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Chapter 23: Problem 90

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.

Short Answer

Expert verified
For the given complexes: (a) The tetrahedral complex \(\left[\mathrm{Zn}(\mathrm{gly})_{2}\right]\) has only 1 possible isomer: ``` N | O--Zn--O | N ``` (b) The square planar complex \([\mathrm{Pt}(\mathrm{gly})_{2}]\) has 2 possible isomers: cis and trans. (c) The octahedral complex \(\left[\mathrm{Co}(\mathrm{gly})_{3}\right]\) has only 1 possible isomer: ``` N | O--Co--O | | N--O N | | O--Co--O | N ```

Step by step solution

01

(a) Tetrahedral Complex: \(\left[\mathrm{Zn}(\mathrm{gly})_{2}\right]\)

Since glycine is a bidentate ligand, it will occupy two coordination sites on the metal ion. There are four coordination sites in total for a tetrahedral complex. Therefore, we can only fit one glycine ligand within the complex, making it \(\left[\mathrm{Zn}(\mathrm{gly})\right]\). The \(\left[\mathrm{Zn}(\mathrm{gly})\right]\) complex has only one possible isomer because the ligands are symmetric, and all coordination sites will end up being occupied by a ligand. Therefore, there is just one isomer possible for \(\left[\mathrm{Zn}(\mathrm{gly})_{2}\right]\) as shown below: ``` N | O--Zn--O | N ```
02

(b) Square Planar Complex: \([\mathrm{Pt}(\mathrm{gly})_{2}]\)

For a square planar complex, we have four coordination sites on the metal ion. Since glycine acts as a bidentate ligand, taking up two sites, only two glycine ligands can be attached to the metal ion. There are two possible arrangements for the glycine ligands: 1. The first isomer's nitrogen and oxygen atoms are at adjacent positions (cis): ``` N | O--Pt--O | N--O ``` 2. The second isomer's nitrogen and oxygen atoms are opposite each other (trans): ``` N N | | O--Pt--O or O--Pt--O | | N N ``` Hence, there are two possible isomers for the square planar complex \([\mathrm{Pt}(\mathrm{gly})_{2}]\).
03

(c) Octahedral Complex: \(\left[\mathrm{Co}(\mathrm{gly})_{3}\right]\)

For an octahedral complex, there are six coordination sites on the metal ion. Since glycine acts as a bidentate ligand, only three glycine ligands will be attached to the metal ion. In this case, all three glycine ligands must be connected, and the only possible arrangement is: ``` N | O--Co--O | | N--O N | | O--Co--O | N ``` There is only one possible isomer for the octahedral complex \(\left[\mathrm{Co}(\mathrm{gly})_{3}\right]\).

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Most popular questions from this chapter

Identify each of the following coordination complexes as either diamagnetic or paramagnetic: (a) \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}\) (b) square planar \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\) (c) \(\left[\mathrm{Ru}(\mathrm{bipy})_{3}\right]^{2+}\) (d) \(\left[\mathrm{CoCl}_{4}\right]^{2-}\)

Sketch the structure of the complex in each of the following compounds and give the full compound name: (a) \(\operatorname{cis}-\left[\operatorname{Co}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{2}\) (b) \(\mathrm{Na}_{2}\left[\mathrm{Ru}\left(\mathrm{H}_{2} \mathrm{O}\right) \mathrm{Cl}_{5}\right]\) (c) \(\operatorname{trans} \mathrm{NH}_{4}\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]\) (d) \(\operatorname{cis}-\left[\operatorname{Ru}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\)

In 2001 , chemists at SUNY-Stony Brook succeeded in synthesizing the complex trans-\(\left[\mathrm{Fe}(\mathrm{CN})_{4}(\mathrm{CO})_{2}\right]^{2-}\), which could be a model of complexes that may have played a role in the origin of life. (a) Sketch the structure of the complex. (b) The complex is isolated as a sodium salt. Write the complete name of this salt. (c) What is the oxidation state of Fein this complex? How many d electrons are associated with the Fe in this complex? (d) Would you expect this complex to be high spin or low spin? Explain.

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).

Determine if each of the following metal complexes is chiral and therefore has an optical isomer: (a) square planar \(\left[\mathrm{Pd}(\mathrm{en})(\mathrm{CN})_{2}\right],(\mathbf{b})\) octahedral \(\left[\mathrm{Ni}(\mathrm{en})\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+},(\mathbf{c})\) octahe- dral \(\operatorname{cis}-\left[\mathrm{V}(\mathrm{en})_{2} \mathrm{ClBr}\right]\)
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