| RESEARCH
RATIONALE |
There are certain transition metal compounds that exhibit
two separate spin characters, High Spin (HS) and Low Spin (LS).
Molecules that exhibit this property are utilized in information
processing, specifically those of memory devices. The purpose of
this research is to synthesize an organometallic polymer from iron and
gold which has such
properties. |
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| Research Background |
Organometallic compounds consist of organic (carbon-containing)
compounds covalently bonded to a metal
ion, typically identified as coordination
compounds. These complexes can be thought of as Lewis Acid-Base
adducts, where the metal ion, commonly a transition
metal, acts as a Lewis acid by accepting electrons from the organic
compounds (Lewis Base). Hemoglobin,
chlorophyll, and
vitamin B-12 coenzymes are common examples of organometallic
compounds where they contain an Iron, a Magnesium, and a Cobalt ion
respectively. The attached organic groups are usually identified as
Ligands and with the central atom they produce a coordination sphere,
similar to that of the heme
complex in a hemoglobin
molecule. Note the coordination number for the Iron in the heme
is 4 due to the fact that it is bonded to 4 ligands. |
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The transition metals are those elements who
characteristically fill d-type (n-1) orbitals, leaving the
outermost s orbital (ns) and the first inner d orbital (n-1)
as the valence shells. Orbitals that share the same first 2 quantum
numbers (n & l) are
commonly described as being degenerate, having the same energy.
Bonding between the metal ion and a ligand is an example of a coordinate
covalent bond where the ligand donates both electrons. The
bond occurs between an atomic/molecular orbital of the ligand and a
hybridized orbital consisting of the ns & nd orbitals.
These hybridized orbitals contain no electrons belonging to metal atom.
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Properties of the transition metal
complexes arise from the electrons not involved in the covalent bonds, but
those of the (n-1) d-orbitals. Crystal field theory suggests
that the ligands can alter the degeneracy of the (n-1) d-orbitals
and elevate the energy of 2 of the orbitals (eg
orbitals) from the remaining 3 (t2g)
orbitals. This splitting creates an energy difference between them,
identified as crystal field splitting. This splitting of orbitals is the basis for
many of the transition metal properties such as color and magnetism. Color
of the transition metal complexes arise from electrons as they fall
from the eg orbitals to the t2g orbitals and
magnetism is created by unpaired electrons in these orbitals. High spin and low spin in
the metal ions is due to the number of unpaired electrons. High spin
is defined as having unpaired electrons in both the eg and t2g
orbitals, while low spin is unpaired electrons in only the t2g
orbitals. Typically, light or heat can
promote the activation of a electron from a ground state (t2g
orbitals) to an excited state (eg orbitals). |
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Jaeson and Dr. Rajca are hoping to
capitalize on the properties of iron & gold to produce new
organometallic polymers which can oscillate between the high spin and low
spin states, thus creating the capability to store information such as
that of a binary system. |
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| Research
Background Links |
Topic |
Site
Link |
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Review of chemical bonding |
http://www.phs.uiuc.edu/~pearman/101Online/notes/Bonding/bonding.html |
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Topics on Coordinate Chemistry. Excellent |
http://wwwchem.uwimona.edu.jm:1104/courses/IC10Kout.html |
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Reactions that involve
transformations of organometallic compounds. For the advanced
reader. |
http://www.chem.ox.ac.uk/icl/dermot/organomet/ |
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Shapes of organometallic complexes
with 3D renderings. |
http://www.chem.ox.ac.uk/mom/clusters/clusters.html# |
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Lots of great information of
organometallics. For the advanced reader. |
http://www.ilpi.com/organomet/index.chtml |
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Uses of organometallics in the
formation of alcohols and ethers. |
http://edie.cprost.sfu.ca/~rhlogan/outlin11.html |
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CD technology |
http://ee.wpi.edu/infoeng/textbook/node176.html |
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Explanations of Molecular Orbital
Theory. For the advanced reader. |
http://www.chem.orst.edu/ch411/scmoth.htm |
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Great link to transition metal
properties. |
http://library.advanced.org/3659/pertable/trametal.html |
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Information about coordination
compounds |
http://netaccess.on.ca/~dbc/cic_hamilton/coord.html |
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http://www.chem.ualberta.ca/~plambeck/che/struct/s0608.htm |
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