Preface
Chapter 4: Results and discussions 4.1 Introduction
4.4 Calculation of the vacant space size
4.4.1 Calculation of the vacant space size with the new defined techniques
4.4.1.5 Comparison of the vacant space sizes calculated with the modified techniques
In summary, the size of the van der Waals radii according to Bondi[3] had an influence on the vacant space sizes. The most notable difference between the complexes is that the largest van der Waals radii resulted in the smallest vacant space size for the G complexes. On the other hand, in the B and A complexes, the highly electronegative fluorine containing complex had a larger vacant space than the smaller hydrogen containing complexes.
4.4.1.5 Comparison of the vacant space sizes calculated with the modified
On the other hand, the (b, c) changes in the vacant space size are identical at the same P(4)-Ru bond lengths for both the techniques. This means that the techniques are similar to one another since they calculate the same trends from the same data.
Figure 4.51: Comparison between the change in the modified Tolman and outer pocket sizes for the vacant space of the G4 complex
In Figure 4.52, the change in the vacant space size of the B4 complex that was calculated with the outer pocket and the modified Tolman techniques, was plotted against the increasing P(4)-Ru bond length. The change in the vacant space size at point (a) is identical in the modified Tolman and the outer pocket techniques for the B4 complex unlike with the G4 complex. Moreover, the changes in the vacant space in the modified Tolman technique are identical to the outer pocket technique at the same (b, c and d) P(4)-Ru bond lengths.
Consequently, the trends for both techniques are identical.
The biggest difference between these two techniques is that the change in the vacant space size is larger for the modified Tolman technique than for the outer pocket technique. The modified Tolman technique is based on the side view of a cone angle like with the Tolman cone angle. On the other hand, the outer pocket technique is based on a view from the top where the midpoint between the substituents (or carbene carbon and chlorines) is calculated.
The radius between the midpoint and the substituents is then used to calculate the dissociating ligand size (or the vacant space). Furthermore, the van der Waals radii according to Bondi[3]
are added to the P-X bond length for both the modified Tolman and the outer pocket techniques.
-10 -8 -6 -4 -2 0 2
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolamn Outer pocket
a
b
c
Figure 4.52: Comparison between the change in the modified Tolman and outer pocket sizes for the vacant space of the B4 complex
In Figure 4.53, the changes in the vacant space calculated with the modified Tolman and the outer pocket techniques are plotted against the increasing P(4)-Ru bond length for the A4 complex. The trend lines for these two techniques are almost identical with a minimal amount of deviation. Furthermore, there was a minimum amount of change in angles observed in the A4 complexes.
In summary, the modified Tolman technique is comparable to the outer pocket technique.
The trends observed in both techniques are almost identical with each other in smaller complexes.
-14 -12 -10 -8 -6 -4 -2 0
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolamn Outer pocket
a b
c d
Figure 4.53: Comparison between the change in the modified Tolman and outer pocket sizes for the vacant space of the A4 complex
The modified Tolman versus the inner pocket technique
The vacant space sizes in the G4 complex were calculated with the modified Tolman and the inner pocket techniques. The changes in the vacant space were then plotted against the increasing P(4)-Ru bond length as shown in Figure 4.54. At (a) the change in the vacant space is different for the modified Tolman and the inner pocket techniques. The change observed in the vacant space is a consequence of the size of the G4 complex, since this change in angles was not observed for the B4 or A4 complexes when calculated with the same techniques.
Furthermore, the changes in the vacant space of the modified Tolman and the inner pocket technique are the same at the (b, c and d) P(4)-Ru bond lengths. Overall, the trend of the change in the vacant space size calculated with the modified Tolman technique is similar to the change in the vacant space size calculated with the inner pocket technique. The only variation is at the first point (a) and the large difference in the vacant space sizes.
-6 -5 -4 -3 -2 -1 0
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolamn Outer pocket
Figure 4.54: Comparison between the change in the modified Tolman and the inner pocket sizes for the vacant space of the G4 complex
The vacant space size in the B4 complex was also calculated with the modified Tolman and the inner pocket techniques. The change in the vacant space size was then plotted against the increasing P(4)-Ru bond length as shown in Figure 4.55. The change in the vacant space sizes (a, b and c) observed in the modified Tolman technique was also observed in the inner pocket technique. Overall, the trends are similar for these two techniques even though the vacant space size calculated with the modified Tolman technique was larger.
Figure 4.55: Comparison between the change in the modified Tolman and the inner pocket sizes for the vacant space of the B4 complex
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolman Inner pocket
a
b c
d
-12 -10 -8 -6 -4 -2 0
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolman Inner pocket
a b
c
In Figure 4.56, the modified Tolman technique is compared to the inner pocket technique for the A4 complex. The change in the vacant space size was plotted against the increasing P(4)- Ru bond length. The trend lines for these two techniques are similar in shape with a deviation at the end of the dissociation. Notably, the trends observed with the outer pocket technique is almost identical to the modified Tolman technique. The largest difference in these trends is the size difference and this size is a consequence of the inner pocket technique not including the van der Waals radii according to Bondi[3] in the calculations. However, both the modified Tolman and the outer pocket techniques include the van der Waals radii according to Bondi. [3] Consequently, the change in the vacant space size calculated with the inner pocket technique is smaller in size than the modified Tolman and the outer pocket techniques.
Figure 4.56: Comparison between the change in the modified Tolman and the inner pocket sizes for the vacant space of the A4 complex
The modified Tolman versus the inner-inner pocket technique
The vacant space sizes of the G4 complex were calculated with the modified Tolman and the inner-inner pocket techniques. Thereafter, the change in the vacant space size was plotted against the increasing P(4)-Ru bond length as shown in Figure 4.57. Notably, the same changes in the vacant space size (a) that were observed in the previous techniques are observed in the inner-inner pocket technique. As mentioned previously, the only reason for the observed change in angles is the large size of the G4 complex. Moreover, all of the changes in the vacant space size (b, c and d) observed in the modified Tolman technique were observed in the inner pocket technique. However, the change in the vacant space sizes
-6 -5 -4 -3 -2 -1 0
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolamn Inner pocket
observed in the inner-inner pocket technique were larger than those observed in the modified Tolman technique. The large difference in the vacant space sizes between the techniques is a consequence of subtracting the van der Waals radii in the inner-inner pocket technique.
Figure 4.57: Comparison between the change in the modified Tolman and the inner-inner pocket sizes for the vacant space of the G4 complex
The vacant space sizes for the B4 complex were calculated with the modified Tolman and the inner-inner pocket techniques. The changes in the vacant space sizes were then plotted against the increasing P(4)-Ru bond length as shown in Figure 4.58. The changes in the vacant space sizes (a and b) observed in the modified Tolman technique were also observed in the inner-inner pocket technique. Overall, the trends are similar for these two techniques. The change in the vacant space size between the modified Tolman and the inner-inner pocket technique is close in size.
-8 -7 -6 -5 -4 -3 -2 -1 0 1
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolamn Inner-Inner pocket
a b
c
Figure 4.58: Comparison between the change in the modified Tolman and the inner-inner pocket sizes for the vacant space of the B4 complex
In Figure 4.59, the modified Tolman technique was compared to the inner-inner pocket technique for the A4 complex. The change in the vacant space sizes was plotted against the increasing P(4)-Ru bond length for the A4 complex. The change in the vacant space size (a) decreased in the inner-inner pocket technique, while the change in the vacant space size slightly increased in the modified Tolman technique.
Furthermore, the changes in the vacant space sizes were close in size, but the difference in the sizes increased towards the end of the dissociation. The large difference in the vacant space size calculated with both the techniques is a consequence of the inner-inner pocket technique that subtracts the van der Waals radii according to Bondi. [3]
On the other hand, the modified Tolman and the outer pocket techniques add the van der Waals radii according to Bondi[3] to the vacant space. Consequently, the size of the vacant space calculated with the inner-inner pocket technique is larger than the vacant space size calculated with the modified Tolman and the outer pocket techniques.
-9 -8 -7 -6 -5 -4 -3 -2 -1 0
2 3 4 5
Change in vacant space (°)
P(4)- Ru (Å)
Modified Tolamn Inner-Inner pocket
a b
Figure 4.59: Comparison between the change in the modified Tolman and the inner-inner pocket sizes for the vacant space of the A4 complex
To summarise, the modified Tolman technique is comparable to the outer pocket, the inner pocket and the inner-inner pocket techniques. The trend lines obtained between these techniques were similar with the largest difference being that the size calculated with the modified Tolman technique was larger than for the outer pocket techniques. However, the vacant space sizes calculated with the modified Tolman was smaller in size than calculated with the inner pocket and the inner-inner pocket techniques. This difference in the vacant space size is a consequence of whether the van der Waals radii according to Bondi[3] were included, added or subtracted in the calculations. Furthermore, the large G4 complex had a notable change in vacant space sizes at 2.978 Å (P(4)-Ru bond length) between the modified Tolman and the other techniques.