Chapter 23

(a) Draw the structure for \(\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2} .\) (b) What is the coordination number for platinum in this complex, and what is the coordination geometry? (c) What is the oxidation state of the platinum? [Section 23.2]

Two Fe(II) complexes are both low spin but have different ligands. A solution of one is green and a solution of the other is red. Which solution is likely to contain the complex that has the stronger-field ligand? [Section 23.6\(]\)

Explain the lanthanide contraction, and describe how it affects the properties of the transition-metal elements.

Sketch a plot of atomic radius versus number of valence \(d\) electrons for the period 5 transition metals, and explain the trend.

The +2 oxidation state is common for almost all the transition metals. Suggest an explanation.

No compounds are known in which scandium is in the +2 oxidation state. Suggest an explanation.

Write out the ground-state electron configurations of (a) \(\mathrm{Ti}^{3+}\) (b) \(\mathrm{Ru}^{2+},(\mathrm{c}) \mathrm{Au}^{3+}\) (d) \(\mathrm{Mn}^{4+}\).

How many electrons are in the valence \(d\) orbitals in these transition-metal ions? (a) \(\mathrm{Co}^{3+},(\mathbf{b}) \mathrm{Cu}^{+}\), (d) \(\mathrm{Os}^{3+}\). (c) \(\mathrm{Cd}^{2+}\)

Explain the difference between a diamagnetic substance and a paramagnetic substance.

Distinguish among a ferromagnetic substance, an antiferromagnetic substance, and a ferrimagnetic substance.

The most important oxides of iron are magnetite, \(\mathrm{Fe}_{3} \mathrm{O}_{4},\) and hematite, \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) (a) What are the oxidation states of iron in these compounds? (b) One of these iron oxides is ferrimagnetic, and the other is antiferromagnetic. Which iron oxide is likely to show which type of magnetism? Explain.

(a) What is the difference between Werner's concepts of primary valence and secondary valence? What terms do we now use for these concepts? (b) Why can the \(\mathrm{NH}_{3}\) molecule serve as a ligand but the \(\mathrm{BH}_{3}\) molecule cannot?

(a) What is the meaning of the term coordination number as it applies to metal complexes? (b) Give an example of a ligand that is neutral and one that is negatively charged. (c) Would you expect ligands that are positively charged to be common? Explain. (d) What type of chemical bonding is characteristic of coordination compounds? Illustrate with the compound \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6} \mathrm{Cl}_{3}\) (e) What are the most common coordination numbers for metal complexes?

A complex is written as \(\mathrm{NiBr}_{2} \cdot 6 \mathrm{NH}_{3}\). (a) What is the oxidation state of the \(\mathrm{Ni}\) atom in this complex? (b) What is the likely coordination number for the complex? (c) If the complex is treated with excess \(\mathrm{AgNO}_{3}(a q),\) how many moles of \(\mathrm{AgBr}\) will precipitate per mole of complex?

A certain complex of metal \(\mathrm{M}\) is formulated as \(\mathrm{MCl}_{3} \cdot 3 \mathrm{H}_{2} \mathrm{O}\). The coordination number of the complex is not known but is expected to be 4 or 6. (a) Would conductivity measurements provide information about the coordination number? (b) In using conductivity measurements to test which ligands are bound to the metal ion, what assumption is made about the rate at which ligands enter or leave the coordination sphere of the metal? (c) Suppose you experimentally determine that this complex exists in aqueous solution as a single species. Suggest a likely coordination number and the number and type of each ligand.

Indicate the coordination number of the metal and the oxidation number of the metal as well as the number and type of each donor atom of the ligands for each of the following complexes: (a) \(\mathrm{Na}_{2}\left[\mathrm{CdCl}_{4}\right]\) (b) \(\mathrm{K}_{2}\left[\mathrm{MoOCl}_{4}\right]\) (c) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Cl}\) (d) \(\left[\mathrm{Ni}(\mathrm{CN})_{5}\right]^{3-}\) (e) \(\mathrm{K}_{3}\left[\mathrm{~V}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) (f) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right] \mathrm{Br}_{2}\)

Indicate the coordination number of the metal and the oxidation number of the metal as well as the number and type of each donor atom of the ligands for each of the following complexes: (a) \(\mathrm{K}_{3}\left[\mathrm{Co}(\mathrm{CN})_{6}\right]\) (b) \(\mathrm{Na}_{2}\left[\mathrm{CdBr}_{4}\right]\) (c) \(\left[\mathrm{Pt}(\mathrm{en})_{3}\right]\left(\mathrm{ClO}_{4}\right)_{4}\) (d) \(\left[\mathrm{Co}(\mathrm{en})_{2}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\right]^{+}\) (e) \(\mathrm{NH}_{4}\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{NCS})_{4}\right]\) (f) \(\left[\mathrm{Cu}(\text { bipy })_{2} \mathrm{I}\right] \mathrm{I}\)

(a) What is the difference between a monodentate ligand and a bidentate ligand? (b) How many bidentate ligands are necessary to fill the coordination sphere of a six-coordinate complex? (c) You are told that a certain molecule can serve as a tridentate ligand. Based on this statement, what do you know about the molecule?

For each of the following polydentate ligands, determine (i) the maximum number of coordination sites that the ligand can occupy on a single metal ion and (ii) the number and type of donor atoms in the ligand: (a) ethylenediamine (en), (b) bipyridine (bipy), (c) the oxalate anion \(\left(\mathrm{C}_{2} \mathrm{O}_{4}{\underline{\phantom{xx}}}^{2-}\right),(\mathrm{d})\) the \(2-\) ion of the porphine molecule (Figure 23.13 ); (e) [EDTA] \(]\) -

Polydentate ligands can vary in the number of coordination positions they occupy. In each of the following, identify the polydentate ligand present and indicate the probable number of coordination positions it occupies: (a) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4}(o\) -phen \()\right] \mathrm{Cl}_{3}\) (b) \(\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \mathrm{Br}\) (c) \(\left[\mathrm{Cr}(\mathrm{EDTA})\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{-}\) (d) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right]\left(\mathrm{ClO}_{4}\right)_{2}\)

Indicate the likely coordination number of the metal in each of the following complexes: (a) \(\left[\mathrm{Rh}(\text { bipy })_{3}\right]\left(\mathrm{NO}_{3}\right)_{3}\) (b) \(\mathrm{Na}_{3}\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2} \mathrm{Cl}_{2}\right]\) (c) \(\left[\mathrm{Cr}(o \text { -phen })_{3}\right]\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{3}\) (d) \(\mathrm{Na}_{2}[\mathrm{Co}(\mathrm{EDTA}) \mathrm{Br}]\)

(a) What is meant by the term chelate effect? (b) What thermodynamic factor is generally responsible for the chelate effect? (c) Why are polydentate ligands often called sequestering agents?

Pyridine \(\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N}\right)\), abbreviated py, is the molecule (a) Why is pyridine referred to as a monodentate ligand? (b) For the equilibrium reaction $$ \left[\mathrm{Ru}(\mathrm{py})_{4}(\mathrm{bipy})\right]^{2+}+2 \mathrm{py} \rightleftharpoons\left[\mathrm{Ru}(\mathrm{py})_{6}\right]^{2+}+\text { bipy } $$ what would you predict for the magnitude of the equilibrium constant? Explain your answer.

Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere: (a) hexaamminechromium(III) nitrate (b) tetraamminecarbonatocobalt(III) sulfate (c) dichlorobis(ethylenediamine) platinum(IV) bromide (d) potassium diaquatetrabromovanadate(III) (e) bis(ethylenediamine) zinc(II) tetraiodomercurate(II)

Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere: (a) tetraaquadibromomanganese(III) perchlorate (b) bis(bipyridyl) cadmium(II) chloride (c) potassium tetrabromo( ortho-phenanthroline)cobaltate (III) (d) cesium diamminetetracyanochromate(III) (e) tris(ethylenediammine)rhodium(III) tris(oxalato)cobaltate(III)

Write the names of the following compounds, using the standard nomenclature rules for coordination complexes: (a) \(\left[\mathrm{Rh}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Cl}\) (b) \(\mathrm{K}_{2}\left[\mathrm{TiCl}_{6}\right]\) (c) \(\mathrm{MoOCl}_{4}\) (d) \(\left[\mathrm{Pt}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\right] \mathrm{Br}_{2}\)

Write names for the following coordination compounds: (a) \(\left[\mathrm{Cd}(\mathrm{en}) \mathrm{Cl}_{2}\right]\) (b) \(\mathrm{K}_{4}\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]\) (c) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{CO}_{3}\right] \mathrm{Cl}\) (d) \(\left[\operatorname{Ir}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\)

By writing formulas or drawing structures related to any one of these three complexes, \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{Cl}\) \(\left[\mathrm{Pd}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{ONO})_{2}\right]\) cis-[ \(\left.\mathrm{V}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]^{+}\) illustrate (a) geometric isomerism, (b) linkage isomerism, (c) optical isomerism, (d) coordination-sphere isomerism.

A four-coordinate complex \(\mathrm{MA}_{2} \mathrm{~B}_{2}\) is prepared and found to have two different isomers. Is it possible to determine from this information whether the complex is square planar or tetrahedral? If so, which is it?

Consider an octahedral complex \(\mathrm{MA}_{3} \mathrm{~B}_{3} .\) How many geometric isomers are expected for this compound? Will any of the isomers be optically active? If so, which ones?

\(\begin{array}{lllll}\text { Sketch all the possible } & \text { stereoisomers } & \text { of }\end{array}\) (a) \(\left[\mathrm{Rh}(\text { bipy })(o \text { -phen })_{2}\right]^{3+}\), (b) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}(\text { bipy }) \mathrm{Br}\right]^{2+},\) (c) square-planar \(\left[\mathrm{Pd}(\mathrm{en})(\mathrm{CN})_{2}\right]\).

(a) Can we see light that is \(300 \mathrm{nm}\) in wavelength? \(500 \mathrm{nm}\) in wavelength? (b) What is meant by the term complementary color? (c) What is the significance of complementary colors in understanding the colors of metal complexes? (d) If a complex absorbs light at \(610 \mathrm{nm},\) what is the energy of this absorption in \(\mathrm{kJ} / \mathrm{mol}\) ?

(a) A complex absorbs light in the range of \(200-300 \mathrm{nm} . \mathrm{Do}\) you expect it to have visible color? (b) A solution of a compound appears green. Does this observation necessarily mean that all colors of visible light other than green are absorbed by the solution? Explain. (c) What information is usually presented in a visible absorption spectrum of a compound? (d) What energy is associated with an absorption at \(440 \mathrm{nm}\) in \(\mathrm{kJ} / \mathrm{mol} ?\)

Is it possible for a low-spin octahedral Fe(II) complex to be paramagnetic? Explain.

If a transition-metal complex has an even number of valence \(\bar{d}\) electrons, does it necessarily mean that the complex is diamagnetic? Explain.

In crystal-field theory, ligands are modeled as if they are point negative charges. What is the basis of this assumption, and how does it relate to the nature of metal-ligand bonds?

Explain why the \(d_{x y}, d_{x z}\), and \(d_{y z}\) orbitals lie lower in energy than the \(d_{z}^{2}\) and \(d_{x^{2}-y^{2}}\) orbitals in the presence of an octahedral arrangement of ligands about the central metal ion.

(a) Sketch a diagram that shows the definition of the crystal-field splitting energy \((\Delta)\) for an octahedral crystal field. (b) What is the relationship between the magnitude of \(\Delta\) and the energy of the d- \(d\) transition for a \(d^{1}\) complex? (c) Calculate \(\Delta\) in \(\mathrm{kJ} / \mathrm{mol}\) if a \(d^{1}\) complex has an absorption maximum at \(545 \mathrm{nm}\).

The \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) ion has an absorption maximum at about \(725 \mathrm{nm},\) whereas the \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}\) ion absorbs at about \(570 \mathrm{nm}\). Predict the color of a solution of each ion. (b) The \(\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}\) ion absorption maximum occurs at about \(545 \mathrm{nm}\), and that of the [Ni(bipy) \(\left._{3}\right]^{2+}\) ion occurs at about \(520 \mathrm{nm}\). From these data, indicate the relative strengths of the ligand fields created by the four ligands involved.

Give the number of (valence) \(d\) electrons associated with the central metal ion in each of the following complexes: (a) \(\mathrm{K}_{3}\left[\mathrm{TiCl}_{6}\right]\) (b) \(\mathrm{Na}_{3}\left[\mathrm{Co}\left(\mathrm{NO}_{2}\right)_{6}\right],\) (c) \(\left[\mathrm{Ru}(\mathrm{en})_{3}\right] \mathrm{Br}_{3},\) (d) \([\mathrm{Mo}(\mathrm{EDTA})] \mathrm{ClO}_{4},(\mathrm{e}) \mathrm{K}_{3}\left[\mathrm{ReCl}_{6}\right] .\)

Give the number of (valence) \(d\) electrons associated with the central metal ion in each of the following complexes: (a) \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\), (b) \(\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]\left(\mathrm{NO}_{3}\right)_{2}\) (c) \(\mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]\) (d) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{ClO}_{4}\), (e) \([\mathrm{Sr}(\mathrm{EDTA})]^{2-}\)

A classmate says, "A weak-field ligand usually means the complex is high spin." Is your classmate correct? Explain.

A classmate says, "A strong-field ligand means that the ligand binds strongly to the metal ion." Is your classmate correct? Explain.

For each of the following metals, write the electronic configu- ration of the atom and its \(2+\) ion: \((\) a) \(M n,\) (b) \(R u,\) (c) \(R h\). Draw the crystal-field energy-level diagram for the \(d\) orbitals of an octahedral complex, and show the placement of the \(d\) electrons for each \(2+\) ion, assuming a strong-field complex. How many unpaired electrons are there in each case?

For each of the following metals, write the electronic configuration of the atom and its \(3+\) ion: (a) \(\mathrm{Ru},(\mathbf{b}) \mathrm{Mo},(\mathbf{c}) \mathrm{Co} .\) Draw the crystal-field energy-level diagram for the \(d\) orbitals of an octahedral complex, and show the placement of the \(d\) electrons for each \(3+\) ion, assuming a weak-field complex. How many unpaired electrons are there in each case?

Draw the crystal-field energy-level diagrams and show the placement of \(d\) electrons for each of the following: (a) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (four unpaired electrons), (b) \(\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (high spin), (c) \(\left[\mathrm{Ru}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{H}_{2} \mathrm{O}\right]^{2+}\) (low spin), (d) \(\left[\operatorname{Ir} \mathrm{Cl}_{6}\right]^{2-}\) (low spin), (e) \(\left[\mathrm{Cr}(\mathrm{en})_{3}\right]^{3+},(\mathrm{f})\left[\mathrm{NiF}_{6}\right]^{4-}\)

Draw the crystal-field energy-level diagrams and show the placement of electrons for the following complexes: (a) \(\left[\mathrm{VCl}_{6}\right]^{3-}\) (b) \(\left[\mathrm{FeF}_{6}\right]^{3-}(\) a high-spin complex \(),(\mathrm{c})\left[\mathrm{Ru}(\mathrm{bipy})_{3}\right]^{3+}\) (a low- spin complex), (d) \(\left[\mathrm{NiCl}_{4}\right]^{2-}\) (tetrahedral), (e) \(\left[\mathrm{PtBr}_{6}\right]^{2-}\) (f) \(\left[\mathrm{Ti}(\mathrm{en})_{3}\right]^{2+}\)

The complex \(\left[\mathrm{Mn}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}\) contains five unpaired electrons. Sketch the energy-level diagram for the \(d\) orbitals, and indicate the placement of electrons for this complex ion. Is the ion a high-spin or a low-spin complex?

(a) A compound with formula \(\mathrm{RuCl}_{3} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) is dissolved in water, forming a solution that is approximately the same color as the solid. Immediately after forming the solution, the addition of excess \(\mathrm{AgNO}_{3}(a q)\) forms \(2 \mathrm{~mol}\) of solid \(\mathrm{AgCl}\) per mole of complex. Write the formula for the compound, showing which ligands are likely to be present in the coordination sphere. (b) After a solution of \(\mathrm{RuCl}_{3} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) has stood for about a year, addition of \(\mathrm{AgNO}_{3}(a q)\) precipitates \(3 \mathrm{~mol}\) of \(\mathrm{AgCl}\) per mole of complex. What has happened in the ensuing time?

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