Try Another Crystal: Crystal-Dependent Disorder of Pentaphosphaferrocene within the Same Crystallization

Abstract

The degree of disorder of [Cp″Fe­(η5-P5)] [Cp″ = η5-1,3-(tBu)2C5H3] molecules with respect to their mirrored positions in the orthorhombic Pca21 space group varies from ∼1 to 24% depending on the single crystal chosen from the same sample for the X-ray structural determination. This unusual behavior is caused by stacking faults in adjacent layers parallel to the (001) direction giving rise to two polytypes. A comprehensive search in the Cambridge Structural Database revealed only a few similar examples of the crystal-dependent disorder caused by stacking faults. Moreover, crystals of [Cp″Fe­(η5-P5)] possessing a low amount of stacking faults demonstrate slight temperature-induced superstructural ordering (modulation) between 20 and 80 K, accompanied by a doubling of the b parameter (b′ → 2 × b).

One-dimensional diffuse scattering of 1,3-di(tert-butyl)cyclopentadienyl pentaphosphaferrocene modelled with closed-form expressions

“…Additional extremely weak reflections are observed at halfintegral k values, which are due to superstructure formation in the [010] direction for the Pca2 1 polytype as described in Peresypkina et al (2022). These reflections are significantly more pronounced for pure Pca2 1 crystals.…”

“…The possible stacking arrangements have already been discussed in Peresypkina et al (2022) and will be briefly recapitulated here. The structure is composed of ordered monoclinic/rectangular layers with p1a1 symmetry and one molecule located on the general position (Figs.…”

“…Diffraction intensities from crystals of Cp 00 FeP 5 prepared according to Fleischmann et al (2015) were collected at the P24 beamline of the PETRA III synchrotron, DESY (Germany) at 20 K (Peresypkina et al, 2022). For all crystals, the structure was refined in the Pca2 1 space group with more or less disorder of the Cp 00 FeP 5 molecule about the y = 1 4 pseudo-reflection plane.…”

“…The minor component was ignored for the modelling of the diffuse scattering. For further data collection and refinement details as well as atomic coordinates, see Peresypkina et al (2022). Atomic form factors where approximated using the polynomial coefficients tabulated in Brown et al (2006).…”

“…Recently, we described crystallization experiments of the ferrocene analogue Cp 00 Fe( 5 -P 5 ), where one cyclopentadienyl (Cp, 5 -C 5 H 5 À ) ring has been formally replaced by Cp 00 = 5 -t Bu 2 C 5 H 3 À , the 1,3-di-tert-butyl substituted analogue of Cp and the second Cp ring has been formally replaced by an aromatic 5 -P 5 À ring. Different crystals extracted from the same sample featured different degrees of disorder (Peresypkina et al, 2022). One of the crystals featured especially pronounced diffuse scattering with reflections indicating two different polytypes.…”