File:BH3 opt summary.PNG

2019-05-24T13:24:36Z

Sna216: Sna216 uploaded a new version of File:BH3 opt summary.PNG

SA inorg comp

2019-05-24T13:23:15Z

Sna216: /* NH3 */

== BH3 ==

Method: B3LYP

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

Summary Table
<pre> Item Value Threshold Converged?
Maximum Force 0.000158 0.000450 YES
RMS Force 0.000079 0.000300 YES
Maximum Displacement 0.000621 0.001800 YES
RMS Displacement 0.000310 0.001200 YES
Predicted change in Energy=-1.466776D-07
Optimization completed.
-- Stationary point found.</pre>
<pre>Low frequencies --- -0.2458 -0.1130 -0.0054 43.9715 45.1306 45.1313
Low frequencies --- 1163.6034 1213.5913 1213.5940</pre>

[[File:SA_BH3_OPT_FREQ_CALC_2.LOG]]

<jmol><jmolApplet>
<title>optimised BH3 molecule</title>
<color>lightgrey</color>
<size>200</size>
<uploadedFileContents>SA_BH3_OPT_FREQ_CALC_2.LOG</uploadedFileContents>
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=== MO Diagram of BH3 ===

[[File:SA_MO.png|700px]]

(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 22/05/18)

=== Vibrations and IR Spectrum ===

[[File:Vibrations_BH3.PNG|350px]][[File:Spectrum_BH3_SA.PNG|700px]]

There less than six peaks in the spectrum, although there are six vibrations.
This is because some of the vibrations are degenerate, i.e. mode 2 and 3, or 5 and 6. They have the same energy so they only result in a single peak.
Mode 3 cannot be observed since the vibration is symmetric and thus there is no change in dipole moment.

[[File:BH3_vibr_SA.gif|none|frame|400px]]

== Association energies ==

=== NH3 ===

[[File:NH3_opt_summary.PNG|350px]]

<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
Predicted change in Energy=-9.844602D-11
Optimization completed.
-- Stationary point found.</pre>

<pre>Low frequencies --- -0.0129 -0.0024 -0.0007 7.1034 8.1048 8.1051
Low frequencies --- 1089.3834 1693.9368 1693.9368
</pre>

[[File:SA_NH3_OPT_FREQ.LOG]]

<jmol><jmolApplet>
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=== NH3-BH3 ===

[[File:NH3BH3_opt_summary.PNG|350px]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000123 0.000450 YES
RMS Force 0.000058 0.000300 YES
Maximum Displacement 0.000585 0.001800 YES
RMS Displacement 0.000320 0.001200 YES
Predicted change in Energy=-1.738521D-07
Optimization completed.
-- Stationary point found.</pre>

<pre>Low frequencies --- -0.0006 -0.0006 0.0010 16.8436 17.4462 37.3291
Low frequencies --- 265.8243 632.2043 639.3227</pre>

[[File:SA_BH3NH3_OPT_FRQ.LOG]]

<jmol><jmolApplet>
<title>optimised NH3-BH3 molecule</title>
<color>lightgrey</color>
<size>200</size>
<uploadedFileContents>SA_BH3NH3_OPT_FRQ.LOG</uploadedFileContents>
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=== Energies ===

E(NH3)= -56.558 au

E(BH3)=

E(NH3BH3)= -83.225 au

== NI3 ==

[[File:NI3_opt_summary.PNG|350px]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000088 0.000450 YES
RMS Force 0.000044 0.000300 YES
Maximum Displacement 0.000859 0.001800 YES
RMS Displacement 0.000481 0.001200 YES
Predicted change in Energy=-1.195113D-07
Optimization completed.
-- Stationary point found.</pre>

<pre>Low frequencies --- -12.3843 -12.3779 -5.6125 -0.0040 0.0194 0.0711
Low frequencies --- 100.9306 100.9313 147.2331</pre>

[[File:SA_NI3_OPT_FREQ_CALC_2.LOG]]

<jmol><jmolApplet>
<title>optimised NI3 molecule</title>
<color>lightgrey</color>
<size>200</size>
<uploadedFileContents>SA_NI3_OPT_FREQ_CALC_2.LOG</uploadedFileContents>
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optimised N-I bond lengthː 2.184 Å

== Metal Carbonyls ==

=== Predictions ===

Going along the periodic table from titanium (Ti) to iron (Fe) the charge on the metal atom becomes more positive. This should stabilise the molecular orbitals.
Moreover, the back donation should decrease, so going fro Ti to Fe the metal-carbon bonds should get weaker while the carbon-oxygen bond gets stronger. The stronger C=O bonds result in higher frequencies for the C=O stretch.

Ti-C bond expected to be strongest
Fe-C bond expected to be weakest

As the more e- density on metal the more back donation
--> stronger M-C bond, weaker C=O bond

Fe longest/weakest:
Because it has least electron density, readily accepts sigma electron density but reluctant in back donation

Fe 2= charge causes contraction of d orbitals, greater repulsion between the e- (all spin paired)
--> less efficient overlap with C=O --> longer bond

=== Symmetric C=O stretch ===

Not observable

[[File:Cr_CO_SYM_STR.gif|none|frame]]

{| class="wikitable" border=1
! Complex !! C=O symmetric stretching frequency (cm-1)
|-
| Ti || 1990
|-
| V || 2095
|-
| Cr || 2189
|-
| Mn || 2265
|-
| Fe || 2322
|}

=== Fe - Complex ===

Method: B3LYP

Basis: 6-31G(d,p) for C=O, LanL2DZ (pseudo potential) for Fe

Fe-C bond length: 1.942

[[File:SA_Fe_sum.PNG|350px]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000054 0.000450 YES
RMS Force 0.000024 0.000300 YES
Maximum Displacement 0.000429 0.001800 YES
RMS Displacement 0.000200 0.001200 YES
Predicted change in Energy=-6.077456D-08
Optimization completed.
-- Stationary point found.
</pre>

<pre>Low frequencies --- -10.5292 -10.5292 -10.5292 0.0012 0.0014 0.0015
Low frequencies --- 82.1285 82.1285 82.1285</pre>

[[File:SA_FE_COMPLEX_OPT_FREQ.LOG]]

<jmol><jmolApplet>
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<uploadedFileContents>SA_FE_COMPLEX_OPT_FREQ.LOG</uploadedFileContents>
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=== Mn - Complex ===

Method: B3LYP

Basis: 6-31G(d,p) for C=O, LanL2DZ (pseudo potential) for Mn

Mn-C bond length: 1.908

[[File:SA_Mn_sum.PNG|350px]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000054 0.000450 YES
RMS Force 0.000024 0.000300 YES
Maximum Displacement 0.000435 0.001800 YES
RMS Displacement 0.000206 0.001200 YES
Predicted change in Energy=-6.975532D-08
Optimization completed.
-- Stationary point found.</pre>

<pre>Low frequencies --- -0.0003 0.0005 0.0006 4.7607 4.7607 4.7607
Low frequencies --- 76.3202 76.3202 76.3202
</pre>

[[File:SA_MN_COMPLEX_OPT_FREQ.LOG]]

<jmol><jmolApplet>
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<color>lightgrey</color>
<size>200</size>
<uploadedFileContents>SA_MN_COMPLEX_OPT_FREQ.LOG</uploadedFileContents>
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=== Cr - Complex ===

Method: B3LYP

Basis: 6-31G(d,p) for C=O, LanL2DZ (pseudo potential) for Cr

Cr-C bond length: 1.915

[[File:SA_Cr_sum.PNG|350px]]

<pre>Item Value Threshold Converged?
Maximum Force 0.000160 0.000450 YES
RMS Force 0.000057 0.000300 YES
Maximum Displacement 0.000218 0.001800 YES
RMS Displacement 0.000078 0.001200 YES
Predicted change in Energy=-9.793326D-08
Optimization completed.
-- Stationary point found.</pre>

<pre>Low frequencies --- -0.0003 -0.0002 0.0004 10.8502 10.8502 10.8502
Low frequencies --- 66.4359 66.4359 66.4359</pre>

[[File:SA_CR_COMPLEX_OPT_FREQ.LOG]]

<jmol><jmolApplet>
<title>optimised Cr-complex molecule</title>
<color>lightgrey</color>
<size>200</size>
<uploadedFileContents>SA_CR_COMPLEX_OPT_FREQ.LOG</uploadedFileContents>
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=== Analysis ===

{| class="wikitable" border=1
! Complex !! Metal-Carbon bond length (Å) !! Charge on Metal!! C=O bond length (Å) !! C=O stretching frequency (cm-1)
|-
| Ti || 2.047 || -2 || 1.183 || 1855
|-
| V || 1.954 || -1 || 1.166 || 1969
|-
| Cr || 1.915 || 0 || 1.149 || 2087
|-
| Mn || 1.908 || +1 || 1.136 || 2198
|-
| Fe || 1.942 || +2 || 1.125 || 2297
|}

Ti and V Data from Shazeen Amir [https://wiki.ch.ic.ac.uk/wiki/index.php?title=MOD:01381641]

A trend is observed. From Ti to Mn the M-C bond length is decreasing, meaning the bond is getting stronger. This is contrary to what was predicted.
Iron is unusual as the Fe-C bond is weaker and longer than the Mn-C bond.
This could be a result of iron not back donating at all, thus making the bond a pure sigma bond.

Iron unusual
spoke to Prof Hunt
Correlation and exchange
too complicated/advanced
Fe 2= : d orbitals of iron contracted --> more repulsion
--> worse overlap ----> longer bond

The electrons are partially transferred from a d-orbital of the metal to anti-bonding molecular orbitals of CO (and its analogues). This electron-transfer (i) strengthens the metal–C bond and (ii) weakens the C–O bond. The strengthening of the M–CO bond is reflected in increases of the vibrational frequencies for the M–C bond (often outside of the range for the usual IR spectrophotometers). Furthermore, the M–CO bond length is shortened. The weakening of the C–O bond is indicated by a decrease in the wavenumber of the νCO band(s) from that for free CO (2143 cm−1), for example to 2060 cm−1 in Ni(CO)4 and 1981 cm−1 in Cr(CO)6, and 1790 cm−1 in the anion [Fe(CO)4]2−.[4] For this reason, IR spectroscopy is an important diagnostic technique in metal–carbonyl chemistry. The article infrared spectroscopy of metal carbonyls discusses this in detail.

=== MOs of Cr-Complex ===

[[Image:Cr_MO_49.jpg|right|thumb|MO 49 - ʈ2ɡ bonding MO]]
[[Image:MO_49.png|350px|left|thumb|MO 53 - ʈ2u non-bonding MO]]

[[Image:Cr_MO_41.PNG|right|thumb|MO 41 - ʈ1ɡ non-bonding MO]]
[[Image:MO_41.png|350px|left|thumb|MO 53 - ʈ2u non-bonding MO]]

[[Image:Cr_MO_53.PNG|right|thumb|MO 53 - ʈ2u non-bonding MO]]
[[Image:MO_53.png|350px|left|thumb|MO 53 - ʈ2u non-bonding MO]]

SA inorg comp

2019-05-24T13:22:36Z

Sna216: /* NH3 */

File:NH3BH3 opt summary.PNG

2019-05-24T13:19:18Z

Sna216: