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Chapter 23: Problem 29

Polydentate ligands can vary in the number of coordination positions they occupy. In each of the following, identify the polydentate ligand present and indicate the probable number of coordination positions it occupies: (a) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4}(o\) -phen \()\right] \mathrm{Cl}_{3}\) (b) \(\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \mathrm{Br}\) (c) \(\left[\mathrm{Cr}(\mathrm{EDTA})\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{-}\) (d) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right]\left(\mathrm{ClO}_{4}\right)_{2}\)

Short Answer

Expert verified
In the given complexes: (a) The polydentate ligand is o-phenanthroline (o-phen), which is a bidentate ligand occupying two coordination positions. (b) The polydentate ligand is oxalate ion (\(\mathrm{C}_{2}\mathrm{O}_{4}\)), which is a bidentate ligand occupying two coordination positions. (c) The polydentate ligand is ethylenediaminetetraacetic acid (EDTA), which is a hexadentate ligand occupying six coordination positions. (d) The polydentate ligand is ethylenediamine (en), which is a bidentate ligand occupying two coordination positions on the metal ion.

Step by step solution

01

(a) Identify the polydentate ligand and its probable coordination positions

In the complex \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4}(o\) -phen \()\right] \mathrm{Cl}_{3}\), the polydentate ligand is "o-phen" which stands for o-phenanthroline. o-phenanthroline can act as a bidentate ligand, meaning it occupies two coordination positions on the metal ion. The nitrogen atoms in the heterocyclic aromatic ring system are the donor atoms that bind to the metal ion.
02

(b) Identify the polydentate ligand and its probable coordination positions

In the complex \(\left[\mathrm{Cr}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)\left(\mathrm{H}_{2}\mathrm{O}\right)_{4}\right] \mathrm{Br}\), the polydentate ligand is \(\mathrm{C}_{2}\mathrm{O}_{4}\) which is the oxalate ion. Oxalate ion can act as a bidentate ligand, as it has two oxygen atoms with lone pairs that can coordinate to the metal ion. The oxalate ion occupies two coordination positions on the metal ion.
03

(c) Identify the polydentate ligand and its probable coordination positions

In the complex \(\left[\mathrm{Cr}(\mathrm{EDTA})\left(\mathrm{H}_{2}\mathrm{O}\right)\right]^{-}\), the polydentate ligand is "EDTA" which stands for ethylenediaminetetraacetic acid. EDTA is a hexadentate ligand, meaning it occupies six coordination positions on the metal ion. The donor atoms in EDTA are the two nitrogen atoms and four oxygen atoms (attached to the carboxylate groups).
04

(d) Identify the polydentate ligand and its probable coordination positions

In the complex \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right]\left(\mathrm{ClO}_{4}\right)_{2}\), the polydentate ligand is "en" which stands for ethylenediamine. Ethylenediamine is a bidentate ligand, as it has two nitrogen atoms with lone pairs that can coordinate to the metal ion. The ethylenediamine ligand occupies two coordination positions on the metal ion. There are two en ligands in this complex, each taking two coordination positions, for a total of four.

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Most popular questions from this chapter

(a) What is the difference between a monodentate ligand and a bidentate ligand? (b) How many bidentate ligands are necessary to fill the coordination sphere of a six-coordinate complex? (c) You are told that a certain molecule can serve as a tridentate ligand. Based on this statement, what do you know about the molecule?

Explain the difference between a diamagnetic substance and a paramagnetic substance.

The molecule dimethylphosphinoethane \(\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{PCH}_{2}^{-}\right.\) \(\mathrm{CH}_{2} \mathrm{P}\left(\mathrm{CH}_{3}\right)_{2},\) which is abbreviated dmpe \(]\) is used as a ligand for some complexes that serve as catalysts. A complex that contains this ligand is \(\mathrm{Mo}(\mathrm{CO})_{4}(\) dmpe \() .\) (a) Draw the Lewis structure for dmpe, and compare it with ethylenediammine as a coordinating ligand. (b) What is the oxidation state of Mo in \(\mathrm{Na}_{2}\left[\mathrm{Mo}(\mathrm{CN})_{2}(\mathrm{CO})_{2}(\) dmpe \()\right] ?(\mathrm{c})\) Sketch the structure of the \(\left[\mathrm{Mo}(\mathrm{CN})_{2}(\mathrm{CO})_{2}(\mathrm{dmpe})\right]^{2-}\) ion, including all the pos- sible isomers.

A Cu electrode is immersed in a solution that is \(1.00 \mathrm{M}\) in \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\) and \(1.00 \mathrm{M}\) in \(\mathrm{NH}_{3}\). When the cathode is a standard hydrogen electrode, the emf of the cell is found to be \(+0.08 \mathrm{~V}\). What is the formation constant for \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+} ?\)

Generally speaking, for a given metal and ligand, the stability of a coordination compound is greater for the metal in the +3 rather than in the +2 oxidation state (for metals that form stable +3 ions in the first place). Suggest an explanation, keeping in mind the Lewis acid-base nature of the metal-ligand bond.
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