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Chapter 23: Problem 91

The coordination complex \(\left[\mathrm{Cr}(\mathrm{CO})_{6}\right]\) forms colorless, diamagnetic crystals that melt at \(90^{\circ} \mathrm{C}\). (a) What is the oxidation number of chromium in this compound? (b) Given that \(\left[\mathrm{Cr}(\mathrm{CO})_{6}\right]\) is diamagnetic, what is the electron configuration of chromium in this compound? (c) Given that \(\left[\mathrm{Cr}(\mathrm{CO})_{6}\right]\) is colorless, would you expect \(\mathrm{CO}\) to be a weak-field or strong-field ligand? (d) Write the name for \(\left[\mathrm{Cr}(\mathrm{CO})_{6}\right]\) using the nomenclature rules for coordination compounds.

Short Answer

Expert verified
(a) The oxidation number of chromium in the compound \([\mathrm{Cr}(\mathrm{CO})_{6}]\) is 0. (b) The electron configuration of chromium in this complex is \([Ar]3d^{10} 4s^0\). (c) CO is a strong-field ligand. (d) The name of the compound is hexacarbonylchromium(0).

Step by step solution

01

(a) Finding the oxidation number of chromium

First, we need to find the charge on the carbonyl ligand (CO). Carbonyl is a neutral ligand, which means its charge is 0. Since there are 6 carbonyls and the complex is neutral, the oxidation number of chromium will also be 0.
02

(b) Electron configuration of chromium

In its neutral state, chromium has the electron configuration \([Ar]3d^5 4s^1\). Since the oxidation state of chromium in the complex is 0, the electron configuration remains unchanged. Considering the diamagnetic nature, which means all electrons are paired up, we need to distribute the 5 electrons present in the 3d orbital within the different orbitals while allowing Cr to form bonds with the ligands. The electron configuration of chromium in its complex is \([Ar]3d^{10} 4s^0\) to allow for 6 bonds to be formed with 6 CO ligands.
03

(c) Identifying the ligand-field strength

The complex is colorless, which indicates that there are no unpaired electrons in the d orbitals and that the energy difference between the d orbitals is large. This suggests that CO is a strong-field ligand.
04

(d) Naming the complex

Using the nomenclature rules, we can name this complex as hexacarbonylchromium(0).

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Most popular questions from this chapter

The value of \(\Delta\) for the \(\left[\mathrm{MoI}_{6}\right]^{3-}\) complex is \(198.58 \mathrm{~kJ} / \mathrm{mol}\). Calculate the expected wavelength of the absorption corresponding to promotion of an electron from the lower energy to the higher-energy \(d\) -orbital set in this complex. Should the complex absorb in the visible range?

Indicate the likely coordination number of the metal in each of the following complexes: (a) $\left[\mathrm{Ru}(\text { bipy })_{3}\right]\left(\mathrm{NO}_{3}\right)_{2}$ (b) $\operatorname{Re}(\text { o-phen })_{2}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}$ (c) \(\mathrm{Pd}(\mathrm{PPh} 3)_{3} \mathrm{Cl}\) (d) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Mn}(\mathrm{EDTA})\)

The molecule dimethylphosphinoethane $\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{PCH}_{2} \mathrm{CH}_{2}\right.$ \(\mathrm{P}\left(\mathrm{CH}_{3}\right)_{2},\) 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 ethylenediamine 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 \()\right] ?(\mathbf{c})\) Sketch the structure of the $\left[\mathrm{Mo}(\mathrm{CN})_{2}(\mathrm{CO})_{2}(\text { dmpe })\right]^{2-}$ ion, including all the possible isomers.

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

(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?
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