Twinned crystals. I. 10-Methyl-l,2-benzanthracene

Abstract

The apparently complicated diffraction patterns from 10-methyl-l,2-benzanthracene (10-methylbenz[a]anthracene) (h{ [ason, Acta Cryst. (1958), 11, 329) can be explained completely in terms of ordinary twinning. The crystals are reflexion-twinned by pseudo-merohedry. (001) being the twin plane.

Structures of nitrogen-containing aromatic compounds. I. The metastable crystalline form of dibenzo-1,3a,4,6a-tetraazapentalene (DBTAP-2)

“…6). A similar phenomenon has been observed in 10-methyl-l,2-benzanthracene (Herbstein, 1964). The skeletal structure of the twinned crystals is shown in Fig.…”

Packing Problems: High Z′ Crystal Structures and Their Relationship to Cocrystals, Inclusion Compounds, and Polymorphism

“…28i,45b Errors such as missed space group symmetry can also artificially increase Z′ as in the 1958 report of the Z′ = 10 structure of 10-methyl-1,2-benzanthracene 97 in which the high Z′ value ("aggregation factor") was initially implicated in the compound's biological activity, only to be later shown to be a twinning artifact. 22a, 98 Generally, however, the number of errors is sufficiently small that underlying statistical trends are not obscured. The CSD lists structures with Z′ values ranging from 1/96 to 32.…”

Solid-state transformations in the β-form of chlorpropamide on cooling to 100 K

“…They can, for example, depend on the volume of coherently scattering domains. In general, on the basis of X-ray analysis only it is not trivial to distinguish between a partly disordered structure and a structure consisting of completely ordered coherently conjugated domains of two types (see Herbstein, 1964;Zorky & Nesterova, 1986, 1993. In the case of the III -form of chlorpropamide, we consider a structure with a stochastic static disorder of the alkyl tails as unrealistic because the gauche conformation of the neighbouring molecules in the space group P2/c would lead to an extremely short distance between their methyl fragments.…”

“…Structures with Z 0 > 1 may be artifacts of structure refinement for crystals of poor quality, e.g. because of unrecognized crystal twinning (Herbstein, 1964). Structures with Z 0 > 1 can indicate that the crystal is actually a domain intergrowth of two or more different polymorphs (Bernstein et al, 2008;Bishop & Scudder, 2009;Bond, 2009;Bond et al, 2007;Zorky & Nesterova, 1986, 1993.…”