The complex stacking disorder of Fe- and Ru-based 1,1′-(3,6-pyrazabolyl)metallocenes

Abstract

1,1′-(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 m[100] reflection and the a[010] 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 (P1) 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.