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A. M.
Introspection 3
Metal complexes are so complicated, yet they are so interesting. So far in class we
have looked at these complexes in a variety of ways, specifically from the view of acid/base
and crystal field theory. They are extremely different and yet have an enormous overlap,
the metals themselves.
First and foremost, we applied the idea of acid base chemistry to metal complexes.
The metals could act as Lewis Acids and could accept electron transfer from the
surrounding ligands. Then, we had to determine which complexes were likely to form and
the strength or stability of the said complex. So, we memorized that hard bases go with
hard acids and soft bases go with soft bases. Although effective, the memorization became
more of a looking up in a table. The information stopped there. We knew that like bonded
with like, but we knew absolutely nothing about the arrangement of electrons or the
preferred geometry.
This is where crystal field theory enters. I have to say that I adore crystal field
theory to a large extent. The information we have been able to abstract from it has been
immense and the concepts have been interesting and relevant. For example, why is one
metal complex blue and another complex with the same metal green? Just turn to crystal
field theory. This theory is comprehensive and insightful. It can give you information
regarding the position of the electrons, the splitting of energy levels in relation to the point
group, and the magnetism. At first the theory was a big overwhelming. Honestly, it’s still
overwhelming. However, by dissecting it piece by piece, rereading the notes and
supplementing with the sections in the book, it began to come together for me. I began to
understand why something was blue rather than green or why something was
paramagnetic rather than diamagnetic. I know that there is still a great deal of learning to
be done regarding metals and crystal field theory, but I am intrigued.
This section was filled with a number of group activities. Although I am not normally
a fan of group activities, these proved to be perfect for enhancing the understanding of the
material and I was left wanting more, not less. The first activity had us uncover how the
point group of a molecule might affect the splitting of orbitals and the arrangement of the
electrons. My group was given a complex of Ni with two Cl ions and four connected
nitrogen groups. It was complicated. It was daunting. Nonetheless, the results were
interesting. We struggled together, as a group, with the ideas about which orbitals would
be increasing in energy and which decreasing. We thoughtfully discussed how the one
pointing directly toward the nitrogen groups would have to be higher than the one pointing
toward the chloride groups. It all came down to field strength. By working through these
ideas together, we were able to strategically decide the placement of the electrons. It was
helpful to also see worked out examples of other point groups from other groups on the
board. After working through a specific example on our own, it was much easier to
properly understand why z2 was higher in energy for D3h, but x2-y2 was higher in energy
for C4v and D4h. All in all, it was a successful activity. The same can be said for the color
(ligand field strength) exercise. By working through each set of complexes and developing
the patterns ourselves, I believe we will have a greater appreciation for the ordered list of
complexes. Although crystal field theory can be difficult, I can honestly say that I prefer it to
acid/base theories of metals.