File:Hb3017 MO54 al2cl4br2.png

2019-05-17T11:09:49Z

Hb3017:

Rep:Mod:29hb301704

2019-05-17T10:06:21Z

== BH3 ==
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017bh3summ.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000015 0.000450 YES
RMS Force 0.000010 0.000300 YES
Maximum Displacement 0.000058 0.001800 YES
RMS Displacement 0.000038 0.001200 YES
</pre>
The link to the BH3 frequency file: [[Media:HB3017 BH3 FREQ.LOG|BH3 frequency file]].
<pre>
Low frequencies --- -10.3498 -3.4492 -1.2454 -0.0055 0.4779 3.2165
Low frequencies --- 1162.9519 1213.1527 1213.1554
</pre>
<jmol><jmolApplet>
<title>Optimised BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL 631G DP D3H OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Infra-red Spectrum ====
{| 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
|-
|2716
|126
|E'
|yes
|asymmetric stretch
|-
|2716
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Hb3017bh3spectrum.png]]

It can be seen from the IR spectrum above that there are only three peaks visible on the spectrum despite there being six different vibrational modes for BH3. One reason for this is because some of the vibrations occur at the occur at the same frequency. At 1213cm-1 there are actually two bending modes contributing to the peak and at 2716cm-1 there are two asymmetrical stretching modes at the same position. The result of this is that there are only two peaks visible for four different modes of vibration. Also, the symmetric stretch at 2582cm-1 does not appear on the IR spectrum because the mode is not IR active. This is because there is no change in dipole during the vibration.

==== MO Diagram for BH3 ====
Below the MO diagram for BH3 can be seen. On this diagram there are two representations of the molecular orbitals: one is from the LCAO and the others are the 'real' MOs generated using Gaussian.
[[File:Hb3017bh3orbs4.png|||The MO diagram for BH3 showing the MOs in terms of LCAO and also the 'real' MOs calculatied on Gaussian]]

=====Are there any significant differences between the real and LCAO MOs?=====

In terms of the differences between the 'real' MOs and the LCAO MOs, there are no very significant differences. For LCAO the areas of electron density are not merged together to form single areas of electron density and the original orbitals involved in the formation of the MO can still be seen. On the other hand, the original orbitals cannot be seen in the 'real' MOs because they fully combine and cancel out to form a molecular orbital that is the correct shape and corresponds to how the areas of electron density in the molecule actually look. Despite this, there is a definite similarity between the 'real' and LCAO MOs and it is very easy to tell which real MO corresponds to which LCAO MO, even though the LCAO MO does not give the true shape of the MO.

The LCAO approach to molecular orbitals, using an MO diagram, shows which orbitals are filled, which are bonding,non-bonding or anti-bonding. However, using the 'real' MO diagram does not give a good indication of what is bonding or antibonding and which molecular orbitals correspond to a bonding/antibonding pair.

=====What does this say about the accuracy and usefulness of qualitative MO theory?=====

Qualitative MO theory using LCAO is useful for finding out which atomic orbitals contribute the the final molecular orbital and is also good for knowing which atoms most of the electron density lies on. However, LCAO is not accurate in terms of getting the correct shape for the molecular orbitals.

=== Association Energies: Ammonia-Borane ===
Ammonia-Borane, NH3BH3, is an acid-base complex can be made in the following reaction:
NH3 + BH3 → NH3BH3
The reaction energy for this process can be found by looking at the energies of the species involved in the reaction.

==== NH3 ====
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017nh3summ.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000012 0.001800 YES
RMS Displacement 0.000008 0.001200 YES
</pre>
The link to the NH3 frequency file: [[Media:HB3017 NH3 FREQ.LOG|NH3 frequency file]]

<pre>
Low frequencies --- -8.5646 -8.5588 -0.0047 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865
</pre>

<jmol><jmolApplet>
<title>Optimised NH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL NH3 631G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== NH3BH3 ====
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017nh3bh3summary.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000531 0.001800 YES
RMS Displacement 0.000296 0.001200 YES
</pre>
The link to the NH3BH3 frequency file: [[Media:HBELL NH3BH3 FREQ.LOG|NH3BH3 frequency file]]

<pre>
V
Low frequencies --- -0.0616 -0.0457 -0.0067 21.6898 21.6957 40.5827
Low frequencies --- 266.0232 632.3610 640.1384
</pre>
<jmol><jmolApplet>
<title>Optimised NH3BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL NH3BH3 C3V OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Association Energy ====
E(NH3)=-56.55777 a.u.

E(BH3)= -26.61532 a.u.

E(NH3BH3)= -83.22469 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)] = -83.22469 - [-56.55777 + (-26.61532)]= -0.0516 a.u.

In kJmol-1, ΔE = -135 kJmol-1

== NI3 ==
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017ni3summ2.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000068 0.000450 YES
RMS Force 0.000044 0.000300 YES
Maximum Displacement 0.000493 0.001800 YES
RMS Displacement 0.000333 0.001200 YES

</pre>

The link the frequency file for NI3 is here: [[Media:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG| NI3 frequency file.]]
<pre>
Low frequencies --- -12.7477 -12.7416 -6.4258 -0.0140 0.0210 0.0991
Low frequencies --- 101.0290 101.0295 147.4197
</pre>

<jmol><jmolApplet>
<title>Optimised NI3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>Hbell ni3 optgen2.log</uploadedFileContents>
</jmolApplet></jmol>

The optimised bond length for this molecule is 2.184Å.

== Lewis Acids and Bases ==
In the diagram below, the five different isomers of Al2Cl4Br2 can be seen along with their point groups.
[[File:Hb3017al2cl4br2pg.png]]
==== (a) 2 bridging Br ions isomer ====
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017al2cl4br2summ.png]]
<pre>
Item Value Threshold Converged?
Maximum Force 0.000008 0.000450 YES
RMS Force 0.000003 0.000300 YES
Maximum Displacement 0.000064 0.001800 YES
RMS Displacement 0.000031 0.001200 YES
</pre>

<jmol><jmolApplet>
<title>Optimised Al2Cl4Br2 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL AL2CL4BR2 GEN2 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

The link the the frequency file for this isomer is here : [[Media:HBELL AL2CL4BR2 GEN2 OPT FREQ.LOG|Al2Cl4Br2 frequency file.]]

<pre>
Low frequencies --- -5.1323 -4.9635 -3.1644 0.0034 0.0038 0.0049
Low frequencies --- 14.8508 63.2858 86.0867
</pre>

==== (b) the isomer with trans terminal Br and bridging Cl ions ====
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017al2cl4br2c2hsumm.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000004 0.000450 YES
RMS Force 0.000002 0.000300 YES
Maximum Displacement 0.000047 0.001800 YES
RMS Displacement 0.000020 0.001200 YES

</pre>

The frequency file for this molecule can be found here: [[Media:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG|Al2Cl4Br2 frquency file.]]

<pre>
Low frequencies --- -4.2803 -2.4949 0.0024 0.0029 0.0034 0.9580
Low frequencies --- 17.7193 48.9824 72.9517
</pre>

<jmol><jmolApplet>
<title>Optimised Al2Cl4Br2 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HB3017 AL2CL4BR2BRIDGE GEN C2H OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Relative energy of these isomers ====
E(Al2Cl4Br2(D2h)) = -2352.40631 a.u.

E(Al2Cl4Br2(C2h)) = -2352.41629 a.u.

ΔE = |E(Al2Cl4Br2(D2h))-E(Al2Cl4Br2(C2h))| = 0.00998 a.u.

ΔE(kJmol-1) = 26 kJmol-1

The isomer bridged with the Cl ions is 26KJ lower in energy than the isomer bridged by the Br ions.

====discuss the relative stability of these conformers with respect to the bridging ions====
==== The dissociation energy of the lowest energy conformer into 2AlCl2Br====
The Al2Cl4Br2 isomer with the two bridging chlorine ions and the terminal trans Br ions can dissociate into AlCl2Br, as shown in the equation below.

Al2Cl4Br2 → AlCl2Br

The dissociation energy of this process can be found by comparing the energy of the dimer to the energy of two AlCl2Br molecules.

===== AlCl2Br =====

Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017alcl2brsumm.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000136 0.000450 YES
RMS Force 0.000073 0.000300 YES
Maximum Displacement 0.000681 0.001800 YES
RMS Displacement 0.000497 0.001200 YES

</pre>

The frequency file for AlCl2Br can be found here:[[Media:HB3017 ALCL2BR GEN OPT.LOG|AlCl2Br frequency file.]]

<pre>
Low frequencies --- -0.0053 -0.0049 -0.0045 1.3568 3.6367 4.2604
Low frequencies --- 120.5042 133.9178 185.8950
</pre>

<jmol><jmolApplet>
<title>Optimised AlCl2Br molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HB3017 ALCL2BR GEN OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

===== Calculating the dissociation energy =====
E(Al2Cl4Br2) = -2352.41629 a.u.

E(AlCl2Br) = -1176.19014 a.u.

ΔE = 2E(AlCl2Br)- E(Al2Cl4Br2) = 0.03601 a.u.

ΔE(kJmol-1) = 95 kJmol-1

====in your wiki present 3 MOs ranging from highly bonding to highly antibonding (from any of the MOs you have visualised). Pick only occupied MOs. Draw a LCAO MO diagram of these orbitals (in chemdraw). Describe and annotate the interactions occurring in the MOs, identify the overal MO character. Refer to your MO course notes for the format of this description.====
[[File:Hb3017 MO41 al2cl4br2.png]]
[[File:Hb3017 MO40 al2cl4br2.png]]

2019-05-16T19:18:17Z

== BH3 ==
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017bh3summ.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000015 0.000450 YES
RMS Force 0.000010 0.000300 YES
Maximum Displacement 0.000058 0.001800 YES
RMS Displacement 0.000038 0.001200 YES
</pre>
The link to the BH3 frequency file: [[Media:HB3017 BH3 FREQ.LOG|BH3 frequency file]].
<pre>
Low frequencies --- -10.3498 -3.4492 -1.2454 -0.0055 0.4779 3.2165
Low frequencies --- 1162.9519 1213.1527 1213.1554
</pre>
<jmol><jmolApplet>
<title>Optimised BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL 631G DP D3H OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Infra-red Spectrum ====
{| 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
|-
|2716
|126
|E'
|yes
|asymmetric stretch
|-
|2716
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Hb3017bh3spectrum.png]]

It can be seen from the IR spectrum above that there are only three peaks visible on the spectrum despite there being six different vibrational modes for BH3. One reason for this is because some of the vibrations occur at the occur at the same frequency. At 1213cm-1 there are actually two bending modes contributing to the peak and at 2716cm-1 there are two asymmetrical stretching modes at the same position. The result of this is that there are only two peaks visible for four different modes of vibration. Also, the symmetric stretch at 2582cm-1 does not appear on the IR spectrum because the mode is not IR active. This is because there is no change in dipole during the vibration.

==== MO Diagram for BH3 ====
Below the MO diagram for BH3 can be seen. On this diagram there are two representations of the molecular orbitals: one is from the LCAO and the others are the 'real' MOs generated using Gaussian.
[[File:Hb3017bh3orbs4.png|||The MO diagram for BH3 showing the MOs in terms of LCAO and also the 'real' MOs calculatied on Gaussian]]

=====Are there any significant differences between the real and LCAO MOs?=====

In terms of the differences between the 'real' MOs and the LCAO MOs, there are no very significant differences. For LCAO the areas of electron density are not merged together to form single areas of electron density and the original orbitals involved in the formation of the MO can still be seen. On the other hand, the original orbitals cannot be seen in the 'real' MOs because they fully combine and cancel out to form a molecular orbital that is the correct shape and corresponds to how the areas of electron density in the molecule actually look. Despite this, there is a definite similarity between the 'real' and LCAO MOs and it is very easy to tell which real MO corresponds to which LCAO MO, even though the LCAO MO does not give the true shape of the MO.

The LCAO approach to molecular orbitals, using an MO diagram, shows which orbitals are filled, which are bonding,non-bonding or anti-bonding. However, using the 'real' MO diagram does not give a good indication of what is bonding or antibonding and which molecular orbitals correspond to a bonding/antibonding pair.

=====What does this say about the accuracy and usefulness of qualitative MO theory?=====

Qualitative MO theory using LCAO is useful for finding out which atomic orbitals contribute the the final molecular orbital and is also good for knowing which atoms most of the electron density lies on. However, LCAO is not accurate in terms of getting the correct shape for the molecular orbitals.

=== Association Energies: Ammonia-Borane ===
Ammonia-Borane, NH3BH3, is an acid-base complex can be made in the following reaction:
NH3 + BH3 → NH3BH3
The reaction energy for this process can be found by looking at the energies of the species involved in the reaction.

==== NH3 ====
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017nh3summ.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000012 0.001800 YES
RMS Displacement 0.000008 0.001200 YES
</pre>
The link to the NH3 frequency file: [[Media:HB3017 NH3 FREQ.LOG|NH3 frequency file]]

<pre>
Low frequencies --- -8.5646 -8.5588 -0.0047 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865
</pre>

<jmol><jmolApplet>
<title>Optimised NH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL NH3 631G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== NH3BH3 ====
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017nh3bh3summary.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000531 0.001800 YES
RMS Displacement 0.000296 0.001200 YES
</pre>
The link to the NH3BH3 frequency file: [[Media:HBELL NH3BH3 FREQ.LOG|NH3BH3 frequency file]]

<pre>
V
Low frequencies --- -0.0616 -0.0457 -0.0067 21.6898 21.6957 40.5827
Low frequencies --- 266.0232 632.3610 640.1384
</pre>
<jmol><jmolApplet>
<title>Optimised NH3BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL NH3BH3 C3V OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Association Energy ====
E(NH3)=-56.55777 a.u.

E(BH3)= -26.61532 a.u.

E(NH3BH3)= -83.22469 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)] = -83.22469 - [-56.55777 + (-26.61532)]= -0.0516 a.u.

In kJmol-1, ΔE = -135 kJmol-1

== NI3 ==
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017ni3summ2.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000068 0.000450 YES
RMS Force 0.000044 0.000300 YES
Maximum Displacement 0.000493 0.001800 YES
RMS Displacement 0.000333 0.001200 YES

</pre>

The link the frequency file for NI3 is here: [[Media:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG| NI3 frequency file.]]
<pre>
Low frequencies --- -12.7477 -12.7416 -6.4258 -0.0140 0.0210 0.0991
Low frequencies --- 101.0290 101.0295 147.4197
</pre>

<jmol><jmolApplet>
<title>Optimised NI3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>Hbell ni3 optgen2.log</uploadedFileContents>
</jmolApplet></jmol>

The optimised bond length for this molecule is 2.184Å.

== Lewis Acids and Bases ==
In the diagram below, the five different isomers of Al2Cl4Br2 can be seen along with their point groups.
[[File:Hb3017al2cl4br2pg.png]]
==== (a) 2 bridging Br ions isomer ====
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017al2cl4br2summ.png]]
<pre>
Item Value Threshold Converged?
Maximum Force 0.000008 0.000450 YES
RMS Force 0.000003 0.000300 YES
Maximum Displacement 0.000064 0.001800 YES
RMS Displacement 0.000031 0.001200 YES
</pre>

<jmol><jmolApplet>
<title>Optimised Al2Cl4Br2 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL AL2CL4BR2 GEN2 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

The link the the frequency file for this isomer is here : [[Media:HBELL AL2CL4BR2 GEN2 OPT FREQ.LOG|Al2Cl4Br2 frequency file.]]

<pre>
Low frequencies --- -5.1323 -4.9635 -3.1644 0.0034 0.0038 0.0049
Low frequencies --- 14.8508 63.2858 86.0867
</pre>

==== (b) the isomer with trans terminal Br and bridging Cl ions ====
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017al2cl4br2c2hsumm.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000004 0.000450 YES
RMS Force 0.000002 0.000300 YES
Maximum Displacement 0.000047 0.001800 YES
RMS Displacement 0.000020 0.001200 YES

</pre>

The frequency file for this molecule can be found here: [[Media:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG|Al2Cl4Br2 frquency file.]]

<pre>
Low frequencies --- -4.2803 -2.4949 0.0024 0.0029 0.0034 0.9580
Low frequencies --- 17.7193 48.9824 72.9517
</pre>

<jmol><jmolApplet>
<title>Optimised Al2Cl4Br2 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HB3017 AL2CL4BR2BRIDGE GEN C2H OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Relative energy of these isomers ====
E(Al2Cl4Br2(D2h)) = -2352.40631 a.u.

E(Al2Cl4Br2(C2h)) = -2352.41629 a.u.

ΔE = |E(Al2Cl4Br2(D2h))-E(Al2Cl4Br2(C2h))| = 0.00998 a.u.

ΔE(kJmol-1) = 26 kJmol-1

The isomer bridged with the Cl ions is 26KJ lower in energy than the isomer bridged by the Br ions.

====discuss the relative stability of these conformers with respect to the bridging ions====
==== The dissociation energy of the lowest energy conformer into 2AlCl2Br====
The Al2Cl4Br2 isomer with the two bridging chlorine ions and the terminal trans Br ions can dissociate into AlCl2Br, as shown in the equation below.

Al2Cl4Br2 → AlCl2Br

The dissociation energy of this process can be found by comparing the energy of the dimer to the energy of two AlCl2Br molecules.

===== AlCl2Br =====

Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017alcl2brsumm.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000136 0.000450 YES
RMS Force 0.000073 0.000300 YES
Maximum Displacement 0.000681 0.001800 YES
RMS Displacement 0.000497 0.001200 YES

</pre>

The frequency file for AlCl2Br can be found here:[[Media:HB3017 ALCL2BR GEN OPT.LOG|AlCl2Br frequency file.]]

<pre>
Low frequencies --- -0.0053 -0.0049 -0.0045 1.3568 3.6367 4.2604
Low frequencies --- 120.5042 133.9178 185.8950
</pre>

<jmol><jmolApplet>
<title>Optimised AlCl2Br molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HB3017 ALCL2BR GEN OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

===== Calculating the dissociation energy =====
E(Al2Cl4Br2) = -2352.41629 a.u.

E(AlCl2Br) = -1176.19014 a.u.

ΔE = 2E(AlCl2Br)- E(Al2Cl4Br2) = 0.03601 a.u.

ΔE(kJmol-1) = 95 kJmol-1

====Is the product more or less stable than the isolated monomers?====

====carry out a MO calcualtion on the lowest energy isomer (only!)====
====visualise all the occupied valence MOs and the lowest 5 unoccupied MOs, you do not need to reproduce them all.====
====in your wiki present 3 MOs ranging from highly bonding to highly antibonding (from any of the MOs you have visualised). Pick only occupied MOs. Draw a LCAO MO diagram of these orbitals (in chemdraw). Describe and annotate the interactions occurring in the MOs, identify the overal MO character. Refer to your MO course notes for the format of this description.====
[[File:Hb3017 MO41 al2cl4br2.png]]

2019-05-16T17:05:52Z

Hb3017:

File:HB3017 ALCL2BR GEN OPT FREQ.LOG

2019-05-16T17:04:51Z

Hb3017:

File:Hb3017alcl2brsumm.png

2019-05-16T16:56:22Z

Hb3017:

Rep:Mod:29hb301704

2019-05-16T16:45:26Z

Hb3017: /* NI3 */

== BH3 ==
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017bh3summ.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000015 0.000450 YES
RMS Force 0.000010 0.000300 YES
Maximum Displacement 0.000058 0.001800 YES
RMS Displacement 0.000038 0.001200 YES
</pre>
The link to the BH3 frequency file: [[Media:HB3017 BH3 FREQ.LOG|BH3 frequency file]].
<pre>
Low frequencies --- -10.3498 -3.4492 -1.2454 -0.0055 0.4779 3.2165
Low frequencies --- 1162.9519 1213.1527 1213.1554
</pre>
<jmol><jmolApplet>
<title>Optimised BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL 631G DP D3H OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Infra-red Spectrum ====
{| 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
|-
|2716
|126
|E'
|yes
|asymmetric stretch
|-
|2716
|126
|E'
|yes
|asymmetric stretch
|}

[[File:Hb3017bh3spectrum.png]]

It can be seen from the IR spectrum above that there are only three peaks visible on the spectrum despite there being six different vibrational modes for BH3. One reason for this is because some of the vibrations occur at the occur at the same frequency. At 1213cm-1 there are actually two bending modes contributing to the peak and at 2716cm-1 there are two asymmetrical stretching modes at the same position. The result of this is that there are only two peaks visible for four different modes of vibration. Also, the symmetric stretch at 2582cm-1 does not appear on the IR spectrum because the mode is not IR active. This is because there is no change in dipole during the vibration.

==== MO Diagram for BH3 ====
Below the MO diagram for BH3 can be seen. On this diagram there are two representations of the molecular orbitals: one is from the LCAO and the others are the 'real' MOs generated using Gaussian.
[[File:Hb3017bh3orbs4.png|||The MO diagram for BH3 showing the MOs in terms of LCAO and also the 'real' MOs calculatied on Gaussian]]

=====Are there any significant differences between the real and LCAO MOs?=====

In terms of the differences between the 'real' MOs and the LCAO MOs, there are no very significant differences. For LCAO the areas of electron density are not merged together to form single areas of electron density and the original orbitals involved in the formation of the MO can still be seen. On the other hand, the original orbitals cannot be seen in the 'real' MOs because they fully combine and cancel out to form a molecualar orbital that is the correct shape and corresponds to how the areas of electron density in the molecule actually look. Despite this, there is a definite similarity between the 'real' and LCAO MOs and it is very easy to tell which real MO corresponds to which LCAO MO, even though the LCAO MO does not give the true shape of the MO.

=====What does this say about the accuracy and usefulness of qualitative MO theory?=====

Qualitative MO theory using LCAO is useful for finding out which atomic orbitals contribute the the final molecular orbital and is also good for knowing which atoms most of the electron density lies on. However, LCAO is not accurate in terms of getting the correct shape for the molecular orbitals.

=== Association Energies: Ammonia-Borane ===
Ammonia-Borane, NH3BH3, is an acid-base complex can be made in the following reaction:
NH3 + BH3 → NH3BH3
The reaction energy for this process can be found by looking at the energies of the species involved in the reaction.

==== NH3 ====
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017nh3summ.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000012 0.001800 YES
RMS Displacement 0.000008 0.001200 YES
</pre>
The link to the NH3 frequency file: [[Media:HB3017 NH3 FREQ.LOG|NH3 frequency file]]

<pre>
Low frequencies --- -8.5646 -8.5588 -0.0047 0.0454 0.1784 26.4183
Low frequencies --- 1089.7603 1694.1865 1694.1865
</pre>

<jmol><jmolApplet>
<title>Optimised NH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL NH3 631G OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== NH3BH3 ====
Method : B3YLP
Basis set : 6-31G

[[File:Hb3017nh3bh3summary.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000122 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000531 0.001800 YES
RMS Displacement 0.000296 0.001200 YES
</pre>
The link to the NH3BH3 frequency file: [[Media:HBELL NH3BH3 FREQ.LOG|NH3BH3 frequency file]]

<pre>
V
Low frequencies --- -0.0616 -0.0457 -0.0067 21.6898 21.6957 40.5827
Low frequencies --- 266.0232 632.3610 640.1384
</pre>
<jmol><jmolApplet>
<title>Optimised NH3BH3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL NH3BH3 C3V OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Association Energy ====
E(NH3)=-56.55777 a.u.

E(BH3)= -26.61532 a.u.

E(NH3BH3)= -83.22469 a.u.

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)] = -83.22469 - [-56.55777 + (-26.61532)]= -0.0516 a.u.

In kJmol-1, ΔE = -135 kJmol-1

== NI3 ==
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017ni3summ2.png]]

<pre>

Item Value Threshold Converged?
Maximum Force 0.000068 0.000450 YES
RMS Force 0.000044 0.000300 YES
Maximum Displacement 0.000493 0.001800 YES
RMS Displacement 0.000333 0.001200 YES

</pre>

The link the frequency file for NI3 is here: [[Media:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG| NI3 frequency file.]]
<pre>
Low frequencies --- -12.7477 -12.7416 -6.4258 -0.0140 0.0210 0.0991
Low frequencies --- 101.0290 101.0295 147.4197
</pre>

<jmol><jmolApplet>
<title>Optimised NI3 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>Hbell ni3 optgen2.log</uploadedFileContents>
</jmolApplet></jmol>

The optimised bond length for this molecule is 2.184Å.

== Lewis Acids and Bases ==
In the diagram below, the five different isomers of Al2Cl4Br2 can be seen along with their point groups.
[[File:Hb3017al2cl4br2pg.png]]
==== (a) 2 bridging Br ions isomer ====
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017al2cl4br2summ.png]]
<pre>
Item Value Threshold Converged?
Maximum Force 0.000008 0.000450 YES
RMS Force 0.000003 0.000300 YES
Maximum Displacement 0.000064 0.001800 YES
RMS Displacement 0.000031 0.001200 YES
</pre>

<jmol><jmolApplet>
<title>Optimised Al2Cl4Br2 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HBELL AL2CL4BR2 GEN2 OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

The link the the frequency file for this isomer is here : [[Media:HBELL AL2CL4BR2 GEN2 OPT FREQ.LOG|Al2Cl4Br2 frequency file.]]

<pre>
Low frequencies --- -5.1323 -4.9635 -3.1644 0.0034 0.0038 0.0049
Low frequencies --- 14.8508 63.2858 86.0867
</pre>

==== (b) the isomer with trans terminal Br and bridging Cl ions ====
Method: B3LYP

Basis Set: 6-31G(d,p)LANL2DZ

[[File:Hb3017al2cl4br2c2hsumm.png]]

<pre>
Item Value Threshold Converged?
Maximum Force 0.000004 0.000450 YES
RMS Force 0.000002 0.000300 YES
Maximum Displacement 0.000047 0.001800 YES
RMS Displacement 0.000020 0.001200 YES

</pre>

The frequency file for this molecule can be found here: [[Media:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG|Al2Cl4Br2 frquency file.]]

<pre>
Low frequencies --- -4.2803 -2.4949 0.0024 0.0029 0.0034 0.9580
Low frequencies --- 17.7193 48.9824 72.9517
</pre>

<jmol><jmolApplet>
<title>Optimised Al2Cl4Br2 molecule</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>HB3017 AL2CL4BR2BRIDGE GEN C2H OPT.LOG</uploadedFileContents>
</jmolApplet></jmol>

==== Relative energy of these isomers ====
E(Al2Cl4Br2(D2h)) = -2352.40631 a.u.
E(Al2Cl4Br2(C2h)) = -2352.41629 a.u.

ΔE = |E(Al2Cl4Br2(D2h))-E(Al2Cl4Br2(C2h))| = 0.00998 a.u.

ΔE(kJmol-1) = 26 kJmol-1

The isomer bridged with the Cl ions is 26KJ lower in energy than the isomer bridged by the Br ions.

====discuss the relative stability of these conformers with respect to the bridging ions====
====determine the dissociation energy for the lowest energy conformer into 2AlCl2Br====
====is the product more or less stable than the isolated monomers?====
====carry out a MO calcualtion on the lowest energy isomer (only!)====
====visualise all the occupied valence MOs and the lowest 5 unoccupied MOs, you do not need to reproduce them all.====
====in your wiki present 3 MOs ranging from highly bonding to highly antibonding (from any of the MOs you have visualised). Pick only occupied MOs. Draw a LCAO MO diagram of these orbitals (in chemdraw). Describe and annotate the interactions occurring in the MOs, identify the overal MO character. Refer to your MO course notes for the format of this description.====

File:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG

2019-05-16T16:44:51Z

Hb3017: Hb3017 uploaded a new version of File:HB3017 AL2CL4BR2BRIDGE GEN C2H OPT FREQ.LOG