- 1.7
- 1.6
- 1.5
- Beta
- Examples (for 1.6a)
- Misc
These keywords requests that the target atom (if specified in the root of the type description) or a bound atom (if used inside the associated bracketed part) should possess a certain physical geometry in terms of its connections. The number of bonds to the target atom and the angles between them are used to determine the geometry.
Note that, for some geometry types, there are several ways for the atom to have this geometry. Also note that, since the geometry is determined by consideration of ideal angles within some tolerance, an atom may not possess no detectable geometry.
Valid geometry keywords and the criteria that are used to identify them are as follows:
For example:
Table 8.15. NETA geometry keywords
| Command | Bonds Required | Description |
|---|---|---|
| unbound | 0 | An unbound atom. Only makes sense when used in the root of a type description. |
| onebond | 1 | The atom has one bond. |
| linear | 2 | Two bonds to the atom, making an angle > 170°. |
| tshape | 3 | Three bonds to the atom, with two bonds making an angle > 170°. |
| trigonal | 3 | Trigonal planar arrangement of three bonds, with the largest of the three angles between 115 and 125°. |
| tetrahedral | 2 | Two bonds to the atom, making an angle between 100 and 115°. |
| tetrahedral | 3 | Three bonds to the atom, with the largest of the angles between 100 and 115°. |
| tetrahedral | 4 | Four bonds to the atom, with the average of the angles laying between 100 and 115°. |
| sqplanar | 4 | Four bonds to the atom, with the average of the angles laying between 115 and 125°. |
| tbp | 5 | Five bonds to the atom are assumed to be trigonal bipyramidal geometry. |
| octahedral | 6 | Six bonds to the atom are assumed to be octahedral geometry. |