Download Problem Set 10 Solutions

Problem Set 10 Solutions
1. For each of the following, provide:
i)
The correct name of the entire compound
ii)
The oxidation state of the transition metal
iii)
The number of d electrons on the transition metal
iv)
The crystal-field energy level diagram for the d orbitals
v)
Whether the complex is high-spin or low-spin
vi)
The total number of unpaired electrons
a) (NH4)[Cr(H2O)6](SO4)2
(3 pts)
Ammonium hexaaquachromium(III) sulfate
Oxidation state of Cr is +3
Cr3+ will have 3 d-electrons:
With three electrons, high-spin and low-spin is the same.
All 3 electrons are unpaired.
b) K4[Os(CN)6] (3 pts)
Potassium hexacyanoosmate(II)
Oxidation state of Os is +2
Os2+ will have 6 d-electrons:
With strong-field CN– ligands, expect this to be low-spin.
There are no unpaired electrons.
c) [Ni(NH3)4(H2O)2](NO3)2
(3 pts)
Tetraamminediaquanickel(II) nitrate
Oxidation state of Ni is +2
Ni2+ will have 8 d-electrons:
With 8 electrons, high-spin and low-spin is the same.
There are two unpaired electrons.
d) Mo(CO)6
(3 pts)
Hexacarbonylmolybdenum(0)
Oxidation state of molybdenum is zero
Mo(0) will have 6 d-electrons:
With the strong-field ligand CO, we expect to have a low-spin configuration.
There are no unpaired electrons.
2. Ruthenium can form complexes with chloride and water ligands with varying stoichiometries. Three
such complexes are:
[RuCl2(H2O)4]+
[RuCl3(H2O)3]
[RuCl4(H2O)2]–
a)
What is the oxidation state of ruthenium in each of these complexes? (All of the complexes have
the same oxidation state.)
The oxidation state is +3. (1 pts)
b)
All of these complexes are low-spin. How many unpaired electrons are found in each of these
complexes?
d5 low spin, so only 1 unpaired electron (1 pts)
c)
These three complexes appear colored red, yellow, and green (but not necessarily in that order).
Match each complex with its apparent color.
First of all, note that Cl– is a weaker-field ligand then H2O. Then the rest is easy: (3 pts)
d)
[RuCl2(H2O)4]+ is yellow
[RuCl3(H2O)3] is red
(it absorbs high-energy violet)
(it absorbs medium-energy green)
[RuCl4(H2O)2]– is green
(it absorbs low-energy red)
Could any of these compounds exhibit geometrical isomerism? Show all the possible geometric
isomers for each of these compounds.
All could exhibit geometrical isomerism: (3 pts)
[RuCl2(H2O)4]+
Cl
Cl
H2 O
H2 O
[RuCl4(H2O)2]–
[RuCl3(H2O)3]
Cl
Ru
OH2
Cl
H2 O
H2 O
Cl
Ru
Cl
Cl
H2 O
Cl
Ru
fac
cis
cis
OH2
OH2
OH2
Cl
Cl
Cl
H2 O
OH2
H2 O
Ru
H2 O
Cl
H2 O
Cl
Ru
OH2
trans
Cl
H2 O
Ru
OH2
Cl
OH2
mer
Cl
Cl
trans
Cl
3. Draw all the unique isomers for the complex [Co(NH3)3(H2O)ClBr]+, which has cobalt in an
octahedral geometry. Identify whether each isomer is chiral or achiral. Predict the number of
unpaired electrons expected for this complex. (3 pts)
NH3
H3 N
H3 N
NH3
Br
Co
Cl
OH2
Br
Cl
NH3
Co
NH3
OH2
chiral
chiral
NH3
H3 N
Cl
Br
Co
OH2
achiral
NH3
NH3
H3 N
Br
OH2
Co
Cl
achiral
NH3
NH3
H3 N
H2 O
Cl
Co
Br
achiral
NH3
This complex should have Co3+, which is usually low-spin, with no unpaired electrons. (1pt)
4. Consider the following two chromium-containing compounds:
Compound A: K3[Cr(CN)6]
Compound B: [Cr(en)Cl(H2O)3]Cl2
en = ethylenediamine, H2NCH2CH2NH2
a)
Provide a systematic name for each compound. (2 pts)
Compound A: potassium hexacyanochromate(III)
Compound B: triaquachloro(ethylenediamine)chromium(III) chloride
b)
One of these compounds is red, the other is yellow. Choose which is which and explain your
choice using the language of crystal field theory. (2 pts)
Compound A is yellow, and Compound B is red. The substance that appears yellow absorbs
violet light, and the substance that appears red absorbs green light. Violet light has a higher
energy than green light, so the substance that appears yellow must absorb light of a higher energy
than the substance that appears red. So the substance that appears yellow must have a larger ∆.
Compound A should have a larger ∆ than Compound B because the cyanide ligand is a stronger
field ligand than ethylenediamine, chloride, or water.
c)
Draw all unique geometric isomers of the complex [Cr(en)Cl(H2O)3]2+. Indicate whether each
one is chiral or achiral. (2 pts)
N
N
OH 2
Cl
Achiral
N
OH 2
N
OH 2
OH 2
Cl
OH 2
OH2
Achiral