Download Chemistry 2000 B Spring 2005 Answers to the Second Problem Set

Chemistry 2000 B
Spring 2005
Transition Metal Coordination Compounds
Answers to the Second Problem Set
Oxtoby 3.8; 19.1 – 19.4 (partial coverage only)
Review Questions
1. What feature of electronic structure distinguishes transition elements, lanthanide elements, and actinide elements from
the other elements and from one another?
2. Write out electron configurations for each element in the first transition series.
3. Write out the electron configuration for the 2+ ion of each metal in the first transition series.
The Review questions can be answered by looking at the material directly in the lecture notes or the text book. For electron
configurations, see Oxtobly Chapter 17.1 – 17.3.
Numerical and Conceptual Problems
1.
Chromium compounds have two common oxidation numbers, +2 and +3. Using an orbital box diagram, show the
electron configuration for chromium in each oxidation state. Are these two oxidation states of chromium expected to
be paramagnetic or diamagnetic?
Neutral Cr is [Ar]4s13d5 (one of the “exceptions”). So for the two ions we get:
Cr2+
[Ar]3d4
↑ ↑ ↑ ↑
3d
Cr3+
[Ar]3d3
↑ ↑ ↑
3d
Both are expected to be paramagnetic because of 4 and 3 unpaired electrons, respectively. Note that we are talking here
about the free ions, not specific coordination complexes, for which different conclusions can sometimes be drawn.
2.
Give the electron configuration for each ion listed here, and tell whether it is paramagnetic or diamagnetic
[Kr]
diamagnetic (a genuine noble gas ion, as are all the Group 3 metal ions)
(a) Y3+
(b) Pt2+
[Xe]4f145d8
paramagnetic as the free ion
(c) Rh3+
[Kr]4d6
paramagnetic as the free ion
(d) V2+
[Ar]3d3
paramagnetic as the free ion
4+
(e) Ce
[Xe]
diamagnetic (also a genuine noble gas ion)
(f) U4+
[Rn]5f2
paramagnetic
3.
Identify two transition metal ions with the following electron configurations
.
:
There are a lot of possible answers. To be accurate, you should use the graph of oxidation states for the TM.
(a) [Ar] 3d6
(b) [Ar] 3d10
(c) [Ar] 3d5
(d) [Ar] 3d8
Mn+, Fe2+, Co3+, Ni4+
Cu+ the only choice for the first row. Ag+ and Au+ are other good choices.
Cr+, Mn2+, Fe3+, Co4+, that is it for the first TM row, but more available in 2nd and 3rd rows.
Co+, Ni2+, Cu3+
NOTE: in any ionic form, including 1+ ions, the 4s level will be completely empty, and any remaining 4s electrons are
demoted to the 3d levels.
4.
Identify another ion of a first series transition metal that is isoelectronic with each of the following:
Again, there are many possible answers. For the first TM series, use the graph of oxidation states once again.
(a) Fe3+
[Ar] 3d5, so Cr+, Mn2+, Co4+
2+
(b) Fe
[Ar] 3d6, so Mn+, Co3+, Ni4+
2+
(c) Zn
[Ar] 3d10, so Cu+
3+
(d) Cr
[Ar]3d3, so Ti+, V2+, Mn4+, Co5+
5.
Write formulas for the following ions or compounds:
(a) potassium tetrachloroplatinate(II)
(b) potassium dicyanocuprate(I)
(c)diaquatetraammineiron(II)
(d) hexaammineiron(III) nitrate
(e) ammonium tetrachlorocuprate(II)
6.
Name the following ligands:
(a) OH–
(b) O2–
(c) I–
(d) C2O42–
7.
K2[PtCl4]
K[Cu(CN)2]
[Fe(OH2)2(NH3)4]2+ (note that this is not a complete salt, just a cation.)
[Fe(NH3)6](NO3)3
(NH4)2[CuCl4]
hydroxo
oxo
iodo
oxallate
The chromium(II) ion in water, [Cr(H2O)6]2+, absorbs light with a wavelength of about 700 nm. What color is the
solution?
Red light is absorbed. We expect the solution to be blue or purplish.
8.
For the complex [Fe(H2O)6]2+ identify
(a) The coordination number of iron The coordination number is six (from the six oxygens in water)
(b) The oxidation state of iron
Fe(II)
(c) The number of unpaired electrons, assuming high spin
This is not a free ion, but an octahedral aqua
complex, so we must consider the splitting of the d orbitals. The electron configuration is [Ar]3d6. For oxygen donors,
the high spin configuration is always found. This means the electron filling pattern will be:
↑ ↑
and hence the complex is expected to have 4 unpaired electrons.
“Split” d orbital pattern:
↑↓ ↑ ↑
(d) Whether the complex is diamagnetic or paramagnetic
Any unpaired electrons means paramagnetic