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Questions and Answers
Which factor primarily influences the rate of hydrolysis in organometallic compounds?
Which factor primarily influences the rate of hydrolysis in organometallic compounds?
How many valence electrons are required for the stability of low-valent transition metal complexes as per the 18-electron rule?
How many valence electrons are required for the stability of low-valent transition metal complexes as per the 18-electron rule?
What characteristic do second-row elements like carbon and nitrogen possess in relation to bonding?
What characteristic do second-row elements like carbon and nitrogen possess in relation to bonding?
What is a key reason that not all organometallic formulas correspond to stable species?
What is a key reason that not all organometallic formulas correspond to stable species?
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Which of the following statements about ligands in organometallic complexes is true?
Which of the following statements about ligands in organometallic complexes is true?
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What defines an organometallic compound?
What defines an organometallic compound?
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What is the significance of stability constants in the estimation of hardness of water?
What is the significance of stability constants in the estimation of hardness of water?
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Which of the following represents the first σ-bonded organometallic compound?
Which of the following represents the first σ-bonded organometallic compound?
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What does hapticity refer to in organometallic chemistry?
What does hapticity refer to in organometallic chemistry?
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Which of the following ligands is classified as an η5-ligand?
Which of the following ligands is classified as an η5-ligand?
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How does electronegativity influence the bonding in organometallic compounds?
How does electronegativity influence the bonding in organometallic compounds?
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Which element(s) can form organometallic compounds according to the established definition?
Which element(s) can form organometallic compounds according to the established definition?
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In hard water titration, which compound is typically used to estimate hardness?
In hard water titration, which compound is typically used to estimate hardness?
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What does an odd ηx value typically indicate about a carbon ligand?
What does an odd ηx value typically indicate about a carbon ligand?
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How many electrons are typically donated by a neutral carbon π-system ligand with an even ηx value?
How many electrons are typically donated by a neutral carbon π-system ligand with an even ηx value?
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Which of the following is an example of a sigma (σ) bonded organometallic compound?
Which of the following is an example of a sigma (σ) bonded organometallic compound?
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Which statement best describes pi (π) bonded organometallic compounds?
Which statement best describes pi (π) bonded organometallic compounds?
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Which condition typically refers to the stability of organometallic compounds?
Which condition typically refers to the stability of organometallic compounds?
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What type of bonding characterizes metal-carbonyl compounds?
What type of bonding characterizes metal-carbonyl compounds?
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According to the 18-electron rule, which of the following would typically be a stable configuration for organometallic compounds?
According to the 18-electron rule, which of the following would typically be a stable configuration for organometallic compounds?
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What factor does NOT influence the stability of organometallic compounds?
What factor does NOT influence the stability of organometallic compounds?
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Study Notes
Ligand Coordination and Electron Donation
- Anionic carbon ligands typically have odd ηx values, such as η5-Cp, η1-CH3, η1-allyl, and η3-allyl.
- The number of electrons donated by these ligands is calculated using the formula x + 1.
- Neutral carbon π-system ligands usually have even ηx values, like η6-C6H6, η2-CH2=CH2, η4-butadiene, and η4-cyclooctadiene.
- The number of electrons donated by neutral ligands corresponds directly to x.
Classification of Organometallic Compounds
- Organometallic compounds can be classified into three categories:
- Sigma (σ) bonded: Involves a sigma bond between the metal and carbon; examples include Grignard reagents (R–Mg–X) and R2Zn compounds.
- Pi (π) bonded: Involves metals bonding with unsaturated hydrocarbon ligands (alkenes, alkynes, benzene).
- Sigma and π-bonded: Combines both bonding types; common in metal-carbonyl complexes with carbon monoxide.
Stability of Organometallic Compounds
- Stability can refer to thermal stability or resistance to chemical attack, influenced by thermodynamic and kinetic factors.
- Organometallic compounds are susceptible to hydrolysis via water, facilitated by:
- The presence of empty low-lying orbitals on the metal.
- The polarity of metal-carbon bonds, wherein greater polarity results in higher hydrolysis rates.
The 18-Electron Rule
- The 18-electron rule is a guideline for assessing the stability of d-block transition metal organometallic complexes.
- It extends the octet rule (8 valence electrons) to include d orbitals, requiring a total of 18 electrons for stability.
- Stable compounds like CH4 adhere to the octet rule, while unstable structures (e.g., CH5) exceed this limit.
Water Hardness and Chelation
- Calcium and magnesium ions in hard water form stable complexes with EDTA (Calcium EDTA and Magnesium EDTA).
- Hardness of water can be measured through titration with Na2EDTA.
- Selective estimation of calcium and magnesium can be achieved due to differences in stability constants of their respective complexes.
Definition and Scope of Organometallic Chemistry
- Organometallics bridge organic and inorganic chemistry, encompassing compounds with one or more metal-carbon bonds.
- Carbon is more electronegative than the metal (M), affecting bond character.
- Definitions include bonding interactions between carbon from organic groups and various metals, extending to derivative compounds of metalloids like boron and silicon.
Historical Context
- Zeise’s Salt, discovered in 1827, marked the first transition metal organometallic compound, with its structure elucidated about 150 years later.
- Diethyl Zinc represents the first σ-bonded organometallic compound, represented by the reaction: 3 C2H5I + 3 Zn → (C2H5)2Zn + C2H5ZnI + ZnI2.
Ligand Nomenclature
- The term "eta-x" denotes the number of carbon atoms in a π-system coordinating to a metal center.
- Hapticity describes the bonding mode of a ligand, exemplified by an η5-cyclopentadienyl ligand that bonds with all five carbons to the metal.
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