its high s-character (50%). This makes the Zn–C bond in Compound I the most polar.
• Compound II: In this compound, Zn is bonded to an sp²-hybridized carbon (double bond), with a moderate level of s-character (33%). This bond is less polar than in Compound I but more polar than in Compound III.
• Compound III: Here, Zn is bonded to an sp³-hybridized carbon (single bond), which has the lowest electronegativity due to the lowest s-character (25%). Thus, the Zn–C bond in Compound III is the least polar.

Therefore, the order of Zn–C bond polarity in the compounds is I > II > III.

Conclusion:

So, the  correct option is 1.

CONCEPT:

Oxidation States of Transition Metals in Metal Carbonyl Complexes

• In transition metal carbonyl complexes, the oxidation state of the metal can be determined by considering the neutral charge of CO ligands (each CO ligand contributes zero charge).
• The reaction involves sodium (Na) as a reducing agent, which typically adds an electron to the complex, altering the oxidation state of the metal.
• In this particular reaction, [Mn(CO)₅]^- (species P) is formed as an intermediate before it reacts with CH₃Cl to form [CH₃Mn(CO)₅] (species Q).

EXPLANATION:

• For species P, [Mn(CO)₅]^-:
  • In the neutral Mn₂(CO)₁₀ dimer, each Mn is initially in the zero oxidation state.
  • Upon reaction with Na, Mn receives an extra electron, resulting in a -1 oxidation state for Mn in [Mn(CO)₅]^- (species P).
• For species Q, [CH₃Mn(CO)₅]:
  • When [Mn(CO)₅]^- reacts with CH₃Cl, it undergoes methylation (addition of CH₃), which neutralizes the negative charge.
  • As a result, Mn in [CH₃Mn(CO)₅] (species Q) has an oxidation state of +1.

Therefore, the oxidation states of Mn in P and Q are -1 and +1, respectively.

Conclusion:

So, the correct option is 1.

Concept:

• The 18-electron rule states that a transition metal complex is most stable when the sum of the metal's valence electrons and the electrons donated by the ligands is 18. This stability arises because 18 electrons complete the valence shell of the metal, effectively filling the s, p, and d orbitals.
• The rule is analogous to the octet rule for main group elements, but it applies to coordination complexes involving d-block metals.

Explanation:

The number of valence electrons in the complex Na₂Fe(CO)₄ (Colman's reagent), we need to count the total number of valence electrons from all contributors:

Fe : The Fe atom in the complex as Fe²⁺ (because it is balanced by Na⁺ ions), it will lose two electrons, so its configuration becomes \(3d^6\). Hence, the valence electrons from Fe are 8 (6 from 3d and 2 from 4s).
CO (Carbonyl ligands): Each CO ligand donates 2 electrons to the metal center. Since there are 4 CO ligands, they contribute a total of \((4 \times 2 = 8)\) electrons.

Charge: The compound has 2- charges on it. So, 2 electrons are added from it.
Counting Total Valence Electrons:
Summing these contributions: \(8 \text{ (from Fe)} + 8 \text{ (from CO)} + 2 (from \ negative \ charge) = 18 \text{ valence electrons.}\)

CONCEPT:

Metal Carbonyls and Their Properties

• Metal carbonyls are complexes composed of a metal center bonded to carbon monoxide ligands.
• Carbon monoxide (CO) acts as a ligand and can donate electron density to the metal (acting as a Lewis base) and can accept electron density from the metal (acting as a Lewis acid).
• pπ-pπ back bonding (also known as π-back bonding) occurs when the metal donates electron density back into the π* anti-bonding orbitals of the CO ligand, strengthening the metal-CO bond.

EXPLANATION:

• In the context of metal carbonyls, CO can act as both a Lewis base and a Lewis acid, due to its ability to donate and accept electron density.
• The metal center in the carbonyl complex primarily acts as a Lewis acid, accepting electron density from the CO ligand's lone pair.
• pπ-pπ back bonding enhances the stability of the metal-carbon monoxide bond by allowing electron density transfer from the metal to the CO ligand.
• 
• Considering these properties:
  • CO acts as a Lewis base and Lewis acid - This is true.
  •  Metal acts as Lewis base and Lewis acid - This is false. The metal primarily acts as a Lewis acid.
  • pπ-pπ back bonding takes place - This is true.
• Therefore, the false statement about metal carbonyls is Option 2.

Therefore, the correct answer is Option 2: Metal acts as Lewis base and Lewis acid.

CONCEPT:

Bonding in Metal Carbonyls (M-CO Bonding)

• Metal carbonyl complexes are compounds where carbon monoxide (CO) acts as a ligand to a metal center, usually a transition metal.
• In these complexes, bonding between the metal and CO involves both σ-bonding and π-backbonding:
  • σ-bonding: The carbon atom in CO donates its lone pair of electrons to the metal. This donation happens through the σ orbital of CO, forming a σ bond between the carbon atom and the metal.
  • π-backbonding (π-bonding): The metal, in turn, donates electron density from its d-orbitals into the π (anti-bonding) orbital of CO, which creates a π bond. This back-donation strengthens the metal-CO interaction by stabilizing the bond.
• Because of this back-donation, the CO bond within the carbonyl complex weakens slightly, and the C≡O bond length increases compared to free CO.

EXPLANATION:

• CO has two key orbitals:
  • σ orbital: This is a bonding orbital between the carbon and oxygen. It can donate electron density (from the lone pair on carbon) to the metal, forming a σ bond.
  • π* orbital: This is the anti-bonding π orbital of CO. It can accept electron density from the metal’s d-orbitals through back-donation, leading to the formation of a π bond.
• In metal carbonyl complexes:
  • The carbon in CO forms a σ bond by donating its lone pair to the metal.
  • The metal’s d-orbitals participate in π-backbonding, donating electrons into the π orbital of CO, which results in a π bond between the metal and CO.

CONCLUSION:

• The correct option is: Option 3: It is π bond between d-orbital of metal and π* orbital of CO

CONCEPT:

18-Electron Rule (Effective Atomic Number Rule)

• The 18-electron rule is a guideline used primarily for transition metal complexes to predict the stability of the metal complex.
• According to this rule, a stable metal complex should have a total of 18 valence electrons (including the metal’s own electrons and those donated by ligands).
• This is because, for many transition metals, having 18 valence electrons provides a closed-shell electron configuration similar to that of noble gases, making the complex stable.
• To check whether a complex follows the 18-electron rule, you need to count the valence electrons contributed by:
  • The metal center (based on its group in the periodic table).
  • The ligands (each ligand typically donates a certain number of electrons).

EXPLANATION:

• Let’s evaluate each complex to see whether it obeys the 18-electron rule:
• Ni(CO)₄ (Nickel tetracarbonyl)
  • Nickel is in the 10th group of the periodic table, so it has 10 valence electrons.
  • Each CO ligand donates 2 electrons, and there are 4 CO ligands, contributing a total of 8 electrons.
  • Total electron count = 10 (from Ni) + 8 (from 4 CO ligands) = 18 electrons.
  • Conclusion: Ni(CO)₄ obeys the 18-electron rule.
• [Cr(NH₃)₆]³⁺ (Hexaamminechromium(III))
  • Chromium is in the 6th group of the periodic table, so it has 6 valence electrons.
  • Each NH₃ ligand donates 2 electrons, and there are 6 NH₃ ligands, contributing a total of 12 electrons.
  • Since the complex has a 3+ charge, we subtract 3 electrons from the total.
  • Total electron count = 6 (from Cr) + 12 (from NH₃) − 3 (due to charge) = 15 electrons.
  • Conclusion: [Cr(NH₃)₆]³⁺ does not obey the 18-electron rule.
• [Fe(CN)₆]⁴⁻ (Hexacyanoferrate(II))
  • Iron in this complex is in the +2 oxidation state (Fe²⁺), so it has 6 valence electrons (8 − 2 = 6).
  • Each CN⁻ ligand donates 2 electrons, and there are 6 CN ligands, contributing a total of 12 electrons.
  • Total electron count = 6 (from Fe) + 12 (from CN ligands) = 18 electrons.
  • Conclusion: [Fe(CN)₆]⁴⁻ obeys the 18-electron rule.
• [Co(NH₃)₆]³⁺ (Hexaamminecobalt(III))
  • Cobalt in this complex is in the +3 oxidation state (Co³⁺), so it has 6 valence electrons (9 − 3 = 6).
  • Each NH₃ ligand donates 2 electrons, and there are 6 NH₃ ligands, contributing a total of 12 electrons.
  • Total electron count = 6 (from Co) + 12 (from NH₃) = 18 electrons.
  • Conclusion: [Co(NH₃)₆]³⁺ obeys the 18-electron rule.

CONCLUSION:

The complex that does not obey the 18-electron rule is Option 2: [Cr(NH₃)₆]³⁺.

CONCEPT:

Structure of Metal Carbonyl Complexes

• Metal carbonyl complexes are coordination compounds consisting of a metal center bonded to carbon monoxide (CO) ligands.
• The nature of the bonding in metal carbonyls can include metal-metal linkages, terminal CO groups, and bridging CO groups, depending on the structure of the complex.
• The oxidation state of the metal in these complexes is important for understanding their reactivity and stability.
• In certain metal carbonyls, the metal may exist in a zero oxidation state, as seen in the case of complexes like [Mn₂(CO)₁₀] and [Co₂(CO)₈].

EXPLANATION:

• The given structures [Mn₂(CO)₁₀] and [Co₂(CO)₈] are metal carbonyl complexes, where both Mn and Co are in zero oxidation states.
• In these complexes, the metal-metal linkage is present, which is a characteristic feature in such compounds, indicating the presence of metal-metal bonds between the metal centers.
• Terminal CO groups are present in the structure, as these CO ligands are directly bonded to the metal centers.
• In [Mn₂(CO)₁₀], there are no bridging CO groups; all CO ligands are terminally bound to the metal centers.
• The metal in both complexes is in the zero oxidation state, as shown by the nature of the bonding and charge balance of the entire molecule.

Hence, the correct answer is the option: Only A, B, D.

CONCEPT:

Isoelectric Species

• Isoelectric species are ions or molecules that have the same number of electrons.
• To determine if species are isoelectric, count the total number of electrons in each species and compare them.

CALCULATION:

• Atomic Numbers:
  • Sn (Tin): 50
  • Se (Selenium): 34
  • Bi (Bismuth): 83
  • Al (Aluminum): 13
• Calculate the number of electrons in each ion:
  • Option 1: Sn^4- and Se₉⁵⁺
    • Sn^4-: 4 + 4 = 8 electrons
    • Se₉⁵⁺: 6 x 9- 5 = 49 electrons (not isoelectronic)
  • Option 2: Se₉⁵⁺ and Bi₉⁵⁺
    • Se₉⁵⁺:  6 x 9- 5 = 49 electrons
    • Bi₉⁵⁺: 5 x 9 - 5 = 40 electrons (not isoelectronic)
  • Option 3: Se₉^4- and Al₉^4-
    • Se₉^4-: 6 x 9- 5 = 50 electrons
    • Al₉^4-: 3 x 9 + 4 = 31  electrons
  • Option 4: Se₉^4- and Bi₉⁵⁺
    • Se₉^4-:  6 x 9- 5 = 50 electrons
    • Bi₉^5-:  5 x 9 +5 = 50 electrons ( isoelectronic)

So, Option 4 Se94-, Bi95- are  isoelectronic

The Correct Answer is b > c > a.

Concept:-

Metallocene: Metallocenes are a class of organometallic compounds where a transition metal is sandwiched between two cyclopentadienyl (Cp) ligands. These compounds have a unique structure and exhibit interesting properties. The Molecular Orbital Theory (MOT) can be used to describe the electronic structure of metallocenes.

Explanation:-

\(e_{1g}^*\)(dxz, dyz) orbital of metallocene are analogous to e_g orbital of octahedral complexes. Thus, greater the number of electron in \(e_{1g}^*\)orbital longer will be the bond length. 

(a). [Fe(η⁵ -Cp)₂]: \(e_{2g}^4\ a_{1g}^2\)

(b).  [Ni(η⁵ -Cp)₂]: \(e_{2g}^4\ a_{1g}^2\ e_{1g}^{*2}\)

(c). [Co(η⁵ -Cp)₂]: \(e_{2g}^4\ a_{1g}^2\ e_{1g}^{*1}\)

• Order of number of electron in \(e_{1g}^{*}\) is b > c >  a.
• Order of Bond Order: a > c > b.
• Order of M-C bond length: b > c >  a.

Conclusion:-

Correct order of M-C bond length of metallocenes (a-c) is b > c > a.

The correct answer is cis-Platin

Concept:-

• Coordination Chemistry: cis-Platin is a coordination complex, and its activity is linked to its coordination to DNA.
• DNA Interaction: The interaction of cis-Platin with DNA is crucial for its anticancer activity.
• Cell Cycle Regulation: cis-Platin affects the cell cycle, leading to cell growth inhibition and apoptosis.

Explanation:-

• cis-Platin is a coordination complex with the chemical formula [PtCl₂​(NH_3​)₂​].
• The central platinum atom is coordinated to two chloride ions and two ammonia molecules in a square planar arrangement.
• 
• cis-Platin is known for its ability to bind to DNA.
• It forms covalent bonds with the purine bases (adenine and guanine) in DNA through a process known as cross-linking.
• cis-Platin induces intrastrand and interstrand cross-links in the DNA molecule.
• In intrastrand cross-linking, adjacent purine bases on the same DNA strand are linked together by covalent bonds.
• In interstrand cross-linking, purine bases on opposite DNA strands are linked.
• Inhibition of DNA Replication and Transcription: The formation of these cross-links interferes with the normal functioning of DNA, inhibiting processes such as replication and transcription.
• The distorted DNA structure hinders the separation of DNA strands and prevents enzymes involved in DNA replication and transcription from functioning properly.
• By interfering with DNA processes, cis-Platin inhibits the growth of rapidly dividing cells, including cancer cells.
• It induces cell cycle arrest and apoptosis in cancer cells.

Conclusion:-

cis-Platin is an important anticancer drug that functions by disrupting DNA structure and processes in rapidly dividing cells, ultimately inhibiting cell growth.