Chapter 23

Draw the structure for \(\mathrm{Pt}(\mathrm{en}) \mathrm{Cl}_{2}\) and use it to answer the following questions: (a) What is the coordination number for platinum in this complex? (b) What is the coordination geometry? (c) What is the oxidation state of the platinum? (d) How many unpaired electrons are there? [Sections \(23.2\) and 23.6]

Draw the Lewis structure for the ligand shown here. (a) Which atoms can serve as donor atoms? Classify this ligand as monodentate, bidentate, or polydentate. (b) How many of these ligands are needed to fill the coordination sphere in an octahedral complex? [Section 23.2] $$ \mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CO}_{2}{\underline{\phantom{xx}}}^{-} $$

Which of the complexes shown here are chiral? [Section 23.4] $$ \mathrm{Cr} \quad \mathrm{Cr}=\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2} \quad \Theta=\mathrm{Cl} \quad \theta=\mathrm{NH}_{3} $$ (1) ( (3) (4)

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]

The lanthanide contraction explains which of the following periodic trends? (a) The atomic radii of the transition metals first decrease and then increase when moving horizontally across each period. (b) When forming ions the transition metals lose their valence s orbitals before their valence \(d\) orbitals. (c) The radii of the period 5 transition metals (Y-Cd) are very similar to the radii of the period 6 transition metals (Lu-Hg).

Which periodic trend is responsible for the observation that the maximum oxidation state of the transition-metal elements peaks near groups \(7 \mathrm{~B}\) and \(8 \mathrm{~B}\) ? (a) The number of valence electrons reaches a maximum at group \(8 \mathrm{~B}\). (b) The effective nuclear charge inereases on moving left across each period. (c) The radii of the transition-metal elements reaches a minimum for group \(8 \mathrm{~B}\) and as the size of the atoms decreases it becomes casier to remove electrons.

For each of the following compounds determine the electron (c) \(\mathrm{NiO}\), (d) \(\mathrm{ZnO}\).

Write out the ground-state electron configurations of (a) \(\mathrm{Ti}^{3+}\), (b) \(\mathrm{Ru}^{24}\), (c) \(\mathrm{Au}^{3+}\), (d) \(\mathrm{Mn}^{4+}\).

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

Which type of substance is attracted by a magnetic field, a diamagnetic substance or a paramagnetic substance?

Which type of magnetic material cannot be used to make permanent magnets, a ferromagnetic substance, an antiferromagnetic substance, or 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. Transition-Metal Complexes (Section 23.2)

a) Using Werner's definition of valence, which property is the same as oxidation number, primary valence or secondary walence? (b) What term do we normally use for the other type of valence? (c) 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 \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6} \mathrm{Cl}_{2}\). (e) What are the most common coordination numbers for metal complexes?

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

Crystals of hydrated chromium(III) chloride are green, have an empirical formula of \(\mathrm{CrCl}_{3} \cdot 6 \mathrm{H}_{2} \mathrm{O}\), and are highly soluble, (a) Write the complex ion that exists in this compound. (b) If the complex is treated with excess \(\mathrm{AgNO}_{3}(a q)\), how many moles of \(\mathrm{AgCl}\) will precipitate per mole of \(\mathrm{CrCl}_{3} * 6 \mathrm{H}_{2} \mathrm{O}\) dissolved in solution? (c) Crystals of anhydreus chromium(III) chloride are violet and insoluble in aqueous solution. The coordination geometry of chromium in these crystals is octahedral as is almost always the case for \(\mathrm{Cr}^{3+}\). How can this be the case if the ratio of \(\mathrm{Cr}\) to \(\mathrm{Cl}\) is not 1:6?

Indicate the coordination number and the oxidation number of the metal 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) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right\rceil \mathrm{Br}_{2}\)

Indicate the coordination number and the oxidation number of the metal 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) \(\mathrm{NH}_{4}\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{2}\left(\mathrm{NCS}_{4}\right]\right.\) (f) \(\left[\mathrm{Cu}(\mathrm{bipy})_{2} \mathrm{I}\right] \mathrm{I}\) common Ligands in Coordination Chemistry Section 23.3)

(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? mathrm{Br}$

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) acetylacetonate ion (acac), (b) phenanthroline (phen), (c) diethylenetriamine, (d) carbonate ion, (e) triphosphate ion.

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) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4}(o-\mathrm{phen})\right] \mathrm{Cl}_{3}\) (b) $\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \

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) \(\mathrm{Na}_{4}\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2} \mathrm{Cl}_{2}\right]\) (c) \(\left[\mathrm{Cr}(0 \text {-phen })_{3}\right]\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{3}\) (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) Would you expect pyridine to act as a monodentate or bidentate ligand? (b) For the equilibrium reaction $$\left[\mathrm{Ru}(\mathrm{py})_{4}(\mathrm{bipy})\right]^{2+}+2 \mathrm{py} \Longrightarrow\left[\mathrm{Ru}(\mathrm{py})_{6}\right]^{2+}+\mathrm{bipy}$$ would you predict the equilibrium constant to be larger or smaller than one?

True or false? The following ligand can act as a bidentate ligand? c1ccc2nc3ccccc3nc2c1

Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere: (a) hexaamminechromium(III) nitrate (b) tetramminecarbonatocobalt(III) sulfate (c) dichlorobis(ethylenediamine)platinum(IV) bromide

Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere: (a) tetraaquadibromemanganese(III) perchlorate (b) bis(bipyridyl)cadmium(II) chloride (c) potassium tetrabromo(ortho-phenanthroline)-cobaltate (III) (d) cesium diamminetetracyanochromate(III) (e) tris(ethylenediamine)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) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{s}\left(\mathrm{CO}_{3}\right)\right] \mathrm{Cl}\) (d) \(\left[\operatorname{lr}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\)

Consider the following three complexes: (Complex 1) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{Cl}\) \(\left(\right.\) Complex 2) \(\left[\mathrm{Pd}\left(\mathrm{NH}_{5}\right)_{2}(\mathrm{ONO})_{2}\right]\) (Complex 3) \(\left[\mathrm{V}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]^{+}\). Which of the three complexes can have (a) geometric isomers, (b) linkage isomers, (c) optical isomers, (d) coordinationsphere isomers?

Consider the following three complexes (Complex 1) \(\left[\mathrm{Co}\left(\mathrm{NH}_{2}\right)_{5} \mathrm{SCN}\right]^{2+}\) (Complex 2) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}_{3}\right]^{2+}\) (Complex 3) \(\mathrm{CoClBx}+5 \mathrm{NH}_{3}\) Which of the three complexes can have (a) geometric isomers, (b) linkage isomers, (c) optical isomers, (d) coordinationsphere isomers?

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

Sketch all the possible stereoisomers of (a) tetrahedral $\left[\mathrm{Cd}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2} \mathrm{Cl}_{2}\right],(\mathbf{b})\( square-planar \)\left[\operatorname{Ir} \mathrm{Cl}_{2}\left(\mathrm{PH}_{3}\right)_{2}\right]^{-},$ (c) octahedral $\left[\mathrm{Fe}(\sigma \text { -phen })_{2} \mathrm{Cl}_{2}\right]^{+}$

(a) If a complex absorbs light at \(610 \mathrm{~nm}\), what color would you expect the complex to be? (b) What is the energy in Joules of a photon with a wavelength of \(610 \mathrm{~nm}\) ? (c) What is the energy of this absorption in \(\mathrm{kJ} / \mathrm{mol}\) ?

(a) A complex absorbs photons with an energy of \(4.51 \times 10^{-19}\). 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?

Identify each of the following coordination complexes as either diamagnetic or paramagnetic: (a) \(\left[\mathrm{ZnCl}_{4}\right]^{2-}\) (b) \(\left[\mathrm{Pd}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\) (c) \(\left[\mathrm{V}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) (d) \(\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}\)

Identify each of the following coordination complexes as either diamagnetic or paramagnetic: (a) \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}\) (b) square planar \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\) (c) \(\left[\mathrm{Ru}(\mathrm{bipy})_{\mathrm{s}}\right]^{2+}\) (d) \(\left[\mathrm{CoCl}_{4}\right]^{2-}\)

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?

The lobes of which \(d\) orbitals point directly between the ligands in (a) octahedral geometry, (b) tetrahedral geometry?

(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 \(d^{2}\) complex? (c) Calculate \(\Delta\) in \(\mathrm{kJ} / \mathrm{mol}\) if a \(d^{1}\) complex has an absorption maximum at \(545 \mathrm{~nm}\).

As shown in Figure 23.26, the \(d-d\) transition of \(\left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) produces an absorption maximum at a wavelength of about \(500 \mathrm{~nm}\). (a) What is the magnitude of \(\Delta\) for \(\left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) in \(\mathrm{kJ} / \mathrm{mol}\) ? (b) How would the magnitude of \(\Delta\) change if the \(\mathrm{H}_{2} \mathrm{O}\) ligands in \(\left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) were replaced with \(\mathrm{NH}_{2}\) ligands?

The colors in the copper-containing minerals malachite (green) and azurite (blue) come from a single \(d\) - \(d\) transition in each compound. (a) What is the electron configuration of the copper ion in these minerals? (b) Based on their colors in which compound would you predict the crystal field splitting \(\Delta\) is larger?

Give the number of (valence) d clectrons associated with the central metal ion in each of the following complexess (a) \(\mathrm{K}_{3}\left[\mathrm{TiCl}_{6}\right]\), (b) \(\mathrm{Na}_{3}\left[\mathrm{Co}\left(\mathrm{NO}_{2}\right)_{6}\right]\), (c) \(\left[\mathrm{Ru}(e n)_{3}\right] \mathrm{Br}_{3}\), (d) \([\mathrm{Mo}(\mathrm{EDTA})] \mathrm{ClO}_{4}\), (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) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{ClO}_{4}\), (c) \([\mathrm{Sr}(\mathrm{EDTA})]^{2-}\) -

A classmate says, "A weak-field ligand usually means the complex is high spin." Is your clasmmate 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 configuration of the atom and its \(2+\) ion: (a) \(\mathrm{Mn}\), (b) \(\mathrm{Ru}\), (c) \(\mathrm{Rh}\). 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) Fe, (b) Mo, (c) 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) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right]^{2+}\) (four unpaired electrons), (b) \(\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (high spin), (c) \(\left[\mathrm{Ru}\left(\mathrm{NH}_{3}\right)_{3}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{2+}\) (low spin), (d) \(\left[\mathrm{IrCl}_{6}\right]^{2-}\) (low spin), (c) \(\left[\mathrm{Cr}(\mathrm{cn})_{3}\right]^{1+}\), (f) \(\left[\mathrm{NiF}_{6}\right]^{4-}\).