Download Concepts in Transition Metal Chemistry – Questions

Concepts in Transition Metal Chemistry – Questions
Chapter 1
1
The electronic configuration of the free manganese and copper atoms are
[Ar]3d54s2 and [Ar]3d104s1. What are the configurations of the free ions Mn4+
and Cu3+?
2
Elements A and B occur in Period 5 of the Periodic Table and each has four
valence electrons. Both are good conductors of electricity. A melts at 2125 K and
B at 505 K. Identify A and B.
3
Titanium forms a black dichloride, TiCl2. What would you see when this
compound is added to dilute acid in the absence of oxygen? Write an equation for
the reaction.
4
A black hydroxide of nickel in oxidation state +3 can be obtained with the formula
NiO(OH). What would you see when this compound is added to dilute sulfuric
acid? Write an equation for the process.
5
State the oxidation state of manganese and the number of 3d electrons associated
with manganese in the following compounds and ions – MnCl2, MnO42−, K2MnF6,
Mn2O7, Mn2(SO4)3.
Chapter 2
1
Use the information in the Appendix and the value Eө[S2O82−|2SO42−] = 2.00 V to
find out which of the following reactions are thermodynamically favourable:
(a) oxidation of Cr2+(aq) by Mn3+(aq);
(b) oxidation of Mn2+(aq) by Co3+(aq);
(c) oxidation of Mn2+(aq) by persulfate;
(d) reduction of persulfate by V2+(aq).
2
Besides defining the resistance of water to oxidation, the couple
O2 + 4H+ + 4e = 2H2O also defines the strength of oxygen (in contact with
aqueous hydrogen ions) as an oxidising agent. How many of the ions Cr2+(aq),
Mn2+(aq), Fe2+(aq) and Co2+(aq) are thermodynamically unstable to oxidation by
oxygen in acid solution?
3
A research paper reports an attempt to make a trihalide of nickel. Which halide is
most likely to have been tried?
4
Seven of the ten first-row transition elements form well-characterised oxides,
M2O3. Which three elements do not do so?
5
The following solid compounds have not yet been prepared: K2VO4, ScCl2, Fe2O7.
For each compound, which of the following statements do you think is most
relevant to the difficulty experienced in preparing it?
(a)
In the first transition series, the electrons in the argon core are not available
for bonding.
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(b)
(c)
As you move across the first transition series, the valence electrons gradually
become more tightly bound.
The compound is unstable with respect to the transition metal and a
compound of higher oxidation state.
Chapter 3
1
Which of the ligands in the structures 1, 2 and 3 match(es) the descriptions below?
A chelating ligand
A bidentate ligand
A tridentate ligand
A bridging ligand
Fe
Fe
O
H2 N
O
CH2
CH2
NH
Fe
NH2 CH2
O
1
2
2
4
5
Fe
NH2 CH2
NH2 CH2
3
Choose the correct description for the binding of the O2 ligand in the structure shown.
O
Co
3
CH2
O
Co
How many stereoisomers are there of the octahedral complex [CoBr2Cl2(en)]− ?
How many of these stereoisomers are optically active?
How many stereoisomers of the octahedral complex, [CoCl3(dien)] should exist?
Dien is NH2CH2CH2NHCH2CH2NH2. Both terminal nitrogens in coordinated dien
must occupy positions adjacent to its central nitrogen in the octahedron.
Bis(benzylacetonato)(diethoxy)titanium has been suggested as an anti-cancer drug.
OO
O
Ti
O
O
O
With drugs it is important to have the correct stereoisomer. How many possible
stereoisomers are there for this complex?
Chapter 4
1
The stability constants for Fe2+ and Fe3+ in the presence of a siderophore exochelin
MN are 5.01 × 1016 and 1.32 × 1039, respectively. Calculate the standard potential
of the (Fe3+|Fe2+) couple in the presence of this siderophore.
2
2
The pH of cow’s milk is 6.6. Which of the following divalent ions when present in
cow’s milk would be expected to be oxidised to the trivalent ion by oxygen on
thermodynamic grounds? Fe2+, Mn2+, Cr2+, Co2+, Ca2+.
3
Which of the given metal ions would be expected to bind to SCN− via the N atom?
Fe3+, Au+, Gd3+, Cu+.
4
Which of the following ions would you expect cysteine to bind to? Ag+, Al3+, Fe3+,
Ca2+, Mn2+, Pt4+.
5
Consider the elements beryllium, cadmium, copper, lanthanum, nickel and
scandium. Three of them occur naturally as oxide ores, the other three are found as
sulfide ores. Using the idea of hard/soft acids and bases which three would be
expected to occur as sulfide ores?
Chapter 5
1
Draw crystal-field energy-level diagrams for the octahedral complexes
[Cr(CN)6]3− and [Fe(CN)6]3−. Label the 3d energy levels and fill electrons into the
levels.
2
Draw crystal-field energy-level diagrams for the tetrahedral complexes [FeCl4]2−,
[VBr4]− and [Co(NCS)4]2− showing only the metal 3d levels and filling in the
electrons.
3
Which of the following ions will have a radius equal to that expected for an ion in
a spherical environment? Assume the ions are present in high-spin octahedral
complexes. Sc3+, Ti3+, V3+, Cr3+, Mn3+, Fe3+, Co3+.
4
What are the crystal field stabilisation energies (CFSE) for the metal ions in the
following trihalides? VF3, CrF3, MnF3, FeF3, CoF3.
Assume that the ion is surrounded by an octahedron of F− ions.
5
How would you expect the intensity of the d↔d bands in the spectra of cis[CoF2en2]+ and trans-[CoF2en2]+ to compare?
6
Which of the following high-spin complexes would you expect to exhibit a Jahn–
Teller distortion?
A [Cr(NH3)6]3+
B [MnCl6]3−
C [Fe(H2O)6]3+
7
You have seen that magnetite, Fe3O4 adopts an inverse spinel structure.
Manganese forms a similar oxide. Will Mn3O4 adopt the normal spinel or inverse
spinel structure?
8
The iron in haemoglobin is in oxidation state +2. The ligands around the iron form
an approximately square pyramidal arrangement. Construct an energy-level
diagram for Fe2+ in haemoglobin assuming the ligands are (a) weak-field and (b)
strong-field.
9
A study of the magnetic properties of Fe ions in horse spleen ferritin showed that
in the reduced state with 8 Fe ions present, the magnetic moment per Fe ion was
4.8 µB. Deduce the oxidation state of ion in the reduced ferritin.
Assume the Fe ions are surrounded by 6 oxygen atoms in an octahedral
arrangement.
10
A tetrahedral complex of chromium in which the Cr is coordinated by O is found
to have a magnetic moment of 1.80 µB. What is the likely oxidation state of Cr in
this complex, +2, +3, +4, +5 or +6?
3
Chapter 6
1
Which of the following combinations of σ-bonding orbitals will form a bonding
combination with a 4s orbital on a metal ion? Assume the 4s orbital has a positive
sign and the metal ion is at the centre of the combination.
+
+
+
−
+
+
+
−
+
−
+
+
−
−
+
−
−
−
+
−
A
B
C
D
E
F
2
In Chapter 5, it was noted that the neutral molecule CO produced strong-field
complexes. What is the main bonding feature that molecular orbital theory uses to
explain this for octahedral complexes?
3
Which of the following ligands when attached to a metal ion will give a bent
(metal–ligand atom–ligand atom) arrangement?
NO+, NO−, O2−, O22+, CN−
4
Which of the following complexes obey the 18-electron rule?
A [PtCl6]2−
B [Pt(NH3)4]2+
C [Fe(CO)5]
D [Ni(CN)4]2−
E [Co(NH3)4(CH3)(cysteine)]2+ (count cysteine as a 2-electron donor
coordinating through S)
5
The electronic spectrum of Ni superoxide dismutase was recorded for both the
oxidised and reduced forms of the enzyme. In the reduced form, the coordination
around Ni is approximately square planar and in the oxidised form it is square
pyramidal. From the intensity and position of the three peaks below, assign each
peak to a type of transition.
peak 1
14 380 cm−1
ε = 300 dm3 mol−1 cm−1
peak 2
17 110 cm−1
ε = 70 dm3 mol−1 cm−1
peak 3
23 290 cm−1
ε = 2020 dm3 mol−1 cm−1
4