File:MO 42 diagram0138.jpg

2019-05-24T13:00:14Z

Saa2417:

File:MO 42 0138.JPG

2019-05-24T12:58:10Z

Saa2417: Saa2417 uploaded a new version of File:MO 42 0138.JPG

Rep:MOD:01381641

2019-05-24T12:56:32Z

Saa2417: /* MO 54 */

=BH3=

'''B3LYP/6-31G(d,p)'''

[[File:BH3_Summary0138.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000009 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000034 0.001800 YES
RMS Displacement 0.000017 0.001200 YES

</pre>

[[File:SHAZEEN_BH3_FREQ.LOG]]

<pre>

Low frequencies --- -2.2126 -1.0751 -0.0054 2.2359 10.2633 10.3194
Low frequencies --- 1162.9860 1213.1757 1213.1784

</pre>

<jmol><jmolApplet>
<title>optimised BH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>SA0138_BH3_OPT_631G.LOG</uploadedFileContents>
</jmolApplet></jmol>

====Vibrational spectrum for BH3====
{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2''
|Yes
|out-of-plane bend
|-
|1213
|14
|E'
|Very slight
|bend
|-
|1213
|14
|E'
|Very slight
|bend
|-
|2582
|0
|A1'
|No
|symmetric stretch
|-
|2715
|126
|E'
|Yes
|asymmetric stretch
|-
|2715
|126
|E'
|Yes
|asymmetric stretch
|}

[[File:BH3_Spectrum0138.PNG]]

Only 3 peaks are see in the spectrum despite there being 6 vibrations as shown in the vibrational data above. There are two sets of degenerate vibrations (same energy), 1213 and 2715 cm-1 which only appear once in the spectrum. Additionally, for a vibration to be IR active, there must be a change in dipole moment. The vibration at 2592 cm-1 represents an symmetric stretch which means the change in dipole moment is zero so this is not observed in the IR spectrum.

[[File:BH3_LCAO_real0138.JPG]]
(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 21/05/19)

No significant differences are seen between the real and LCAO MOs which shows that qualitative MO theory is useful in predicting real MOs to a high level of accuracy. The real MOs show regions of electron density and nodes in areas predicted by LCAO MOs.

=NH3=

'''B3LYP/6-31G(d,p)'''

[[File:NH3_Summary0138.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000005 0.000450 YES
RMS Force 0.000003 0.000300 YES
Maximum Displacement 0.000013 0.001800 YES
RMS Displacement 0.000007 0.001200 YES

</pre>

[[File:SA01381_NH3_FREQ_NEW.LOG ‎]]

<jmol><jmolApplet>
<title>optimised NH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>0138_NH3_OPT_NEW.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre>

Low frequencies --- -11.1928 -11.1561 -0.0035 0.0252 0.1457 25.7625
Low frequencies --- 1089.6648 1694.1744 1694.1747

</pre>

=NH3BH3=

'''B3LYP/6-31G(d,p)'''

[[File:Nh3Bh3_Summary0138.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000233 0.000450 YES
RMS Force 0.000083 0.000300 YES
Maximum Displacement 0.000981 0.001800 YES
RMS Displacement 0.000370 0.001200 YES

</pre>

[[File:SA0138_NH3BH3_FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised NH3BH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>SA0138_NH3BH3_OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre>

Low frequencies --- -0.0675 -0.0573 -0.0065 16.7107 16.7164 41.6318
Low frequencies --- 265.4937 634.5843 640.0012

</pre>

=Calculating Association Energy=

E(NH3)= -56.55776863 a.u.
E(BH3)= -26.61532364 a.u.
E(NH3BH3)= -83.22468856 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
ΔE=(-83.22468856)-[(-56.55776863)+(-26.61532364)]
ΔE = -0.05159629 a.u.

ΔE= -135 kJ/mol

This value shows that the B-N dative bond is weak (bond enthalpy = +135 kJ/mol) compared to other bond enthalpy values. [https://labs.chem.ucsb.edu/zakarian/armen/11---bonddissociationenergy.pdf] For example, the bond enthalpy of a C-C bond is approximately 350 kJ/mol. This is more than twice the calculated B-N dative bond.

=NI3=

[[File:NI3_summary_table01381.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000067 0.000450 YES
RMS Force 0.000044 0.000300 YES
Maximum Displacement 0.000486 0.001800 YES
RMS Displacement 0.000363 0.001200 YES

</pre>

[[File:NI3_OPTIMISATION+FREQ_NEW0138.LOG]]

<pre>

Low frequencies --- -12.7375 -12.7314 -6.2898 -0.0040 0.0188 0.0633
Low frequencies --- 101.0325 101.0332 147.4122

</pre>

==Investigating Metal Carbonyl Complexes==

====Prediction====
Going across the 3d complexes from Ti to Fe, the M-C bond length is expected to increase (weaker M-C bond). The C=O bond length is expected to decrease (i.e. stronger C=O bond) and therefore the C=O stretching frequency should increase. As you go from Ti-->Fe, the decreasing negative charge on the metal centre leads to contraction of the d orbitals and hence a less efficient overlap of M(dπ) with CO π*. This would result in a weaker M-C bond.

==='''[Ti(CO)6]2-'''===

[[File:Ti_complex0138_summary.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000118 0.000450 YES
RMS Force 0.000042 0.000300 YES
Maximum Displacement 0.000244 0.001800 YES
RMS Displacement 0.000096 0.001200 YES

</pre>

<pre>

Low frequencies --- -0.0003 0.0007 0.0008 14.2245 14.2245 14.2245
Low frequencies --- 30.7497 30.7497 30.7497

</pre>

[[File:TI_OPT+FREQ0138.LOG]]

<jmol><jmolApplet>
<title>optimised [V(CO)6]^1- molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>TI_OPT+FREQ0138.LOG</uploadedFileContents>
</jmolApplet></jmol>

==='''[V(CO)6]-'''===

[[File:V_complex0138_summary.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000070 0.000300 YES
Maximum Displacement 0.001210 0.001800 YES
RMS Displacement 0.000591 0.001200 YES

</pre>
<pre>

Low frequencies --- 0.0006 0.0007 0.0010 14.1311 14.1311 14.1311
Low frequencies --- 52.8916 52.8916 52.8916

</pre>

[[File:VANADIUM0138_OPT+FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised [V(CO)6]^1- molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>VANADIUM0138_OPT+FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

==='''[Cr(CO)6]'''===

[[File:Cr_complex0138_summary.JPG]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000160 0.000450 YES
RMS Force 0.000057 0.000300 YES
Maximum Displacement 0.000225 0.001800 YES
RMS Displacement 0.000084 0.001200 YES

</pre>

<pre>

Low frequencies --- -0.0014 -0.0008 -0.0007 10.8502 10.8502 10.8502
Low frequencies --- 66.4359 66.4359 66.4359

</pre>

[[File:CR0138_OPT+FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised [Cr(CO)6] molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>CR0138_OPT+FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

===Comparing Complexes===

====Calculations Data====

{| class="wikitable"
|+
|-
|M Complex || M-C Bond Length (Å) || Charge on M || C=O Stretching Frequency|| C=O Bond Length (Å)
|-
|Titanium
|2.047
|2-
|1855
|1.183
|-
|Vanadium
|1.954
|1-
|1969
|1.166
|-
|Chromium
|1.915
|0
|2087
|1.149
|-
|Manganese
|1.908
|1+
|2198
|1.136
|-
|Iron
|1.942
|2+
|2297
|1.125
|}

Mn and Fe Data taken from [https://wiki.ch.ic.ac.uk/wiki/index.php?title=SA_inorg_comp]

====Comparing M-C Bond length====

As you go from left to right, the M-C bond length decreases until Mn and then there is an increase from Mn to Fe. The observation from Ti-->Fe contradicts the initial prediction. However, the trend observed in the C=O bond lengths was as predicted before calculations. There was a decrease in the bond length (suggesting a stronger C=O bond) and stretching frequency. Thi

DISCUSS FE BOND ANOMALY correlation and exchange theory - too advanced
Fe 2+ charge causes contraction of the d orbitals, greater repulsion between the electrons (all spin paried) hence less efficient overlap with the CO, longer bond length

====Comparing C=O stretching frequencies====

The totally symmetric C=O vibrations for these complexes cannot be analysed as they are not IR active (zero intensity). This is because there is no change in dipole moment. For each of the complexes, these are listed below.

{| class="wikitable"
|+
|-
|M Complex || Symmetric C=O Stretching Frequency
|-
|Titanium
|1990
|-
|Vanadium
|2095
|-
|Chromium
|2189
|-
|Manganese
|2265
|-
|Iron
|2322
|}

====LCAOs vs real MOs for [Cr(CO)6]====

====='''MO 42'''=====

[[File:MO_43_diagram0138.jpg]][[File:MO_42_0138.JPG]]

The images above show MO 43 for [Cr(CO)6]. This is a filled bonding orbital orbital with mainly in-phase interactions. There are no contributions from the ligands along the x-axis. The C from CO is sp3 hybridised. It has a smaller contribution to the ligand FO as it electropositive and higher in energy. There are in-phase interactions between the the C-O valence orbitals as well as between the C sp3 and Cr dx2-y2. End-on overlap results in σ interaction.

====='''MO 49'''=====

[[File:MO_49_diagram0138.jpg|500px]][[File:MO_49_0138.JPG]]

The images above show the HOMO for the [Cr(CO)6] complex. This is a filled bonding orbital with a t2g symmetry. There are out-of phase interactions within the ligand FO and in-phase bonding interactions between the Cr dyz and C pz orbital. There are no contributions from the ligands along the x axis. There is greater contribution from the C in the ligand FO as it is closer in energy compared to O. There is also greater contribution from the Cr in the MO compared to the ligand FO as it is closer in energy. The ligand orbital is the C-O π* orbital which is higher in energy compered to the dyz orbital.

====='''MO 54'''=====

[[File:MO_54_diagram0138.jpg]][[File:MO_54_0138.JPG]]

MO 54 represents a non-bonding orbital with a t2u symmetry. It has no contribution from the Cr orbital which shows that it is non-bonding. There are out-of phase interactions between the C and O p orbitals which suggests this MO is high in energy. The ligand FO is an anti-bonding FO. O is more electronegative than C so its valence p orbitals are low in energy. Hence it has a smaller contribution to the ligand FO which is antibonding.

Rep:MOD:01381641

2019-05-24T12:52:05Z

Saa2417: /* MO 49 */

=BH3=

'''B3LYP/6-31G(d,p)'''

[[File:BH3_Summary0138.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000009 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000034 0.001800 YES
RMS Displacement 0.000017 0.001200 YES

</pre>

[[File:SHAZEEN_BH3_FREQ.LOG]]

<pre>

Low frequencies --- -2.2126 -1.0751 -0.0054 2.2359 10.2633 10.3194
Low frequencies --- 1162.9860 1213.1757 1213.1784

</pre>

<jmol><jmolApplet>
<title>optimised BH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>SA0138_BH3_OPT_631G.LOG</uploadedFileContents>
</jmolApplet></jmol>

====Vibrational spectrum for BH3====
{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2''
|Yes
|out-of-plane bend
|-
|1213
|14
|E'
|Very slight
|bend
|-
|1213
|14
|E'
|Very slight
|bend
|-
|2582
|0
|A1'
|No
|symmetric stretch
|-
|2715
|126
|E'
|Yes
|asymmetric stretch
|-
|2715
|126
|E'
|Yes
|asymmetric stretch
|}

[[File:BH3_Spectrum0138.PNG]]

Only 3 peaks are see in the spectrum despite there being 6 vibrations as shown in the vibrational data above. There are two sets of degenerate vibrations (same energy), 1213 and 2715 cm-1 which only appear once in the spectrum. Additionally, for a vibration to be IR active, there must be a change in dipole moment. The vibration at 2592 cm-1 represents an symmetric stretch which means the change in dipole moment is zero so this is not observed in the IR spectrum.

[[File:BH3_LCAO_real0138.JPG]]
(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 21/05/19)

No significant differences are seen between the real and LCAO MOs which shows that qualitative MO theory is useful in predicting real MOs to a high level of accuracy. The real MOs show regions of electron density and nodes in areas predicted by LCAO MOs.

=NH3=

'''B3LYP/6-31G(d,p)'''

[[File:NH3_Summary0138.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000005 0.000450 YES
RMS Force 0.000003 0.000300 YES
Maximum Displacement 0.000013 0.001800 YES
RMS Displacement 0.000007 0.001200 YES

</pre>

[[File:SA01381_NH3_FREQ_NEW.LOG ‎]]

<jmol><jmolApplet>
<title>optimised NH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>0138_NH3_OPT_NEW.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre>

Low frequencies --- -11.1928 -11.1561 -0.0035 0.0252 0.1457 25.7625
Low frequencies --- 1089.6648 1694.1744 1694.1747

</pre>

=NH3BH3=

'''B3LYP/6-31G(d,p)'''

[[File:Nh3Bh3_Summary0138.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000233 0.000450 YES
RMS Force 0.000083 0.000300 YES
Maximum Displacement 0.000981 0.001800 YES
RMS Displacement 0.000370 0.001200 YES

</pre>

[[File:SA0138_NH3BH3_FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised NH3BH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>SA0138_NH3BH3_OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre>

Low frequencies --- -0.0675 -0.0573 -0.0065 16.7107 16.7164 41.6318
Low frequencies --- 265.4937 634.5843 640.0012

</pre>

=Calculating Association Energy=

E(NH3)= -56.55776863 a.u.
E(BH3)= -26.61532364 a.u.
E(NH3BH3)= -83.22468856 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
ΔE=(-83.22468856)-[(-56.55776863)+(-26.61532364)]
ΔE = -0.05159629 a.u.

ΔE= -135 kJ/mol

This value shows that the B-N dative bond is weak (bond enthalpy = +135 kJ/mol) compared to other bond enthalpy values. [https://labs.chem.ucsb.edu/zakarian/armen/11---bonddissociationenergy.pdf] For example, the bond enthalpy of a C-C bond is approximately 350 kJ/mol. This is more than twice the calculated B-N dative bond.

=NI3=

[[File:NI3_summary_table01381.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000067 0.000450 YES
RMS Force 0.000044 0.000300 YES
Maximum Displacement 0.000486 0.001800 YES
RMS Displacement 0.000363 0.001200 YES

</pre>

[[File:NI3_OPTIMISATION+FREQ_NEW0138.LOG]]

<pre>

Low frequencies --- -12.7375 -12.7314 -6.2898 -0.0040 0.0188 0.0633
Low frequencies --- 101.0325 101.0332 147.4122

</pre>

==Investigating Metal Carbonyl Complexes==

====Prediction====
Going across the 3d complexes from Ti to Fe, the M-C bond length is expected to increase (weaker M-C bond). The C=O bond length is expected to decrease (i.e. stronger C=O bond) and therefore the C=O stretching frequency should increase. As you go from Ti-->Fe, the decreasing negative charge on the metal centre leads to contraction of the d orbitals and hence a less efficient overlap of M(dπ) with CO π*. This would result in a weaker M-C bond.

==='''[Ti(CO)6]2-'''===

[[File:Ti_complex0138_summary.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000118 0.000450 YES
RMS Force 0.000042 0.000300 YES
Maximum Displacement 0.000244 0.001800 YES
RMS Displacement 0.000096 0.001200 YES

</pre>

<pre>

Low frequencies --- -0.0003 0.0007 0.0008 14.2245 14.2245 14.2245
Low frequencies --- 30.7497 30.7497 30.7497

</pre>

[[File:TI_OPT+FREQ0138.LOG]]

<jmol><jmolApplet>
<title>optimised [V(CO)6]^1- molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>TI_OPT+FREQ0138.LOG</uploadedFileContents>
</jmolApplet></jmol>

==='''[V(CO)6]-'''===

[[File:V_complex0138_summary.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000070 0.000300 YES
Maximum Displacement 0.001210 0.001800 YES
RMS Displacement 0.000591 0.001200 YES

</pre>
<pre>

Low frequencies --- 0.0006 0.0007 0.0010 14.1311 14.1311 14.1311
Low frequencies --- 52.8916 52.8916 52.8916

</pre>

[[File:VANADIUM0138_OPT+FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised [V(CO)6]^1- molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>VANADIUM0138_OPT+FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

==='''[Cr(CO)6]'''===

[[File:Cr_complex0138_summary.JPG]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000160 0.000450 YES
RMS Force 0.000057 0.000300 YES
Maximum Displacement 0.000225 0.001800 YES
RMS Displacement 0.000084 0.001200 YES

</pre>

<pre>

Low frequencies --- -0.0014 -0.0008 -0.0007 10.8502 10.8502 10.8502
Low frequencies --- 66.4359 66.4359 66.4359

</pre>

[[File:CR0138_OPT+FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised [Cr(CO)6] molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>CR0138_OPT+FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

===Comparing Complexes===

====Calculations Data====

{| class="wikitable"
|+
|-
|M Complex || M-C Bond Length (Å) || Charge on M || C=O Stretching Frequency|| C=O Bond Length (Å)
|-
|Titanium
|2.047
|2-
|1855
|1.183
|-
|Vanadium
|1.954
|1-
|1969
|1.166
|-
|Chromium
|1.915
|0
|2087
|1.149
|-
|Manganese
|1.908
|1+
|2198
|1.136
|-
|Iron
|1.942
|2+
|2297
|1.125
|}

Mn and Fe Data taken from [https://wiki.ch.ic.ac.uk/wiki/index.php?title=SA_inorg_comp]

====Comparing M-C Bond length====

As you go from left to right, the M-C bond length decreases until Mn and then there is an increase from Mn to Fe. The observation from Ti-->Fe contradicts the initial prediction. However, the trend observed in the C=O bond lengths was as predicted before calculations. There was a decrease in the bond length (suggesting a stronger C=O bond) and stretching frequency. Thi

DISCUSS FE BOND ANOMALY correlation and exchange theory - too advanced
Fe 2+ charge causes contraction of the d orbitals, greater repulsion between the electrons (all spin paried) hence less efficient overlap with the CO, longer bond length

====Comparing C=O stretching frequencies====

The totally symmetric C=O vibrations for these complexes cannot be analysed as they are not IR active (zero intensity). This is because there is no change in dipole moment. For each of the complexes, these are listed below.

{| class="wikitable"
|+
|-
|M Complex || Symmetric C=O Stretching Frequency
|-
|Titanium
|1990
|-
|Vanadium
|2095
|-
|Chromium
|2189
|-
|Manganese
|2265
|-
|Iron
|2322
|}

====LCAOs vs real MOs for [Cr(CO)6]====

====='''MO 42'''=====

[[File:MO_43_diagram0138.jpg]][[File:MO_42_0138.JPG]]

The images above show MO 43 for [Cr(CO)6]. This is a filled bonding orbital orbital with mainly in-phase interactions. There are no contributions from the ligands along the x-axis. The C from CO is sp3 hybridised. It has a smaller contribution to the ligand FO as it electropositive and higher in energy. There are in-phase interactions between the the C-O valence orbitals as well as between the C sp3 and Cr dx2-y2. End-on overlap results in σ interaction.

====='''MO 49'''=====

[[File:MO_49_diagram0138.jpg|500px]][[File:MO_49_0138.JPG]]

The images above show the HOMO for the [Cr(CO)6] complex. This is a filled bonding orbital with a t2g symmetry. There are out-of phase interactions within the ligand FO and in-phase bonding interactions between the Cr dyz and C pz orbital. There are no contributions from the ligands along the x axis. There is greater contribution from the C in the ligand FO as it is closer in energy compared to O. There is also greater contribution from the Cr in the MO compared to the ligand FO as it is closer in energy. The ligand orbital is the C-O π* orbital which is higher in energy compered to the dyz orbital.

====='''MO 54'''=====

[[File:MO_54_diagram0138.jpg]][[File:MO_54_0138.JPG]]

Rep:MOD:01381641

2019-05-24T12:29:48Z

Saa2417: /* MO 42 */

=BH3=

'''B3LYP/6-31G(d,p)'''

[[File:BH3_Summary0138.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000009 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000034 0.001800 YES
RMS Displacement 0.000017 0.001200 YES

</pre>

[[File:SHAZEEN_BH3_FREQ.LOG]]

<pre>

Low frequencies --- -2.2126 -1.0751 -0.0054 2.2359 10.2633 10.3194
Low frequencies --- 1162.9860 1213.1757 1213.1784

</pre>

<jmol><jmolApplet>
<title>optimised BH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>SA0138_BH3_OPT_631G.LOG</uploadedFileContents>
</jmolApplet></jmol>

====Vibrational spectrum for BH3====
{| class="wikitable"
|+
|-
|wavenumber (cm-1) || Intensity (arbitrary units) || symmetry || IR active? || type
|-
|1163
|93
|A2''
|Yes
|out-of-plane bend
|-
|1213
|14
|E'
|Very slight
|bend
|-
|1213
|14
|E'
|Very slight
|bend
|-
|2582
|0
|A1'
|No
|symmetric stretch
|-
|2715
|126
|E'
|Yes
|asymmetric stretch
|-
|2715
|126
|E'
|Yes
|asymmetric stretch
|}

[[File:BH3_Spectrum0138.PNG]]

Only 3 peaks are see in the spectrum despite there being 6 vibrations as shown in the vibrational data above. There are two sets of degenerate vibrations (same energy), 1213 and 2715 cm-1 which only appear once in the spectrum. Additionally, for a vibration to be IR active, there must be a change in dipole moment. The vibration at 2592 cm-1 represents an symmetric stretch which means the change in dipole moment is zero so this is not observed in the IR spectrum.

[[File:BH3_LCAO_real0138.JPG]]
(MO diagram for BH3, Lecture 4 Tutorial Problem Model Answers, P. Hunt, [http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf], accessed 21/05/19)

No significant differences are seen between the real and LCAO MOs which shows that qualitative MO theory is useful in predicting real MOs to a high level of accuracy. The real MOs show regions of electron density and nodes in areas predicted by LCAO MOs.

=NH3=

'''B3LYP/6-31G(d,p)'''

[[File:NH3_Summary0138.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000005 0.000450 YES
RMS Force 0.000003 0.000300 YES
Maximum Displacement 0.000013 0.001800 YES
RMS Displacement 0.000007 0.001200 YES

</pre>

[[File:SA01381_NH3_FREQ_NEW.LOG ‎]]

<jmol><jmolApplet>
<title>optimised NH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>0138_NH3_OPT_NEW.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre>

Low frequencies --- -11.1928 -11.1561 -0.0035 0.0252 0.1457 25.7625
Low frequencies --- 1089.6648 1694.1744 1694.1747

</pre>

=NH3BH3=

'''B3LYP/6-31G(d,p)'''

[[File:Nh3Bh3_Summary0138.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000233 0.000450 YES
RMS Force 0.000083 0.000300 YES
Maximum Displacement 0.000981 0.001800 YES
RMS Displacement 0.000370 0.001200 YES

</pre>

[[File:SA0138_NH3BH3_FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised NH3BH3 molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>SA0138_NH3BH3_OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

<pre>

Low frequencies --- -0.0675 -0.0573 -0.0065 16.7107 16.7164 41.6318
Low frequencies --- 265.4937 634.5843 640.0012

</pre>

=Calculating Association Energy=

E(NH3)= -56.55776863 a.u.
E(BH3)= -26.61532364 a.u.
E(NH3BH3)= -83.22468856 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)]
ΔE=(-83.22468856)-[(-56.55776863)+(-26.61532364)]
ΔE = -0.05159629 a.u.

ΔE= -135 kJ/mol

This value shows that the B-N dative bond is weak (bond enthalpy = +135 kJ/mol) compared to other bond enthalpy values. [https://labs.chem.ucsb.edu/zakarian/armen/11---bonddissociationenergy.pdf] For example, the bond enthalpy of a C-C bond is approximately 350 kJ/mol. This is more than twice the calculated B-N dative bond.

=NI3=

[[File:NI3_summary_table01381.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000067 0.000450 YES
RMS Force 0.000044 0.000300 YES
Maximum Displacement 0.000486 0.001800 YES
RMS Displacement 0.000363 0.001200 YES

</pre>

[[File:NI3_OPTIMISATION+FREQ_NEW0138.LOG]]

<pre>

Low frequencies --- -12.7375 -12.7314 -6.2898 -0.0040 0.0188 0.0633
Low frequencies --- 101.0325 101.0332 147.4122

</pre>

==Investigating Metal Carbonyl Complexes==

====Prediction====
Going across the 3d complexes from Ti to Fe, the M-C bond length is expected to increase (weaker M-C bond). The C=O bond length is expected to decrease (i.e. stronger C=O bond) and therefore the C=O stretching frequency should increase. As you go from Ti-->Fe, the decreasing negative charge on the metal centre leads to contraction of the d orbitals and hence a less efficient overlap of M(dπ) with CO π*. This would result in a weaker M-C bond.

==='''[Ti(CO)6]2-'''===

[[File:Ti_complex0138_summary.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000118 0.000450 YES
RMS Force 0.000042 0.000300 YES
Maximum Displacement 0.000244 0.001800 YES
RMS Displacement 0.000096 0.001200 YES

</pre>

<pre>

Low frequencies --- -0.0003 0.0007 0.0008 14.2245 14.2245 14.2245
Low frequencies --- 30.7497 30.7497 30.7497

</pre>

[[File:TI_OPT+FREQ0138.LOG]]

<jmol><jmolApplet>
<title>optimised [V(CO)6]^1- molecule</title>
<color>black</color>
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<uploadedFileContents>TI_OPT+FREQ0138.LOG</uploadedFileContents>
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==='''[V(CO)6]-'''===

[[File:V_complex0138_summary.JPG]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000198 0.000450 YES
RMS Force 0.000070 0.000300 YES
Maximum Displacement 0.001210 0.001800 YES
RMS Displacement 0.000591 0.001200 YES

</pre>
<pre>

Low frequencies --- 0.0006 0.0007 0.0010 14.1311 14.1311 14.1311
Low frequencies --- 52.8916 52.8916 52.8916

</pre>

[[File:VANADIUM0138_OPT+FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised [V(CO)6]^1- molecule</title>
<color>black</color>
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<uploadedFileContents>VANADIUM0138_OPT+FREQ.LOG</uploadedFileContents>
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==='''[Cr(CO)6]'''===

[[File:Cr_complex0138_summary.JPG]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000160 0.000450 YES
RMS Force 0.000057 0.000300 YES
Maximum Displacement 0.000225 0.001800 YES
RMS Displacement 0.000084 0.001200 YES

</pre>

<pre>

Low frequencies --- -0.0014 -0.0008 -0.0007 10.8502 10.8502 10.8502
Low frequencies --- 66.4359 66.4359 66.4359

</pre>

[[File:CR0138_OPT+FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised [Cr(CO)6] molecule</title>
<color>black</color>
<size>250</size>
<uploadedFileContents>CR0138_OPT+FREQ.LOG</uploadedFileContents>
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===Comparing Complexes===

====Calculations Data====

{| class="wikitable"
|+
|-
|M Complex || M-C Bond Length (Å) || Charge on M || C=O Stretching Frequency|| C=O Bond Length (Å)
|-
|Titanium
|2.047
|2-
|1855
|1.183
|-
|Vanadium
|1.954
|1-
|1969
|1.166
|-
|Chromium
|1.915
|0
|2087
|1.149
|-
|Manganese
|1.908
|1+
|2198
|1.136
|-
|Iron
|1.942
|2+
|2297
|1.125
|}

Mn and Fe Data taken from [https://wiki.ch.ic.ac.uk/wiki/index.php?title=SA_inorg_comp]

====Comparing M-C Bond length====

As you go from left to right, the M-C bond length decreases until Mn and then there is an increase from Mn to Fe. The observation from Ti-->Fe contradicts the initial prediction. However, the trend observed in the C=O bond lengths was as predicted before calculations. There was a decrease in the bond length (suggesting a stronger C=O bond) and stretching frequency. Thi

DISCUSS FE BOND ANOMALY correlation and exchange theory - too advanced
Fe 2+ charge causes contraction of the d orbitals, greater repulsion between the electrons (all spin paried) hence less efficient overlap with the CO, longer bond length

====Comparing C=O stretching frequencies====

The totally symmetric C=O vibrations for these complexes cannot be analysed as they are not IR active (zero intensity). This is because there is no change in dipole moment. For each of the complexes, these are listed below.

{| class="wikitable"
|+
|-
|M Complex || Symmetric C=O Stretching Frequency
|-
|Titanium
|1990
|-
|Vanadium
|2095
|-
|Chromium
|2189
|-
|Manganese
|2265
|-
|Iron
|2322
|}

====LCAOs vs real MOs for [Cr(CO)6]====

====='''MO 42'''=====

[[File:MO_43_diagram0138.jpg]][[File:MO_42_0138.JPG]]

The images above show MO 43 for [Cr(CO)6]. This is a filled bonding orbital orbital with mainly in-phase interactions. There are no contributions from the ligands along the x-axis. The C from CO is sp3 hybridised. It has a smaller contribution to the ligand FO as it electropositive and higher in energy. There are in-phase interactions between the the C-O valence orbitals as well as between the C sp3 and Cr dx2-y2. End-on overlap results in σ interaction.

====='''MO 49'''=====

[[File:MO_49_diagram0138.jpg|500px]][[File:MO_49_0138.JPG]]

====='''MO 54'''=====

[[File:MO_54_diagram0138.jpg]][[File:MO_54_0138.JPG]]

Rep:MOD:01381641

2019-05-24T11:52:38Z

Saa2417: