Table 1. Comparison of bond lengths, polyhedral volumes, various distortion metrics and hydrogen-bond parameters (Å, °) in α-ammonium carbamate.
The values are from the outputs of CASTEP and measurements on HRPD, a powder X-ray diffraction experiment (Baisch et al., 2006 ▸) and a single-crystal X-ray diffraction experiment (Adams & Small, 1973 ▸). Note that the HRPD sample was deuterated. Atomic labels in Baisch et al. (2006 ▸) correspond to: H11 = H3, H12 = H2, H22 = H5, H23 = H6, H24 = H4 and N2 = N1, according to the labelling of Adams & Small (1973 ▸). The distortion index is based on bond lengths in the polyhedra and was defined by Baur (1974 ▸). ‘Quadratic elongation’ gives a quantative measure of polyhedral distortion, which is independent of the effective polyhedron size (Robinson et al., 1971 ▸), and ‘bond-angle variance’ gives a quantative measure of how the bond angles in the tetrahedra deviate from the ideal value of 109.28 – lower values equate to bond angles closer to the ideal (Robinson et al., 1971 ▸).
| DFT athermal | HRPD neutron 4.2 K | X-ray 293 (2) K (Baisch et al., 2006 ▸) | X-ray 295 K (Adams & Small, 1973 ▸) | |
|---|---|---|---|---|
| C1—O1 | 1.300 | 1.247 (5) | 1.269 (3) | 1.270 (5) |
| C1—O2 | 1.285 | 1.272 (5) | 1.266 (2) | 1.279 (4) |
| C1—N2 | 1.361 | 1.362 (4) | 1.340 (3) | 1.348 (5) |
| N2—H(D)1 | 1.034 | 1.018 (5) | 0.84 (3) | 0.85 (6) |
| N2—H(D)2 | 1.019 | 1.002 (5) | 0.81 (3) | 0.83 (7) |
| N1—H(D)3 | 1.044 | 1.067 (4) | 0.94 (4) | 1.00 (5) |
| N1—H(D)4 | 1.055 | 1.052 (5) | 0.93 (3) | 0.85 (6) |
| N1—H(D)5 | 1.051 | 1.076 (5) | 0.93 (3) | 0.91 (6) |
| N1—H(D)6 | 1.064 | 1.049 (5) | 0.93 (3) | 0.75 (6) |
| NH(D)4 volume | 0.5987 | 0.6106 | 0.4166 | 0.3205 |
| Distortion index | 0.0057 | 0.0098 | 0.0028 | 0.08704 |
| Quadratic elongation | 1.001 | 1.0026 | 1.0026 | 1.0615 |
| Bond-angle variance | 3.4483 | 10.2483 | 9.7185 | 114.3099 |
| H(D)1⋯O1 | 1.863 | 1.949 (5) | 2.16 (3) | 2.12 (5) |
| H(D)2⋯O1† | 2.516 | 2.405 (5) | 2.70 (3) | 2.64 (6) |
| H(D)3⋯O2 | 1.674 | 1.690 (5) | 1.82 (3) | 1.77 (5) |
| H(D)4⋯O2 | 1.762 | 1.792 (5) | 1.93 (3) | 2.13 (5) |
| H(D)5⋯O1 | 1.767 | 1.779 (5) | 1.93 (3) | 1.93 (6) |
| H(D)6⋯O1 | 1.862 | 1.914 (6) | 2.03 (3) | 2.19 (6) |
| N2—H(D)1⋯O1 | 177.1 | 171.2 (4) | 174.7 (8) | 174 (5) |
| N2—H(D)2⋯O1† | 148.0 | 150.4 (4) | 149.9 (8) | 158 (1) |
| N1—H(D)3⋯O2 | 170.2 | 170.1 (4) | 171.4 (8) | 166 (4) |
| N1—H(D)4⋯O2 | 164.3 | 166.2 (4) | 162.4 (8) | 138 (5) |
| N1—H(D)5⋯O1 | 170.3 | 170.5 (4) | 168.5 (8) | 173 (4) |
| N1—H(D)6⋯O1 | 157.5 | 158.4 (4) | 155.4 (7) | 158 (5) |
Notes: (†) in Adams & Small (1973 ▸), this is suggested to not be a hydrogen bond.