Download [E]ven the most difficult problems in chemical experimentation can

Ch. 154a
Problem Set 1
Due 1/17/17
[E]ven the most difficult problems in
chemical experimentation can be solved
by the hands of a master.
|Adolf von Baeyer
This will make him famous, even though
he has no talent for chemistry.
|Adolf von Baeyer
The first problem set for this course is meant to exercise your ability to account for the stability or
instability of inorganic/organometallic molecules.
Problem 1
A) As we discussed in class, one can rationalize a great deal in organometallic chemistry based upon
the simple knowledge that stable electronic structures result when the occupation of bonding/non-bonding
orbitals is maximized and the occupation of destabilized (i.e. anti-bonding) orbitals is minimized. For a
ligand type and metal of your choosing, demonstrate with a qualitative MO diagram the origin behind what
is commonly called the \18-electron rule" and the \16-electron rule" for octahedral and square planar type
structures, respectively.
B) Explain why Cr(NO)4 is an electronically stable molecule, and propose an oxidation state and a
valence number for the Cr center.
1
Ch. 154a
Problem Set 1
Due 1/17/17
Problem 2
For each of the molecules shown below (some of which are hypothetical):
(a) Provide an electron count, mentioning whether there is any ambiguity and assigning what you think is
the best count (this is not totally subjective, so be careful). For some ligands, electron counting can
change depending on the ligand conformation (e.g., linear versus bent NO). If there is any ambiguity
as to the structure and thus the count, sketch the one you think leads to the most stable structure and
count.
(b) Assign a formal oxidation state to each metal.
(c) Assign a valence number to each metal
(d) If there is more than one metal, state whether your valence electron count suggests the presence of
direct M-M bonding, and if so the bond order.
(e) Mention whether you think the molecule might be electronically stable.
2
Ch. 154a
Problem Set 1
Due 1/17/17
Problem 3
What is the maximum reasonable M-M bond order in each molecule below?
A)
B)
M
M
Co
Co
M = V, Cr, Mn
Problem 4
Create valence electron counting problems of your own. Find four literature TM compounds published in
2013 or later that you think provide an interesting example for an electron counting problem/discussion,
and provide a valence electron count, a valence number assignment, and an oxidation number
assignment for each metal in the complex.
3