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Terms to know
Tellurium
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Symbol: Te
Atomic Number: 52
Atomic weight: 127.60
GROUP: 16 the Chalcogens
[Kr].4d10.5s2.5p4
Melting point [/K]: 722.66
Boiling point [/K]: 1261
solid at 298 K
Colour: silvery lustrous grey
Oxidation numbers: 2,4,6
History
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Ligand: A Lewis base that bonds to a metal ion to form a complex ion
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Lewis Base: A species that can form a covalent bond by donating an
electron pair
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Lewis Acid: A species that can form a covalent bond by accepting an
electron pair
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Trigonal Bipyriamidal: Five atoms (or four and a lone electron pair) are
bonded to a central atom
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Octahedral: The geometry of a molecule in which six vertices or a
regular octahedron with the central atom at the centre
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Dimer: a molecule formed by the joining together of two identical
molecules
Discovered in 1783 by Franz Joseph Muller von Reichenstein in Romainia. It was named by M. Klanroth
The origin of its name: From the Latin word "tellus" meaning "earth“
Uses
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semiconductors
alloying with cast iron, copper and stainless steel
addition to lead to prevent corrosion
Ceramics
Tinting Glass
Synthesis and Crystal structure of the
monomeric organotellurium(IV)
trihalides: trans-2-ethoxy-cyclohexyltellurium(IV),
trichloro,(2-chlorobicyclo[2.2.1]hept-7yl)-λ4-tellurane,
and
mesityltellurium(IV) tribromide
Focus of the Article
• To FIND the conformation of three
different organotellurium trihalides
compounds
• To COMPARE the conformation with that
predicted by VSEPR
• To EXPLAIN why and when deviations
from VSEPR theory occur and how to
avoid them
By Dainis Dakternieks, Jenny O’Connell, Edward R.T. Tiekink
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Organometallic Synthesis Of
Tellurium
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Organometallic compounds contain carbon-metallic bonds.
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Some more familiar Organometallic compounds are the
organolithium and organomagnesium compounds (Grignard
reagents)
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Tellurium is capable of forming organometallic compounds
because of its’ ability to act as a Lewis acid
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Three different organotellurium compounds have been
synthesis and their molecular and crystal structure has been
determined through crystallography and compared with the
predicted VSEPR structures.
Not All Organotellurium compounds have
Trigonal bipyramidal structure
The most common organometallics are those with the
molecular formula R2TeX2 and RTeX3
R=organic group
X= Halide (Br, Cl)
R2TeX2 has the predicted structure trigonal bipyrimidal
RTeX3 have been found to have octahedral geometry due
to intermolecular and intramolecular attractions.
The Expected Conformation
• Tellurium like other atoms in the 16th group
has six valence electrons.
Organotellurium
Trihalides
RTeX3
• Tellurium is capable of bonding to four ligands
Intermolecular secondary
bonding interactions
• The tellurium atom has four of it’s six valence
electrons participating in bonds, leaving one
lone pair.
• VSEPR would give the structure as trigonal
bipyramidal with the lone pair of electrons in
the equatorial position.
Oligomeric or polymeric
Octahedral geometries
Secondary intramolecular interactions
monomeric
Pseudo octahedral
Trigonal bipyramidal
Geometry
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The synthesis
• The authors of the article prepared three
different organotellurium trihalides compounds
• 1) Trans-2-ethoxy-cyclohexyltellurium(IV)
trichloride
Characterization
• All were characterized using H-NMR as
well as crystallography
• the crystallography was preformed at room
temperature and yielded the bond lengths
of the compounds as well as the angles.
• 2) Trichloro(2-chlorobicyclo[2.2.1]-hept-7-yl)-λ4tellurane
• 3) Mesityltellurium(IV) tribromide
1) Refluxing Cl4Te in dried ethanol with
cyclohexene for 2hrs, filter and recrystallize with
petroleum spirits.
2) Dissolve norbornylene and Cl4Te and CCl4,reflux
for 3hrs, recrystallize from hot CCl4.
3) Make a solution of Br , CH2Cl2 and dimesityl
ditelluride, when reaction is complete rotovap off
excess Br and CH2Cl2.
Results
It was found that two of the compounds
synthesized (1 and 2) had very similar
geometries due to intramolecular interactions.
The geometry was found to be typical of
organotellurium trihalide molecules
Compound 3 was to have a structure different from
the first two compounds because of a lack of
intramolecular interactions.
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The Compounds
Compound
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C8H15Cl3O
Te
361.2 g/mol
Molecular
Formula
Molecular
mass
Crystal size 0.10x0.16x
0.32 mm
Density
1.866
g/cm3
Compound Compound
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3
C7H10Cl4Te C9H11Br3Te
363.6 g/mol 486.5 g/mol
0.03x0.15x
0.30 mm
2.227
g/cm3
0.03x0.03x
0.08 mm
2.497
g/cm3
• The S,S, isomer is only capable of forming
loosely attracted dimers between the
tellurium atom and the oxygen atom.
• The difference in length is caused by the
orientation of the lone pair of electrons out
toward one of the chlorides causing the
bond length in the S,S isomer to length.
• The other two bonds are not effected by
the arrangement of the lone pair and thus
are shorter then the bond lengths on the
R,R, isomer
Trans-2-ethoxy-cyclohexyltellurium(IV) trichloride
• The geometry of compound 1 was found to be
somewhere between Trigonal bipyramidal and octahedral
as suggested earlier
• Has two isomers an S,S isomer and an R,R isomer
• The major difference between these two isomers noted in
the article was the length of the Te---Cl bonds.
• The explanation for this arises when the ability of the
molecule to form a dimer or a chains examined.
• It was found that the R,R isomer can form a chain with
intermolecular interactions between the Tellurium atom
and the chlorides on other molecules.
• The formation of a chain lengths two of the Te—Cl
bonds as the Cl is pulled toward the Te atom on the other
molecule
Trichloro(2-chlorobicyclo[2.2.1]-hept-7-yl)-λ4-tellurane
Found to have similar geometry to compound
1Somewhere between trigonal bipyramidal and
octahedral
The major intramolecular interaction is between the
Te atom and the chloride atom on the norbonyl
group. Which forms a quasi bond
Like compound 1 compound two is capable
of forming a loose dimer between two molecules
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Conclusions
Mesityltellurium(IV) tribromide
• In this final compound there are no significant
inter- or intramolecular interactions
• The conformation of the molecule matches that
predicted by VSEPR theory because of the lack
of interactions
• This anomaly for organotellurium trihalides
arises because of the halide group bonded to
the tellurium
• As well as the lack of electronegative species on
the organic group
• The conclusion in the article primarily surround the fact that
the it was found that the Te atom prefers a pseudo-octahedral
conformation (5 bonds and one lone pair).
• This can be achieve through inter or intramolecular
interactions
• This tendency can be weakened by the use of bulky organic
groups like the one used in compound three, however some
intermolecular interactions still may occur
• The use of a halide that will weaken the Lewis acidity of the
tellurium atom will further prevent intermolecular interaction,
leading to the formation of molecular species with
conformations consistent with the VSEPR theory
Why??
• The Br group on the Tellurium reduces the
Tellurium’s Lewis acidity making it less
willing to interact with Lewis bases
• The molecule is capable of forming very
loosely associated dimers which cause
some deviation in the Te---Br bond
lengths.
• Organometallic compounds are particularly
important to the formation of new bonds.
• Finding new compounds that can participate in
similar reactions is very important
• Especially if we are able to direct the
stereochemistry of the new compounds being
formed.
• This would be useful especially for
pharmaceutical research
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