Fabio, Perhaps you could try using two planar constraints instead of one, one for each of two fragments of the 13 atoms to be planar, and include several atoms in common in the fragments.
Silvina.
Fabio, Perhaps you could try using two planar constraints instead of one, one for each of two fragments of the 13 atoms to be planar, and include several atoms in common in the fragments.
Silvina.