Organometallic Chemistry EAN Rule

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

According to the 18-electron rule, what is the primary reason for the instability of organometallic complexes with more than 18 electrons?

  • The excess electrons promote the formation of free radicals, leading to decomposition.
  • The excess electrons lead to a violation of Hund's rule, making the complex unstable.
  • The excess electrons cause repulsion between the metal and ligands, leading to instability.
  • The excess electrons occupy antibonding orbitals, weakening the metal-ligand bonds. (correct)

A metal complex with less than 18 electrons in its valence shell is likely to be unstable because:

  • The complex will readily decompose upon slight heating. (correct)
  • The metal will have a higher electron affinity, making it less reactive.
  • The metal will be too reactive with other molecules.
  • The ligands will be more easily replaced.

The 18-electron rule applies primarily to:

  • All metal complexes, regardless of the metal's identity.
  • All transition metal complexes.
  • Only complexes with a main group metal as the central atom.
  • Only organometallic complexes with transition metals. (correct)

The 18-electron rule is useful for predicting:

<p>The stability of organometallic complexes. (D)</p> Signup and view all the answers

According to the 18-electron rule, what should be done to determine the total number of electrons in the valence shell of a metal in an organometallic complex?

<p>Count the number of electrons in the metal's valence shell in its zero oxidation state and add the electrons donated by the ligands. (A)</p> Signup and view all the answers

What does the term 'degenerate orbitals' refer to in the context of the 18-electron rule?

<p>Orbitals with the same energy level. (C)</p> Signup and view all the answers

Which of the following terms describes an orbital that is symmetric to the plane of reflection?

<p>1 (D)</p> Signup and view all the answers

What is the primary difference between the definitions of 'gerade' and 'ungerade' in relation to the 18-electron rule?

<p>Gerade orbitals are symmetric to the center of inversion, while ungerade orbitals are asymmetric to the center of inversion. (D)</p> Signup and view all the answers

Which of the following is a primary metal carbonyl?

<p>Fe(CO)5 (C)</p> Signup and view all the answers

Which of the following methods is NOT used to prepare metal carbonyls?

<p>Oxidation of a secondary metal carbonyl (B)</p> Signup and view all the answers

What is the role of Zn in the reaction 2CrCl3 + 12CO + 3Zn/Hg→ 2Cr(CO)6 + 3ZnCl2 + 3Hg?

<p>Reducing agent (B)</p> Signup and view all the answers

Which of the following metal carbonyl hydrides is correctly represented?

<p>H2Co(CO)4 (A)</p> Signup and view all the answers

Which of the following reactions is an example of the formation of a secondary metal carbonyl from a primary metal carbonyl?

<p>2Fe(CO)5 → Fe2(CO)9 + CO (B)</p> Signup and view all the answers

In the molecular orbital diagram of CO, what is the nature of the HOMO that interacts with the metal?

<p>σ-bonding (C)</p> Signup and view all the answers

Which of the following compounds is a metal carbonyl nitrosyl?

<p>Co(CO)3NO (D)</p> Signup and view all the answers

What is the main difference between a primary and a secondary metal carbonyl?

<p>The number of metal atoms present (C)</p> Signup and view all the answers

Which of the following reactions is an example of a redox reaction used to prepare alkyl-transition metal compounds?

<p>2Zn + 2CH3I → Zn(CH3)2 + ZnI2 (D)</p> Signup and view all the answers

Which of the following statements accurately describes the preparation of carbonyl-transition metal compounds using a metal salt?

<p>The metal is always reduced from a higher oxidation state to a lower one. (B)</p> Signup and view all the answers

What is the main characteristic that distinguishes a sigma-bond metathesis reaction from a simple double replacement reaction?

<p>Sigma-bond metathesis always involves the formation of a C-H bond in methane as a by-product. (D)</p> Signup and view all the answers

Which of the following is a key factor that allows the olefin metathesis reaction to be driven to completion in the direction of producing terminal olefins?

<p>High pressure of ethylene gas (A)</p> Signup and view all the answers

Based on the information provided, how do the reactivity of organometallic compounds depend on the nature of the organic ligands?

<p>Organometallic compounds react more readily with nucleophiles when the organic ligands are electron-donating. (C)</p> Signup and view all the answers

Which of the following statements is NOT true about the preparation of alkyl-transition metal compounds?

<p>The resulting alkyl-transition metal compounds always have a neutral charge. (B)</p> Signup and view all the answers

Which of the following statements correctly describes the role of CO in the preparation of carbonyl-transition metal compounds?

<p>CO acts as a ligand, coordinating to the metal center and stabilizing the compound. (C)</p> Signup and view all the answers

Which of the following examples is NOT a common type of reaction involving organometallic compounds?

<p>Hydroboration (D)</p> Signup and view all the answers

What is the effect of back donation on the ν(CO) band of a carbonyl complex?

<p>It causes the band to shift to lower energy. (A)</p> Signup and view all the answers

What is the difference between a terminal and a bridging carbonyl ligand?

<p>Terminal carbonyls are bonded to one metal atom, while bridging carbonyls are bonded to two or more. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of metal carbonyls?

<p>They are always stable in air. (A)</p> Signup and view all the answers

What is the effect of increasing the number of metal atoms coordinated to a bridging carbonyl ligand on the ν(CO) band?

<p>The ν(CO) band shifts to lower energy. (C)</p> Signup and view all the answers

How does the back donation from a metal to a CO ligand affect the strength of the C-O bond?

<p>Back donation weakens the C-O bond. (C)</p> Signup and view all the answers

Which of the following is an example of a non-classical carbonyl complex?

<p>A complex with a very high ν(CO) band. (B)</p> Signup and view all the answers

Which of the following is a common way to stabilize metal carbonyls that do not obey the EAN rule?

<p>Adding a reducing agent. (D)</p> Signup and view all the answers

Why are most metal carbonyls crystalline solids at room temperature?

<p>Due to strong intermolecular interactions. (B)</p> Signup and view all the answers

What is the primary reason electrons from the d-orbitals of the metal donate electrons to the CO orbitals in metal carbonyls?

<p>The presence of unoccupied antibonding π* orbitals in CO. (B)</p> Signup and view all the answers

Which of the following describes how σ donation affects the electron density in metal carbonyls?

<p>Increases electron density on the metal and decreases electron density on the CO ligand. (B)</p> Signup and view all the answers

What is the effect of π backbonding on the electron density in a metal carbonyl?

<p>Decreases electron density on the metal and increases electron density on the CO ligand. (C)</p> Signup and view all the answers

What technique is used to experimentally measure the C-O bond stretching vibration in metal carbonyls?

<p>Infrared (IR) spectroscopy (A)</p> Signup and view all the answers

How does the C-O stretching frequency change in a metal carbonyl compared to free CO?

<p>The C-O stretching frequency decreases in metal carbonyls. (B)</p> Signup and view all the answers

What is the significance of the HOMO in CO?

<p>The HOMO is responsible for donating electron density to the metal. (B)</p> Signup and view all the answers

What is the effect of π backbonding on the C-O bond in metal carbonyls?

<p>The C-O bond length increases. (A)</p> Signup and view all the answers

Which of the following factors influences the strength of the metal-carbonyl bond?

<p>All of the above. (D)</p> Signup and view all the answers

What is the effective atomic number (EAN) of the cobalt atom in [(C7H7)Co(CO)3] according to the 18-electron rule?

<p>18 (B)</p> Signup and view all the answers

Which of the following organometallic compounds is likely to be unstable according to the 18-electron rule?

<p>CH3TiCl3 (C)</p> Signup and view all the answers

What is the coordination number of the metal in the complex [Ni(η5-C5H5)(NO)] if its effective atomic number (EAN) is 18?

<p>3 (C)</p> Signup and view all the answers

What is the most likely reason for the stability of square planar 16-electron complexes?

<p>These complexes have a special stability associated with the coordination geometry. (A)</p> Signup and view all the answers

Which of the following statements about the 18-electron rule is NOT true?

<p>The rule is applicable to all organometallic complexes. (C)</p> Signup and view all the answers

Which of the following ligands is most likely to contribute two electrons to the metal center in an organometallic complex?

<p>Carbonyl (CO) (D)</p> Signup and view all the answers

What is the most likely reason for the deviation from the 18-electron rule in some organometallic complexes?

<p>The presence of bulky ligands. (D)</p> Signup and view all the answers

Which of the following is NOT a typical method for preparing organometallic complexes?

<p>Electrolysis. (A)</p> Signup and view all the answers

Flashcards

Organometallic compounds

Compounds with at least one metal-to-carbon bond, where carbon is part of an organic group.

Types of bonds in organometallics

These can be single (M-C), double (M=C), or triple (M≡C) bonds between metal and carbon.

Metathesis reaction

A double replacement reaction, where metal alkyls can react with halides, exchanging groups.

Carbene and carbyne compounds

Types of organometallics featuring divalent (carbene) or trivalent (carbyne) carbon centers.

Signup and view all the flashcards

Carbonyl complexes

Organometallic compounds where metals bond with carbon monoxide (CO).

Signup and view all the flashcards

Ligand substitution reaction

A reaction in which one ligand in a complex is replaced by another ligand.

Signup and view all the flashcards

Sigma-bond metathesis

A reaction forming a C—H bond in methane from cleaving a C—H bond in another compound.

Signup and view all the flashcards

Olefin Metathesis

A reaction rearranging carbon-carbon double bonds in alkenes, creating new olefins.

Signup and view all the flashcards

18-Electron Rule

A rule stating stable organometallic compounds have 18 electrons in their valence shell.

Signup and view all the flashcards

Sidgwick-Bailey's Rule

Another name for the 18-electron rule, named after its proposers.

Signup and view all the flashcards

Valence Shell

The outermost shell of electrons around an atom, crucial for bonding.

Signup and view all the flashcards

Transition Metals

Metals that often form stable organometallic complexes, usually with variable oxidation states.

Signup and view all the flashcards

Ligands

Atoms, ions, or molecules that donate electron pairs to a central metal in a complex.

Signup and view all the flashcards

Kinetic Stability

A measure of how likely a compound is to react or decompose under conditions.

Signup and view all the flashcards

Bonding Orbitals

Orbitals that can hold electrons and contribute to the bonding of a complex.

Signup and view all the flashcards

Decomposition in Organometallics

The breakdown of organometallic compounds when electron count deviates from the 18-electron rule.

Signup and view all the flashcards

Stability of Complexes

Complexes with exactly 18 electrons are stable; fewer or more are typically unstable.

Signup and view all the flashcards

Square Planar Complexes

Complexes with 16 electrons that exhibit special stability despite being below 18.

Signup and view all the flashcards

Valence Electrons

Electrons in the outer shell of an atom that can participate in bonding.

Signup and view all the flashcards

Steric Effects

Effects that arise from the size and spatial arrangement of ligands affecting complex stability.

Signup and view all the flashcards

Effective Atomic Number Rule

A rule used to predict the stability of metal complexes based on total electron count.

Signup and view all the flashcards

Metal Carbonyl

Compounds formed when CO coordinates with a metal, classified as primary or secondary.

Signup and view all the flashcards

Primary Metal Carbonyl

Metal carbonyls containing only one metal, e.g., Fe(CO)5 and Ni(CO)4.

Signup and view all the flashcards

Secondary Metal Carbonyl

Metal carbonyls containing two or more metals, e.g., Fe2(CO)8 or Os3(CO)12.

Signup and view all the flashcards

Metal Carbonyl Halides

Metal carbonyls with coordinated halogen; examples include Mn(CO)5I.

Signup and view all the flashcards

Metal Carbonyl Hydrides

Metal carbonyls that include hydrogen; examples are HMn(CO)5 and HCo(CO)4.

Signup and view all the flashcards

Direct Reaction Method

A method to prepare metal carbonyls by directly reacting metals with CO.

Signup and view all the flashcards

Bonding in Metal Carbonyl

Describes how CO binds with metal through sigma and pi bonds based on molecular orbital theory.

Signup and view all the flashcards

UV Photolysis

A process where primary metal carbonyls are irradiated to yield secondary metal carbonyls.

Signup and view all the flashcards

Back bonding

A phenomenon where electrons from metal d-orbitals are donated to empty π*-antibonding orbitals of CO.

Signup and view all the flashcards

σ-donor function

The ability of CO to donate electron density directly to a metal orbital through its HOMO.

Signup and view all the flashcards

Ï€-acceptor interaction

The process where a metal donates electron density to the empty π*-antibonding orbitals of CO.

Signup and view all the flashcards

C-O bond strength

Determined by both σ-donation and π-acceptance interactions, affecting stability and length.

Signup and view all the flashcards

Infrared (IR) spectroscopy

A technique showing changes in CO bond vibrations due to coordination with metal.

Signup and view all the flashcards

C-O stretch energy

The energy difference in C-O stretching in free CO vs coordinated CO, indicating bond strength.

Signup and view all the flashcards

X-ray crystallography

A method providing precise measurements of C-O distance in metal carbonyls.

Signup and view all the flashcards

C-O distance in CO

Uncoordinated CO has a C-O distance of 112.8 pm, which increases when the bond weakens.

Signup and view all the flashcards

Bridging Carbonyls

CO bonded to multiple metal atoms, acting as a bridge in a complex.

Signup and view all the flashcards

C-O Stretching Vibration

The energy associated with the vibration of the C-O bond in carbonyl complexes.

Signup and view all the flashcards

Terminal vs Bridging Ligands

Terminal ligands are bonded to one metal, while bridging ligands connect two or more metals.

Signup and view all the flashcards

Electron Density in Bridging CO

Increased when CO bridges multiple metal atoms, enhancing bonding.

Signup and view all the flashcards

Stability of Metal Carbonyls

Carbonyls are generally stable if obeying the EAN rule; instability arises with improper electron counts.

Signup and view all the flashcards

Odd Atomic Number Metals

Metals with an odd number of electrons often have difficulty obeying the EAN rule.

Signup and view all the flashcards

Crystalline Solids

Most metal carbonyls exist as crystalline solids at room temperature.

Signup and view all the flashcards

Toxicity of Metal Carbonyls

Many metal carbonyls are soluble in organic solvents and highly toxic if ingested.

Signup and view all the flashcards

Study Notes

Organometallic Chemistry

  • Effective Atomic Number (EAN) Rule (18-Electron Rule): Stable organometallic compounds typically have 18 electrons in their outermost shell. This rule, also known as Sidgwick-Bailey's rule, guides the chemistry of many organometallic complexes. Although exceptions exist, it often predicts stability.

  • Metal's Electron Count: Organometallic complex stability depends on the total number of valence electrons of the metal. The total electron count includes those contributed by the metal and the ligands. Positive charges subtract electrons, and negative charges add electrons.

  • Stability and Electron Count: If the valence shell has less than 18 electrons , the complex may be unstable and decompose on heating. Complexes with more than 18 electrons are also unstable due to electrons being moved to anti-bonding orbitals.

  • Transition Metals: Most metals in organometallic compounds are transition metals, as these are capable of having and accepting electrons. Therefore, the valence shell must be greater than 4.

  • Ligand Contribution: Each ligand donates specific electrons towards the metal to fulfill the 18-electron rule. The number of electrons contributed by a ligand depends on its nature and the type of bonding. Ligands such as H, Cl, Br, I, OH, OR, CN, CH3, CR3 have various electron donating schemes.

  • Application of EAN Rule: The 18-electron rule is a useful guide for predicting the stability and most probable structures of organometallic complexes. It helps predict the most probable structure of newly synthesized complexes.

  • Metal-Ligand Bonding: M-C (carbon to metal) bonds can be single, double, or triple. Transition metals can form Ï€ bonds with hydrocarbons.

Organometallic Compounds

  • Classification: Organometallic compounds are compounds that contain a metal-carbon bond where the carbon is a part of an organic group. These can be primary or secondary metal carbonyls, depending on the number of metals involved, e.g., Fe(CO)5, Fe2(CO)8.

  • Preparation Methods (examples): Organometallic compounds are prepared via several methods, one example being a redox reaction and double displacement.

  • Metallocenes: Certain organometallics, like ferrocene, cobaltocene, and nickelocene, have sandwich structures. (They are characterized by having cyclic ligands that are bonded to the metal).

  • Reactivity: Reactivity of organometallic compounds depends upon the nature of the ligands and the metal to which they are attached.

  • Reactions: Reactions can be ligand substitution or insertion.

Additional Concepts

  • Photolysis: Photolysis of primary metal carbonyls can lead to the formation of secondary metal carbonyls.

  • Sigma-Bond Metathesis Involves the formation of a C–H bond as a byproduct. It's part of the overall reactivity picture for organometallics.

  • Olefin Metathesis: A reaction where the carbon-carbon double bonds are cut and rearranged in a statistical fashion.

  • Bridging Carbonyls: Carbon monoxide (CO) can act as a bridge between two metal centers in a complex. The coordination of CO to multiple metal centers affects the carbon-oxygen bond strength and vibrational energies.

  • Metal carbonyl halides and hydrides: When halogen or hydrogen are coordinated to the metal, the compounds are called metal carbonyl halides or metal carbonyl hydrides.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

CHM 303 Organometallic Chemistry Past Paper 2022 PDF

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser