Organometallic chemistry/Cone Angles

When a ligand is attached to a central metal atom, it is generally free to rotate. As it does so, the ligand sweeps out a region of space that is shaped like a cone, and the cone angle refers to the angle at its apex.

Exact Cone Angle

If the geometry of a ligand is known, either through crystallography or computations, an exact cone angle (θ°) can be calculated. No assumptions about the geometry are made–as in the Tolman method–since the structure can be obtained for a ligand in any environment by several experimental and theoretical methods. A Mathematica script is freely available which will compute the cone angle for any ligand with known Cartesian coordinates. Calculating the cone angle for specific instances, rather than applying a universal value, opens up the possibility to track the change in sterics over the course of a reaction.