1,10-(3,6-Pyrazabolyl)ferrocene Fc(BHpz)2 and the corresponding ruthenocene Rc(BHpz)2 crystallize as order–disorder (OD) structures with layers of Pma(m) symmetry. Since the m100 reflection and the a010 glide reflection planes of adjacent layers do not overlap, given one layer, the adjacent layer can be placed in four distinct, but geometrically equivalent, positions. There are accordingly four polytypes of a maximum degree of order (MDO). One analyzed Fc(BHpz)2 crystal was composed of a mixture of the MDO1 polytype in four distinct orientations and the MDO3 polytype. A second crystal was essentially a single crystal of one out of two orientation of MDO3. In two analyzed crystals of Rc(BHpz)2, the MDO1 polytype (P-1) was the major polytype and was observed in four or two orientation states, respectively. Pronounced diffuse scattering is attributed to a complex disorder, which cannot be explained by simple growth models. One Rc(BHpz)2 crystal features additional peaks in the diffraction pattern attributed to fragments of MDO3.
Stoeger et al. (Thu,) studied this question.