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Chapter 23: Problem 87

In 2001 , chemists at SUNY-Stony Brook succeeded in synthesizing the complex trans-[Fe(CN) \(\left._{4 (\mathrm{CO})_{2}\right]^{2-},\) 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 com- (c) What is the oxidation state of Fe plete name of this salt. in 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.

Short Answer

Expert verified
The complex trans-[Fe(CN)\(_4\)(CO)\(_2\)]\(^{2-}\) has an octahedral geometry, with Iron (Fe) as the central atom and Cyanide (CN\(^{-}\)) and Carbon Monoxide (CO) as ligands. The complete name of the sodium salt is Sodium trans-tetracyanodihydroxoiron(II). The oxidation state of Fe is +2, and there are 6 d electrons associated with it in this complex. The strong-field ligands and octahedral geometry result in a low-spin complex.

Step by step solution

01

(a) Sketching the structure of the complex.

First, we have to identify the ligands, central atom, and the overall charge in the complex compound trans-[Fe(CN)\(_4\)(CO)\(_2\)]\(^{2-}\). 1. Central atom: Iron (Fe) 2. Ligands: Cyanide (CN\(^{-}\)) and Carbon Monoxide (CO) 3. Charge: 2- The complex has the prefix "trans," which indicates that the ligands are located across from each other in an octahedral geometry. Draw an octahedron with Fe in the center. There are four CN ligands and two CO ligands. Place the CN ligands on four of the vertices of the octahedron, with the C of the CN ligand bonded to Fe. Place the CO ligands on the two opposite vacant vertices of the octahedron, with their carbon atoms bonded to Fe.
02

(b) Writing the complete name of the sodium salt.

Since the complex ion has an overall charge of 2-, we need two sodium ions (each with a 1+ charge) to balance the charge of the compound. The complete name of this salt is Sodium trans-tetracyanodihydroxoiron(II).
03

(c) Oxidation state of Fe and the number of d electrons.

To determine the oxidation state of Fe, we must consider the charges of the ligands and the overall charge of the complex: Fe + 4(-1) + x = -2, where x is the charge from CO ligands, which is neutral (0). Therefore, Fe = +2. As Fe has an oxidation state of +2, the electron configuration for Fe\(^{2+}\) is [Ar] 3d\(^6\), meaning that there are 6 d electrons associated with Fe in this complex.
04

(d) Predicting high-spin or low-spin complex.

To predict the high-spin or low-spin nature of the complex, first, we need to know the nature of ligands and the coordination complex's geometry. The complex has an octahedral geometry, and both CN\(^{-}\) and CO are strong-field ligands and lead to a strong crystal field splitting. In an octahedral geometry, when the ligands are strong-field, they force the electrons to pair up in the lower energy d orbitals, resulting in a low-spin complex. Therefore, this complex is expected to be low-spin due to the strong-field ligands.

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Most popular questions from this chapter

Give the number of (valence) \(d\) electrons associated with the central metal ion in each of the following complexes: (a) $\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right] \mathrm{Cl}_{2}$, (b) $\mathrm{K}_{2}\left[\mathrm{Cu}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}\right]$, (c) \(\left[\mathrm{Os}(\mathrm{en})_{3}\right] \mathrm{Cl}_{3}\), (d) \([\mathrm{Cr}(\mathrm{EDTA})] \mathrm{SO}_{4}\), , (e) $\left[\mathrm{Cd}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Cl}_{2}$

Consider an octahedral complex, \(\mathrm{MA}_{2} \mathrm{~B}_{4}\). How many geometric isomers are expected for this compound? Will any of the isomers be optically active? If so, which ones?

The square-planar complex $\left[\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2}\right]$ only forms in one of two possible geometric isomers. Which isomer is not observed: cis or trans?

Explain why the transition metals in periods 5 and 6 have nearly identical radii in each group.

If the lobes of a given \(d\) -orbital point directly at the ligands, will an electron in that orbital have a higher or lower energy than an electron in a \(d\) -orbital whose lobes do not point directly at the ligands?
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