A new polymorph of dichloridotriphenylantimony

In a new polymorphic form of dichloridotriphenylantimony, [Sb(C₆H₅)₃Cl₂], there are two crystallographically unique molecules in the asymmetric unit and it has been determined that this polymorph is one of two kinetically favoured phases of pure dichloridotriphenylantimony, both of which have Z′ > 1. A third polymorph, corresponding to (C₆H₅)₃SbCl_1.8F_0.2, is also known and has Z′ = 2. By contrast, the thermodynamically preferred polymorph of pure (C₆H₅)₃SbCl₂ has Z′ = 1. A brief comparison of the known polymorphic forms of dichloridotriphenylantimony is presented.     

A new polymorph of tetraphenyldiboroxane

A new polymorph of tetraphenyldiboroxane [or oxybis(diphenylborane)], C₂₄H₂₀B₂O, (Ia), has been found. It is monoclinic, like the already known form, (Ib), and can be refined in the same space group, namely P2₁/c, or in the equivalent setting P2₁/n. The molecular conformations of the two polymorphs differ in the rotations of two of the phenyl rings about the B—C bonds, leading to markedly different packing patterns and cell dimensions.     

A new polymorph of phenylselenium trichloride

A second polymorph of phenylselenium trichloride, PhSeCl₃ or C₆H₅Cl₃Se, is disclosed, which is comprised of asymmetric chlorine‐bridged noncovalent dimer units rather than polymeric chains. These dimers are each weakly bound to an adjacent dimer through noncovalent Se…Cl bonding interactions. Phenyl rings within each dimer are oriented in a syn fashion. Density functional theory (DFT) calculations reveal that the putative anti isomer is within 5 kJ mol^?1 of the experimentally observed form. This structure represents the first additional polymorph discovered for an organoselenium trihalide compound.     

A new polymorph and two pseudopolymorphs of pyrimethamine

Due to its donor–acceptor–donor site, the antimalarial drug pyrimethamine [systematic name: 5‐(4‐chlorophenyl)‐6‐ethylpyrimidine‐2,4‐diamine] is a potential component of a supramolecular synthon. During a cocrystallization screen, one new polymorph of solvent‐free pyrimethamine, C₁₂H₁₃ClN₄, (I), and two pseudopolymorphs, pyrimethamine dimethyl sulfoxide monosolvate, C₁₂H₁₃ClN₄·C₂H₆OS, (Ia), and pyrimethamine N‐methylpyrrolidin‐2‐one monosolvate, C₁₂H₁₃ClN₄·C₅H₉NO, (Ib), were obtained. In (I), (Ia), (Ib) and the previously reported polymorph, the pyrimethamine molecules exhibit similar conformations and form R²₂(8) dimers stabilized by a pair of N—H...N hydrogen bonds. However, the packing arrangements are completely different. In (I), the dimers are connected by two additional N—H...N hydrogen bonds to form ribbons and further connected into a two‐dimensional network parallel to (100), while layers containing N—H...Cl hydrogen‐bonded pyrimethamine ribbons are observed in the packing of the known polymorph. In the two pseudopolymorphs, two pyrimethamine molecules are linked to form R²₂(8) dimers and the solvent molecules are connected to the dimers by R²₃(8) interactions involving two N—H...O hydrogen bonds. These arrangements are connected to form zigzag chains by N—H...Cl interactions in (Ia) and to form ribbons by N—H...N interactions in (Ib). Unexpectedly, a reaction between pyrimethamine and N‐methylpyrrolidin‐2‐one occurred during another cocrystallization experiment from a solvent mixture of N‐methylpyrrolidin‐2‐one and dimethyl sulfoxide, yielding solvent‐free 5,5′‐{[5‐(4‐chlorophenyl)‐6‐ethylpyrimidine‐2,4‐diyl]bis(azanediyl)}bis(1‐methylpyrrolidin‐2‐one), C₂₂H₂₇ClN₆O₂, (II). In the packing of (II), the pyrimethamine derivatives are N—H...O hydrogen bonded to form ribbons. A database study was carried out to compare the molecular conformations and hydrogen‐bonding interactions of pyrimethamine.     

A new polymorph of 2,6‐diaminopyridine

2,6‐Diaminopyridine (26‐DAP, C₅H₇N₃) is a common intermediate in the synthesis of aromatic azo chromophores, which are widespread in the dyes and pigments industry. Sublimation of commercial 26‐DAP powder yielded a new polymorph, denoted Form II, which grew as colorless orthorhombic needles. Recrystallization from acetone or toluene also yielded Form II as the major phase. Thermal analysis shows that Form II is a less stable polymorph and it converts upon heating at 335 K to the previously reported Form I.     

A new polymorph of FeAlO3 at high pressure

Synchrotron X-ray diffraction measurements confirmed that a new polymorph of FeAlO3 could be synthesized at about 1800 K and 72 GPa. This phase can be indexed on an orthorhombic cell and transforms into the trigonal form on release of pressure. The c/a ratio of about 2.71 of the trigonal phase suggests corundum structure of FeAlO3 rather than LiNbO3 or ilmenite structure. This conclusion also suggests that the high-pressure orthorhombic phase could be the Rh2O3(II) structure rather than the GdFeO3-type perovskite structure.     

A new polymorph of the gastrokinetic drug cisapride monohydrate

Cisapride monohydrate (systematic name: 4‐amino‐5‐chloro‐N‐{(3RS,4SR)‐1‐[3‐(4‐fluorophenoxy)propyl]‐3‐methoxypiperidin‐4‐yl}‐2‐methoxybenzamide monohydrate), C₂₃H₂₉ClFN₃O₄·H₂O, is a nondopamine‐blocking gastrokinetic drug. A new polymorph of cisapride monohydrate has been reported nearly three decades after the report of its first known crystal structure [Collin et al. (1989). J. Mol. Struct. 214 , 159–175]. The second polymorph is also monoclinic, but with different unit‐cell parameters. A comparison of both polymorphic forms shows that the difference is thus not in the molecular conformation but in the arrangements of molecules in the crystal packing. The crystal morphology of two forms was predicted with the BFDH model in Materials Studio and inferred that the powder of the new polymorph has better flowability than the original polymorph. The results of DSC (differential scanning calorimetry) analysis and slurry experiments show that both polymorphs are stable at room temperature.     

A new polymorph of Cu3B2O6

A new polymorph of nonacopper(II) bis(orthoborate) bis(hexaoxodiborate), Cu₉(BO₃)₂(B₂O₆)₂, or Cu₃B₂O₆ with Z′ = 3, has a pseudo‐layered monoclinic structure containing BO₃ triangles and B₂O₆ units consisting of corner‐sharing BO₃ triangles and BO₄ tetrahedra. The compound was obtained during an investigation of the Li–Cu–B–O system. In contrast to the triclinic form of Cu₃B₂O₆, the layers are linked to one another by BO₄ tetrahedra.     

A new polymorph of triphenylmethylamine: the effect of hydrogen bonding

Crystallization of the hexane reaction mixture after treatment of LiGe(OCH₂CH₂NMe₂)₃ with Ph₃CN₃ gives rise to a new triclinic (space group P) polymorph of triphenylmethylamine, C₁₉H₁₇N, (I), containing dimers formed by N—H...N hydrogen bonds, whereas the structure of the known orthorhombic (space group P2₁2₁2₁) polymorph of this compound, (II), consists of isolated molecules. While the dimers in (I) lie across crystallographic inversion centres, the molecules are not truly related by them. The centrosymmetric structure is due to the statistical disordering of the amino H atoms participating in the N—H...N hydrogen‐bonding interactions, and thus the inversion centre is superpositional. The conformations and geometric parameters of the molecules in (I) and (II) are very similar. It was found that the polarity of the solvent does not affect the capability of triphenylmethylamine to crystallize in the different polymorphic modifications. The orthorhombic polymorph, (II), is more thermodynamically stable under normal conditions than the triclinic polymorph, (I). The experimental data indicate the absence of a phase transition in the temperature interval 120–293 K. The densities of (I) (1.235 Mg m⁻³) and (II) (1.231 Mg m⁻³) at 120 K are practically equal. It would seem that either the kinetic factors or the effects of the other products of the reaction facilitating the hydrogen‐bonded dimerization of triphenylmethylamine molecules are the determining factor for the isolation of the triclinic polymorph (I) of triphenylmethylamine.     

A new sulfate acid polymorph of 1,3‐dihydrobenzotriazole

A new sulfate acid polymorph of 1,3‐dihydrobenzotriazole, viz. 1,3‐dihydrobenzotriazolium hydrogensulfate, C₆H₆N₃⁺·HSO₄⁻, differs from an existing polymorph in that the polymeric interaction between the HSO₄⁻ anions, together with different classical (D—H...A) and nonclassical (C—H...A) interactions, changes the space group.     

A new polymorph of succinylcholinium diiodide: comparison of succinylcholinium structures

The title compound {systematic name: trimethyl[2‐({4‐oxo‐4‐[2‐(trimethylazaniumyl)ethoxy]butanoyl}oxy)ethyl]azanium diiodide}, C₁₄H₃₀N₂O₄²⁺·2I⁻, is a salt of the succinylcholinium cation. There is one formula unit in the asymmetric unit, represented by two anions and two halves of two cations which lie on centres of inversion. The component species are stabilized by electrostatic interactions, and C—H...I and C—H...O hydrogen bonds are also present.     

A new polymorph of 5-fluorouracil found following computational crystal structure predictions

A new polymorph of 5-fluorouracil has been obtained following a manual polymorph screen inspired by a computational crystal structure prediction search. It corresponds to the structure that was predicted to be the global minimum in lattice energy. The difficulty of crystallizing this simple structure with a rational hydrogen-bonding motif can be rationalized from the differential solvation of the functional groups.     

A new monoclinic polymorph of methyl p‐amino­benzoate

Single crystals of methyl‐p‐amino­benzoate (MAB), C₈H₉NO₂, were obtained during the synthesis of 4‐amino‐N′‐(5‐nitro‐2‐thienylmethylene)benzohydrazide. A P2₁/c polymorph [a = 8.5969 (4) Å, b = 5.6053 (2) Å, c = 15.5397 (7) Å and β = 96.172 (2)°] of MAB was found and the intra‐ and intermolecular geometries were compared with those of the pre­viously known C2/c structure [a = 16.242 (2) Å, b = 8.113 (2) Å, c = 12.724 (2) Å and β = 69.17 (1)°; Xianti (1983). Jiegou Huaxue, 2 , 219–221].     

A new polymorph of ammonium succinate – serendipity in action

Succinic acid has been known since 1546 and was first chemically identified in the mid‐19th century. In an attempt to prepare a molecular salt of succinic acid with (S)‐(?)‐α‐methylbenzylamine, we have obtained the second polymorph of the monoammonium salt of succinic acid, NH₄⁺·C₄H₅O₄^?. The crystal structure determination proves the structure of the ionic compound and the intimate role of the ammonium ion in the structure, which is compared to the earlier described polymorph.     

Ferrocenecarboxylic anhydride: identification of a new polymorph

A new monoclinic polymorph of ferrocenecarboxylic anhydride, [Fe₂(C₅H₅)₂(C₁₂H₈O₃)], was obtained. Three molecules are present in the asymmetric unit, two of them being nearly identical (r.m.s. deviation = 0.11 Å), with the Fe atoms on the same side of the anhydride functional group. In the third molecule, the two Fe atoms are located at opposite sides of the functional group (ferrocene–ferrocene pseudo‐torsion angle = 146.2°), a very unsual feature in metallocene anhydrides. A network of weak intermolecular hydrogen bonds was also disclosed.     

Physico-chemical characterisation of a new polymorph of caffeine

Caffeine is a widely used drug substance. Two polymorphic forms and one hydrate of caffeine are known. Thanks to scanning transitiometry, the curves pressure versus temperature, P = f(T), of the caffeine were plotted. A (temperature, pressure) unary phase diagram was deduced. It confirms the existence of a new polymorph of caffeine at low pressure synthesized by sublimation. Its identification and its physico-chemical properties were determined using a variety of experimental methods: X-ray powder diffraction, differential scanning calorimeter, thermogravimetric analysis, thermally stimulated current and electrochemical impedance.