Chapter 21

Both $\mathrm{Ni}{\left({\mathrm{NH}}_3\right)}_4^{2+}$ and $\mathrm{Ni}(\mathrm{SCN}{)}_4^{2-}$ have four ligands. The first is paramagnetic, and the second is diamagnetic. Are the complex ions tetrahedral or square planar? Explain.

Which is more likely to be paramagnetic, $\mathrm{Fe}(\mathrm{CN}{)}_6^{4-}$ or $\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6^{2+}$ ? Explain.

A metal ion in a high-spin octahedral complex has two more unpaired electrons than the same ion does in a low-spin octahedral complex. Name some possible metal ions for which this would be true.

What is the lanthanide contraction? How does the lanthanide contraction affect the properties of the 4$d$ and 5$d$ transition metals?

Four different octahedral chromium coordination compounds exist that all have the same oxidation state for chromium and have ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{Cl}}^{-}$ as the ligands and counterions. When 1 mole of each of the four compounds is dissolved in water, how many moles of silver chloride will precipitate upon addition of excess ${\mathrm{AgNO}}_3?$

Figure 21.17 shows that the cis isomer of $\mathrm{Co}(\mathrm{en}{)}_2{\mathrm{Cl}}_2^{+}$ is optically active while the trans isomer is not optically active. Is the same true for $\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Cl}}_2+?$ Explain.

A certain first-row transition metal ion forms many different colored solutions. When four coordination compounds of this metal, each having the same coordination number, are dissolved in water, the colors of the solutions are red, yellow, green, and blue. Further experiments reveal that two of the complex ions are paramagnetic with four unpaired electrons and the other two are diamagnetic. What can be deduced from this information about the four coordination compounds?

Oxalic acid is often used to remove rust stains. What properties of oxalic acid allow it to do this?

${\mathrm{CoCl}}_4^{2-}$ forms a tetrahedral complex ion and $\mathrm{Co}(\mathrm{CN}{)}_6^{3-}$ forms an octahedral complex ion. What is wrong about the following statements concerning each complex ion and the $d$ orbital splitting diagrams? a. ${\mathrm{CoCl}}_4^{2-}$ is an example of a strong-field case having two unpaired electrons. b. Because ${\mathrm{CN}}^{-}$ is a weak-field ligand, $\mathrm{Co}(\mathrm{CN}{)}_6^{3-}$ will be a low-spin case having four unpaired electrons.

The compound $\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{\mathrm{Cl}}_2$ is green, whereas $\mathrm{Ni}{\left({\mathrm{NH}}_3\right)}_6{\mathrm{Cl}}_2$ is violet. Predict the predominant color of light absorbed by each compound. Which compound absorbs light with the shorter wavelength? Predict in which compound $\mathrm{\Delta }$ is greater and whether ${\mathrm{H}}_2\mathrm{O}$ or ${\mathrm{NH}}_3$ is the stronger field ligand. Do your conclusions agree with the spectrochemical series?