PSEUDOSYMMETRIC MOLECULAR SHAPE RESULTING IN DISORDER IN THE CRYSTALLINE STATE

The structures Of [(C4Me4)NiL]PF6 and [(C5Me5)CrL]PF6 where L is the t ripod ligand [eta3-CpCo{P(O)(OEt)2}3]- were determined by single cryst al X-ray diffraction studies. The cations are expected to have point s ymmetry 1 (C1) or m (C(s)); in the crystal they show apparent 2mm (C2v ) symmetry and are disordered. An explanation for this behaviour is of fered by the fact that these molecules have a pseudosymmetric shape. A n approach for visualizing the shape and packing of medium-sized molec ules is presented.