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Chapter 23: Problem 21

(a) Using Werner's definition of valence, which property is the same as oxidation number, primary valence or secondary valence? (b) What term do we normally use for the other type of valence? (c) Why can \(\mathrm{NH}_{3}\) serve as a ligand but BH \(_{3}\) cannot?

Short Answer

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(a) Primary valence is the same as the oxidation number according to Werner's definition of valence. (b) The term used for the other type of valence is secondary valence or coordination number. (c) \(\mathrm{NH}_{3}\) can serve as a ligand because it has a lone pair of electrons on the nitrogen atom, while \(\mathrm{BH}_{3}\) cannot serve as a ligand since it lacks a lone pair of electrons on the boron atom.

Step by step solution

01

(a) Primary or secondary valence as oxidation number

Primary valence corresponds to the oxidation number in Werner's definition of valence. This reflects the charge on the central metal ion when all its ligands are removed.
02

(b) Term for the other type of valence

The other type of valence, which is not the same as the oxidation number, is called secondary valence or coordination number. This refers to the number of ligand atoms directly bonded to the central metal ion in a coordination complex.
03

(c) Ligand capabilities of \(\mathrm{NH}_{3}\) and \(\mathrm{BH}_{3}\)

\(\mathrm{NH}_{3}\) can serve as a ligand because it has a lone pair of electrons on the nitrogen atom, which can donate to a central metal ion to form a coordinate covalent bond. However, \(\mathrm{BH}_{3}\) cannot serve as a ligand as it does not have a lone pair of electrons on the boron atom to form a coordinate covalent bond with a central metal ion.

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Most popular questions from this chapter

Many trace metal ions exist in the blood complexed with amino acids or small peptides. The anion of the amino acid glycine (gly), can act as a bidentate ligand, coordinating to the metal through nitrogen and oxygen atoms. How many isomers are possible for (a) \(\left[\mathrm{Zn}(\mathrm{gly})_{2}\right]\) (tetrahedral), \((\mathbf{b})[\mathrm{Pt}(\mathrm{g}] \mathrm{y})_{2} ]\) (square planar), \((\mathbf{c})\left[\operatorname{Cog}(\mathrm{gly})_{3}\right](\) octahedral)? Sketch all possible isomers. Use the symbol to represent the ligand.

Which transition metal atom is present in each of the following biologically important molecules: (a) hemoglobin, (b) chlorophyls, (c) siderophores, (d) hemocyanine.

One of the more famous species in coordination chemistry is the Creutz-Taube complex: It is named for the two scientists who discovered it and initially studied its properties. The central ligand is pyrazine, a planar six-membered ring with nitrogens at opposite sides. (a) How can you account for the fact that the complex, which has only neutral ligands, has an odd overall charge? (b) The metal is in a low-spin configuration in both cases. Assuming octahedral coordination, draw the \(d\)-orbital energy-level diagram for each metal. (c) In many experiments the two metal ions appear to be in exactly equivalent states. Can you think of a reason that this might appear to be so, recognizing that electrons move very rapidly compared to nuclei?

(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 \(E^{\circ}\) values for two low-spin iron complexes in acidic solution are as follows: \(\left[\mathrm{Fe}(o-\mathrm{phen})_{3}\right]^{3+}(a q)+\mathrm{e}^{-} \Longrightarrow\) \(\quad\quad\quad\quad\quad\quad\quad\) \(\left[\mathrm{Fe}(o-\mathrm{phen})_{3}\right]^{2+}(a q) \quad E^{\circ}=1.12 \mathrm{V}\) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}(a q)+\mathrm{e}^{-} \rightleftharpoons\) \(\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}(a q) \quad E^{\circ}=0.36 \mathrm{V}\) (a) Is it thermodynamically favorable to reduce both Fe(III) complexes to their Fe(II) analogs? Explain. (b) Which complex, \(\left[\mathrm{Fe}(o-\mathrm{phen})_{3}\right]^{3+}\) or \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-},\) is more difficult to reduce? (c) Suggest an explanation for your answer to (b).
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