Rep:Mod:ECN0511MP

Name: Estella Chin Ning
CID: 00697238

Lewis Acids and Bases Mini Project

Introduction

This mini project aims to explore and analyse the conformers, vibrations and MOs of Al₂Cl₄Br₂.
Firstly, the four possible Al₂Cl₄Br₂ isomers that can be formed from AlCl₂Br monomers were determined. They are:

Determining the Point Groups of each isomer

The point group symmetry of each isomer was then determined by identifying the symmetry elements present.

Table 1: Optimisation Comparison Table
	Isomer 1	Isomer 2	Isomer 3	Isomer 4
Structure
Symmetry Elements	E, 3 х C₂, 3 x σ_v, 3 x σ_h, 3 x S₂, i	E	E, C₂, σ_h, i	E, C₂, 2 x σ_v
Point Group	D_2h	C₁	C_2h	C_2v

Optimisation

Optimisation of energies for each isomer was then determined by first using a 3-21G optimisation, followed by a 6-31G (d,p) optimisation, then a gen [full basis set 6-31G(d,p) on Al and Cl and a PP LANL2DZdp on Br] calculation to get the final optimised structure and energy. The results are presented below.

Isomer 1

3-21G Optimisation

The results of the Al₂Cl₄Br₂ Isomer 1 3-21G optimisation are summarised in Table 2 below.

Table 2: Al₂Cl₄Br₂ Isomer 1 3-21G Optimisation
Link to log file of 3-21G Optimised Al₂Cl₄Br₂ Isomer 1
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	3-21G
Final energy	-7438.22199842 a.u.
RMS gradient norm	0.00001806 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 18 minutes 14 seconds

The expected point group symmetry of D_2h is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

 Item               Value     Threshold  Converged?
 Maximum Force            0.000037     0.000450     YES
 RMS     Force            0.000013     0.000300     YES
 Maximum Displacement     0.000987     0.001800     YES
 RMS     Displacement     0.000296     0.001200     YES
 Predicted change in Energy=-2.344066D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

6-31G (d,p) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 1 6-31G (d,p) optimisation are summarised in Table 3 below.

Table 3: Al₂Cl₄Br₂ Isomer 1 6-31G (d,p) Optimisation
Link to log file of 6-31G (d,p) Optimised Al₂Cl₄Br₂ Isomer 1
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	6-31G (d,p)
Final energy	-7469.54264936 a.u.
RMS gradient norm	0.00003193 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 6 minutes 39.5 seconds

The expected point group symmetry of D_2h is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000117     0.000450     YES
 RMS     Force            0.000044     0.000300     YES
 Maximum Displacement     0.001392     0.001800     YES
 RMS     Displacement     0.000557     0.001200     YES
 Predicted change in Energy=-1.401266D-07
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Gen (6-31G (d,p) and LanL2DZ) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 1 Gen (6-31G (d,p) and LanL2DZ) optimisation are summarised in Table 4 below.

Table 4: Al₂Cl₄Br₂ Isomer 1 Gen (6-31G (d,p) and LanL2DZ) Optimisation
Link to log file of Gen (6-31G (d,p) and LanL2DZ) Optimised Al₂Cl₄Br₂ Isomer 1
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	Gen (6-31G (d,p) and LanL2DZ)
Final energy	-2352.40630796 a.u.
RMS gradient norm	0.00000777 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 3 minutes 58.2 seconds

The expected point group symmetry of D_2h is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

 Item               Value     Threshold  Converged?
 Maximum Force            0.000029     0.000450     YES
 RMS     Force            0.000011     0.000300     YES
 Maximum Displacement     0.000682     0.001800     YES
 RMS     Displacement     0.000283     0.001200     YES
 Predicted change in Energy=-1.422361D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Isomer 2

3-21G Optimisation

The results of the Al₂Cl₄Br₂ Isomer 2 3-21G optimisation are summarised in Table 5 below.

Table 5: Al₂Cl₄Br₂ Isomer 2 3-21G Optimisation
Link to log file of 3-21G Optimised Al₂Cl₄Br₂ Isomer 2
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	3-21G
Final energy	-7438.22542072 a.u.
RMS gradient norm	0.00001098 a.u.
Dipole moment	1.66 D
Point group	C₁
Time taken for calculation	0 days 0 hours 16 minutes 12.3 seconds

The expected point group symmetry of C₁ is attained in the optimisation calculation above. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000016     0.000450     YES
 RMS     Force            0.000006     0.000300     YES
 Maximum Displacement     0.000799     0.001800     YES
 RMS     Displacement     0.000354     0.001200     YES
 Predicted change in Energy=-7.627394D-09
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

6-31G (d,p) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 2 6-31G (d,p) optimisation are summarised in Table 6 below.

Table 6: Al₂Cl₄Br₂ Isomer 2 6-31G (d,p) Optimisation
Link to log file of 6-31G (d,p) Optimised Al₂Cl₄Br₂ Isomer 2
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	6-31G (d,p)
Final energy	-7469.53985968 a.u.
RMS gradient norm	0.00002265 a.u.
Dipole moment	1.05 D
Point group	C₁
Time taken for calculation	0 days 0 hours 8 minutes 51.6 seconds

The expected point group symmetry of C₁ is attained in the optimisation calculation above. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

 Item               Value     Threshold  Converged?
 Maximum Force            0.000039     0.000450     YES
 RMS     Force            0.000018     0.000300     YES
 Maximum Displacement     0.000914     0.001800     YES
 RMS     Displacement     0.000320     0.001200     YES
 Predicted change in Energy=-3.933296D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Gen (6-31G (d,p) and LanL2DZ) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 2 Gen (6-31G (d,p) and LanL2DZ) optimisation are summarised in Table 7 below.

Table 7: Al₂Cl₄Br₂ Isomer 2 Gen (6-31G (d,p) and LanL2DZ) Optimisation
Link to log file of Gen (6-31G (d,p) and LanL2DZ) Optimised Al₂Cl₄Br₂ Isomer 2
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	Gen (6-31G (d,p) and LanL2DZ)
Final energy	-2352.41110039 a.u.
RMS gradient norm	0.00005450 a.u.
Dipole moment	0.13 D
Point group	C₁
Time taken for calculation	0 days 0 hours 3 minutes 33.6 seconds

The expected point group symmetry of C₁ is attained in the optimisation calculation above. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000085     0.000450     YES
 RMS     Force            0.000037     0.000300     YES
 Maximum Displacement     0.001698     0.001800     YES
 RMS     Displacement     0.000689     0.001200     YES
 Predicted change in Energy=-1.740389D-07
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Isomer 3

3-21G Optimisation

The results of the Al₂Cl₄Br₂ Isomer 3 3-21G optimisation are summarised in Table 8 below.

Table 8: Al₂Cl₄Br₂ Isomer 3 3-21G Optimisation
Link to log file of 3-21G Optimised Al₂Cl₄Br₂ Isomer 3
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	3-21G
Final energy	-7438.22904525 a.u.
RMS gradient norm	0.00002142 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 9 minutes 29.9 seconds

The expected point group symmetry of C_2h is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000046     0.000450     YES
 RMS     Force            0.000013     0.000300     YES
 Maximum Displacement     0.001133     0.001800     YES
 RMS     Displacement     0.000378     0.001200     YES
 Predicted change in Energy=-4.356919D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

6-31G (d,p) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 3 6-31G (d,p) optimisation are summarised in Table 9 below.

Table 9: Al₂Cl₄Br₂ Isomer 3 6-31G (d,p) Optimisation
Link to log file of 6-31G (d,p) Optimised Al₂Cl₄Br₂ Isomer 3
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	6-31G (d,p)
Final energy	-7469.53758654 a.u.
RMS gradient norm	0.00003242 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 8 minutes 43.2 seconds

The expected point group symmetry of C_2h is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000052     0.000450     YES
 RMS     Force            0.000024     0.000300     YES
 Maximum Displacement     0.000617     0.001800     YES
 RMS     Displacement     0.000308     0.001200     YES
 Predicted change in Energy=-7.219445D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Gen (6-31G (d,p) and LanL2DZ) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 3 Gen (6-31G (d,p) and LanL2DZ) optimisation are summarised in Table 10 below.

Table 10: Al₂Cl₄Br₂ Isomer 3 Gen (6-31G (d,p) and LanL2DZ) Optimisation
Link to log file of Gen (6-31G (d,p) and LanL2DZ) Optimised Al₂Cl₄Br₂ Isomer 3
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	Gen (6-31G (d,p) and LanL2DZ)
Final energy	-2352.41629239 a.u.
RMS gradient norm	0.00003186 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 3 minutes 37.6 seconds

The expected point group symmetry of C_2h is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

 Item               Value     Threshold  Converged?
 Maximum Force            0.000050     0.000450     YES
 RMS     Force            0.000018     0.000300     YES
 Maximum Displacement     0.000427     0.001800     YES
 RMS     Displacement     0.000169     0.001200     YES
 Predicted change in Energy=-1.597545D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Isomer 4

3-21G Optimisation

The results of the Al₂Cl₄Br₂ Isomer 4 3-21G optimisation are summarised in Table 11 below.

Table 11: Al₂Cl₄Br₂ Isomer 4 3-21G Optimisation
Link to log file of 3-21G Optimised Al₂Cl₄Br₂ Isomer 4
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	3-21G
Final energy	-7438.22885199 a.u.
RMS gradient norm	0.00003640 a.u.
Dipole moment	2.1693 D
Point group	C₁
Time taken for calculation	0 days 0 hours 20 minutes 43.6 seconds

The expected point group symmetry of C_2v is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000079     0.000450     YES
 RMS     Force            0.000026     0.000300     YES
 Maximum Displacement     0.001760     0.001800     YES
 RMS     Displacement     0.000594     0.001200     YES
 Predicted change in Energy=-5.836772D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

6-31G (d,p) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 4 6-31G (d,p) optimisation are summarised in Table 12 below.

Table 12: Al₂Cl₄Br₂ Isomer 4 6-31G (d,p) Optimisation
Link to log file of 6-31G (d,p) Optimised Al₂Cl₄Br₂ Isomer 4
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	6-31G (d,p)
Final energy	-7469.53765574 a.u.
RMS gradient norm	0.00003383 a.u.
Dipole moment	1.1525 D
Point group	C₁
Time taken for calculation	0 days 0 hours 7 minutes 36.0 seconds

The expected point group symmetry of C_2v is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000053     0.000450     YES
 RMS     Force            0.000025     0.000300     YES
 Maximum Displacement     0.001133     0.001800     YES
 RMS     Displacement     0.000329     0.001200     YES
 Predicted change in Energy=-8.040274D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Gen (6-31G (d,p) and LanL2DZ) Optimisation

The results of the Al₂Cl₄Br₂ Isomer 4 Gen (6-31G (d,p) and LanL2DZ) optimisation are summarised in Table 13 below.

Table 13: Al₂Cl₄Br₂ Isomer 4 Gen (6-31G (d,p) and LanL2DZ) Optimisation
Link to log file of Gen (6-31G (d,p) and LanL2DZ) Optimised Al₂Cl₄Br₂ Isomer 4
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	Gen (6-31G (d,p) and LanL2DZ)
Final energy	-2352.41628070 a.u.
RMS gradient norm	0.00001475 a.u.
Dipole moment	0.15 D
Point group	C₁
Time taken for calculation	0 days 0 hours 5 minutes 4.0 seconds

The expected point group symmetry of C_2v is not attained in the optimisation calculation above. This is because higher accuracy calculations are required to attain the correct point group symmetry of the Al₂Cl₄Br₂ molecule. In addition, the gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000040     0.000450     YES
 RMS     Force            0.000016     0.000300     YES
 Maximum Displacement     0.001320     0.001800     YES
 RMS     Displacement     0.000411     0.001200     YES
 Predicted change in Energy=-2.520994D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Optimisation Summary

The comparison of the results from the final optimisation step (Gen: 6-31G (d,p) and LanL2DZ) between the 4 Al₂Cl₄Br₂ isomers are summarised in Table 14 below.

Table 14: Optimisation Comparison Table
Summary	Isomer 1	Isomer 2	Isomer 3	Isomer 4
Structure
Final energy (a.u.)	-2352.40630796	-2352.41110039	-2352.41629239	-2352.41628070
Final energy (kJmol^-1)	-6,176,242.759	-6,176,255.343	-6,176,268.975	-6,176,268.943
Final energy relative to the lowest energy conformer (Isomer 3) (kJmol^-1)	+26.216	+13.632	0	+0.03186
RMS gradient norm (a.u.)	0.00000777	0.00005450	0.00003186	0.00001475
Dipole moment	0.00 D	0.13 D	0.00 D	0.15 D
Time taken for calculation	0 days 0 hours 3 minutes 58.2 seconds	0 days 0 hours 3 minutes 33.6 seconds	0 days 0 hours 3 minutes 37.6 seconds	0 days 0 hours 5 minutes 4.0 seconds

Discussion: Position of Br atoms w.r.t stability of different conformers

Comparing the final energies of the conformers, the stability of the 4 different isomers can be ranked in the order (from least stable to most stable):

Isomer 1 < Isomer 2 < Isomer 4 < Isomer 3

The difference in stabilities can be rationalised by the position of the Br atoms in the conformers:
1. Whether the Br atoms are bridging or terminal atoms
2. If the 2 Br atoms are terminal atoms (Isomers 3 and 4), whether the Br atoms are cis or trans to each other

1. Bridging or terminal Br atoms
When a Br atom is in a bridging position, it forms 2 Al - Br bonds as compared to 1 Al - Br bond when it is in a terminal position. Since a Br atom has a relatively larger size as compared to a Cl atom, it has more diffuse atomic orbitals, and hence form a less effective overlap with the atomic orbitals of the Al atom, resulting in the formation of a weaker Al - Br bond as compared to a Al - Cl bond. This means that a bridging Br atom (2 x weak Al - Br bonds) will result in a higher energy, less stable conformer as compared to a bridging Cl atom (2 x strong Al - Cl bonds). This effect is additive; the more the number of bridging Br atoms, the more the number of Al - Br bonds, the less stable the conformer. Comparing the different isomers, isomer 1 has 2 bridging Br atoms and 4 x Al - Br bonds, isomer 2 has 1 bridging Br atom, 1 terminal Br atom and 3 x Al - Br bonds, while both isomers 3 and 4 have 0 bridging Br atoms, 2 terminal Br atoms and 2 Al - Br bonds. This results in the observed trend of relative stabilities Isomer 1 < Isomer 2 < Isomers 3 & 4.

2. Cis or trans Br atoms
Although both isomers 3 and 4 do not contain bridging Br atoms, isomer 3 is slightly more stable than isomer 4, which can be explained by the arrangement of the terminal Br atoms relative to each other. Isomer 3 contains the Br atoms in a trans arrangement (opposite sides), while isomer 4 contains the Br atoms arranged in a cis arrangement (same side). Consequently, isomer 3 has no net dipole moment as the dipole moments cancel each other as compared to isomer 4 which has a net dipole moment of 0.15 D (c.f. Table 13). Non-polar molecules are relatively more stable than their polar isomers as they are less reactive. Hence, this gives us the observed trend of relative stabilities Isomer 1 < Isomer 2 < Isomers 4 < Isomer 3.

Dissociation Energy for Isomer 3

The dissociation energy for the lowest energy conformer of Al₂Cl₄Br₂ (Isomer 3) into 2 AlCl₂Br monomers were then computed. This was done by first optimising the energies of a AlCl₂Br molecule in the same way as before (3-21G, 6-31G (d,p), gen (6-31 (d,p) and LanL2DZ)).

Optimisation of AlCl₂Br Monomers

3-21G Optimisation

The results of the AlCl₂Br 3-21G optimisation are summarised in Table 15 below.

Table 15: AlCl₂Br 3-21G Optimisation
Link to log file of 3-21G Optimised AlCl₂Br
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	3-21G
Final energy	-3719.09049394 a.u.
RMS gradient norm	0.00009870 a.u.
Dipole moment	1.13 D
Point group	C₁
Time taken for calculation	0 days 0 hours 3 minutes 37.1 seconds

The gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000148     0.000450     YES
 RMS     Force            0.000082     0.000300     YES
 Maximum Displacement     0.001216     0.001800     YES
 RMS     Displacement     0.000823     0.001200     YES
 Predicted change in Energy=-1.795635D-07
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

6-31G (d,p) Optimisation

The results of the AlCl₂Br 6-31G (d,p) optimisation are summarised in Table 16 below.

Table 16: AlCl₂Br 6-31G (d,p) Optimisation
Link to log file of 6-31G (d,p) Optimised AlCl₂Br
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	6-31G (d,p)
Final energy	-33.74850546 a.u.
RMS gradient norm	0.00003286 a.u.
Dipole moment	0.69 D
Point group	C₁
Time taken for calculation	0 days 0 hours 2 minutes 4.5 seconds

The gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000121     0.000450     YES
 RMS     Force            0.000065     0.000300     YES
 Maximum Displacement     0.001490     0.001800     YES
 RMS     Displacement     0.000940     0.001200     YES
 Predicted change in Energy=-1.514838D-07
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Gen (6-31G (d,p) and LanL2DZ) Optimisation

The results of the AlCl₂Br Gen (6-31G (d,p) and LanL2DZ) optimisation are summarised in Table 17 below.

Table 17: AlCl₂Br Gen (6-31G (d,p) and LanL2DZ) Optimisation
Link to log file of Gen (6-31G (d,p) and LanL2DZ) Optimised AlCl₂Br
Link to D-Space
File Type	.log
Calculation type	FOPT
Calculation method	RB3LYP
Basis set	Gen (6-31G (d,p) and LanL2DZ)
Final energy	-1176.19013709 a.u.
RMS gradient norm	0.00001883 a.u.
Dipole moment	0.11 D
Point group	C₁
Time taken for calculation	0 days 0 hours 1 minutes 22.0 seconds

The gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Item               Value     Threshold  Converged?
 Maximum Force            0.000041     0.000450     YES
 RMS     Force            0.000025     0.000300     YES
 Maximum Displacement     0.000401     0.001800     YES
 RMS     Displacement     0.000244     0.001200     YES
 Predicted change in Energy=-1.323149D-08
 Optimization completed.
    -- Stationary point found.

The table above shows that the forces have converged, meaning that for a small displacement, the energy does not change. This further confirms the successful optimisation of the molecule.

Calculation of Dissociation Energy

The comparison table of reaction energies between AlCl₂Br and Al₂Cl₄Br₂ can be found in Table 18 below.

Table 18: Comparison of AlCl₂Br and Al₂Cl₄Br₂ reaction energies
E (AlCl₂Br) / a.u.	- 1176.19013709
E (Al₂Cl₄Br₂, Isomer 3) / a.u.	- 2352.41629239
Energy Difference/ a.u.	- 2352.41629239 - ( - 1176.19013709 - 1176.19013709 ) = - 0.036018
Energy Difference = Association Energy / kJmol^-1	- 0.036018 x 2625.50 = - 94.565259 = - 90 (Accuracy up to 10kJ/mol)
Dissociation Energy / kJmol^-1	94.565259 = - 90 (Accuracy up to 10kJ/mol)

Discussion: Comparison of Reactant and Product Stabilities

The product is more stable than the reactant. This can be inferred from the negative association energy, meaning that the combination of 2 AlCl₂Br molecules to form isomer 3 of Al₂Cl₄Br₂ is an exothermic process involving the release of energy. In the same way, since the dissociation energy is positive, this suggests that the breaking up of the Al₂Cl₄Br₂ dimer molecule into 2 AlCl₂Br monomer molecules is an endothermic process, i.e., energy is required to convert the more stable Al₂Cl₄Br₂ dimer molecule into 2 less stable AlCl₂Br monomer molecules.

Frequency Analysis

The frequency analysis for each conformer was then calculated and the results presented below.

Isomer 1

The results of the frequency calculations are summarised in Table 19 below.

Table 19: Isomer 1 Frequency Calculations
Link to log file of Isomer 1 Frequency analysis
Link to D-Space
File Type	.log
Calculation type	FREQ
Calculation method	RB3LYP
Basis set	Gen (6-31 (d,p) and LanL2DZ)
Final energy	-2352.40630796 a.u. (Same (up to last 2 d.p.) as that recorded in optimisation step)
RMS gradient norm	0.00000777 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 4 minutes 16.1 seconds

The gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Low frequencies ---   -5.1406   -5.0830   -3.1891   -0.0024   -0.0014    0.0008
Low frequencies ---   14.8596   63.2584   86.0498

The low frequencies are within the range of ± 15 cm^-1 and close to 0, indicating that the method employed in the frequency calculations was sufficiently accurate.

Isomer 2

The results of the frequency calculations are summarised in Table 20 below.

Table 20: Isomer 2 Frequency Calculations
Link to log file of Isomer 2 Frequency analysis
Link to D-Space
File Type	.log
Calculation type	FREQ
Calculation method	RB3LYP
Basis set	Gen (6-31 (d,p) and LanL2DZ)
Final energy	-2352.41110039 a.u. (Same (up to last 2 d.p.) as that recorded in optimisation step)
RMS gradient norm	0.00005448 a.u.
Dipole moment	0.13 D
Point group	C₁
Time taken for calculation	0 days 0 hours 4 minutes 4.3 seconds

The gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Low frequencies ---   -3.6216   -2.0558   -0.0006    0.0007    0.0029    3.2124
Low frequencies ---   17.3982   55.7388   80.0202

The low frequencies are within the range of ± 15 cm^-1 and close to 0, indicating that the method employed in the frequency calculations was sufficiently accurate.

Isomer 3

The results of the frequency calculations are summarised in Table 21 below.

Table 21: Isomer 3 Frequency Calculations
Link to log file of Isomer 3 Frequency analysis
Link to D-Space
File Type	.log
Calculation type	FREQ
Calculation method	RB3LYP
Basis set	Gen (6-31 (d,p) and LanL2DZ)
Final energy	-2352.41629239 a.u. (Same (up to last 2 d.p.) as that recorded in optimisation step)
RMS gradient norm	0.00003185 a.u.
Dipole moment	0.00 D
Point group	C₁
Time taken for calculation	0 days 0 hours 4 minutes 25.2 seconds

The gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Low frequencies ---   -3.1697   -2.0334    0.0017    0.0024    0.0027    1.4953
Low frequencies ---   17.8868   49.0567   72.9517

The low frequencies are within the range of ± 15 cm^-1 and close to 0, indicating that the method employed in the frequency calculations was sufficiently accurate.

Isomer 4

The results of the frequency calculations are summarised in Table 22 below.

Table 22: Isomer 4 Frequency Calculations
Link to log file of Isomer 4 Frequency analysis
Link to D-Space
File Type	.log
Calculation type	FREQ
Calculation method	RB3LYP
Basis set	Gen (6-31 (d,p) and LanL2DZ)
Final energy	-2352.41628070 a.u. (Same (up to last 2 d.p.) as that recorded in optimisation step)
RMS gradient norm	0.00001475 a.u.
Dipole moment	0.17 D
Point group	C₁
Time taken for calculation	0 days 0 hours 4 minutes 26.4 seconds

The gradient is less than 0.0001 (expected gradient = 0 for a stationary point), indicating that the molecule has indeed been optimised.

Low frequencies ---   -2.2625   -1.6206   -0.0032   -0.0010    0.0012    3.6729
Low frequencies ---   17.0797   51.2950   78.5578

The low frequencies are within the range of ± 15 cm^-1 and close to 0, indicating that the method employed in the frequency calculations was sufficiently accurate.

Infrared (IR) Spectra

Table 23: Infrared Spectra of the 4 Al₂Cl₄Br₂ Isomers
Isomer No.	No. of observed IR Peaks (cm^-1)	Frequency of observed IR Peaks (cm^-1)
1	8	15, 108, 126, 138, 241, 341, 467, 616
2	18	17, 56, 80, 92, 107, 109,121, 149, 154, 186, 211, 257, 289, 385, 423, 493, 574, 614
3	9	18, 49, 117, 120, 160, 280, 413, 421, 579
4	15	17, 79, 99, 103, 121, 123, 158, 194, 279, 308, 413, 420, 461, 570, 582

Discussion: Conformer symmetry & No. of IR peaks

The number of bands that are visible in a IR spectrum is directly related to the number of vibrations which give rise to a change in the net dipole moment of the molecule. That is, a vibration is only IR active when it is associated with a change in the net dipole moment of the molecule. When 2 or more different vibrations are associated with the same energy, they give rise to degenerate peaks and hence only 1 peak shows up in the IR spectrum. However, for the 4 different isomers of Al₂Cl₄Br₂, no degenerate peaks were detected in the calculations, hence the difference in the number of IR peaks in the 4 spectra can be attributed to the difference in the number of vibrations which cause a change in the net dipole moment of each conformer.

The higher the symmetry of the isomer, the more the number of symmetrical stretching and bending vibrational modes. These vibrations do not change the net dipole moment of the molecule, giving rise to IR peaks with zero intensity that do not show up in the IR spectrum. Thus, more symmetrical molecules have fewer bands in their IR spectrum. This is corroborated by the difference in the number of IR peaks observed in the table above; the most symmetrical isomer (isomer 1) has the fewest number of IR peaks (most peaks with zero intensity), while the least symmetrical isomer (isomer 2) has the most number of IR peaks (no peaks with zero intensity).

Comparing Vibrational Frequencies

Isomer 1

‎

Table 24 : Al - Br Vibrational Modes of Al₂Cl₄Br₂ Isomer 1
No.	Vibration	Description	Position of Stretching Br atom	Al - Br Stretch		Frequency (cm^-1)	Intensity
No.	Vibration	Description	Position of Stretching Br atom	Nature	Position	Frequency (cm^-1)	Intensity
1.		The 2 Al atoms move towards and away from the 2 Br atoms in a concerted motion (in and out from the center of the molecule), together with the simultaneous movement of the Cl atoms towards and away from the center of the molecule in the same direction of the Al atom, causing only the simultaneous stretching of the bridging Br - Al bonds (the Al-Br bonds lengthen and shorten at the same time). The 2 bridging Br atoms are stationary.	Both bridging	Symmetric	13	247	0
2.		The 2 Al atoms move towards and away from the 2 Br atoms in an alternated motion (in and out from the center of the molecule), together with the simultaneous movement of the Cl atoms towards and away from the center of the molecule in the same direction of the Al atom nearer to them, causing only the alternated stretching of the bridging Br - Al bonds (2 Al-Br bonds lengthen and shorten at the same time). The 2 bridging Br atoms are stationary.	Both bridging	Asymmetric	12	241	100
3.		The 2 Al atoms move towards the Br atoms, one Br atom at a time, in a concerted motion. This causes the simultaneous Al-Br-Al stretching (Al-Br bonds in a Al-Br-Al fragment lengthens and shortens at the same time, alternating with the lengthening and shortening of the Al-Br bonds in the other Al-Br-Al fragment). The bridging Br atoms and the terminal Cl atoms are stationary.	Both bridging	Symmetric	14	341	161
4.		The 2 Al atoms move towards the Br atoms, one Br atom at a time, in an alternated motion. (As one Al atom moves towards one Br atom, the other Al atom moves towards the other Br atom) This causes the alternating Al-Br-Al stretching (Al-Br bonds in a Al-Br-Al fragment take turns to lengthen and shorten, and the same happens to the Al-Br bonds in the other Al-Br-Al fragment). The bridging Br atoms and the terminal Cl atoms are stationary.	Both bridging	Asymmetric	11	197	0

Isomer 2

‎

Table 25 : Al - Br Vibrational Modes of Al₂Cl₄Br₂ Isomer 2
No.	Vibration	Description	Position of Stretching Br atom	Al - Br Stretch		Frequency (cm^-1)	Intensity
No.	Vibration	Description	Position of Stretching Br atom	Nature	Position	Frequency (cm^-1)	Intensity
1.		The Al atom situated between the terminal and bridging Br atoms move up and down along the terminal Cl - Al bond axis, while the terminal Cl atom attached to it moves towards and away from it in a concerted motion. This results in both the terminal Br - Al and terminal Cl - Al bond stretching. All other atoms remain stationary (including the 2 Br atoms).	Only terminal	-	17	574	122
2.		The Al atom situated between the terminal and bridging Br atoms move left and right along the bridging Cl - Al bond axis. This results in both the terminal Br - Al and bridging Cl - Al bond stretching. All other atoms remain stationary (including the 2 Br atoms).	Only terminal	-	15	423	274
3.		The 2 Al atoms move towards the bridging Cl and Br atoms, one atom at a time, while the bridging Cl atom moves towards and away from the Al atoms, in a concerted motion. This causes the simultaneous Al-bridging Br-Al stretching (Al-Br bonds in a Al-Br-Al fragment lengthens and shortens at the same time, alternating with the lengthening and shortening of the Al-bridging Cl bonds in the Al-bridging Cl-Al fragment). The terminal Cl atoms and the 2 Br atoms are stationary.	Only bridging	-	14	385	153
4.		The 2 Al atoms move, in an alternating fashion, towards the bridging Br and Cl atoms, one atom at a time, while the bridging Br atom moves towards and away from its adjacent Al atoms concertedly.(As one Al atom moves towards the bridging Br atom, the other Al atom moves towards the bridging Cl atom) This causes the alternating Al-bridging Br-Al stretching (Al-bridging Br bonds in a Al-bridging Br-Al fragment take turns to lengthen and shorten, and the same happens to the Al-bridging Cl bonds in the Al-bridging Cl-Al fragment). The terminal Br and Cl atoms and the bridging Cl atoms are stationary.	Only bridging	-	11	211	21

The nature of the Al - Br stretching cannot be classified into symmetrical and asymmetrical stretching as the molecule is not a symmetrical one.

Isomer 3

Table 26 : Al - Br Vibrational Modes of Al₂Cl₄Br₂ Isomer 3
No.	Vibration	Description	Position of Stretching Br atom	Al - Br Stretch		Frequency (cm^-1)	Intensity
No.	Vibration	Description	Position of Stretching Br atom	Nature	Position	Frequency (cm^-1)	Intensity
1.		The 2 Al atoms move up and down, in a concerted motion, along the terminal Cl - Al bond axis, while the 2 terminal Cl atoms move towards and away from the Al atoms at the same time. This causes the alternating stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond shortens). The bridging Cl atoms and the terminal Br atoms are stationary.	Both terminal	Asymmetric	18	580	316
2.		The 2 Al atoms move up and down, in an alternating fashion, along the terminal Cl - Al bond axis, while the 2 terminal Cl atoms move towards and away from the Al atoms at the same time. This causes the concerted stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond lengthens as well). The bridging Cl atoms and the terminal Br atoms are stationary.	Both terminal	Symmetric	17	575	0
3.		The 2 Al atoms move in and out, in a concerted fashion, towards the 2 bridging Cl atoms (towards and away from the center of the molecule), along the Al - bridging Cl bond axis. This causes the concerted stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond lengthens as well). The bridging Cl atoms and the terminal Br and Cl atoms are stationary.	Both terminal	Symmetric	16	459	0
4.		The 2 Al atoms move in and out, in an alternating fashion, towards the 2 bridging Cl atoms (towards and away from the center of the molecule), along the Al - bridging Cl bond axis. This causes the alternating stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond shortens). The bridging Cl atoms and the terminal Br and Cl atoms are stationary.	Both terminal	Asymmetric	15	421	439

Isomer 4

‎

Table 27 : Al - Br Vibrational Modes of Al₂Cl₄Br₂ Isomer 4
No.	Vibration	Description	Position of Stretching Br atom	Al - Br Stretch		Frequency (cm^-1)	Intensity
No.	Vibration	Description	Position of Stretching Br atom	Nature	Position	Frequency (cm^-1)	Intensity
1.		The 2 Al atoms move up and down, in a concerted motion, along the terminal Cl - Al bond axis, while the 2 terminal Cl atoms move towards and away from the Al atoms at the same time. This causes the concerted stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond lengthens as well). The bridging Cl atoms and the terminal Br atoms are stationary.	Both terminal	Symmetric	18	582	278
2.		The 2 Al atoms move up and down, in an alternating fashion, along the terminal Cl - Al bond axis, while the 2 terminal Cl atoms move towards and away from the Al atoms at the same time. This causes the alternating stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond shortens). The bridging Cl atoms and the terminal Br atoms are stationary.	Both terminal	Asymmetric	17	570	32
3.		The 2 Al atoms move in and out, in a concerted fashion, towards the 2 bridging Cl atoms (towards and away from the center of the molecule), along the Al - bridging Cl bond axis. This causes the concerted stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond lengthens as well). The bridging Cl atoms and the terminal Br and Cl atoms are stationary.	Both terminal	Symmetric	16	461	35
4.		The 2 Al atoms move in and out, in an alternating fashion, towards the 2 bridging Cl atoms (towards and away from the center of the molecule), along the Al - bridging Cl bond axis. This causes the alternating stretching of the Al - Br bonds (As one Al-Br bond lengthens, the other Al-Br bond shortens). The bridging Cl atoms and the terminal Br and Cl atoms are stationary.	Both terminal	Asymmetric	15	420	410

Comparison of Al-Br Vibrational Frequencies

Table 28: Comparison table of Key Al-Br Vibrational Frequencies
	Isomer 1	Isomer 2	Isomer 3	Isomer 4
Structure
Position of Br atom(s) involved in stretching	Both bridging	One bridging, one terminal	Both terminal	Both terminal
Al-Br Stretch Frequency Position	11-14	11,14 (Only bridging) 15,17 (Only terminal)	15-18	15-18
Frequency Range (cm^-1)	197-341	211-574	421-580	420-582

Discussion: Comparison of Key Vibrational Frequencies

As can be inferred from Table 28, Isomer 1, whose 4 key vibrational modes all entails the stretching of the Al-bridging Br bonds, have a lower Al-Br stretch frequency position (11-14) and corresponding frequency range (197-341 cm^-1) as compared to Isomers 3 and 4, whose 4 key vibrational modes all entails the stretching of the Al-terminal Br bonds (Al-Br stretch frequency position: 15-18; Corresponding frequency range: 421-582 (Isomer 3) and 420-582 (Isomer 4)). This can be rationalised by the fact that the bridging Al-Br bonds are weaker than the terminal Al-Br bonds. The reason for this phenomenon is that the terminal Al-Br bond consists of a normal 2C-2e covalent bond, whereby the terminal Br atom only has to share 1 electron, while the bridging Al-Br bonds consist of 1 normal Al-Br covalent bond and 1 dative Al-Br bond. Since the electronegative Br atom now has to share 3 of its electrons over 3 atoms (Al-Br-Al fragment), this results in weaker bridging Al-Br bonds relative to terminal Al-Br bonds. A weaker Al-Br bond results in a lower Al-Br bond strength and corresponding lower force constant (k), which is directly proportional to the frequency of the vibration. Hence, bond stretching involving terminal Br atoms will have higher frequencies as compared to those involving bridging Br atoms. As such, a lower vibration frequency range can be expected for isomer 1 as compared to isomers 3 and 4, which corroborates with the frequency calculations.

Isomer 2, which contains 2 vibrational modes from the Al-terminal Br bond stretching and 2 vibrational modes from the Al-bridging Br bond stretching, has Al-Br stretch frequency positions that falls within the range of both the Al-bridging Br stretching and Al-terminal Br stretching (11,14 (bridging range) 15,17 (terminal range)). This trend is also observed in its corresponding frequency range; the frequencies 211 cm^-1 and 385 cm^-1 fall within the bridging range, while the frequencies 423 cm^-1 and 574 cm^-1 fall within the terminal range. In conclusion, these findings show that the computational calculations provide frequency results that correspond with what we would expect theoretically.

Molecular Orbitals of Al₂Cl₄Br₂ (Isomer 3)

A MO Calculation of the lowest energy conformer of Al₂Cl₄Br₂ (Isomer 3) was then carried out, and the relevant links to the log file and the d-space can be found below.
Link to log file
Link to D-Space
The occupied, non-core MO structures of Al₂Cl₄Br₂ (Isomer 3) are depicted in Figure 2.

Figure 2: Occupied, non-core MO structures

5 MOs ranging from highly bonding to highly antibonding were then chosen, and the interactions occuring in those MOs were analysed and described in Table 29.

Table 29 : Description of 5 Chosen MO Interactions
MO No.	Energy	Description	Overall Interaction
54	-0.06385	The 2 bridging Cl atoms are aligned parallel to each other, and hence their p orbitals undergo strong, through space, in-phase bonding interactions (light blue arrows). Weak, through space, in-phase bonding interactions (green arrows) are present between the p AOs of the terminal Cl and Br atoms that are attached to different Al atoms. There are strong, through-space, out of phase, antibonding interactions (dark blue arrows) present between the p AOs of the 2 bridging Cl atoms and the 2 terminal Br atoms. The p AOs of the terminal Cl and Br atoms that are attached to the same Al atom also undergo moderate, through space, out-of-phase, antibonding interactions (red arrows). There are also 4 p atomic orbital nodes (pink dots) present at the terminal Cl and Br atoms, as well as 3 nodal planes (pink dotted line): 2 that cuts vertically through the 2 Al atoms, and 1 that cuts horizontally through the Al and bridging Cl atoms, increasing the antibonding character of the MO. Hence, this MO is overall strongly antibonding as there are stronger and more antibonding elements present than bonding interactions. The electron density is moderately delocalised over the entire MO as can be observed by the spread of the electron density over most of the atoms of the molecule, however, the lack of electron density observed over the bonds and the Al atoms indicate that the MO is not strongly delocalised over the entire molecule. NO AO interactions are present.	Strongly antibonding
46	-0.37179	Moderate, through space, in-phase bonding interactions (dark blue arrows) are present between the p AOs of the 2 bridging Cl atoms that are aligned parallel to each other. There are strong, through space, out-of-phase antibonding interactions (red and light blue arrows) present between the terminal Cl and Br atoms, and the bridging Cl atoms due to the close proximity of the relevant p orbitals. There are also 6 p atomic orbital nodes (pink dots) present at the Cl and Br atoms, as well as 3 nodal planes (pink dotted line) that cuts horizontally and vertically through the 2 Al atoms, increasing the antibonding character of the MO. Hence, this MO is overall antibonding as there are stronger and more antibonding elements present than bonding interactions. The electron density is largely delocalised over the entire MO as can be observed by the large spread of the electron density over all the atoms of the molecule, except for the 2 Al atoms. No AO interactions are present.	Moderately antibonding
37	-0.51122	There are very strong, in-phase bonding interactions between the adjacent Al s AO, the terminal Cl and Br p AOs and the bridging Cl p AOs, all of which are orientated in the correct phase for favourable strong bonding overlap. The p AOs of the terminal Br and Cl atoms, and the bridging Cl atoms, that are attached to the same Al atom have strong, through space, in-phase bonding interactions (red arrows).The p AOs of the terminal Br and Cl atoms that are attached to the same Al atom have moderate, through space, in-phase bonding interactions (light blue arrows). The p AOs of the bridging Cl atoms and the terminal Br or Cl atoms undergo moderate, through space, out-of-phase antibonding interactions (green arrows). The p AOs of the terminal cis Cl and Br atoms that are attached to different Als undergo very weak, through space, out-of-phase antibonding interactions (dark blue arrows) due to their distant proximity with respect to each other. There are also 4 p atomic orbital nodes (pink dots) present at the terminal Cl and Br atoms, as well as a nodal plane (pink dotted line) that cuts through the center of the molecule, through the 2 bridging Cl atoms, increasing the antibonding character of the MO. The balance of the strong AO and through space bonding interactions and the multiple antibonding interactions and nodes give rise to an overall non-bonding character of the MO. The electron density is delocalised over the entire MO as can be observed by the large spread of the electron density over all the atoms of the molecule.	Non-bonding
36	-0.77930	There are very weak, through space, in-phase bonding interactions (blue arrows) between the 2 terminal Br atoms that are arranged trans and hence are situated far away from each other. This gives rise to a very weakly bonding (almost non-bonding) interaction. The MO is not delocalised as the electron density is largely localised on the 2 terminal Br atoms, as visualised by the electron density cloud only present on the Br atoms. No AO interactions are present.	Weakly bonding
31	-0.91061	There are strong, through space, in-phase bonding interactions (blue arrows) between the 2 bridging Cl s orbitals that are situated within close proximity to one another. This gives rise to a overall strongly bonding interaction. The MO is not delocalised as the electron density is largely localised on the 2 bridging Cl atoms, as visualised by the electron density cloud only present on the bridging Cl atoms.	Strongly bonding

Lewis Acids and Bases Mini Project

Introduction

Determining the Point Groups of each isomer

Optimisation

Isomer 1

3-21G Optimisation

6-31G (d,p) Optimisation

Gen (6-31G (d,p) and LanL2DZ) Optimisation

Isomer 2

3-21G Optimisation

6-31G (d,p) Optimisation

Gen (6-31G (d,p) and LanL2DZ) Optimisation

Isomer 3

3-21G Optimisation

6-31G (d,p) Optimisation

Gen (6-31G (d,p) and LanL2DZ) Optimisation

Isomer 4

3-21G Optimisation

6-31G (d,p) Optimisation

Gen (6-31G (d,p) and LanL2DZ) Optimisation

Optimisation Summary

Discussion: Position of Br atoms w.r.t stability of different conformers

Dissociation Energy for Isomer 3

Optimisation of AlCl2Br Monomers

3-21G Optimisation

6-31G (d,p) Optimisation

Gen (6-31G (d,p) and LanL2DZ) Optimisation

Calculation of Dissociation Energy

Discussion: Comparison of Reactant and Product Stabilities

Frequency Analysis

Isomer 1

Isomer 2

Isomer 3

Isomer 4

Infrared (IR) Spectra

Discussion: Conformer symmetry & No. of IR peaks

Comparing Vibrational Frequencies

Isomer 1

Isomer 2

Isomer 3

Isomer 4

Comparison of Al-Br Vibrational Frequencies

Discussion: Comparison of Key Vibrational Frequencies

Molecular Orbitals of Al2Cl4Br2 (Isomer 3)

Optimisation of AlCl₂Br Monomers

Molecular Orbitals of Al₂Cl₄Br₂ (Isomer 3)