Table 2. Energies and Structural Indices for [Fe(bpp)2]2+ Minimized along Distortion Pathways A–D (Chart 4)a.
| pathway A | ||||||||
| ϕ/° | 180.0b | 172.6 | 165.0c | 160.0c | 155.0c | 150.0c | 145.0c | 140.0c |
| θ/° | 89.0b | 87.0 | 84.1 | 82.2 | 78.9 | 74.2 | 71.3 | 68.8 |
| θ′/° | 88.0b | 85.2 | 82.0 | 78.7 | 74.8 | 71.0 | 68.0 | 65.0 |
| ΔE{ϕ}/kcal mol–1d | 0 | +0.02 | 0.00 | +0.14 | +0.51 | +1.13 | +2.25 | +3.94 |
| pathway B | ||||||||
| ϕ/° | 180.0b | 164.4 | 163.8 | 160.8 | 157.9 | 157.3 | 157.0 | |
| θ/° | 89.0b | 79.8 | 77.3 | 70.8 | 65.1 | 59.8 | 55.3 | |
| θ′/° | 88.0b | 79.3d | 76.6d | 71.8d | 66.8d | 63.6d | 60.6d | |
| ΔE{θ′}/kcal mol–1e | 0 | +0.19 | +0.46 | +1.26 | +2.63 | +4.49 | +7.12 | |
| Pathway C | ||||||||
| ϕ/° | 180.0b | 165.0c | 160.0c | 155.0c | 150.0c | 145.0c | 140.0c | |
| θ/° | 89.0b | 89.4 | 89.4 | 89.3 | 89.3 | 87.9 | 88.1 | |
| θ′/° | 88.0b | 89.5 | 89.5 | 89.2 | 89.2 | 87.5 | 87.4 | |
| ΔE{ϕ}/kcal mol–1e | 0 | +0.37 | +0.69 | +1.22 | +2.04 | +3.17 | +5.05 | |
| pathway D | ||||||||
| ϕ/° | 180.0b | 180.0 | 179.9 | 179.8 | 179.8 | 180.0 | 180.0 | |
| θ/° | 89.0b | 85.3 | 80.3 | 75.2 | 69.7 | 64.1 | 58.3 | |
| θ′/° | 88.0b | 84.8d | 81.3d | 78.1d | 75.0d | 72.2d | 69.6d | |
| ΔE{θ′}/kcal mol–1e | 0 | +0.05 | +0.65 | +1.74 | +3.40 | +5.68 | +8.47 |
a
Pathways A and C were minimized by fixing ϕ at different values, with no other restraints. Pathways B and D were accessed by constraining θ′ with fixed interligand torsions, while allowing ϕ to refine. Computed energies for each minimization are listed in Table S6.
b
This is the “undistorted” minimization of this molecule where θ was constrained to be near, but not exactly, 90°—see the text for more details.
c
Fixed value.
d
Constrained during the minimization—see the text for details.
e
ΔE{i} = E{i} – E{undistorted} (i = ϕ or θ′).