Chapter 22

A platinum-containing compound, known as Magnus's green salt, has the formula \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{PtCl}_{4}\right]\) (in which both platinum ions are \(\mathrm{Pt}^{2+}\) ). Name the cation and the anion.

Early in the 20th century, coordination compounds sometimes were given names based on their colors. Two compounds with the formula \(\operatorname{CoCl}_{3} \cdot 4 \mathrm{NH}_{3}\) were named praseo-cobalt chloride (praseo = green ) and violio-cobalt chloride (violet color). We now know that these compounds are octahedral cobalt complexes and that they are cis and trans isomers. Draw the structures of these two compounds, and name them using systematic nomenclature.

Give the formula and name of a square-planar complex of \(\mathrm{Pt}^{2+}\) with one nitrite ion $$\left(\mathrm{NO}_{2}^{-}\right.$$, which binds to \(\mathrm{Pt}^{2+}\) through \(\mathrm{N}\) ), one chloride ion, and two ammonia molecules as ligands. Are isomers possible? If so, draw the structure of each isomer, and tell what type of isomerism is observed.

Give the formula of the coordination complex formed from one \(\mathrm{Co}^{3+}\) ion, two ethylenediamine molecules, one water molecule, and one chloride ion. Is the complex neutral or charged? If charged, give the net charge on the ion.

How many geometric isomers of the complex ion \(\left[\mathrm{Cr}(\text { dmen })_{3}\right]^{3+}\) can exist? (dmen is the bidentate ligand \(1,1-\) dimethylethy-lenediamine. $$\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}$$

From experiment, we know that \(\left[\mathrm{CoF}_{6}\right]^{3-}\) is paramagnetic and \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\) is diamagnetic. Using the ligand field model, depict the electron configuration for each ion, and use this model to explain the magnetic property. What can you conclude about the effect of these ligands on the magnitude of \(\Delta_{0} ?\)

Three geometric isomers are possible for \(\left[\mathrm{Co (\mathrm{en})\left(\mathrm{NH}_{3}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{3+} .\) One of the three is chiral; that is, it has a non-superimposable mirror image. Draw the structures of the three isomers. Which one is chiral?

The complex \(\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) has five unpaired electrons, whereas \(\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]^{4-}\) has only one. Using the ligand field model, depict the electron configuration for each ion. What can you conclude about the effects of the different ligands on the magnitude of \(\Delta_{0} ?\)

Experiments show that \(\mathrm{K}_{4}\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]\) is paramagnetic and has two unpaired electrons. The related complex \(\mathrm{K}_{4}\left[\mathrm{Cr}(\mathrm{SCN})_{6}\right]\) is paramagnetic and has four unpaired electrons. Account for the magnetism of each compound using the ligand field model. Predict where the SCN - ion occurs in the spectrochemical series relative to CN \(^{-}\).

Give a systematic name or the formula for the following: (a) \(\left(\mathrm{NH}_{4}\right)_{2}\left[\mathrm{CuCl}_{4}\right]\) (b) tetraaquadichlorochromium(III) chloride (c) aquabis(ethylenediamine) thiocyanatocobalt(III) nitrate

The complex ion \(\left[\mathrm{Co}\left(\mathrm{CO}_{3}\right)_{3}\right]^{3-},\) an octahedral complex with bidentate carbonate ions as ligands, has one absorption in the visible region of the spectrum at \(640 \mathrm{nm}\). From this information, (a) Predict the color of this complex and explain your reasoning. (b) Is the carbonate ion a weak- or strong-field ligand? (c) Predict whether \(\left[\mathrm{Co}\left(\mathrm{CO}_{3}\right)_{3}\right]^{3-}\) will be paramagnetic or diamagnetic.

A manganese compound has the formula \(\mathrm{Mn}(\mathrm{CO})_{x}\left(\mathrm{CH}_{3}\right)_{y}\) To find the empirical formula of the compound, you burn 0.225 g of the solid in oxygen and isolate \(0.283 \mathrm{g}\) of \(\mathrm{CO}_{2}\) and \(0.0290 \mathrm{g}\) of \(\mathrm{H}_{2} \mathrm{O} .\) What is the empirical formula for the compound? That is, what are the values of \(x\) and \(y ?\)

Nickel and palladium both form complexes of the general formula \(\mathrm{M}\left(\mathrm{PR}_{3}\right)_{2} \mathrm{Cl}_{2}\). (The ligand \(\mathrm{PR}_{3}\) is a phosphine such as \(\mathrm{P}\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3},\) triphenylphosphine. It is a Lewis base. The nickel( II) compound is paramagnetic whereas the palladium(II) compound is diamagnetic. (a) Explain the magnetic properties of these compounds. (b) How many isomers of each compound are expected?

Two different coordination compounds containing one cobalt(III) ion, five ammonia molecules, one bromide ion, and one sulfate ion exist. The dark violet form (A) gives a precipitate upon addition of aqueous \(\mathrm{BaCl}_{2}\). No reaction is seen upon addition of aqueous \(\mathrm{BaCl}_{2}\) to the violet- red form \((\mathrm{B})\) Suggest structures for these two compounds, and write a chemical equation for the reaction of (A) with aqueous \(\mathrm{BaCl}_{2}\).

A 0.213 -g sample of uranyl(VI) nitrate, \(\mathrm{UO}_{2}\left(\mathrm{NO}_{3}\right)_{2},\) is dissolved in \(20.0 \mathrm{mL}\) of \(1.0 \mathrm{M}\) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and shaken with Zn. The zinc reduces the uranyl ion, \(\mathrm{UO}_{2}^{2+},\) to a uranium ion, \(\mathrm{U}^{n+}\). To determine the value of \(n,\) this solution is titrated with \(\mathrm{KMnO}_{4} .\) Permanganate is reduced to \(\mathrm{Mn}^{2+}\) and \(\mathrm{U}^{n+}\) is oxidized back to \(\mathrm{UO}_{2}^{2+}\) (a) In the titration, \(12.47 \mathrm{mL}\) of \(0.0173 \mathrm{M} \mathrm{KMnO}_{4}\) was required to reach the equivalence point. Use this information to determine the charge on the ion \(\mathrm{U}^{n+}\). (b) With the identity of \(\mathrm{U}^{n+}\) now established, write a balanced net ionic equation for the reduction of \(\mathrm{UO}_{2}^{2+}\) by zinc (assume acidic conditions). (c) Write a balanced net ionic equation for the oxidation of \(\mathrm{U}^{n+}\) to \(\mathrm{UO}_{2}^{2+}\) by \(\mathrm{MnO}_{4}^{-}\) in acid.

Fireworks contain \(\mathrm{KClO}_{3}\). To analyze a sample for the amount of \(\mathrm{KClO}_{3}\) a chemist first reacts the sample with excess iron(II), $$\begin{array}{r}\mathrm{ClO}_{3}^{-}(\mathrm{aq})+6 \mathrm{Fe}^{2+}(\mathrm{aq})+6 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \longrightarrow \\\\\mathrm{Cl}^{-}(\mathrm{aq})+9 \mathrm{H}_{2} \mathrm{O}(\ell)+6 \mathrm{Fe}^{3+}(\mathrm{aq})\end{array}$$ and then titrates the resulting solution with \(\mathrm{Ce}^{4+}\) [in the form of \(\left.\left(\mathrm{NH}_{4}\right)_{2}\mathrm{Ce}\left(\mathrm{NO}_{3}\right)_{6}\right]\) $$\mathrm{Fe}^{2+}(\mathrm{aq})+\mathrm{Ce}^{4+}(\mathrm{aq}) \longrightarrow \mathrm{Fe}^{3+}(\mathrm{aq})+\mathrm{Ce}^{3+}(\mathrm{aq}) $$ to determine the quantity of iron(II) that did not react with \(\mathrm{ClO}_{3}^{-}\). (This is referred to as a "back titration." Suppose a 0.1342-g sample of a firework was treated with 50.00 mL. of \(0.0960 \mathrm{M} \mathrm{Fe}^{2+}\) The unreacted \(\mathrm{Fe}^{2+}\) ions then required \(12.99 \mathrm{mL}\) of \(0.08362 \mathrm{M} \mathrm{Ce}^{4+} .\) What is the weight percent of \(\mathrm{KClO}_{3}\) in the original sample?

In this question, we explore the differences between metal coordination by monodentate and bidentate ligands. Formation constants, \(K_{t}\), for \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}(\mathrm{aq})\) and \(\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}(\mathrm{aq})\) are as follows: \(\mathrm{Ni}^{2+}(\mathrm{aq})+6 \mathrm{NH}_{3}(\mathrm{aq}) \longrightarrow\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}(\mathrm{aq}) \quad K_{\mathrm{f}}=10^{8}\) \(\mathrm{Ni}^{2+}(\mathrm{aq})+3 \mathrm{en}(\mathrm{aq}) \longrightarrow\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}(\mathrm{aq})\) \(K_{f}=10^{18}\) The difference in \(K_{f}\) between these complexes indicates a higher thermodynamic stability for the chelated complex, caused by the chelate effect. Recall that \(K\) is related to the standard free energy of the reaction by \(\Delta_{r} G^{\circ}=-R T \ln K\) and \(\Delta_{r} G^{\circ}=\) \(\Delta_{r} H^{\circ}-T \Delta_{r} S^{\circ} .\) We know from experiment that \(\Delta_{t} H^{\circ}\) for the \(\mathrm{NH}_{3}\) reaction is \(-109 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}\) and \(\Delta_{i} H^{\circ}\) for the ethylenediamine reaction is \(-117 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} .\) Is the difference in \(\Delta_{r} H^{\circ}\) suffi- cient to account for the \(10^{10}\) difference in \(K_{f} ?\) Comment on the role of entropy in the second reaction.