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BH3

3D View Of Optimised BH3

Smf115 (talk) 23:51, 16 May 2018 (BST)Very nice structure information and presentation throughout, good addition of the geomotries on the jmols!

Calculation Results For Optimised BH3

Summary Table
File Type .log
Calculation Type FOPT
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
Energy -26.61532 a.u.
RMS Gradient Norm 0.00008 a.u.
Dipole Moment 0.00 Debye
Point Group CS
Calculation Time 3 min 1 s
Item Table 
         Item             Value       Threshold  Converged?
 Maximum Force            0.000203     0.000450     YES
 RMS     Force            0.000098     0.000300     YES
 Maximum Displacement     0.000867     0.001800     YES
 RMS     Displacement     0.000415     0.001200     YES
Optimised Parameters 
                               Optimized Parameters   
                              (Angstroms and Degrees)  
                           
 Name  Definition              Value          Derivative Info.                

 R1    R(1,2)                  1.1924         -DE/DX =    0.0                 
 R2    R(1,3)                  1.1928         -DE/DX =   -0.0002              
 R3    R(1,4)                  1.1926         -DE/DX =   -0.0002              
 A1    A(2,1,3)              119.9864         -DE/DX =    0.0                 
 A2    A(2,1,4)              119.999          -DE/DX =    0.0                 
 A3    A(3,1,4)              120.0146         -DE/DX =    0.0                 
 D1    D(2,1,4,3)            180.0            -DE/DX =    0.0
BH3 optimisation *.log file

Frequency Analysis

Low Frequencies
Low frequencies    -0.2268   -0.0080    0.0008   22.1147   22.1159   24.1363
Low frequencies  1163.1747 1213.2735 1213.2737

BH3 frequency *.log file

Vibrations
ν~max/cm−1 Intensity (arbitrary units) Irreducible representation IR active? Vibration Type
1163 93 A2 ✓ Wagging
1213 14 E Slightly In-plane scissoring
1213 14 E Slightly In-plane stretch
2582 0 A ✗ In-plane symmetric stretch
2715 126 E ✓ Antisymmetric stretch
2715 126 E ✓ Symmetric stretch
Calculated IR spectrum
Calculated IR spectrum of BH3.

We expected to see 6 vibrations from the 3N-6 rule for non-linear molecules. However, we only observe 3 in the spectrum. Peak at 2582 cm-1 has zero intensity because the vibration is an in-plane, fully symmetric stretch. The degenerate pair of peaks at 1213 cm-1 should have zero intensity because the E irreducible representation doesn't have the same symmetry species as the displacements x,y or z (see D3h character table). However, because the optimised structure of BH3 is not completely symmetric, the E vibrations can non-zero intensity.

Molecular Orbitals

Figure showing the first 8 LCAO MOs for BH3.[1] The computed MOs (in colour) are shown beside each LCAO MO.

The shapes and phases of the LCAO MOs are accurate for the lower 5 MOs. However, the shapes of the 3 highest energy LCAO MOs are slightly different to the computed MO shapes. Despite this, qualitative MO theory perfectly predicts orbital degeneracies and provides a useful, accurate way of determining orbital shapes for BH3.

Smf115 (talk) 23:51, 16 May 2018 (BST)Good annotation of the MO diagram and mention to both the similarities and differences.

Association Energy

NH3

3D View Of Optimised NH3
Calculation Results For Optimised NH3
Summary Table
File Type .log
Calculation Type FOPT
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
Energy -56.55777 a.u.
RMS Gradient Norm 0.00000 a.u.
Dipole Moment 1.85 Debye
Point Group C3v
Calculation Time 2 min 2 s
Item Table 
         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
Optimised Parameters 
                               Optimized Parameters   
                              (Angstroms and Degrees)  
                           
 Name  Definition              Value          Derivative Info.                

 R1    R(1,2)                  1.018          -DE/DX =    0.0                 
 R2    R(1,3)                  1.018          -DE/DX =    0.0                 
 R3    R(1,4)                  1.018          -DE/DX =    0.0                
 A1    A(2,1,3)              105.7446         -DE/DX =    0.0                 
 A2    A(2,1,4)              105.7446         -DE/DX =    0.0                 
 A3    A(3,1,4)              105.7446         -DE/DX =    0.0                
 D1    D(2,1,4,3)           -111.8637         -DE/DX =    0.0
NH3 optimisation *.log file
Frequency Analysis
Low Frequencies
Low frequencies    -0.0138   -0.0032   -0.0015    7.0783    8.0932    8.0937
Low frequencies  1089.3840 1693.9368 1693.9368

NH3 frequency *.log file

NH3BH3

3D View Of Optimised NH3BH3
Calculation Results For Optimised NH3BH3
Summary Table
File Type .log
Calculation Type FOPT
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
Energy -83.22469 a.u.
RMS Gradient Norm 0.00006 a.u.
Dipole Moment 5.57 Debye
Point Group C1
Calculation Time 2 min 48 s
Item Table 
         Item             Value       Threshold  Converged?
 Maximum Force            0.000123     0.000450     YES
 RMS     Force            0.000058     0.000300     YES
 Maximum Displacement     0.000515     0.001800     YES
 RMS     Displacement     0.000296     0.001200     YES
Optimised Parameters 
                               Optimized Parameters   
                              (Angstroms and Degrees)  
                           
 Name  Definition              Value          Derivative Info.                

 R1    R(1,7)                  1.0186         -DE/DX =   -0.0001              
 R2    R(2,7)                  1.0186         -DE/DX =   -0.0001              
 R3    R(3,7)                  1.0186         -DE/DX =   -0.0001             
 R4    R(4,8)                  1.21           -DE/DX =   -0.0001              
 R5    R(5,8)                  1.21           -DE/DX =   -0.0001              
 R6    R(6,8)                  1.21           -DE/DX =   -0.0001              
 R7    R(7,8)                  1.6681         -DE/DX =   -0.0001              
 A1    A(1,7,2)              107.8687         -DE/DX =    0.0                 
 A2    A(1,7,3)              107.8687         -DE/DX =    0.0                 
 A3    A(1,7,8)              111.0301         -DE/DX =    0.0                 
 A4    A(2,7,3)              107.8686         -DE/DX =    0.0                 
 A5    A(2,7,8)              111.0296         -DE/DX =    0.0                 
 A6    A(3,7,8)              111.0297         -DE/DX =    0.0                 
 A7    A(4,8,5)              113.8744         -DE/DX =    0.0                 
 A8    A(4,8,6)              113.8743         -DE/DX =    0.0                 
 A9    A(4,8,7)              104.5966         -DE/DX =    0.0                 
 A10   A(5,8,6)              113.8744         -DE/DX =    0.0                 
 A11   A(5,8,7)              104.5969         -DE/DX =    0.0                 
 A12   A(6,8,7)              104.597          -DE/DX =    0.0                 
 D1    D(1,7,8,4)            179.9996         -DE/DX =    0.0                 
 D2    D(1,7,8,5)            -60.0004         -DE/DX =    0.0                 
 D3    D(1,7,8,6)             59.9997         -DE/DX =    0.0                 
 D4    D(2,7,8,4)            -60.0002         -DE/DX =    0.0                 
 D5    D(2,7,8,5)             59.9997         -DE/DX =    0.0                 
 D6    D(2,7,8,6)            179.9999         -DE/DX =    0.0                 
 D7    D(3,7,8,4)             59.9995         -DE/DX =    0.0                 
 D8    D(3,7,8,5)            179.9995         -DE/DX =    0.0                 
 D9    D(3,7,8,6)            -60.0004         -DE/DX =    0.0
NH3BH3 optimisation *.log file
Frequency Analysis
Low Frequencies
Low frequencies    -0.0251   -0.0030    0.0012   17.1236   17.1258   37.1326
Low frequencies   265.7816  632.2034  639.3483

NH3BH3 frequency *.log file

Energy Calculation

Molecule E(RB3LYP)/Ha
BH3 -26.61532
NH3 -56.55777
NH3BH3 -83.22469

The dissociation energy is therefore (E(NH3) + E(BH3)) - E(NH3BH3) = - 26.61532 - 56.55777 + 83.22469 Ha. Since Ha = 2625.499638(65) kJ/mol, the dissociation energy = + 135 kJ/mol. This value is accurate when compared to the literature value of 145 kJ/mol.[2] When this bond dissociation energy is compared to that of the covalent CH3-H bond, 423 kJ/mol,[3] it is clear that the B-N bond is much weaker than a covalent bond. However, when compared to the hydrogen bond strength for a water-neon molecule pair, 0.77 kJ/mol,[4] the B-N bond is a medium strength dative bond.

Smf115 (talk) 22:13, 15 May 2018 (BST)Really thorough and well referenced answer and calculation. Good attention to the accuracy of the figures recorded.

BBr3

3D View Of Optimised BBr3

Calculation Results For Optimised BBr3

Summary Table
File Type .log
Calculation Type FOPT
Calculation Method RB3LYP
Basis Set Gen
Energy -64.43645 a.u.
RMS Gradient Norm 0.00001 a.u.
Dipole Moment 0.00 Debye
Point Group CS
Calculation Time 0 min 35 s
Item Table 
         Item             Value       Threshold  Converged?
 Maximum Force            0.000011     0.000450     YES
 RMS     Force            0.000007     0.000300     YES
 Maximum Displacement     0.000047     0.001800     YES
 RMS     Displacement     0.000031     0.001200     YES
Optimised Parameters 
                               Optimized Parameters   
                              (Angstroms and Degrees)  
                           
 Name  Definition              Value          Derivative Info.                

 R1    R(1,2)                  1.934          -DE/DX =    0.0                 
 R2    R(1,3)                  1.934          -DE/DX =    0.0                 
 R3    R(1,4)                  1.9339         -DE/DX =    0.0                 
 A1    A(2,1,3)              119.9973         -DE/DX =    0.0                 
 A2    A(2,1,4)              120.0028         -DE/DX =    0.0                 
 A3    A(3,1,4)              119.9999         -DE/DX =    0.0                 
 D1    D(2,1,4,3)            180.0            -DE/DX =    0.0
BBr3 optimisation *.log file

Frequency Analysis

Low Frequencies
Low frequencies    -0.0001    0.0002    0.0002    0.6823    1.2779    2.4660
Low frequencies   155.9396  155.9490  267.6878

BBr3 frequency B3LYP/6-31G(d,p)LANL2DZ DSpace link

Ionic Liquids: Designer Solvents

NMe4+

3D View Of Optimised NMe4+
Calculation Results For Optimised NMe4+
Summary Table
File Type .log
Calculation Type Opt+Freq
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
Energy -214.18127 a.u.
RMS Gradient Norm 0.00007 a.u.
Dipole Moment 0.00 Debye
Point Group C1
Charge 1
Calculation Time 4 min 5 s
Item Table 
         Item             Value       Threshold  Converged?
 Maximum Force            0.000249     0.000450     YES
 RMS     Force            0.000036     0.000300     YES
 Maximum Displacement     0.000853     0.001800     YES
 RMS     Displacement     0.000253     0.001200     YES
Optimised Distances 
                               Optimized Parameters   
                              (Angstroms)  
                           
 Name  Definition              Value          Derivative Info.                

 R1    R(1,2)                  1.0901         -DE/DX =    0.0                 
 R2    R(1,3)                  1.0901         -DE/DX =    0.0                 
 R3    R(1,4)                  1.0902         -DE/DX =    0.0                 
 R4    R(1,13)                 1.5095         -DE/DX =    0.0                
 R5    R(5,7)                  1.0901         -DE/DX =    0.0                 
 R6    R(5,8)                  1.0902         -DE/DX =    0.0                 
 R7    R(5,9)                  1.0901         -DE/DX =    0.0                
 R8    R(5,13)                 1.5095         -DE/DX =    0.0                 
 R9    R(6,10)                 1.0902         -DE/DX =    0.0                 
 R10   R(6,11)                 1.0901         -DE/DX =    0.0                 
 R11   R(6,12)                 1.0901         -DE/DX =    0.0                 
 R12   R(6,13)                 1.5095         -DE/DX =    0.0                 
 R13   R(13,14)                1.5088         -DE/DX =    0.0002              
 R14   R(14,15)                1.0903         -DE/DX =   -0.0001              
 R15   R(14,16)                1.0903         -DE/DX =   -0.0001             
 R16   R(14,17)                1.0903         -DE/DX =   -0.0001
NMe4+ optimisation *.log file
Frequency Analysis
Low Frequencies
Low frequencies   -12.9787   -9.0238   -4.8995    0.0005    0.0007    0.0010
Low frequencies   182.1725  287.2913  287.9973

NMe4+ frequency *.log file

Charge Distribution
Atom Charge
H +0.269
C -0.483
N -0.295

The total charge on the NMe4+ is equally distributed among the four methyl sites.[5] The traditional picture of NMe4+ would localize a "formal" +1 charge on nitrogen for convenience - a reflection of the electron count associated with the isolated neutral atom compared to the atom in the molecule of concern. This computational result, which assigns a negative NBO charge on nitrogen, differs from the traditional model. Additionaly, the positive charge actually resides on the hydrogen atoms - invalidating the traditional picture.

Molecular Orbitals

Using this representation of the fragment orbitals, it is clear to see the fragment orbitals of MO11, MO19 and MO10 below.

Although there is a weak "in-phase" interaction between the three "p-like" methyl fragment orbitals and the fourth "s-like" orbital in MO19, MO19 possesses more nodes than MO11. It's greater antibonding character means that MO19 is higher in energy than MO11.

MO10 is highly symmetric because it comprises 4, "s-like" methyl fragment orbitals and an "s" orbital on nitrogen of opposite phase. It is lower in energy than MO11 and MO19 because there is much greater total "s" character compared to the "p" character of MO11/MO19. The shapes of the LCAO MOs accurately predict the true MO shapes for MO19, MO11 and MO10.

Smf115 (talk) 23:44, 16 May 2018 (BST)Correct LCAO approach showing understanding of how to derive MOs this way. However, a better approach would be to choose the MO here and then to break it down in to it's fragments as the ones show here aren't fully correct. Consider the BH3 MOs seen in your lectures and how these relate to the CH3 ligand FO's.

PMe4+

3D View Of Optimised PMe4+
Calculation Results For Optimised PMe4+
Summary Table
File Type .log
Calculation Type Opt+Freq
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
Energy -500.82701 a.u.
RMS Gradient Norm 0.00004 a.u.
Dipole Moment 0.00 Debye
Point Group C1
Charge 1
Calculation Time 4 min 7 s
Item Table 
         Item             Value       Threshold  Converged?
 Maximum Force            0.000068     0.000450     YES
 RMS     Force            0.000023     0.000300     YES
 Maximum Displacement     0.001006     0.001800     YES
 RMS     Displacement     0.000350     0.001200     YES
Optimised Distances 
                               Optimized Parameters   
                              (Angstroms)  
                           
 Name  Definition              Value          Derivative Info.                

 R1    R(1,2)                  1.0933         -DE/DX =    0.0                 
 R2    R(1,3)                  1.0933         -DE/DX =    0.0                 
 R3    R(1,4)                  1.0933         -DE/DX =    0.0                 
 R4    R(1,13)                 1.8165         -DE/DX =    0.0                 
 R5    R(5,7)                  1.0933         -DE/DX =    0.0                 
 R6    R(5,8)                  1.0933         -DE/DX =    0.0                 
 R7    R(5,9)                  1.0933         -DE/DX =    0.0                
 R8    R(5,13)                 1.8166         -DE/DX =   -0.0001              
 R9    R(6,10)                 1.0933         -DE/DX =    0.0                 
 R10   R(6,11)                 1.0933         -DE/DX =    0.0                 
 R11   R(6,12)                 1.0933         -DE/DX =    0.0                 
 R12   R(6,13)                 1.8166         -DE/DX =    0.0                 
 R13   R(13,14)                1.8165         -DE/DX =    0.0                 
 R14   R(14,15)                1.0933         -DE/DX =    0.0                 
 R15   R(14,16)                1.0933         -DE/DX =    0.0                 
 R16   R(14,17)                1.0933         -DE/DX =    0.0
PMe4+ optimisation *.log file
Frequency Analysis
Low Frequencies
Low frequencies    -7.0674   -0.0028   -0.0017   -0.0012    3.8043    6.4753
Low frequencies   155.9547  191.2644  191.9015

PMe4+ frequency *.log file

Charge Distribution
Atom Charge
H +0.298
C -1.060
P +1.667

In PMe4+ the phosphorus atom accommodates more positive charge than the nitrogen atom does in NMe4+ (+1.667 vs -0.295). This can be explained by the electronegativities of C,N and P - 2.55, 3.04 and 2.19 (Pauling scale) respectively. N is the most electronegative atom so its negative calculated NBO charge is reasonable. On the other hand, P is the least electronegative atom so its significant positive NBO charge is fair.


Smf115 (talk) 23:40, 16 May 2018 (BST)Good explaination of the charges due to the electronegativities, however, comparison of the C and H charges across the molecules would have improved the discussion.


Smf115 (talk) 23:53, 16 May 2018 (BST)Overall a well presented wiki report with a strong first section and further consideration of the MOs needed in the second section.

References

  1. ↑ Hunt Research Group, http://www.huntresearchgroup.org.uk/teaching/teaching_comp_lab_year2a/Tut_MO_diagram_BH3.pdf, (accessed May 2018).
  2. ↑ J. S. Binkley and L. R. Thorne, J. Chem. Phys., 1983, 79, 2932.
  3. ↑ B. E. Knox and H. B. Palmer, Chem. Rev. (Washington, DC, U. S.), 1961, 61, 247-255.
  4. ↑ M. Losonczy and J. W. Moskowitz, J. Chem. Phys., 1974, 61, 2438.
  5. ↑ S. Garde, G. Hummer and M. E. Paulaitis, J. Chem. Phys., 1998, 108, 1553.
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