2019-05-24T12:33:53Z

Bs517: /* Results */

= AX3 section =
== BH3 ==
RB3LYP/6-31G(d,p) level
[[File:Bs517 0sHZHEwXQC.png|none|thumb]]
Item Value Threshold Converged?
Maximum Force 0.000046 0.000450 YES
RMS Force 0.000023 0.000300 YES
Maximum Displacement 0.000182 0.001800 YES
RMS Displacement 0.000091 0.001200 YES

Frequency analysis log file: [[Media:BS517_BH3_FREQ.LOG|BS517_BH3_FREQ.LOG]]

Low frequencies --- -0.4072 -0.1962 -0.0055 25.2514 27.2430 27.2460
Low frequencies --- 1163.1897 1213.3128 1213.3155

<jmol><jmolApplet>
<title>BH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BS517_BH3_FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

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

[[File:Bs517 H8NTqPHnf8.png|none|thumb|400px]]

We can see that the calculated IR spectrum only shows three peaks, whereas we calculated 6 vibrational modes. The reason for this is that there are two pairs of degenerate vibrations (number 2 and 3 and number 5 and 6) and our symmetric stretch (number 4) is IR inactive because it does not change the dipole moment of the molecule.

[[File:Bs517 BH3 mo.jpg|none|thumb|500px]]

As we can see from the qualitative MO diagram of BH3, the qualitative LCAO orbitals are more or less good approximations of the real ones, especially for the more bonding orbitals. The most noticeable differences are the same phase regions next to each other 'fuse together' and opposite phase regions expand much more in the opposite direction. Another difference is the relative size of the parts of the orbitals corresponding to different atomic/fragment orbitals. This might be one of the hardest things to predict in MO diagrams. One more empirical observation is that the more nodes an orbital has (the more anti-bonding it is), the difference between the LCAO and the real orbitals increases. With this in mind, I think it is safe to say, that qualitative MO diagrams and LCAO molecular orbitals are very useful, especially in the bonding and the HOMO-LUMO region, but their accuracy drastically decreases as we go to the anti-bonding region.

== NH3 ==
RB3LYP/6-31G(d,p) level
[[File:Bs517 2ijeTgoby8.png|none|thumb]]
Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000014 0.001800 YES
RMS Displacement 0.000009 0.001200 YES

Frequency analysis log file: [[Media:BS517 NH3 OPT FREQ.LOG|BS517 NH3 OPT FREQ.LOG]]

Low frequencies --- -0.0128 -0.0020 0.0018 7.1034 8.1048 8.1051
Low frequencies --- 1089.3834 1693.9368 1693.9368

<jmol><jmolApplet>
<title>NH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BS517 NH3 OPT FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

== NI3 ==
RB3LYP/6-31G(d,p)LANL2DZ level
[[File:Bs517 FnnGNf9elb.png|none|thumb]]
Item Value Threshold Converged?
Maximum Force 0.000002 0.000450 YES
RMS Force 0.000002 0.000300 YES
Maximum Displacement 0.000024 0.001800 YES
RMS Displacement 0.000014 0.001200 YES

Frequency analysis log file: [[Media:BS517 NI3 FREQ.LOG|BS517 NI3 FREQ.LOG]]

Low frequencies --- -12.5520 -12.5458 -6.0044 -0.0040 0.0191 0.0664
Low frequencies --- 100.9969 100.9976 147.3377

<jmol><jmolApplet>
<title>NI3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BS517 NI3 FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

N-I bond distance: 2.184 Å

= NH3BH3 section=
== NH3BH3 ==
RB3LYP/6-31G(d,p) level
[[File:Bs517 kIKQ43xrHc.png|none|thumb]]
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

Frequency analysis log file: [[Media:BS517 NH3BH3 OPT FREQ.LOG|BS517 NH3BH3 OPT FREQ.LOG]]

Low frequencies --- -0.0015 -0.0013 -0.0001 16.8436 17.4462 37.3291
Low frequencies --- 265.8243 632.2043 639.3227

<jmol><jmolApplet>
<title>NH3</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BS517 NH3BH3 OPT FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

== NH3BH3 bond energies ==

E(NH3)=-56.558±0.002 Eh

E(BH3)=-26.615±0.002 Eh

E(NH3BH3)=-83.225±0.002 Eh

ΔE=E(NH3BH3)-[E(NH3)+E(BH3)] = -0.052±0.006 Eh = -136±15 kJ/mol

This is much less negative than the bond association energy of it's isoelectronic counterpart, ethane (ΔE=-377 kJ/mol<ref name=CRChb/>) (i.e. the H3N–BH3 bond is much weaker than the H3C–CH3 bond). As it is weaker than a notoriously weak peroxide bond (O–O single bond, ΔE=-142 kJ/mol<ref name=wiredbond/>), we can safely say that it is a very week bond.

= Project: d6 metal carbonyls =

Project done in collaboration with Nicholas Walker, link to his wiki: [[Nw3817|[LINK]]]

== [Cr(CO)6] ==
RB3LYP/6-31G(d,p)LANL2DZ level
[[File:Bs517 kIJg7pLIS1.png|none|thumb]]
Item Value Threshold Converged?
Maximum Force 0.000110 0.000450 YES
RMS Force 0.000041 0.000300 YES
Maximum Displacement 0.000705 0.001800 YES
RMS Displacement 0.000334 0.001200 YES
Frequency analysis log file: [[Media:BS517 CR(CO)6 OPT FREQ.LOG|BS517 CR(CO)6 OPT FREQ.LOG]]

Low frequencies --- 0.0011 0.0011 0.0012 11.7482 11.7482 11.7482
Low frequencies --- 66.6574 66.6574 66.6574

<jmol><jmolApplet>
<title>Cr(CO)6</title>
<color>black</color>
<size>200</size>
<uploadedFileContents>BS517 CR(CO)6 OPT FREQ.LOG</uploadedFileContents>
</jmolApplet></jmol>

Results in agreement with those of Nicholas Walker [[Nw3817#.5BCr.28CO.296.5D|[LINK]]]

== [V(CO)6]- ==
RB3LYP/6-31G(d,p)LANL2DZ level
[[File:Bs517 qoLxKN1pDK.png|none|thumb]]
Item Value Threshold Converged?
Maximum Force 0.000390 0.000450 YES
RMS Force 0.000162 0.000300 YES
Maximum Displacement 0.001626 0.001800 YES
RMS Displacement 0.000709 0.001200 YES

Frequency analysis log file: [[Media:BS517 V(CO)6- OPT freq.log|BS517 V(CO)6- OPT freq.log]]

Low frequencies --- -0.0006 0.0002 0.0011 13.1372 13.1372 13.1372
Low frequencies --- 52.2227 52.2228 52.2228



== [Mn(CO)6]+ ==
RB3LYP/6-31G(d,p)LANL2DZ level
[[File:Bs517 bpjyNTLlLr.png|none|thumb]]
Item Value Threshold Converged?
Maximum Force 0.000179 0.000450 YES
RMS Force 0.000067 0.000300 YES
Maximum Displacement 0.001359 0.001800 YES
RMS Displacement 0.000648 0.001200 YES

Frequency analysis log file: [[Media:BS517 Mn(CO)6+ OPT freq.log|BS517 Mn(CO)6+ OPT freq.log]]

Low frequencies --- -0.0012 -0.0011 -0.0008 7.2213 7.2214 7.2214
Low frequencies --- 76.3323 76.3323 76.3323



== [Ti(CO)6]2- ==
Results taken from Nicholas Walker [[Nw3817#.5BTi.28CO.296.5D2-|[LINK]]]

== [Fe(CO)6]2+ ==
Results taken from Nicholas Walker [[Nw3817#.5BTi.28CO.296.5D2-|[LINK]]]

== Results ==
=== Predictions and computational measurement of the changes in C‑O and M‑C bond lengths and C‑O stretching frequencies ===

{| class="wikitable"
|+
|-
|Property|| Predicted trend || [Ti(CO)6]2- || [V(CO)6]-|| [Cr(CO)6] || [Mn(CO)6]+ || [Fe(CO)6]2+ || Trend
|-
| Total charge || || 2- || 1- || 0 || 1+ || 2+ ||
|-
| Metal oxidation state || || -2 || -1 || 0 || +1 || +2 ||
|-
| C‑O bond length, d(C‑O)/Å|| Predicted to decrease along the period due to decreasing back-donation into C‑O π* orbitals with increasing metal oxidation state. This destabilises the C‑O bonds, making them longer. || 1.183 || 1.658 || 1.149 || 1.136 || 1.126 || As predicted, the C‑O bond length decreases with the decreasing electron density on the metal. This is primarily due to back-donation from the M d orbitals into the empty π*(C‑O) orbitals. This interaction increases the overall stability of the complex, but decreases the C‑O bond order (and thus bond strength). The less electrons density there is on the metal, the less prominent this effect gets. For the Fe complex, d(C‑O) is equal (withing experimental error) to the C‑O bond length in carbon monoxide (d(CO)=1.1283 Å<ref name=CRChb/>), meaning that in that complex, the CO-s act as simple L type sigma donating ligands.
|-
| M‑C bond length, d(M‑C)/Å|| Predicted to mostly depend on two factors, moving along the period the increasing metal oxidation state decreases back-donation and weakens the M‑C bonds making them longer, but having less electrons around the metal centre means more contracted d orbitals and shorter M‑C bonds. Qualitative predictions of the relative intensity of these effects is hard, my prediction is a decreasing M‑C bond length due to d orbital contraction.|| 2.047 || 1.954 || 1.915 || 1.909 || 1.942 ||d(M‑C) starts decreasing as we move along the period, but we hit a minimum at the 1+ charged metal centre state (Mn). As discussed before, more electron density means more back donation, but less electron density means more orbital contraction. Having the shortest M‑C in the 1+ case means, that both effects are important, and they are of similar magnitude.
|-
| C‑O asymmetric stretching frequency, ν(C‑O)/cm-1||Predicted to increase along the period due to increasing C‑O bond strength.|| 1857 || 1970 || 2086 || 2199 || 2297 || IR stretching frequencies are really good indicators of bond strengths. As predicted, stretching frequencies increase moving along the period due to decreasing back-donation meaning stronger C‑O bonds. These triply degenerate asymmetric stretches are IR active (they change the net dipole moment of the complex) and as such, they can be measured experimentally as well.
|-
| C‑O totally symmetric stretching frequency, ν(C‑O)/cm-1||Predicted to increase along the period due to increasing C‑O bond strength.|| 1992 || 2097|| 2189 || 2265|| 2322|| For the same reason as for the asymmetric stretching frequencies, the symmetric stretching frequencies increase as well as we move to the right in the periodic table. As these totally symmetric stretched do not change the net dipole moment of the complex, they are IR inactive, and cannot be measured experimentally. Their computational predictions should be just as precise as that the asymmetric ones.
|}

= References =
<references>
<ref name=wiredbond>Common Bond Energies - Wired Chemist, http://www.wiredchemist.com/chemistry/data/bond_energies_lengths.html [accessed 23/05/2019]</ref>
<ref name=CRChb>CRC Handbook of Chemistry and Physics, 96th Edition</ref>
</references>

Bs517-Y2Inorganic

File:Bs517 bpjyNTLlLr.png

2019-05-24T09:55:18Z

Bs517: