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Chapter 23: Problem 88

When Alfred Werner was developing the field of coordination chemistry, it was argued by some that the optical activity he observed in the chiral complexes he had prepared was due to the presence of carbon atoms in the molecule. To disprove this argument, Werner synthesized a chiral complex of cobalt that had no carbon atoms in it, and he was able to resolve it into its enantiomers. Design a cobalt(III) complex that would be chiral if it could be synthesized and that contains no carbon atoms. (It may not be possible to synthesize the complex you design, but we will not worry about that for now.)

Short Answer

Expert verified
A chiral cobalt(III) complex with no carbon atoms can be designed using ammonia (NH3) as a monodentate ligand and nitrite (NO2-) as a bidentate ligand. The complex would have an octahedral geometry and can be represented as: \[ \text{Co}(\text{NH}_3)_3(\text{NO}_2-\text{ONO})^{2+} \]

Step by step solution

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1. Understanding Chirality

A chiral molecule has a non-superimposable mirror image, which means it cannot be superimposed onto its mirror image. In coordination complexes, chirality often arises when the central metal is bonded to ligands in a non-planar arrangement, such as in an octahedral or tetrahedral geometry.
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2. Determine the oxidation state of Cobalt

Since the given metal is cobalt(III), it has an oxidation state of +3.
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3. Choose a coordination number and geometry

For a chiral complex, we should choose a non-planar geometry. An octahedral geometry is a common choice for cobalt(III) complexes as it allows for a coordination number of 6.
04

4. Selecting ligands that do not contain carbon atoms

We need to choose ligands that do not have carbon atoms and can form a chiral complex. One option is to use ammonia (NH3) as a monodentate ligand and nitrite (NO2-) as a bidentate ligand, which can bind to cobalt in two different ways: either as a nitro group (NO2) with nitrogen binding to the central metal or as a nitrito group (ONO) with oxygen binding to the central metal.
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5. Design the chiral cobalt(III) complex

To create a chiral complex, we can use three ammonia ligands and one nitrite ligand, binding cobalt in a bidentate fashion. The resulting complex would have an octahedral geometry and be chiral: \[ \text{Co}(\text{NH}_3)_3(\text{NO}_2-\text{ONO})^{2+} \] This chiral cobalt(III) complex would have the required non-carbon-containing ligands and, while it may not be possible to synthesize it, it would fulfill the requirements of the exercise.

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Most popular questions from this chapter

(a) A complex absorbs photons with an energy of 4.51 \(\times 10^{-19} \mathrm{J}\) . What is the wavelength of these photons? (b) If this is the only place in the visible spectrum where the complex absorbs light, what color would you expect the complex to be?

Indicate the coordination number and the oxidation number of the metal for each of the following complexes: (a) \(\mathrm{Na}_{2}\left[\mathrm{CdCl}_{4}\right]\) (b) \(\mathrm{K}_{2}\left[\mathrm{MoOCl}_{4}\right]\) (c) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Cl}\) (d) \(\left[\mathrm{Ni}(\mathrm{CN})_{5}\right]^{3-}\) (e) \(\mathrm{K}_{3}\left[\mathrm{V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) (f) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right] \mathrm{Br}_{2}\)

(a) In early studies it was observed that when the complex \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{Br}\) was placed in water, the electrical conductivity of a 0.05\(M\) solution changed from an initial value of 191 \(\mathrm{ohm}^{-1}\) to a final value of 374 \(\mathrm{ohm}^{-1}\) over a period of an hour or so. Suggest an explanation for the observed results.(See Exercise 23.69 for relevant comparison data.) (b) Write a balanced chemical equation to describe the reaction. (c) \(A 500\)-mL solution is made up by dissolving 3.87g of the complex. As soon as the solution is formed, and before any change in conductivity has occurred, a 25.00-mL portion of the solution is titrated with 0.0100 \(\mathrm{M} \mathrm{AgNO}_{3}\) solution. What volume of AgNO \(_{3}\) solution do you expect to be required to precipitate the free \(\operatorname{Br}^{-}(a q) ?(\mathbf{d})\) Based on the response you gave to part (b), what volume of \(\mathrm{AgNO}_{3}\) solution would be required to titrate a fresh 25.00 -mL sample of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{Br}\) after all conductivity changes have occurred?

The lanthanide contraction explains which of the following periodic trends? (a) The atomic radii of the transitionmetals first decrease and then increase when moving horizontally across each period. (b) When forming ions the period 4 transition metals lose their 4\(s\) electrons before their 3\(d\) electrons. (c) The radii of the period 5 transition metals \((\mathrm{Y}-\mathrm{Cd})\) are very similar to the radii of the period 6 transition metals \((\mathrm{Lu}-\mathrm{Hg}).\)

Write the names of the following compounds, using the standard nomenclature rules for coordination complexes: (a) \(\left[\mathrm{Rh}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Cl}\) (b) \(\mathrm{K}_{2}\left[\mathrm{TiCl}_{6}\right]\) (c) \(\mathrm{MoOCI}_{4}\) (d) \(\left[\operatorname{Pt}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\right] \mathrm{Br}_{2}\)
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