Bad Example of Report 3

OVERALL: 54/100
Presentation: 4/10
Chelating Ligands on a Metal complex
Comment [YA1]: Vague.
Joffrey Baratheon, Chemistry 151 L
Section: Th:2:00pm-6:00pm
TA: Yashar Abdollahian
Abstract:
Comment [YA2]: 7/10
This paper will reports the synthesis and characterization of Vanadium (IV)
Oxy(acetylacetone) and how a ligand bonds with this Vanadium in this complex. The product is
obtained by first oxidizing the reagent Vanadium(V) oxide and then and acid base reaction takes
Comment [YA3]: Vague.
place with Acetylacetone to obtain the final Vanadium (IV) Oxy(acetylacetone) complex. The
whole reaction must take place in a fume hood since the compound emits and strong odorous
smell. The reaction started as a sort of dark green brownish color and eventually led to blue
crystals, which is the color of the actual product meaning a successful synthesis. The amount
weighed turned out to be 11.49g for a percent yield of (157% yield), which is a too much product
which implies some impurities may be present in the final yield. Noticeable IR peaks are at
998cm- for V=O stretching and 1543cm- for C=O stretching.
Introduction:
The synthesis of Vanadium (IV) Oxy(acetylacetone) wais possible due to the fact presence
of a chelating agent, which binds to the center of the metal ion. Yet before this is accomplished,
the Vanadium (V) Oxide must be reduced from a V+5 to a V+4. The simple mechanism, which
explains this, would be the oxidation-reduction reaction. Although this isn’t the main purpose of
the lab, iIt is important to note since it turns the Vanadium(V) into its most stable configuration of
Vanadium(IV)1. Although the in this lab the Vanadium4+ ion is bonded to an Oxygen and a sulfate
Comment [YA4]: awkward wording
anion in the intermediate phase of the reaction. Hence it is important to reduce the Vanadium5+
Comment [YA5]: awkward wording.
ion into a more stable one, which can be used to understand chelation better.
The idea of chelation means or it describes the way particle ligands bond to a central metal
ion, in our case Vandium4+. Chelation occurs simply because it is a more stable confirmation as
opposed to regular bonding with the central atom. Figure 1 shows in more detailed view as to
Comment [YA6]: vague
how the chelating reagent ligand bonds with the central metal ion in order to form a ring. This
only occurs when the ligand being bindedinteracting with the metal ion has two covalent bonds
Comment [YA7]: they both aren’t covalent.
with the ion. The ligand must also be a polydentate ligand, which simply refers to having two
atoms bonding with one metal ion. Hence the formation of the ring as seen in Figure 1. The two
Comment [YA8]: Not quite the correct
explanation
binding atoms on the polydentate ligand form a ring around the metal ion. In the case of the lab
Comment [YA9]: You already said it.
the polydentate ligand is Acetylacetonate which is added in the second step of the reaction.
Although the bond is theoretically a covalent bond with one oxygen atom, the other oxygen atom
bond is a dative bond. Covalent bond just means that the ligand atom shares one electron with the
Comment [YA10]: Awkward wording
metal ion in order to form a covalent bond. Whereas a dative bond, one atom, namely the second
Oxygen ligand supplies both the electrons from the ligand to form the dative bond. Although
theoretically these should be the two bonds present, the complex is delocalized, which just means
a double bond is spread out about the ring. The reason for this is that it is just more stable to have
a double bond spread out in a ring since it brings the most stability. The final structure of the
product can be seen in Figure 2 where the correct delocalized structure is seen.
Comment [YA11]: It’s not so much that the
complex is delocalized, as it is the electrons
that are delocalized.
Comment [YA12]: you should type out the figure
captions in the future.
The structure of the product in the lab can be easily identified using Valence shell electron
pair repulsion theory (VSEPR theory). This acronym stands for Valence shell electron pair
repulsion theory and it basically guesses the structure of any complex. It uses information based
on the central atom and the molecules bonded around it to elucidate the structure geometry. The
theory takes into account the free electron pairs as well. There are many different ways of actually
classifying molecule structures but a simple way is to count the number of atoms bonded to the
central atom. Then you take into account the number of unbounded pairs of electrons to that
Comment [YA13]: colloquial
central atom. In the end VSEPR gives you an equation of MXE where M is the central atom, X is
Comment [YA14]: it doesn’t give you an
equation.
the number of atoms bonded to it, and E is the number of paired electrons. Depending on which
formula the VSEPR theory predicts, a certain structure fits it and that is how VSEPR helps predict
the shape of a molecule.
Comment [YA15]: What?
Although the lab studies only the effect of chelating and understanding how that works,
the Vanadium(IV)oxy(acetylacetonate) complex has uses outside of the lab. The VO2+ ion is the
Comment [YA16]: You need to find applications
of the final product.
most common of the transition metal oxy-cations2. It is also important because of its simple
magnetic and spectral properties. It in simple terms can be used to identify and even prove many
theories such as Crystal Field and Molecular orbital theory. The complex has other uses to like
being coupled with t-butyl-hydroperoxide in order to convert thiols into disulfides3. The purpose
Comment [YA17]: You don’t want simple terms.
You need to explain fully.
of the VO2+ ion in the reaction stated above is too regenerate the oxidant used to convert thiols
into disulfides. This is important to do because the ion is relatively cheap to make and disulfides
are important because in the industry they can be used to volcanize agents for rubber. Thus this
Comment [YA18]: Citation/?
ion will facilitate the process. This is why the ion of VO2+ is important outside of the lab.
Experimental:
Comment [YA19]: 4/5
Instrument name and model number?
Procedure for this lab can be found on the Chemistry 151L handout4. The lab handout
does not say to do IR but IR was ran on the molecule.
Comment [YA20]: Awkward wording.
Results and Discussion:
Comment [YA21]: 14/35
Role of ethanol?
Deprotonation of acac?
Free vs bound acac comparison?
The product obtained at the end wais Vanadium (IV) Oxy(acetylacetone) and the yield
was 157%. This excess of yield might be because of water still in the sample contributing to the
mass of the product weighed or some solvent still left un-evaporated in the solution. To fix this
error simply allow the solution to evaporate fully with just a tiny amount of solvent left yet this is
Comment [YA22]: Wasn’t a factor because it was
recrystallized in chloroform, which is very
volatile and would be minimal in mass
increase. You most likely had unreacted
vanadium oxide in your product.
hard to accomplish in such a small scale laboratory. The colors in the solution to begin with were
Comment [YA23]: Colloquial.
a dark green color when initially only Vanadium(V) Oxide was present. As the reaction
Comment [YA24]: It was yellow
proceeded and acetylacetone was added the solution began to turn a blue-ish color indicating the
formation of the Vanadyl Acetylacetonate.
The molecular shape of this compound is closely related too trigonal bipyramidal. This is
because there are 5 bonded atoms attached to the center atom, which gives the equation MX5 that
correlates to a trigonal bipyramidal structure. This can be seen when looking at the molecules
structure in figure two where there are 5 atoms bonded to the center atom. As for the IR peaks,
Comment [YA25]: No. It’s square planar because
the chelating ligands prevent it from forming
trigonal bipyramidal.
only two matter. The peak at the V=O bond, which is theoretically at 985cm- and the C=O bond
peak at 1760-1665cm-. The peaks in Figure 3 show peaks at 998cm- correspond to V=O
stretching which is fairly close to the theoretical and a peak at 1543cm- which corresponds to the
Comment [YA26]: Theoretical or experimental?
C=O bond. Although the C=O bond is quite far away from the actual peak, V=O is close to it
which at least says that the compound is of oxidation number of 4+. Whether there is a carbon
oxygen double bond present is unknown since the peaks are to spread out. So the IR cannot
conclude there is a ring around the metal ion.
Figure 3: IR of Vanadyl Acetylacetonate
The product obtained in the lab is formally known by its IUPAC name, which is just a
formal way of identifying a molecule. Its IUPAC name is oxobis(2,4pentanedionato)vanadium(IV). The correct balanced equation for the whole experiment can be
seen in Figure 4.
Comment [YA27]: Missing steps.
Conclusion:
Comment [YA28]: 7/10
In conclusion the experiment was a success despite the draw back of not being able to
conclude if the product was Vanadium (IV) Oxy(acetylacetone) with just half correct
information on the IR. Though the lab did teach showthat that certain ligands would form a ring
Comment [YA29]: What about bound vs. free
acac IR comparison?
around a metal ion if given the right conditions. Such conditions include that the ligand had to be
Comment [YA30]: Sentence fragment.
polydentate. Though theThe color of the compound does say that the reaction went to completion
since the final product wais supposed to be blue crystals. The IR peak at 998cm- further proves
by a little that indeed there was a complex in the crystals that resembled that of Vanadium (IV)
Oxy(acetylacetone) since its structure has a V=O. So for the most part the final product obtained
Comment [YA31]: Awkward wording.
Comment [YA32]: colloquial
indeed was Vanadium (IV) Oxy(acetylacetone) according to the color and one IR peak.
References:
1. Greenwood, Norman,; Earnshaw, Alan,; Chemistry of the Elements:Oxford’Pergamon
Press,p.1157
2. Bernal, Ivan,; Rieger,H Philip,; Solvent effects on the optical and electron spin resonance
spectra of Vandyl acetylacetonate:August 3,1963,pp.256-260
Comment [YA33]: this would never be acceptable
in a real publication. You have to consider that
this class is preparing you for scientific writing
in the future.
Comment [YA34]: 8/15
not enough references.
3. Sadagopan, Raghavan,; Suju, Joseph:Catalytic oxidation of thiols to disulfides:Synthetic
Communications,Volume 31,issue10,2001,pg.1477-1480
4. Oliver, S. Expt 3. Synthesis of Vanadium (IV) Oxy(acetylacetonate) 151L, Spring 2013
Appendix: