Coordination Complexes and Organometallic Compounds
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Questions and Answers

What is a key difference between coordination complexes and organometallic compounds?

  • Organometallic compounds are generally soluble in water.
  • Coordination complexes have fixed d-electron counts.
  • Organometallic compounds often resemble organic compounds. (correct)
  • Coordination complexes are usually neutral.

    • Which counting method is recommended for quickly determining electron counts in coordination complexes?

  • Neutral-ligand method (correct)
  • Oxidation number method
  • Charge balancing method
  • Donor-pair method

    • What is the total number of valence electrons in the complex [IrBr2(CH3)(CO)(PPh3)2]?

  • 19
  • 17
  • 18 (correct)
  • 16

    • What oxidation state is assigned to the Iridium in [IrBr2(CH3)(CO)(PPh3)2]?

    <p>+3</p> Signup and view all the answers

    How many electrons does the η6-C6H6 ligand donate in the complex [Cr(η5-C5H5)(η6-C6H6)]?

    <p>6</p> Signup and view all the answers

    Which of the following complexes does not obey the 18-electron rule?

    <p>[Cr(η5-C5H5)(η6-C6H6)]</p> Signup and view all the answers

    In the donor-pair method, why are some ligands treated as charged?

    <p>To simplify electron counting.</p> Signup and view all the answers

    How does the solubility of organometallic compounds compare to coordination complexes?

    <p>Organometallic compounds are soluble in organic solvents.</p> Signup and view all the answers

    What happens to the CO bond strength as the metal-carbon bond strength increases?

    <p>The CO bond strength decreases.</p> Signup and view all the answers

    Which complex exhibits the weakest CO bond strength among the following?

    <p>[Ti(CO)6]2-</p> Signup and view all the answers

    Which of the following statements about back-bonding is correct?

    <p>Back-bonding involves a filled d orbital of the metal donating electrons.</p> Signup and view all the answers

    Which of the following complexes follows the 18-electron rule?

    <p>Mn(CO)6</p> Signup and view all the answers

    In the given complexes, which has the highest CO IR stretching frequency?

    <p>[Mn(CO)6]+</p> Signup and view all the answers

    What contribution does the Group 6 Cr atom make to the electron count in a Cr(I) complex?

    <p>5 electrons</p> Signup and view all the answers

    Which of the following factors contributes to the stability of the organometallic complex known as Zeise's salt?

    <p>Strong-field ligands</p> Signup and view all the answers

    What is the oxidation number of the Pt center in Zeise’s salt?

    <p>+2</p> Signup and view all the answers

    How many electrons does each CO ligand contribute in a complex?

    <p>2 electrons</p> Signup and view all the answers

    Which geometry is adopted by the stable complexes formed with a d8 metal ion?

    <p>Square planar</p> Signup and view all the answers

    What total valence electron count results in a stable Mn(-1) complex?

    <p>18 electrons</p> Signup and view all the answers

    What is the oxidation number of the metal atom in a complex that has a total charge of -1 and all neutral ligands?

    <p>-1</p> Signup and view all the answers

    What is the total electron count in a complex formed by a d8 metal ion with four neutral ligands and three negative ligands?

    <p>16 electrons</p> Signup and view all the answers

    What is the oxidation number of the Ir center before the oxidative addition reaction occurs?

    <p>+1</p> Signup and view all the answers

    What is the valence electron count required for the metal center to readily undergo oxidative addition?

    <p>16</p> Signup and view all the answers

    During the bonding of dihydrogen to a metal atom, which component involves σ donation?

    <p>σ donation from H-H bond electrons</p> Signup and view all the answers

    After the oxidative addition reaction, what does the oxidation number of the Ir center become?

    <p>+3</p> Signup and view all the answers

    What happens to the strength of the H-H bond as π backbonding from the metal increases?

    <p>It decreases.</p> Signup and view all the answers

    What is the oxidation state of the dihydrogen ligand after it has been added to the metal center?

    <p>-1</p> Signup and view all the answers

    Which statement accurately describes the role of the lone pair on the carbon atom in the context of metal carbonyls?

    <p>Acts as a σ donor</p> Signup and view all the answers

    How does the molecular geometry of the complex relate to its valence electron count?

    <p>Higher electron count often leads to more complex geometries.</p> Signup and view all the answers

    Study Notes

    Coordination Complexes vs. Organometallic Compounds

    • Coordination complexes are typically charged, have variable d-electron counts, and dissolve in water.
    • Organometallic compounds are often neutral, have fixed d-electron counts (18 or 16), and dissolve in organic solvents.
    • Organometallic compounds share properties with organic compounds, such as low melting points and some being liquid at room temperature.

    18-Electron Rule

    • The 18-electron rule is a guideline for predicting the stability of organometallic complexes.
    • It states that a stable complex should have 18 valence electrons around the metal atom.

    Calculating Valence Electrons

    • There are two methods for calculating valence electrons:
      • Neutral-ligand method: ligands are treated as neutral
      • Donor-pair method: ligands donate electrons in pairs
    • Neutral-ligand method is quicker for simple examples.
    • Donor-pair method reveals oxidation number of the metal.

    Zeise's Salt

    • Zeise's salt, [Pt(C2H4)Cl3]-, is a stable ethene complex.
    • Its stability is attributed to strong-field ligands and a d8 metal ion.
    • The Pt atom has an oxidation number of +2, contributing 8 valence electrons.
    • The ligands (3 Cl- and ethene) donate 8 electrons via the donor-pair method.
    • This results in a total of 16 valence electrons, making the complex stable.

    Dihydrogen as a Ligand

    • Dihydrogen can act as a neutral 2-electron donor ligand.
    • Bonding involves:
      • σ donation from the H-H bond to the metal
      • π backdonation from the metal to the σ* antibonding orbital of H2
    • As π backdonation increases, the H-H bond weakens and the structure trends towards a dihydride.

    Oxidative Addition

    • Oxidative addition is a reaction where the metal center is formally oxidized.
    • The metal's oxidation number increases.
    • The reaction requires a metal center with 16 valence electrons.
    • The reaction results in 18 valence electrons for the metal.

    Metal Carbonyls

    • Metal carbonyls feature a unique bonding interaction between the metal and CO.
    • The CO lone pair donates electrons to an empty metal d orbital (σ donation).
    • The metal d orbitals backdonate electrons to the empty antibonding CO orbitals (π backdonation).
    • Stronger metal-carbon bonds weaken the CO bond.

    CO IR Stretching Frequencies

    • IR stretching frequencies of CO ligands reflect the strength of the CO bond.
    • Higher frequencies indicate stronger CO bonds.
    • The degree of π backdonation impacts CO bond strength.
    • More π backdonation weakens the CO bond, resulting in lower frequencies.

    18-Electron Rule for 3d Metal Carbonyls

    • The 18-electron rule is obeyed by many 3d metal carbonyls:
      • Cr(CO)6
      • Mn2(CO)10
      • Fe(CO)5
      • Co2(CO)8
      • Ni(CO)4
    • These complexes exhibit a stability in accordance with the 18-electron rule.

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    Description

    Explore the key differences between coordination complexes and organometallic compounds, focusing on their characteristics, stability guidelines like the 18-electron rule, and methods for calculating valence electrons. Also, learn about specific compounds such as Zeise's salt and how their properties relate to broader concepts in chemistry.

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