Problem Set 3

CHEM 153 - Advanced Inorganic Chemistry
PROBLEM SET 3 (due 29 January, 2010)
1. Consider the following oxo complexes:
a. [L 5 VO] 2+ V IV d 1
b. [L 5 CrO] 3+ Cr V d 1
c. [L 5 CrO] 2+ Cr IV d 2
d. [L 5 MnO] 3+ Mn V d 2
e. [L 5 MnO] 2+ Mn IV d 3
f. [L 5 FeO] 2+ Fe IV d 4
Part 1:
Construct an MO diagram for C 4v [L 5 MO] n+ (L is an uncharged ligand, for
example, H 2 O or NH 3 ) using the following orbitals: five metal 3d orbitals, one set
of five ligand F orbitals, and the oxo 2pF + two 2pB orbitals.
Part 2:
Using your MO diagram, for each of the above examples, fill in the d electrons
and predict the ground-state electronic configuration. With this prediction,
calculate the metal-oxo bond order. Based on your results, do you think that a
complex of the form [L 5 CoO] n+ could exist Why or why not
Part 3:
a. Larry Que and coworkers reported the synthesis and isolation of a nonheme
ferryl complex (Science 2003, 299, 1037-1039). What are the Fe-O bond
properties (bond length and bond order) Are they consistent with your
predictions for 6-coordinate Fe IV How do the reported Mössbauer spectra
support these findings
b. The electronic structures and spectroscopic properties of Que’s nonheme
ferryl complex have been investigated in Ed Solomon’s laboratory (J. Am.
Chem. Soc. 2004, 126, 5378-7379). An absorption system in the 10,000 cm !1
region, called band I by Solomon, is assigned to the (xy)6(x 2 !y 2 ) transition in
the ferryl spectrum. What is the electronic configuration of the excited state
formed by this transition What is the value of S (the spin quantum number)
for this excited state The energies of the transitions associated with bands I
and II are at much lower energies than the corresponding transitions in d 1
metal-oxo complexes such as [L 5 VO] 2+ and [L 5 CrO] 3+ . How does Solomon
account for these differences
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2. In 1993, Wilkinson and Hursthouse reported
(Polyhedron, 1993, 12, 2009-2012) the preparation
and X-ray crystal structure of Ir(O)(mes) 3 (mes =
mesityl, 2,4,6-trimethylphenyl), a complex that lies
beyond the oxo wall. The drawing to the right was
extracted from this paper.
Part 1:
Construct an MO diagram for C 3v Ir(O)(mes) 3 using the following orbitals: five
metal 5d orbitals, one set of three ligand F orbitals, and the oxo 2pF + two 2pB
orbitals.
Part 2:
Using your MO diagram, fill in the d electrons and predict the ground-state
electronic configuration. With this prediction, is the metal-oxo bond order shown
above correct Why or why not Do you think that a complex of the form
[Ir(O)(mes) 3 ] 2! could exist Why or why not
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3. The 4K single crystal polarized
electronic absorption spectrum of the
tetragonal molybdenyl ion in
(Ph 4 As)[MoOCl 4 ] is shown to the right.
Part 1:
a. Draw the molecular structure of
the [MoOCl 4 ] ! ion, determine the
oxidation state of the Mo center
and its d-electron count.
b. Construct an LF diagram for
[MoOCl 4 ] ! using the following
orbitals: five Mo 4d orbitals, four
Cl ! F orbitals, eight Cl ! B orbitals
and the oxo F + 2B orbitals.
Give the term symbol for the
ground electronic state.
c. On the basis of your LF diagram, assign the absorption bands with maxima at
~640 and ~430 nm to specific electronic transitions (give the electronic
configurations and state designations for both excited states).
Part 2:
The [MoOCl 4 ] ! ion has 12 normal modes of vibration with the following
symmetries and frequencies (< refers to a stretching mode; B and * refer to
deformation or bending modes):
vibration cm !1
a 1 :

a. On the basis of your assignment of the lower energy electronic absorption
band, in which vibrational mode(s) would you expect to see fine structure
Can you explain the fine structure that appears in the lower energy band
b. An enlarged view of the higher energy band appears at the bottom of the
page. Examine the vibrational fine structure in this band and assign it to a
ground-state vibrational mode. Discuss whether a distortion in this mode is
consistent with the assignment of the electronic transition.
c. Perform a Franck-Condon analysis of the vibrational fine structure of the
higher energy absorption band. What S HR -value gives the best fit to the
observed spectrum If the force constant for the distorting mode is 1.91
mdyne/Å, give the magnitude of the distortion in the normal mode ()Q). Use
group theory to define the normal mode in terms of bond stretching
coordinates to estimate the magnitude of the distortion in the individual
bonds.
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