Two cubic polymorphs of AlGeLi

Aluminium germanium lithium, AlGeLi, crystallizes in two cubic dimorphs. The structure of the F3m form, already inferred from powder data, has been confirmed by both powder and single‐crystal X‐ray diffraction studies. The second dimorph, not previously identified, adopts a disordered centrosymmetric structure with space group Fmm.     

Two polymorphs of 1,8‐dichloroanthracene

A second, monoclinic, polymorph of the title compound, C₁₄H₈Cl₂, has been found. In addition to the structure of this monoclinic form, the structure of the previously described orthorhombic form [Desvergne, Chekpo & Bouas‐Laurent (1978). J. Chem. Soc. Perkin Trans. 2, pp. 84–87; Benites, Maverick & Fronczek (1996). Acta Cryst. C 52 , 647–648] has been redetermined at low temperature and using modern methods. The low‐temperature structure of the orthorhombic form is of significantly higher quality than the previously published structure and additional details can be derived. A comparison of the crystal packing of the two forms with a focus on weak intermolecular C—H...Cl interactions shows the monoclinic structure to have one such interaction linking the molecules into infinite ribbons, while two crystallographically independent C—H...Cl interactions give rise to an interesting infinite three‐dimensional network in the orthorhombic crystal form.     

Two polymorphs of afobazole from powder diffraction data

Afobazole {systematic name: 2‐[2‐(morpholin‐4‐yl)ethylsulfanyl]‐1H‐benzimidazole} is a new anxiolytic drug and Actins, Auzins & Petkune [(2012). Eur. Patent EP10163962] described four polymorphic modifications. In the present study, the crystal structures of two monoclinic polymorphs, 5‐ethoxy‐2‐[2‐(morpholin‐4‐ium‐4‐yl)ethylsulfanyl]‐1H‐benzimidazol‐3‐ium dichloride, C₁₅H₂₃N₃O₂S²⁺·2Cl⁻, (II) and (IV), have been established from laboratory powder diffraction data. The crystal packing and conformation of the dications in (II) and (IV) are different. In (II), there are channels in the [001] direction, which offer atmospheric water molecules an easy way of penetrating into the crystal structure, thus explaining the higher hygroscopicity of (II) compared with (IV).     

Two crystal polymorphs of a flavonoid from Melicope ellyrana

The crystal structure determinations of two crystalline components of the hexane extract of the fruit of the indigenous Australian tree Melicope ellyrana have shown them to be polymorphs of the same compound, namely the flavonoid 4′,5-di­hydroxy-3,3′,8-tri­methoxy-7-(3-methyl­but-2-enyl­oxy)­flavone [systematic name: 5-hydroxy-2-(4-hydroxy-3-methoxy­phenyl)-3,8-di­methoxy-7-(3-methyl­but-2-enyl­oxy)-4H-1-benzo­pyran-4-one], C₂₃H₂₄O₈. The two polymorphs, one monoclinic (polymorph A) and the other triclinic (polymorph B), show significant conformational differences, particularly in the enyl­oxy side chain, while only one (polymorph A) shows intermolecular hydrogen bonding.     

Crystal structure of the 2-hydroxy-3,3,4-trimethyl-2-oxo-5-cyanimino-1, 4,2-diazaphospholidine diethylammonium salt

Crystal structure of the 2-hydroxy-3,3,4-trimethyl-2-oxo-5-cyanimino-1,4,2-diazaphospholidine diethylammonium salt (I) was studied by X-ray diffraction analysis: space group P2₁/c, a=9.773(1), b=12.7617(8), c=12.064(2) Å, β=95.02(1)°, Z=4; R=0.041 (CAD-4 automatic diffractometer, λCuK_α, 2518 independent reflections with I≥3δ). In anion I, the P atom (forming two Pō sesquibonds) has a considerably distorted tetrahedral coordination. In the extended flattened molecular fragment of anion I involving 7 atoms [P?N?C(?N)=N?C≡N], the π-electron densities of the atoms are conjugated. The five-membered heterocycle of anion I has a distorted P,C₃-half-chair conformation. The crystal structure of compound I has interionic hydrogen bonds linking anions I into centrosymmetric H-dimers and also linking anions I and Et₂NH ₂ ⁺ into centrosymmetric H-tetramers.     

Two tautomeric polymorphs of 2,6‐dichloropurine

Two polymorphs of 2,6‐dichloropurine, C₅H₂Cl₂N₄, have been crystallized and identified as the 9H‐ and 7H‐tautomers. Despite differences in the space group and number of symmetry‐independent molecules, they exhibit similar hydrogen‐bonding motifs. Both crystal structures are stabilized by intermolecular N—H...N interactions that link adjacent molecules into linear chains, and by some nonbonding contacts of the C—Cl...π type and by π–π stacking interactions, giving rise to a crossed two‐dimensional herringbone packing motif. The main structural difference between the two polymorphs is the different role of the molecules in the π–π stacking interactions.     

Two polymorphs of chlorido(cyclohexyldiphenylphosphine)gold(I)

The title compound, [AuCl(C₁₈H₂₁P)], a monomeric two‐coordinate gold(I) complex, has been characterized at 100 K as two distinct monoclinic polymorphs, one from a single crystal, (Is), and one from a pseudo‐merohedrally twinned crystal, (It). The molecular structures in the two monoclinic [P2₁/n for (Is) and P2₁/c for (It)] polymorphs are similar; however, the packing arrangements in the two lattices differ considerably. The structure of (It) is pseudo‐merohedrally twinned by a twofold rotation about the a* axis.     

Two cuprous cyanide polymorphs: diamond net versus 3,4-connected net

Hydrothermal reactions generated two cuprous cyanide polymorphs with similar hexagonal [Cu2(CN)3](-) layers but different supramolecular arrays.     

Two polymorphs of safinamide,a selective and reversible inhibitor of monoamine oxidase B

Two polymorphs of safinamide {systematic name: (2S)‐2‐[4‐(3‐fluorobenzyloxy)benzylamino]propionamide}, C₁₇H₁₉FN₂O₂, a potent selective and reversible monoamine oxidase B (MAO‐B) inhibitor, are described. Both forms are orthorhombic and regarded as conformational polymorphs due to the differences in the orientation of the 3‐fluorobenzyloxy and propanamide groups. Both structures pack with layers in the ac plane. In polymorph (I), the layers have discrete wide and narrow regions which are complementary when located next to adjacent layers. In polymorph (II), the layer has long flanges protruding from each side, which interdigitate when packed with the adjacent layers. N—H...O hydrogen bonds are present in both structures, whereas N—H...F hydrogen bonding is seen in polymorph (I), while N—H...N hydrogen bonding is seen in polymorph (II).     

Two polymorphs of N‐(2,6‐difluorophenyl)formamide

The structures of two distinct polymorphic forms of N‐(2,6‐difluorophenyl)formamide, C₇H₅F₂NO, have been studied using single crystals obtained under different crystallizing conditions. The two forms crystallize in different space groups, viz. form (Ia) in the orthorhombic Pbca and form (Ib) in the monoclinic P2₁ space group. Each polymorph crystallizes with one complete molecule in the asymmetric unit and they have a similar molecular geometry, showing a trans conformation with the formamide group being out of the plane of the aromatic ring. The packing arrangements of the two polymorphs are quite different, with form (Ia) having molecules that are stacked in an alternating arrangement, linked into chains of N—H...O hydrogen bonds along the crystallographic a direction, while form (Ib) has its N—H...O hydrogen‐bonded molecules stacked in a linear fashion. A theoretical study of the two structures allows information to be gained regarding other contributing interactions, such as π–π and weak C—H...F, in their crystal structures.     

Two polymorphs of bis(2‐carbamoylguanidinium) fluorophosphonate dihydrate

Two polymorphs of bis(2‐carbamoylguanidinium) fluorophosphonate dihydrate, 2C₂H₇N₄O⁺·FO₃P²⁻·2H₂O, are presented. Polymorph (I), crystallizing in the space group Pnma, is slightly less densely packed than polymorph (II), which crystallizes in Pbca. In (I), the fluorophosphonate anion is situated on a crystallographic mirror plane and the O atom of the water molecule is disordered over two positions, in contrast with its H atoms. The hydrogen‐bond patterns in both polymorphs share similar features. There are O—H...O and N—H...O hydrogen bonds in both structures. The water molecules donate their H atoms to the O atoms of the fluorophosphonates exclusively. The water molecules and the fluorophosphonates participate in the formation of R⁴₄(10) graph‐set motifs. These motifs extend along the a axis in each structure. The water molecules are also acceptors of either one [in (I) and (II)] or two [in (II)] N—H...O hydrogen bonds. The water molecules are significant building elements in the formation of a three‐dimensional hydrogen‐bond network in both structures. Despite these similarities, there are substantial differences between the hydrogen‐bond networks of (I) and (II). The N—H...O and O—H...O hydrogen bonds in (I) are stronger and weaker, respectively, than those in (II). Moreover, in (I), the shortest N—H...O hydrogen bonds are shorter than the shortest O—H...O hydrogen bonds, which is an unusual feature. The properties of the hydrogen‐bond network in (II) can be related to an unusually long P—O bond length for an unhydrogenated fluorophosphonate anion that is present in this structure. In both structures, the N—H...F interactions are far weaker than the N—H...O hydrogen bonds. It follows from the structure analysis that (II) seems to be thermodynamically more stable than (I).