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Chapter 23: Problem 22

(a) What is the meaning of the term coordination number as it applies to metal complexes? (b) Give an example of a ligand that is neutral and one that is negatively charged. (c) Would you expect ligands that are positively charged to be common? Explain. (d) What type of chemical bonding is characteristic of coordination compounds? Illustrate with the compound \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6} \mathrm{Cl}_{3}\) (e) What are the most common coordination numbers for metal complexes?

Short Answer

Expert verified
Coordination number refers to the number of ligand atoms directly bonded to the central metal atom/ion in a coordination compound through coordinate covalent bonds. An example of a neutral ligand is ammonia (\(NH_{3}\)), and a negatively charged ligand is chloride ion (\(Cl^-\)). Positively charged ligands are less common due to unfavorable electrostatic attraction with positively charged metal ions. Coordination compounds' chemical bonding is characterized by coordinate covalent bonding. The most common coordination numbers are 4 (square planar or tetrahedral) and 6 (octahedral).

Step by step solution

01

(a) Meaning of Coordination Number

Coordination number is the number of ligand atoms directly bonded to the central metal atom/ion in a coordination compound. It indicates the number of electron pairs that the central metal atom/ion accepts from the ligands, leading to the formation of coordinate covalent bonds.
02

(b) Neutral and Negatively Charged Ligands

A neutral ligand is a ligand that does not carry any charge and forms a coordinate covalent bond with the central metal atom/ion. An example of a neutral ligand is ammonia (\(NH_{3}\)). A negatively charged ligand is a species that carries a negative charge and forms a coordinate covalent bond with the central metal atom/ion. An example of a negatively charged ligand is chloride ion (\(Cl^-\)).
03

(c) Positively Charged Ligands

Positively charged ligands are not as common as neutral or negatively charged ligands. This is because metal ions (central atom in coordination complexes) generally tend to be positively charged, and the electrostatic attraction between the central metal and the positively charged ligand would be unfavorable, making it difficult for them to form coordinate covalent bonds.
04

(d) Chemical Bonding in Coordination Compounds

The chemical bonding in coordination compounds is characterized by coordinate covalent bonding, which involves the donation of an electron pair from the ligand to the central metal atom/ion. In the given compound, \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6} \mathrm{Cl}_{3}\), the cobalt ion (\(Co^{3+}\)) acts as the central metal ion which forms coordinate covalent bonds with six ammonia ligands (\(NH_{3}\)).
05

(e) Common Coordination Numbers

The most common coordination numbers for metal complexes are 4, which represents a square planar or tetrahedral geometry, and 6, which represents an octahedral geometry. Other coordination numbers such as 2, 5, and 7 can also be observed, but they are relatively less common.

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Most popular questions from this chapter

For each of the following metals, write the electronic configu- ration of the atom and its \(2+\) ion: \((\) a) \(M n,\) (b) \(R u,\) (c) \(R h\). Draw the crystal-field energy-level diagram for the \(d\) orbitals of an octahedral complex, and show the placement of the \(d\) electrons for each \(2+\) ion, assuming a strong-field complex. How many unpaired electrons are there in each case?

A classmate says, "A strong-field ligand means that the ligand binds strongly to the metal ion." Is your classmate correct? Explain.

The \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) ion has an absorption maximum at about \(725 \mathrm{nm},\) whereas the \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}\) ion absorbs at about \(570 \mathrm{nm}\). Predict the color of a solution of each ion. (b) The \(\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}\) ion absorption maximum occurs at about \(545 \mathrm{nm}\), and that of the [Ni(bipy) \(\left._{3}\right]^{2+}\) ion occurs at about \(520 \mathrm{nm}\). From these data, indicate the relative strengths of the ligand fields created by the four ligands involved.

Although the cis configuration is known for \(\left[\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2}\right], \mathrm{no}\) trans form is known. (a) Explain why the trans compound is not possible. (b) Would \(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\) be more likely than en \(\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)\) to form the trans compound? Explain.

The red color of ruby is due to the presence of Cr(III) ions at octahedral sites in the close-packed oxide lattice of \(\mathrm{Al}_{2} \mathrm{O}_{3} .\) Draw the crystal-field splitting diagram for Cr(III) in this environment. Suppose that the ruby crystal is subjected to high pressure. What do you predict for the variation in the wavelength of absorption of the ruby as a function of pressure? Explain.
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