Inorganic Chemistry DTU Laboratory Report

Inorganic Chemistry DTU Laboratory Report

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Inorganic Chemistry DTU Laboratory Report

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Inorganic Chemistry DTU Laboratory Report

Experiment 1

Introduction

Organic molecules are commonly diamagnetic while the transition metals complexes tend to be paramagnetic. According to Hund’s rule, electrons fill the orbitals for the orbitals with similar energy to maximize the unpaired electrons before their pairing. Therefore, knowing the number of the unpaired electrons in a metal complex helps in understanding their oxidation states and geometry; properties which have a significant impact on their reactivity and spectroscopy. Magnetic susceptibility is among the many ways used in measuring the number of unpaired electrons; this is based on the magnetization of the material in an applied magnetic field. The unpaired electrons are usually attracted to the magnetic field with the attraction being proportionate to the magnetic field strength. The purpose of this experiment is to calculate the unpaired electrons in a metal complex and explore the relationship between temperature and paramagnetism.

Inorganic Chemistry DTU Laboratory Report

Summary of Results and Structures

The results indicated that the number of unpaired electrons could be calculated proportionally to the strength of magnetic field attraction. In terms of the effect of the ligands on the geometry, the study found that ligands affected the metal coordination geometry and properties. According to Poklonski et al. (2021), the sterically demanding ligands in the metal centre limit the ability of the other ligands to bind compared to the one binding through the small excited groups. Also, the geometric coordination of the metals is strongly affected by the size of the central ion. The ligands may either donate a single pair of electrons or two pairs and this affects the ability of metals to form complexes, orientation and their stability.

Answer to the Series of Discussion Questions

Paramagnetic material becomes good material materials when placed in a strong magnetic field. According to Curie’s law, the magnetization of paramagnetic materials is inversely proportional to temperature (Poklonski et al., 2021). Curie’s law is expressed as:

M= C(B/T)

Where, C= the curie’s constant, T is the temperature in kelvin and B is the applied magnetic field.

Conclusion

The results were consistent with the theoretical definitions. The temperature affected the paramagnetism negatively.

References

  1. A. Poklonski, A. N. Dzeraviaha, S. A. Vyrko, A. G. Zabrodskii, A. I. Veinger, and P. V. Semenikhin, AIP Advances11, 2021, 5, 055016.

Experiment 2

Introduction

The CO is an L-type ligand and thus does not affect the oxidation state of the centre of the metal on binding, but, increases the electron could by two. The two carbonyl ligand bonding interactions include the ligand-to-metal n → dσ and metal-to-ligand. The frequency of the CO stretching increases as one moves from left to right across the periodic table. Furthermore, the back bonding orbital interactions worsen with the increase in the electronegative late transition metals Tuschel, David. The purpose of the experiment was to identify the chemical environment and assign the NMR spectrum. Also, the experiment aimed at determining the relationship between the CO ligand stretching frequencies and the electron density of the metal centre.

Summary of Results and Structures

The group theory helps in predicting the relationship between the symmetries in the normal modes and the IR C-O vibrational modes in a molecule. The strength of the IR depends on the vibrational transitions dipole moment.

Answer to the Series of Discussion Questions

The CO ligand stretching frequencies increases with the electron density of a metal centre. The complexed CO has a lower frequency compared to the free CO. The frequencies identified on the results output for the Mo(CO)6 during the 240 minutes reaction were 1980.93cm-1, 1887.32cm-1, and 1750.61cm-1. The results indicated that electron density reduces the CO stretching frequency because of the enhanced back bonding. Also, the IR stretching modes increase with symmetry (Willock 2019).

Conclusion

The findings in the experiment show that CO stretching frequency varied with the electron density in the metal centre.

Reference

Molecular symmetry. Willock, D. John Wiley & Sons, 2009.

T, David. Spectroscopy, 2014, 29.2, 14.

Experiment 3

Introduction

The J-coupling in the NMR spectroscopy define the relative distances and the angles of the chemical bonds; therefore, it determines the interactions between the pairs of the proton. According to Chalmers, et al, the coupling pathway in the metal complex occurs through the metal atoms. Besides, the magnitude of the J-coupling reduces to 26-117 Hz in the square-planar complexes. The purpose of the experiment was to determine the consequences of the partial abundance in the NMR spectra.

Summary of Results and Structures

The metal coordination geometry depends on many factors including the oxidation state and size the metal cation. The interaction between the electrons at the metal centre occurs through coupling of the magnetic fields that eventually generates the orbital motion. The energy is determined by the quantum numbers.

Answer to the Series of Discussion Questions

The NMR spectra depends on the electron density and the electronegativity of the surrounding groups. The fact that only a small percentage of the carbon atoms contribute to the magnetic signal implies that the electron acquisition depends on the partial abundance. Having high partial abundance increases the signal generation in the NMR spectra.

Conclusion

The partial abundance increases the signalling in an NMR spectra.

Reference

  1. Jardón-Álvarez, Reuveni, G., Harchol, A. and Leskes, M, The journal of physical chemistry letters, 2020, 11.14, 5439-5445.

Experiment 4

Introduction

The electron transition occurs when the atoms or a molecule absorbs the electromagnetic radiation. The molar absorptivity indicates the magnitude of the absorbing chromophores. The molar absorptivity is calculated as ϵ=A/cl, where A is the sample absorbance, c is the concentration in moles per litre and 1 cm is the length of the light path. The purpose of the experiment was to determine the relationship between light absorption at different wavelengths.

Summary of the Results

Complex Mass of powdered complex used/g Mr Solvent used The concentration of prepared solution/moldm3
[Cr(H2O)6](NO3)3.3H2O 0.4088   Water 0.001
[Cr(en)3]Cl3 0.2668   Water 0.001
[Cr(H2O)4Cl2].Cl.2H2O 0.4984   Water 0.001
Cr(acac)3 0.3484   Toluene 0.001

 

Fig1: The diagram indicating the absorption wavelength for the Cr(acac)3 sample.

Answer to the Series of Discussion Questions

The d-d transition takes place between the metal orbitals while charge transfer takes place between a ligand and metal orbitals. The UV-Vis selection rule states that the S to S or T to T transitions are allowed. However, the S to T or T to S transition are not allowed. Finally, the transition metals tend to be less reactive and this means that the complexes can be easily transformed.

Conclusion

The transition metals form weak complexes that can be easily altered because they are less reactive.

References

B A., Chalmers. Inorganic Chemistry, 2018, 57.6, 3387-3398.

 

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