text: A halogen bond is almost collinear with the halogen atom's other, conventional bond, but the geometry of the electron-charge donor may be much more complex.
  * Multi-electron donors such as ethers and amines prefer halogen bonds collinear with the lone pair and donor nucleus.
  * Pyridine derivatives tend to donate halogen bonds approximately coplanar with the ring, and the two  angles are about 120°. 
  * Carbonyl, thiocarbonyl-, and selenocarbonyl groups, with a trigonal planar geometry around the Lewis donor atom, can accept one or two halogen bonds.
  Anions are usually better halogen-bond acceptors than neutral species: the more dissociated an ion pair is, the stronger the halogen bond formed with the anion.