Virtual issue on polymorphism

A. Linden

Acta Crystallographica Section C is pleased to announce the publication of its first virtual issue. The issue is dedicated to the subject of polymorphism and includes papers relating to this topic published in Section C between January 2010 and November 2011.

Two polymorphs of a lead(II) complex with 8-hydroxy-2-methylquinoline and thiocyanate

G. Mohammadnezhad, M. M. Amini and V. Langer

Two distinct polymorphs of bis(₂-methylquinolin-8-olato)-³N,O:O;³O:N,O-bis[(isothiocyanato-N)lead(II)], [Pb₂(C₁₀H₈NO)₂(NCS)₂], (I), forming dinuclear complexes from a methanolic solution containing lead(II) nitrate, 2-methylquinolin-8-ol (M-Hq) and KSCN, crystallized concomitantly as colourless prisms [form (Ia)] and long thin colourless needles [form (Ib)]. In both cases, the complexes lie across a centre of inversion. The polymorphs differ substantially in their conformation and in their interactions, viz. PbS and - for form (Ia) and PbS, Pb and C-H for form (Ib).

Two concomitant polymorphs of N,N'-bis[4-(diethylamino)phenyl]terephthaldiamide

P. Kus, J. Borek and P. G. Jones

The title compound, C₂₈H₃₄N₄O₂, crystallizes simultaneously as a monoclinic, (Im), and a (twinned) triclinic polymorph, (It), from d₆-dimethyl sulfoxide. Polymorph (It) (P, Z = 1) displays the standard `ladder' packing for this group of compounds, with neighbouring inversion-symmetric molecules related by translation and connected by hydrogen bonds of the form N-HO=C. Polymorph (Im) (Cc, Z = 4) has no imposed symmetry; there are three independent hydrogen bonds, one classical N-HO=C and a bifurcated system with N-HO=C augmented by a short C-HO=C interaction. Each molecule is thereby linked to four neighbouring molecules, two lower and two higher, so that a crosslinked three-dimensional pattern is formed rather than the standard ladder.

Two polymorphs of chlorido(cyclohexyldiphenylphosphine)gold(I)

I. A. Guzei, I. Arachchige and S. A. Ivanov

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 solid phases of pyrimidin-1-ium hydrogen chloranilate monohydrate determined at 225 and 120 K

K. Gotoh, T. Asaji and H. Ishida

The crystal structures of two solid phases of the title compound, C₄H₅N₂⁺·C₆HCl₂O₄^-·H₂O, have been determined at 225 and 120 K. In the high-temperature phase, stable above 198 K, the transition temperature of which has been determined by ³⁵Cl nuclear quadrupole resonance and differential thermal analysis measurements, the three components are held together by O-HO, NHO, C-HO and C-HCl hydrogen bonds, forming a centrosymmetric 2+2+2 aggregate. In the NHO hydrogen bond formed between the pyrimidin-1-ium cation and the water molecule, the H atom is disordered over two positions, resulting in two states, viz. pyrimidin-1-ium-water and pyrimidine-oxonium. In the low-temperature phase, the title compound crystallizes in the same monoclinic space group and has a similar molecular packing, but the 2+2+2 aggregate loses the centrosymmetry, resulting in a doubling of the unit cell and two crystallographically independent molecules for each component in the asymmetric unit. The H atom in one NHO hydrogen bond between the pyrimidin-1-ium cation and the water molecule is disordered, while the H atom in the other hydrogen bond is found to be ordered at the N-atom site with a long N-H distance [1.10 (3) Å].

p-Phenylenediamine and its dihydrate: two-dimensional isomorphism and mechanism of the dehydration process, and N-HN and N-H interactions

A. Czapik, H. Konowalska and M. Gdaniec

p-Phenylenediamine can be obtained as the dihydrate, C₆H₈N₂·2H₂O, (I), and in its anhydrous form, C₆H₈N₂, (II). The asymmetric unit of (I) contains one half of the p-phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p-phenylenediamine molecules are arranged in layers stabilized by N-H interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in-plane rotation of every fourth p-phenylenediamine molecule by ca 60°. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional.

The 293 K structure of tetradehydrohaliclonacyclamine A

I. W. Mudianta, M. J. Garson and P. V. Bernhardt

The polycyclic title compound {systematic name: (1S,16S,17S,31S)-3,20-diazatetracyclo[15.15.0^1,17.1^3,31.1^16,20]tetratriaconta-6,8,23,25-tetraene}, C₃₂H₅₂N₂, has recently been isolated and characterized structurally, in solution by NMR spectroscopy and in the solid state by X-ray crystallography. At 130 K the structure is monoclinic (P2₁, Z = 4) and comprises two molecules in the asymmetric unit with distinctly different conformations in the twelve-C-atom bridging chains. We report that, at 250 K, a phase change from monoclinic to orthorhombic (P22₁2₁, Z = 4) occurs. The higher-temperature phase is structurally characterized herein at 293 K. The two different conformers resolved in the monoclinic low-temperature form merge to give a single disordered molecule in the asymmetric unit of the high-temperature phase.

A new polymorph of benzene-1,2-diamine: isomorphism with 2-aminophenol and two-dimensional isostructurality of polymorphs

A. Czapik and M. Gdaniec

A new crystalline form of benzene-1,2-diamine, C₆H₈N₂, crystallizing in the space group Pbca, has been identified during screening for cocrystals. The crystals are constructed from molecular bilayers parallel to (001) that have the polar amino groups directed to the inside and the aromatic groups, showing a herringbone arrangement, directed to the outside. The known monoclinic form and the new orthorhombic polymorph exhibit two-dimensional isostructurality as the crystals consist of nearly identical bilayers. In the monoclinic form, neighbouring bilayers are generated by a unit translation along the a axis, whereas in the orthorhombic form they are generated by a c-glide. Moreover, the new form of benzene-1,2-diamine is essentially isomorphous with the only known form of 2-aminophenol.

A new modification of thallium chromate related to the -K₂SO₄ family

J. Fábry, M. Dusek, K. Fejfarová, R. Krupková and P. Vanek

The title structure is a new modification of Tl₂CrO₄. There are four independent Tl⁺ cations and two [CrO₄]^2- anions in the structure. It is closely related to the already known modification, which belongs to the -K₂SO₄ family with two independent cations and one anion. In both modifications, the cations and anions are situated on crystallographic mirror planes. The volume of the asymmetric unit of the title structure is 0.4% smaller than that of the known modification belonging to the -K₂SO₄ family. The other difference between the two modifications is seen in the environment of the cations. In the title structure, none of the Tl⁺ cations is underbonded, in contrast with the modification isostructural with -K₂SO₄. In the -K₂SO₄ family with simple cations, underbonding of one of the constituent cations is typical. The dependence of the unit-cell parameters on temperature does not indicate a phase transition in the interval 90-300 K.

Monoclinic Cu₂Se₃Sn

L. D. Gulay, M. Daszkiewicz, T. A. Ostapyuk, O. S. Klymovych and O. F. Zmiy

A previously unknown modification of dicopper(I) triselenostannate(IV), Cu₂Se₃Sn, has been obtained from the Cu₂Se-SnSe₂ quasi-binary system and investigated using X-ray single-crystal diffraction. The Se atoms are stacked in a closest-packed arrangement with the layers in the sequence ABC. The Cu atoms occupy one-third of the tetrahedral interstices, whereas the Sn atoms are located in one-sixth of the tetrahedral interstices. All the atoms occupy general positions. The structure possesses pseudo-inversion symmetry. The Cu₂Se₃Sn structure investigated in this paper (96 atoms per unit cell, ordered distribution of Cu and Sn over 12 cation positions) is a superstructure of the reported cubic (eight atoms per unit cell, random distribution of Cu and Sn over one cation position) and monoclinic (24 atoms per unit cell, ordered distribution of Cu and Sn over three cation positions) modifications.

A new polymorph of dichloridotriphenylantimony

D. J. MacDonald, M. C. Jennings and K. E. Preuss

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.

Hydrogen-bonded supramolecular networks of N,N'-bis(4-pyridylmethyl)oxalamide and 4,4'-{[oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrate

G.-H. Lee

The molecule of N,N'-bis(4-pyridylmethyl)oxalamide, C₁₄H₁₄N₄O₂, (I) or 4py-ox, has an inversion center in the middle of the oxalamide group. Adjacent molecules are then linked through intermolecular N-HN and C-HO hydrogen bonds, forming an extended supramolecular network. 4,4'-{[Oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrate, C₁₄H₁₆N₄O₂²⁺·2NO₃^-, (II), contains a diprotonated 4py-ox cation and two nitrate counter-anions. Each nitrate ion is hydrogen bonded to four 4py-ox cations via intermolecular N-HO and C-HO interactions. Adjacent 4py-ox cations are linked through weak C-HO hydrogen bonding between an -pyridinium C atom and an oxalamide O atom, forming a two-dimensional extended supramolecular network.

A third polymorph of 4-(2,6-difluorophenyl)-1,2,3,5-dithiadiazolyl

E. M. Fatila, M. C. Jennings, J. Goodreid and K. E. Preuss

The crystal structure of a third polymorphic form of the known 4-(2,6-difluorophenyl)-1,2,3,5-dithiadiazolyl radical, C₇H₃F₂N₂S₂, is reported. This new polymorph represents a unique crystal-packing motif never before observed for 1,2,3,5-dithiadiazolyl (DTDA) radicals. In the two known polymorphic forms of the title compound, all of the molecules form cis-cofacial dimers, such that two molecules are -stacked with like atoms one on top of the other, a common arrangement for DTDA species. By contrast, the third polymorph, reported herein, contains two crystallographically unique molecules organized such that only 50% are dimerized, while the other 50% remain monomeric radicals. The dimerized molecules are arranged in the trans-antarafacial mode. This less common dimer motif for DTDA species is characterized by - interactions between the S atoms [SS = 3.208 (1) Å at 110 K], such that the two molecules of the dimer are related by a centre of inversion. The most remarkable aspect of this third polymorph is that the DTDA dimers are co-packed with monomers. The monomeric radicals are arranged in one-dimensional chains directed by close lateral intermolecular contacts between the two S atoms of one DTDA heterocycle and an N atom of a neighbouring coplanar DTDA heterocycle [SN = 2.857 (2) and 3.147 (2) Å at 110 K].

[VO(SeO₃)(H₂O)₂]·0.5H₂O

W. T. A. Harrison

In poly[[diaquaoxido[₃-trioxidoselenato(2-)]vanadium(IV)] hemihydrate], {[VO(SeO₃)(H₂O)₂]·0.5H₂O}_n, the octahedral V(H₂O)₂O₄ and pyramidal SeO₃ building units are linked by V-O-Se bonds to generate ladder-like chains propagating along the [010] direction. A network of O-HO hydrogen bonds helps to consolidate the structure. The O atom of the uncoordinated water molecule lies on a crystallographic twofold axis. The title compound has a similar structure to those of the reported phases [VO(OH)(H₂O)(SeO₃)]₄·2H₂O and VO(H₂O)₂(HPO₄)·2H₂O.

-Zn₃(AsO₃)₂

W. T. A. Harrison

In the title compound, trizinc(II) diarsenite or trizinc(II) bis[trioxidoarsenate(III)], the constituent polyhedra that make up the structure are very distorted ZnO₄ tetrahedra and AsO₃ trigonal pyramids. These species fuse together to generate a three-dimensional network containing unusual edge-sharing tetrahedra, with a ZnZn separation of 2.903 (3) Å. The structure also features eight-ring pseudo-channels occupied by the As^III lone pairs of electrons. The title compound is a polymorph of the mineral reinerite, which also features edge-shared ZnO₄ tetrahedra.

Bis(hinokitiolato)copper(II): modification (III)

D. M. Ho

Bis(hinokitiolato)copper(II), Cu(hino)₂, exhibits both antibacterial and antiviral properties, and has been previously shown to exist in two modifications. A third modification has now been confirmed, namely tetrakis(₂-3-isopropyl-7-oxocyclohepta-1,3,5-trien-1-olato)bis(3-isopropyl-7-oxocyclohepta-1,3,5-trien-1-olato)tricopper(II)-bis(₂-3-isopropyl-7-oxocyclohepta-1,3,5-trien-1-olato)bis[(3-isopropyl-7-oxocyclohepta-1,3,5-trien-1-olato)copper(II)] (1/1), [Cu(C₁₀H₁₁O₂)₂]₃·[Cu(C₁₀H₁₁O₂)₂]₂, where 3-isopropyl-7-oxocyclohepta-1,3,5-trien-1-olate is the systematic name for the hinokitiolate anion. This new modification is composed of discrete [cis-Cu(hino)₂]₂[trans-Cu(hino)₂] trimers and [cis-Cu(hino)₂]₂ dimers. The Cu atoms are bridged by ₂-O atoms from the hinokitiolate ligands to give distorted square-pyramidal and distorted octahedral Cu^II coordination environments. Hence, the Cu^II environments are CuO₅/CuO₆/CuO₅ for the trimer and CuO₅/CuO₅ for the dimer. Each trimer and dimer has crystallographically imposed inversion symmetry. The trimer has never been observed before, the dimer has been seen only once before, and the combination of the two together in the same lattice is unprecedented. The CuO₅ cores exhibit four strong basal Cu-O bonds [1.915 (2)-1.931 (2) Å] and one weak apical Cu-O bond [2.652 (2)-2.658 (2) Å]. The CuO₆ core exhibits four strong equatorial Cu-O bonds [1.922 (2)-1.929 (2) Å] and two very weak axial Cu-O bonds [2.911 (3) Å]. The bite angles for the chelating hinokitiolate ligands range from 83.13 (11) to 83.90 (10)°.

Polymorphs of DABCO monohydrate as structural analogues of NaCl

B. Wicher and M. Gdaniec

A new crystalline form of 1,4-diazabicyclo[2.2.2]octane (DABCO) monohydrate, C₆H₁₂N₂·H₂O, crystallizing in the space group P3₁, has been identified during screening for cocrystals. There are three DABCO and three water molecules in the asymmetric unit, with two DABCO molecules exhibiting disorder over two positions related by rotation around the NN axis. As in the monoclinic C2/c (Z' = 2) polymorph, the molecular components are connected via O-HN hydrogen bonds into a polymeric structure that consists of linear O-HN(CH₂CH₂)₃NH-O segments, which are approximately mutually perpendicular. The two polymorphic forms of DABCO monohydrate can be considered as structural analogues of NaCl, with the nearly globular DABCO molecules showing distorted cubic closest packing and all octahedral interstices occupied by water molecules.

Two new structures in the glycine-oxalic acid system

N. A. Tumanov, E. V. Boldyreva and N. E. Shikina

Glycinium semi-oxalate-II, C₂H₆NO₂⁺·C₂HO₄^-, (A), and diglycinium oxalate methanol disolvate, 2C₂H₆NO₂⁺·C₂O₄^2-·2CH₃OH, (B), are new examples in the glycine-oxalic acid family. (A) is a new polymorph of the known glycinium semi-oxalate salt, (C). Compounds (A) and (C) have a similar packing of the semi-oxalate monoanions with respect to the glycinium cations, but in (A) the two glycinium cations and the two semi-oxalate anions in the asymmetric unit are non-equivalent, and the binding of the glycinium cations to each other is radically different. Based on this difference, one can expect that, although the two forms grow concomitantly from the same batch, a transformation between (A) and (C) in the solid state should be difficult. In (B), two glycinium cations and an oxalate anion, which sits across a centre of inversion, are linked via strong short O-HO hydrogen bonds to form the main structural fragment, similar to that in diglycinium oxalate, (D). Methanol solvent molecules are embedded between the glycinium cations of neighbouring fragments. These fragments form a three-dimensional network via N-HO hydrogen bonds. Salts (B) and (D) can be obtained from the same solution by, respectively, slow or rapid antisolvent crystallization.

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

K. Ravikumar and B. Sridhar

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-HO hydrogen bonds are present in both structures, whereas N-HF hydrogen bonding is seen in polymorph (I), while N-HN hydrogen bonding is seen in polymorph (II).

Ezetimibe anhydrate, determined from laboratory powder diffraction data

J. Brüning, E. Alig and M. U. Schmidt

Ezetimibe {systematic name: (3R,4S)-1-(4-fluorophenyl)-3-[(3S)-3-(4-fluorophenyl)-3-hydroxypropyl]-4-(4-hydroxyphenyl)azetidin-2-one}, C₂₄H₂₁F₂NO₃, is used to lower cholesterol levels by inhibiting cholesterol resorption in the human intestine. The crystal structure of ezetimibe anhydrate was solved from laboratory powder diffraction data by means of real-space methods using the program DASH [David et al. (2006). J. Appl. Cryst. 39, 910-915]. Subsequent Rietveld refinement with TOPAS Academic [Coelho (2007). TOPAS Academic User Manual. Version 4.1. Coelho Software, Brisbane, Australia] led to a final R_wp value of 8.19% at 1.75 Å resolution. The compound crystallizes in the space group P2₁2₁2₁ with one molecule in the asymmetric unit. The molecules are closely packed and two intermolecular hydrogen bonds form an extended hydrogen-bond architecture.

Structural comparison of three N-(4-halogenophenyl)-N'-[1-(2-pyridyl)ethylidene]hydrazine hydrochlorides

J. Heilmann-Brohl, M. Wagner, H.-W. Lerner and M. Bolte

2-{1-[(4-Chloroanilino)methylidene]ethyl}pyridinium chloride methanol solvate, C₁₃H₁₃ClN₃⁺·Cl^-·CH₃OH, (I), crystallizes as discrete cations and anions, with one molecule of methanol as solvent in the asymmetric unit. The N-C-C-N torsion angle in the cation indicates a cis conformation. The cations are located parallel to the (02) plane and are connected through hydrogen bonds by a methanol solvent molecule and a chloride anion, forming zigzag chains in the direction of the b axis. The crystal structure of 2-{1-[(4-fluoroanilino)methylidene]ethyl}pyridinium chloride, C₁₃H₁₃FN₃⁺·Cl^-, (II), contains just one anion and one cation in the asymmetric unit but no solvent. In contrast with (I), the N-C-C-N torsion angle in the cation corresponds with a trans conformation. The cations are located parallel to the (100) plane and are connected by hydrogen bonds to the chloride anions, forming zigzag chains in the direction of the b axis. In addition, the crystal packing is stabilized by weak - interactions between the pyridinium and benzene rings. The crystal of (II) is a nonmerohedral monoclinic twin which emulates an orthorhombic diffraction pattern. Twinning occurs via a twofold rotation about the c axis and the fractional contribution of the minor twin component refined to 0.324 (3). 2-{1-[(4-Fluoroanilino)methylidene]ethyl}pyridinium chloride methanol disolvate, C₁₃H₁₃FN₃⁺·Cl^-·2CH₃OH, (III), is a pseudopolymorph of (II). It crystallizes with two anions, two cations and four molecules of methanol in the asymmetric unit. Two symmetry-equivalent cations are connected by hydrogen bonds to a chloride anion and a methanol solvent molecule, forming a centrosymmetric dimer. A further methanol molecule is hydrogen bonded to each chloride anion. These aggregates are connected by C-HO contacts to form infinite chains. It is remarkable that the geometric structures of two compounds having two different formula units in their asymmetric units are essentially the same.

Green chemistry synthesis: 2-amino-3-[(E)-(2-pyridyl)methylideneamino]but-2-enedinitrile monohydrate and 5-cyano-2-(2-pyridyl)-1-(2-pyridylmethyl)-1H-imidazole-4-carboxamide

M. Altaf and H. Stoeckli-Evans

The title compounds, C₁₀H₉N₅O·H₂O (L1·H₂O) and C₁₆H₁₂N₆O (L2), were synthesized by solvent-free aldol condensation at room temperature. L1, prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 1:1 molar ratio, crystallized as a monohydrate. L2 was prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 2:1 molar ratio. By varying the conditions of crystallization it was possible to obtain two polymorphs, viz. L2-I and L2-II; both crystallized in the monoclinic space group P2₁/c. They differ in the orientation of one pyridine ring with respect to the plane of the imidazole ring. In L2-I, this ring is oriented towards and above the imidazole ring, while in L2-II it is rotated away from and below the imidazole ring. In all three molecules, there is a short intramolecular N-HN contact inherent to the planarity of the systems. In L1·H₂O, this involves an amino H atom and the C=N N atom, while in L2 it involves an amino H atom and an imidazole N atom. In the crystal structure of L1·H₂O, there are N-HO and O-HO intermolecular hydrogen bonds which link the molecules to form two-dimensional networks which stack along [001]. These networks are further linked via intermolecular N-HN(cyano) hydrogen bonds to form an extended three-dimensional network. In the crystal structure of L2-I, symmetry-related molecules are linked via N-HN hydrogen bonds, leading to the formation of dimers centred about inversion centres. These dimers are further linked via N-HO hydrogen bonds involving the amide group, also centred about inversion centres, to form a one-dimensional arrangement propagating in [100]. In the crystal structure of L2-II, the presence of intermolecular N-HO hydrogen bonds involving the amide group results in the formation of dimers centred about inversion centres. These are linked via N-HN hydrogen bonds involving the second amide H atom and the cyano N atom, to form two-dimensional networks in the bc plane. In L2-I and L2-II, C-H and - interactions are also present.

A monohydrate pseudopolymorph of 3,4-dihydroxybenzophenone and the role of water in the crystal assembly of benzophenones

I. M. R. Landre, T. E. Souza, R. S. Corrêa, F. T. Martins and A. C. Doriguetto

During a polymorphism screening of hydroxybenzophenone derivatives, a monohydrate pseudopolymorph of (3,4-dihydroxyphenyl)(phenyl)methanone, C₁₃H₁₀O₃·H₂O, (I), was obtained. Structural relationships and the role of water in crystal assembly were established on the basis of the known anhydrous form [Cox, Kechagias & Kelly (2008). Acta Cryst. B64, 206-216]. The crystal packing of (I) is stabilized by classical intermolecular O-HO hydrogen bonds, generating a three-dimensional network.

Powder X-ray studies of meso-hexamethyl propylene amine oxime (meso-HMPAO) in two different phases

M. Al-Ktaifani and M. Rukiah

Two different forms of meso-3,3'-[2,2-dimethylpropane-1,3-diylbis(azanediyl)]dibutan-2-one dioxime, commonly called meso-hexamethyl propylene amine oxime (HMPAO), C₁₃H₂₈N₄O₂, designated and , were isolated by fractional crystallization and their crystal structures were determined by powder X-ray diffraction using the direct-space method with the parallel tempering algorithm. The form was first crystallized from acetonitrile solution, while the form was obtained by recrystallization of the phase from diethyl ether. The form crystallizes in the triclinic system (space group P), with one molecule in the asymmetric unit, while the crystal of the form is monoclinic (space group P2₁/n), with one molecule in the asymmetric unit. In both phases, the molecules have similar conformations and RS/EE geometric isomerism. The crystal packing of the two phases is dominated by intermolecular hydrogen-bonding interactions between the two O-H oxime groups of an individual molecule and the amine N atoms of two different adjacent molecules, which lead to segregation of extended poly(meso-HMPAO) one-dimensional chains along the c direction. The structures of the two phases are primarily different due to the different orientations of the molecules in the chains.

A low-temperature phase of bis(tetrabutylammonium) octa-₃-chlorido-hexachlorido-octahedro-hexatungstate

D. H. Johnston, C. M. Brown, A. S. Yu and J. C. Gallucci

The title compound, (C₁₆H₃₆N)₂[W₆Cl₁₄], undergoes a reversible phase transition at 268 (1) K. The structure at 150 and 200 K has monoclinic (P2₁/c) symmetry. Both crystallographically independent tungsten chloride cluster anions sit on crystallographic inversion centers [symmetry codes: (-x, -y + 1, -z) and (-x + 1, -y + 2, -z)]. Two previous studies at room temperature describe the structure in the space group P2₁/n with a unit-cell volume approximately half the size of the low-temperature unit cell [Zietlow, Schaefer et al. (1986). Inorg. Chem. 25, 2195-2198; Venkataraman et al. (1999). Inorg. Chem. 38, 828-830]. The unit cells of the room- and low-temperature polymorphs are closely related. The hydrocarbon chain of one of the tetrabutylammonium cations is disordered at both 150 and 200 K.

Two three-dimensional networks in two polymorphs of biphenyl-4,4'-diaminium bis(3-carboxy-4-hydroxybenzenesulfonate) dihydrate

W. Yin, X. Huang, X. Xu and X. Meng

Two polymorphs of biphenyl-4,4'-diaminium bis(3-carboxy-4-hydroxybenzenesulfonate) dihydrate, C₁₂H₁₄N₂²⁺·2C₇H₅O₆S^-·2H₂O, have been obtained and crystallographically characterized. Polymorph (I) crystallizes in the space group P2₁/c with Z' = 2 and polymorph (II) in the space group P with Z' = 0.5. The benzidinium cation in (II) is located on a crystallographic inversion centre. In both (I) and (II), the sulfonic acid H atoms are transferred to the benzidine N atoms, forming dihydrated 1:2 molecular adducts (base-acid). In the crystal packings of (I) and (II), the component ions are linked into three-dimensional networks by combinations of X-HO (X = O, N and C) hydrogen bonds. In addition, - interactions are observed in (I) between inversion-related benzene rings [centroid-centroid distances = 3.632 (2) and 3.627 (2) Å]. In order to simplify the complex three-dimensional networks in (I) and (II), we also give their rationalized topological analyses.

Twinned low-temperature structures of tris(ethylenediamine)zinc(II) sulfate and tris(ethylenediamine)copper(II) sulfate

M. Lutz

Tris(ethylenediamine)zinc(II) sulfate, [Zn(C₂H₈N₂)₃]SO₄, (I), undergoes a reversible solid-solid phase transition during cooling, accompanied by a lowering of the symmetry from high-trigonal P1c to low-trigonal P and by merohedral twinning. The molecular symmetries of the cation and anion change from 32 (D₃) to 3 (C₃). This lower symmetry allows an ordered sulfate anion and generates in the complex cation two independent N atoms with significantly different geometries. The twinning is the same as in the corresponding Ni complex [Jameson et al. (1982). Acta Cryst. B38, 3016-3020]. The low-temperature phase of tris(ethylenediamine)copper(II) sulfate, [Cu(C₂H₈N₂)₃]SO₄, (II), has only triclinic symmetry and the unit-cell volume is doubled with respect to the room-temperature structure in P1c. (II) was refined as a nonmerohedral twin with five twin domains. The asymmetric unit contains two independent formula units, and all cations and anions are located on general positions with 1 (C₁) symmetry. Both molecules of the Cu complex are in elongated octahedral geometries because of the Jahn-Teller effect. This is in contrast to an earlier publication, which describes the complex as a compressed octahedron [Bertini et al. (1979). J. Chem. Soc. Dalton Trans. pp. 1409-1414].

The structural phase transition in SrV₆O₁₁

Y. Hata, Y. Kanke and E. Kita

Single-crystal X-ray diffraction and specific heat studies establish that strontium hexavanadium undecaoxide, SrV₆O₁₁, undergoes a P6₃/mmc to inversion twinned P6₃mc structural transition as the temperature is lowered through 322 K. The P6₃/mmc and P6₃mc structures have been determined at 353 K and at room temperature, respectively. For the room-temperature structure, seven of the ten unique atoms lie on special positions, and for the 353 K structure all of the seven unique atoms sit on special positions. The P6₃/mmc to P6₃mc structural phase transition, accompanied by a magnetic transition, is a common characteristic of AV₆O₁₁ compounds, independent of the identity of the A cations.

Polymorphism in 2-(4-hydroxy-2,6-dimethylanilino)-5,6-dihydro-4H-1,3-thiazin-3-ium chloride

J. Gutierrez, R. Eisenberg, G. Herrensmith, T. Tobin, T. Li and S. Long

Details of the structures of two conformational polymorphs of the title compound, C₁₂H₁₇N₂OS⁺·Cl^-, are reported. In form (I) (space group P), the two N-H groups of the cation are in a trans conformation, while in form (II) (space group P2₁/c), they are in a cis arrangement. This results in different packing and hydrogen-bond arrangements in the two forms, both of which have extended chains lying along the a direction. In form (I), these chains are composed of centrosymmetric R₄²(18) (N-HCl and O-HCl) hydrogen-bonded rings and R₂²(18) (N-HO) hydrogen-bonded rings. In form (II), the chains are formed by centrosymmetric R₄²(18) (N-HCl and O-HCl) hydrogen-bonded rings and by R₄²(12) (N-HCl) hydrogen-bonded rings.

Anhydrous 1:1 proton-transfer compounds of isonipecotamide with picric acid and 3,5-dinitrosalicylic acid: 4-carbamoylpiperidinium 2,4,6-trinitrophenolate and two polymorphs of 4-carbamoylpiperidinium 2-carboxy-4,6-dinitrophenolate

G. Smith and U. D. Wermuth

The structures of the anhydrous 1:1 proton-transfer compounds of isonipecotamide (piperidine-4-carboxamide) with picric acid and 3,5-dinitrosalicylic acid, namely 4-carbamoylpiperidinium 2,4,6-trinitrophenolate, C₆H₁₃N₂O⁺·C₆H₂N₃O₇^-, (I), and 4-carbamoylpiperidinium 2-carboxy-4,6-dinitrophenolate [two forms of which were found, the monoclinic -polymorph, (II), and the triclinic -polymorph, (III)], C₆H₁₃N₂O⁺·C₇H₃N₂O₇^-, have been determined at 200 K. All three compounds form hydrogen-bonded structures, viz. one-dimensional in (II), two-dimensional in (I) and three-dimensional in (III). In (I), the cations form centrosymmetric cyclic head-to-tail hydrogen-bonded homodimers [graph set R₂²(14)] through lateral duplex piperidinium-amide N-HO interactions. These dimers are extended into a two-dimensional network structure through further interactions with phenolate and nitro O-atom acceptors, including a direct symmetric piperidinium-phenol/nitro N-HO,O cation-anion association [graph set R₁²(6)]. The monoclinic polymorph, (II), has a similar R₁²(6) cation-anion hydrogen-bonding interaction to (I) but with an additional conjoint symmetrical R¹₂(4) interaction as well as head-to-tail piperidinium-amide N-HO,O hydrogen bonds and amide-carboxyl N-HO hydrogen bonds, giving a network structure which includes large R₄³(20) rings. The hydrogen bonding in the triclinic polymorph, (III), is markedly different from that of monoclinic (II). The asymmetric unit contains two independent cation-anion pairs which associate through cyclic piperidinium-carboxyl N-HO,O' interactions [graph set R₁²(4)]. The cations also show the zigzag head-to-tail piperidinium-amide N-HO hydrogen-bonded chain substructures found in (II), but in addition feature amide-nitro and amide-phenolate N-HO associations. As well, there is a centrosymmetric double-amide N-HO_carboxyl bridged bis(cation-anion) ring system [graph set R₄²(8)] in the three-dimensional framework. The structures reported here demonstrate the utility of the isonipecotamide cation as a synthon with previously unrecognized potential for structure assembly applications. Furthermore, the structures of the two polymorphic 3,5-dinitrosalicylic acid salts show an unusual dissimilarity in hydrogen-bonding characteristics, considering that both were obtained from identical solvent systems.

Two new polymorphs of 2,6-diaminopyrimidin-4(3H)-one monohydrate

N. Suleiman Gwaram, H. Khaledi, H. Mohd Ali and M. M. Olmstead

The title compound, C₄H₆N₄O·H₂O, crystallized simultaneously as a triclinic and a monoclinic polymorph from an aqueous solution of 2,4-diaminopyrimidin-6-ol. Previously, an orthorhombic polymorph was isolated under the same experimental conditions. The molecular geometric parameters in the two present polymorphs and the previously reported orthorhombic polymorph are similar, but the structures differ in the details of their crystal packing. In the triclinic system, the diaminopyrimidinone molecules are connected to one another via N-HO and N-HN hydrogen bonding to form infinite chains in the [011] direction. The chains are further hydrogen bonded to the water molecules, resulting in a three-dimensional network. In the monoclinic system, the diaminopyrimidinone molecules are hydrogen bonded together into two-dimensional networks parallel to the bc plane. The water molecules link the planes to form a three-dimensional polymeric structure.

Five pseudopolymorphs and a cocrystal of nitrofurantoin

M. Tutughamiarso, M. Bolte, G. Wagner and E. Egert

The antibiotic nitrofurantoin {systematic name: (E)-1-[(5-nitro-2-furyl)methylideneamino]imidazolidine-2,4-dione} is not only used for the treatment of urinary tract infections, but also illegally applied as an animal food additive. Since derivatives of 2,6-diaminopyridine might serve as artificial receptors for its recognition, we crystallized one potential drug-receptor complex, nitrofurantoin-2,6-diacetamidopyridine (1/1), C₈H₆N₄O₅·C₉H₁₁N₃O₂, (I·II). It is characterized by one N-HN and two N-HO hydrogen bonds and confirms a previous NMR study. During the crystallization screening, several new pseudopolymorphs of both components were obtained, namely a nitrofurantoin dimethyl sulfoxide monosolvate, C₈H₆N₄O₅·C₂H₆OS, (Ia), a nitrofurantoin dimethyl sulfoxide hemisolvate, C₈H₆N₄O₅·0.5C₂H₆OS, (Ib), two nitrofurantoin dimethylacetamide monosolvates, C₈H₆N₄O₅·C₄H₉NO, (Ic) and (Id), and a nitrofurantoin dimethylacetamide disolvate, C₈H₆N₄O₅·2C₄H₉NO, (Ie), as well as a 2,6-diacetamidopyridine dimethylformamide monosolvate, C₉H₁₁N₃O₂·C₃H₇NO, (IIa). Of these, (Ia), (Ic) and (Id) were formed during cocrystallization attempts with 1-(4-fluorophenyl)biguanide hydrochloride. Obviously nitrofurantoin prefers the higher-energy conformation in the crystal structures, which all exhibit N-HO and C-HO hydrogen-bond interactions. The latter are especially important for the crystal packing. 2,6-Diacetamidopyridine shows some conformational flexibility depending on the hydrogen-bond pattern.

A dynamic disorder-linked reversible phase transition in a new chloroform solvate of cis-dichloridobis(triethylphosphane)platinum(II)

K. B. Dillon, J. A. K. Howard, P. K. Monks, M. R. Probert and H. J. Shepherd

The title compound, cis-dichloridobis(triethylphosphane)platinum(II) chloroform monosolvate, [PtCl₂(C₆H₁₅P)₂]·CHCl₃, has been obtained from ligand scrambling in the cis-[PtCl₂(Cyp₂PCl)(PEt₃)] (Cyp = cyclopentyl) system in CHCl₃ solvent. Unlike the two previously reported unsolvated polymorphs, which are both monoclinic, the compound crystallizes in an orthorhombic setting. Furthermore, the system exhibits a reversible temperature-dependent structural phase transition, coupling a reduction in anisotropic displacement parameters and a reduction in crystallographic symmetry on cooling. The high-temperature phase adopts space group Pnma with the complex and solvent molecules sitting across a crystallographic mirror plane (Z' = 0.5). The low-temperature phase adopts the space group P2₁2₁2₁ with Z' = 1.

A new polymorph of 1,4-dibromo-2,5-dimethylbenzene: HBr and Br versus BrBr interactions

P. G. Jones and P. Kus

A new polymorph, (Ib), of the title compound, C₈H₈Br₂, crystallizes in the space group P2₁/n, the same as the known polymorph (Ia) but with Z = 2 (imposed inversion symmetry) rather than Z = 4. The molecular structures are closely similar because the molecule has no degrees of torsional freedom except for methyl groups, but the packing arrangements are completely different. Polymorph (Ia) is characterized by linked trapezia of BrBr interactions, whereas polymorph (Ib) features HBr and Br interactions.

L-Cysteinium semioxalate: a new monoclinic polymorph or a hydrate?

V. S. Minkov and E. V. Boldyreva

The title compound, C₃H₈NO₂S⁺·C₂HO₄^-, (I), crystallizes in the monoclinic C2 space group and is a new form (possibly a hydrate) of L-cysteinium semioxalate with a stoichiometric cation-anion ratio of 1:1. In contrast to the previously known orthorhombic form of L-cysteinium semioxalate, (I) has a layered structure resembling those of monoclinic L-cysteine, as well as of DL-cysteine and its oxalates. The conformations of the cysteinium cation and the oxalate anion in (I) differ substantially from those in the orthorhombic form. The structure of (I) has voids with a size sufficient to incorporate water molecules. The residual density, however, suggests that if water is in fact present in the voids, it is strongly disordered and its amount does not exceed 0.3 molecules per void. The difference in conformation of the cysteinium cations in (I) and in the orthorhombic form is similar to that in DL-cysteine under ambient conditions and in DL-cysteine under high pressure or at low temperature.

Synthetic ferric sulfate trihydrate, Fe₂(SO₄)₃·3H₂O, a new ferric sulfate salt

W. Xu and J. B. Parise

Ferric sulfate trihydrate has been synthesized at 403 K under hydrothermal conditions. The structure consists of quadruple chains of [Fe₂(SO₄)₃(H₂O)₃] parallel to [010]. Each quadruple chain is composed of equal proportions of FeO₄(H₂O)₂ octahedra and FeO₅(H₂O) octahedra sharing corners with SO₄ tetrahedra. The chains are joined to each other by hydrogen bonds. This compound is a new hydration state of Fe₂(SO₄)₃·nH₂O; minerals with n = 0, 5, 7.25-7.75, 9 and 11 are found in nature.

Two polymorphs of tetraethylammonium [hydrogen tris(3,5-dimethylpyrazolyl)borato]di-₂-sulfido-disulfido(²-tetrasulfido)ditungsten(V) with Z' = 1 and 2

A. Beheshti, W. Clegg, N. Ebrahimi Filoori and L. Russo

Two polymorphs of the title compound, (C₈H₂₀N)[W₂S₄(S₄)(C₁₅H₂₂BN₆)], have been obtained unexpectedly by attempted recrystallization of a mixed-metal-sulfur cluster complex from different solvents. The dinuclear complex anion contains W^V in two different coordination environments, one of them distorted octahedral with a tris(pyrazolyl)borate anion, a terminal sulfide and two bridging sulfide ligands, the other distorted square-pyramidal with a terminal sulfide, two bridging sulfide and a chelating tetrasulfide ligand. The three independent anions in the two polymorphs have essentially the same geometry. The central W₂S₂ ring is a slightly folded rhombus with acute angles at the S atoms, and the WS₄ chelate ring is an envelope with one noncoordinating S atom as the flap. The second polymorph, with Z' = 2 and pseudo-inversion symmetry relating the anions of the asymmetric unit, also displays pseudo-translation features in its layer structure, and all examined crystals were found to be twinned, possibly as a consequence of this structural feature.

Conformational polymorphism of (E,E)-N,N'-bis(4-nitrobenzylidene)benzene-1,4-diamine

A. Collas, M. Zeller and F. Blockhuys

Two polymorphs of (E,E)-N,N'-bis(4-nitrobenzylidene)benzene-1,4-diamine, C₂₀H₁₄N₄O₄, (I), have been identified. In each case, the molecule lies across a crystallographic inversion centre. The supramolecular structure of the first polymorph, (I-1), features stacking based on - interactions assisted by weak hydrogen bonds involving the nitro groups. The second polymorph, (I-2), displays a perpendicular arrangement of molecules linked via the nitro groups, combined with weak C-HO hydrogen bonds. Both crystal structures are compared with that of the carbon analogue (E,E)-1,4-bis[2-(4-nitrophenyl)ethenyl]benzene, (II).

Pseudopolymorphs of 2,6-diaminopyrimidin-4-one and 2-amino-6-methylpyrimidin-4-one: one or two tautomers present in the same crystal

V. Gerhardt, M. Tutughamiarso and M. Bolte

The derivatives of pyrimidin-4-one can adopt either a 1H- or a 3H-tautomeric form, which affects the hydrogen-bonding interactions in cocrystals with compounds containing complementary functional groups. In order to study their tautomeric preferences, we crystallized 2,6-diaminopyrimidin-4-one and 2-amino-6-methylpyrimidin-4-one. During various crystallization attempts, four structures of 2,6-diaminopyrimidin-4-one were obtained, namely solvent-free 2,6-diaminopyrimidin-4-one, C₄H₆N₄O, (I), 2,6-diaminopyrimidin-4-one-dimethylformamide-water (3/4/1), C₄H₆N₄O·1.33C₃H₇NO·0.33H₂O, (Ia), 2,6-diaminopyrimidin-4-one dimethylacetamide monosolvate, C₄H₆N₄O·C₄H₉NO, (Ib), and 2,6-diaminopyrimidin-4-one-N-methylpyrrolidin-2-one (3/2), C₄H₆N₄O·1.5C₅H₉NO, (Ic). The 2,6-diaminopyrimidin-4-one molecules exist only as 3H-tautomers. They form ribbons characterized by R²₂(8) hydrogen-bonding interactions, which are further connected to form three-dimensional networks. An intermolecular N-HN interaction between amine groups is observed only in (I). This might be the reason for the pyramidalization of the amine group. Crystallization experiments on 2-amino-6-methylpyrimidin-4-one yielded two isostructural pseudopolymorphs, namely 2-amino-6-methylpyrimidin-4(3H)-one-2-amino-6-methylpyrimidin-4(1H)-one-dimethylacetamide (1/1/1), C₅H₇N₃O·C₅H₇N₃O·C₄H₉NO, (IIa), and 2-amino-6-methylpyrimidin-4(3H)-one-2-amino-6-methylpyrimidin-4(1H)-one-N-methylpyrrolidin-2-one (1/1/1), C₅H₇N₃O·C₅H₇N₃O·C₅H₉NO, (IIb). In both structures, a 1:1 mixture of 1H- and 3H-tautomers is present, which are linked by three hydrogen bonds similar to a Watson-Crick C-G base pair.

Poly[(₃-benzene-1,4-diacetato)[₂-1,4-bis(1,2,4-triazol-1-yl)butane]cadmium(II)]: self assembly into a three-dimensional supramolecular framework based on [Cd(₃-benzene-1,4-diacetate)] double chains

J. Wang, J.-Q. Tao and X.-J. Xu

The title compound, [Cd(C₁₀H₈O₄)(C₈H₁₂N₆)]_n, crystallizes with an asymmetric unit comprising a divalent Cd^II atom, a benzene-1,4-diacetate (PBEA^2-) ligand and a complete 1,4-bis(1,2,4-triazol-1-yl)butane (BTB) ligand. [Cd(PBEA)]_n double chains, arranged parallel to the c axis, are formed through an exo-tridentate binding mode of the PBEA^2- ligands. These [Cd(PBEA)]_n double chains are pillared by tethering BTB ligands, in which the BTB shows a trans-trans-trans conformation, to establish [Cd(PBEA)(BTB)]_n two-dimensional coordination polymer (4,4)-layer slab patterns. The three-dimensional supramolecular architecture is formed by C-HO hydrogen bonds and C-H interactions.

Two polymorphs of (2-carboxyethyl)(phenyl)phosphinic acid

Q.-S. Hu, X.-Z. Zhang, S.-F. Luo, Y.-H. Sun and Z.-Y. Du

Two polymorphs of (2-carboxyethyl)(phenyl)phosphinic acid, C₉H₁₁O₄P, crystallize in the chiral P2₁2₁2₁ space group with similar unit-cell parameters. They feature an essentially similar hydrogen-bonding motif but differ slightly in their detailed geometric parameters. For both polymorphs, the unequivocal location of the hydroxy H atoms together with the expected differences in the P-O bond lengths establish unequivocally that both forms contain the S isomer; the protonated phosphinic acid and carboxy O atoms serve as hydrogen-bond donors, while the second phosphinic acid O atom acts as a double hydrogen-bond acceptor and the remaining carboxy O atom is not involved in hydrogen bonding. Thus, an undulating two-dimensional supramolecular layer aggregate is formed based on an R₄³(20) ring unit. Such polymorphism derives from the rotation of the C-C single bonds between the two hydrogen-bond-involved carboxy and phosphinic acid moieties.

1,5-Dianilinopentane-1,3,5-trione: a crystal structure containing two polymorphic domains

J. W. Bats, J. Brüning and M. U. Schmidt

Single crystals of the title compound, C₁₇H₁₆N₂O₃, were obtained by gas diffusion. The observed diffraction pattern is compatible with a superposition of reflections from two monoclinic unit cells with the space group C2/c. The two cells share the a and b axes but not the c axis. Both structures contain layers parallel to (001), with molecules connected by intermolecular N-HO=C hydrogen bonds. The bonding between adjacent layers is weak. Layer displacements result in a crystal structure containing two closely related polymorphic domains. The structure of one polymorph can be derived from the structure of the other if subsequent layers are displaced by (a/4, b/4, 0) for odd-numbered layers and by (a/4, -b/4, 0) for even-numbered layers. Three different crystals were analysed and their observed diffraction patterns were similar, showing all three crystals to contain the polymorphic domain structure.

A new rhombohedral modification of EuNi₅In

I. Bigun, V. Smetana and Y. Kalychak

A rhombohedral modification of europium pentanickel indide, r-EuNi₅In, crystallizes in the Rm space group and adopts the UCu₅In structure type. The structure is closely related to the hexagonal, h-EuNi₅In, form (CeNi₅Sn type). Both EuNi₅In modifications are composed of CaCu₅ (EuNi₅)-, MgCu₂ (InNi₂)- and NiAs (EuNi)-type slabs in a 1:2:1 ratio. The atoms in the structure have high coordination numbers, viz. 20 and 18 for europium, 14 for indium, and 12 and 10 for nickel. The structure features a two-dimensional network of ²[Ni₈] tetrahedral clusters arranged in the ab plane.

1-(9H-Carbazol-4-yloxy)-3-{[2-(2-methoxyphenoxy)ethyl]amino}propan-2-ol hemihydrate: a carvedilol solvatomorph

F. Díaz, A. Benassi, M. Quintero, G. Polla, E. Freire and R. Baggio

In the title racemic hemihydrated solvatomorph of carvedilol (carv), C₂₄H₂₆N₂O₄·0.5H₂O, the asymmetric unit contains two independent organic moieties and one water molecule. Within this 2(carv)·H₂O unit, the molecular components are strongly linked by hydrogen bonds and the unit acts as the basic building block for the crystal structure. Interactions parallel to (10) generate hydrogen-bonded layers which are further linked by much weaker C-HN/O interactions. The conformations of the organic molecules, as well as the hydrogen-bonding interactions connecting them, are compared with other related structures in the literature.

Polysulfonylamines. CXCI. The `almost' polymorphs rac-trans-2-aminocyclohexan-1-aminium di(methanesulfonyl)azanide and its 0.11-hydrate

C. Wölper, N. Anwar, N. Gulzar, P. G. Jones and A. Blaschette

The title compound, C₆H₁₅N₂⁺·C₂H₆NO₄S₂^-, crystallizes as a 0.11-hydrate, (I), in the space group C2; the asymmetric unit consists of two cations (one of each enantiomer), one anion on a general position, two half anions, each with the N atom on a twofold axis, and approximately one fifth of a water molecule. The general anion departs significantly from the usual conformation: it lacks one of the typical `W'-shaped sequence of O-S-N-S-O atoms. The compound also crystallizes in the solvent-free form, (II), in the space group P2₁/c, with one formula unit in the asymmetric unit. Both compounds form ribbons of hydrogen-bonded cation dimers parallel to the b axis. In (I), there are two independent ribbons of opposite chirality, each involving one anion on a special position, and these ribbons are connected by hydrogen bonds to the anion on a general position, resulting in a layer structure parallel to (100). In (II), the chains are connected by hydrogen bonds, and again a layer structure parallel to (100) results.

N-(tert-Butoxycarbonyl)--aminoisobutyryl--aminoisobutyric acid methyl ester: two polymorphic forms in the space group P2₁/n

H. G. Gebreslasie, Ø. Jacobsen and C. H. Görbitz

The title compound (systematic name: methyl 2-{2-[(tert-butoxycarbonyl)amino]-2-methylpropanamido}-2-methylpropanoate), C₁₄H₂₆N₂O₅, (I), crystallizes in the monoclinic space group P2₁/n in two polymorphic forms, each with one molecule in the asymmetric unit. The molecular conformation is essentially the same in both polymorphs, with the -aminoisobutyric acid (Aib) residues adopting and values characteristic of -helical and mixed 3₁₀- and -helical conformations. The helical handedness of the C-terminal residue (Aib2) is opposite to that of the N-terminal residue (Aib1). In contrast to (I), the closely related peptide Boc-Aib-Aib-OBn (Boc is tert-butoxycarbonyl and Bn is benzyl) adopts an _L-P_II backbone conformation (or the mirror image conformation). Compound (I) forms hydrogen-bonded parallel -sheet-like tapes, with the carbonyl groups of Aib1 and Aib2 acting as hydrogen-bond acceptors. This seems to represent an unusual packing for a protected dipeptide containing at least one ,-disubstituted residue.

Concomitant polymorphism in the stereoselective synthesis of a -benzyl--hydroxyaspartate analogue

S. Mekki, V. Rolland, S. Bellahouel, A. van der Lee and M. Rolland

Two concomitant polymorphs, (I) and (II), of a -benzyl--hydroxyaspartate analogue [systematic name: dibenzyl 2-benzyl-2-hydroxy-3-(4-methylphenylsulfonamido)succinate], C₃₂H₃₁NO₇S, crystallize from a mixture of ethyl acetate and cyclohexane at ambient temperature. The structure of (I) has triclinic (P) symmetry and that of (II) monoclinic (P2₁/c) symmetry. Both crystal structures are made up of a stacking of homochiral racemic dimers (2S,3S and 2R,3R) which are internally connected by a similar R₂²(9) hydrogen-bonding pattern consisting of intermolecular N-HO and O-HO hydrogen bonds. The centroid of the racemic dimer lies on an inversion centre. The main structural difference between the two polymorphs is the conformational orientation of two of the four aromatic rings present in the molecule. Polymorph (II) is found to be twinned by reticular merohedry with twin index 3 and twin fractions 0.854 (1) and 0.146 (1).

Solvatomorphism in (E)-2-(2,6-dichloro-4-hydroxybenzylidene)hydrazinecarboximidamide

J. Gutierrez, R. Eisenberg, G. Herrensmith, T. Tobin, T. Li and S. Long

The structures of orthorhombic (E)-4-(2-{[amino(iminio)methyl]amino}vinyl)-3,5-dichlorophenolate dihydrate, C₈H₈Cl₂N₄O·2H₂O, (I), triclinic (E)-4-(2-{[amino(iminio)methyl]amino}vinyl)-3,5-dichlorophenolate methanol disolvate, C₈H₈Cl₂N₄O·2CH₄O, (II), and orthorhombic (E)-amino[(2,6-dichloro-4-hydroxystyryl)amino]methaniminium acetate, C₈H₉Cl₂N₄O⁺·C₂H₃O₂^-, (III), all crystallize with one formula unit in the asymmetric unit, with the molecule in an E configuration and the phenol H atom transferred to the guanidine N atom. Although the molecules of the title compounds form extended chains via hydrogen bonding in all three forms, owing to the presence of different solvent molecules, those chains are connected differently in the individual forms. In (II), the molecules are all coplanar, while in (I) and (III), adjacent molecules are tilted relative to one another to varying degrees. Also, because of the variation in hydrogen-bond-formation ability of the solvents, the hydrogen-bonding arrangements vary in the three forms.

Weak C-HCl-Pd interactions toward conformational polymorphism in trans-dichloridobis(triphenylphosphane)palladium(II)

R. S. Corrêa, A. E. Graminha, J. Ellena and A. A. Batista

A new triclinic polymorph of the title compound, [PdCl₂(C₁₈H₁₅P)₂], has two independent molecules in the unit cell, with the Pd atoms located on inversion centres. One molecule has an eclipsed conformation, whereas the second molecule adopts a gauche conformation. The molecules with a gauche conformation are involved in weak intermolecular C-HCl-Pd interactions with symmetry-related molecules. It is suggested that C-HCl-Pd interactions are mainly responsible for the existence of conformational differences, which contribute to the polymorph formation. In the crystal, there are layers of eclipsed and gauche molecules separated by normal van der Waals interactions.

1,2-Bis[(pyridin-2-ylmethyl)sulfanyl]ethane and its dimorphic hydrochloride salt

A. Lennartson and C. J. McKenzie

Although having been described as a liquid in the literature for 41 years, 1,2-bis[(pyridin-2-ylmethyl)sulfanyl]ethane, C₁₄H₁₆N₂S₂, (I), has now been obtained as monoclinic crystals via a new and convenient method of purification. Molecules of (I) are located on crystallographic inversion centres and are held together by C-HN and C-HS interactions, resulting in the formation of a three-dimensional network structure. In addition, two polymorphs of the corresponding hydrochloride salt, 2-[({2-[(pyridin-1-ium-2-ylmethyl)sulfanyl]ethyl}sulfanyl)methyl]pyridin-1-ium dichloride, C₁₄H₁₈N₂S₂²⁺·2Cl^-, (II) and (III), have been isolated. Molecules of (II) and (III) have similar conformations and are located on inversion centres. Both polymorphs form three-dimensional networks through N-HCl, C-HCl and C-HS interactions. The structure of (III) displays voids of 35 Å³.

A tetragonal form of dysprosium orthomolybdate at room temperature

S. Dorzhieva, I. Chumak, A. Sarapulova, D. Mikhailova, J. Bazarova and H. Ehrenberg

In the present tetragonal modification of dysprosium orthomolybdate, Dy₂(MoO₄)₃, the Dy, one Mo and one O atom are located on a mirror plane with Wyckoff symbol 4e, while another Mo atom is located on a fourfold inverse axis, Wyckoff symbol 2a. A single crystal was selected from a polycrystalline mixture of the Dy₂O₃-ZrO₂-MoO₃ system and was stable at room temperature for at least three months. The structure refinement does not indicate the presence of Zr on the Dy sites (to within 1% accuracy). Thus, the stabilization of the tetragonal form is due to disordered positions for a second O atom and split positions for a third O atom that also maintain the DyO₇ coordination, which is not expected for short Dy-O distances [2.243 (6)-2.393 (5) Å].

A new polymorph of succinylcholinium diiodide: comparison of succinylcholinium structures

R. Pazout, J. Maixner, M. Dusek and B. Kratochvíl

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-HI and C-HO hydrogen bonds are also present.

A variable-temperature study of 1,2-bis(dimethylamino)-1,2-bis(2,6-dimethylanilino)diborane

A. S. Batsanov, G. Bramham, N. C. Norman and C. A. Russell

The title compound, C₂₀H₃₂B₂N₄, is monoclinic at ambient temperature but triclinic (pseudo-monoclinic) below 150 K. The structures of the two phases, determined at 200 and 120 K, respectively, are very similar, the molecular symmetry being crystallographic C₂ and approximate (local) C₂, respectively. There is significant conjugation within each N-B-N moiety, but none between them or between the N-B-N and arene moieties.

Concomitant but disappearing: two polymorphs of 1,4-bis(tribromomethyl)benzene

P. G. Jones, H. Hopf, A. Silaghi and C. Näther

The title compound, C₈H₄Br₆, (I), initially crystallized from deuterochloroform as the comcomitant polymorphs (Ia) (prisms, space group P2₁/n, Z = 2) and (Ib) (hexagonal plates, space group C2/c, Z = 4). The molecules in both forms display crystallographic inversion symmetry. All further attempts to crystallize the compound led exclusively to (Ib), so that (Ia) may be regarded as a `disappearing polymorph'. Surprisingly, however, the density of (Ia) is greater than that of (Ib). The only significant difference between the molecular structures is the orientation of the CBr<sub>3</sub> groups. The molecular packing of both structures is largely determined by BrBr interactions, although (Ia) also displays a C-HBr hydrogen bond and both polymorphs display one Br contact. For (Ia), six of the eight contacts combine to form a tube-like substructure parallel to the a axis. For (Ib), the two shortest BrBr contacts link `half' molecules consisting of C-CBr₃ groups to form double layers parallel to (001) in the regions z , .

A new polymorph and two pseudopolymorphs of pyrimethamine

M. Tutughamiarso and M. Bolte

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-HN hydrogen bonds. However, the packing arrangements are completely different. In (I), the dimers are connected by two additional N-HN hydrogen bonds to form ribbons and further connected into a two-dimensional network parallel to (100), while layers containing N-HCl 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-HO hydrogen bonds. These arrangements are connected to form zigzag chains by N-HCl interactions in (Ia) and to form ribbons by N-HN 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-HO hydrogen bonded to form ribbons. A database study was carried out to compare the molecular conformations and hydrogen-bonding interactions of pyrimethamine.

Polymorphic form IV of olanzapine

R. Thakuria and A. Nangia

2-Methyl-4-(4-methylpiperazin-1-yl)-10H-thieno[2,3-b][1,5]benzodiazepine, C₁₇H₂₀N₄S, commonly known as olanzapine, is a psychotropic agent that belongs to the thienobenzodiazepine class of drugs. A new polymorph form IV was obtained upon attempted cocrystallization with nicotinamide in a 1:1 ratio from an ethyl acetate solution. Two butterfly-like molecules form centrosymmetric dimers stabilized by weak C-H interactions between the 4-methylpiperazin-1-yl fragment and the benzene/thiophene aromatic system. Form IV consists of a herringbone arrangement of dimers, whereas the previously reported form II has parallel dimers. Both crystal structures are sustained by an N-HN hydrogen bond.

Two tautomeric polymorphs of 2,6-dichloropurine

M. E. García-Rubiño, D. Choquesillo-Lazarte, M. C. Núñez and J. M. Campos

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-HN interactions that link adjacent molecules into linear chains, and by some nonbonding contacts of the C-Cl type and by - 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 - stacking interactions.

Sulfapyridine (polymorph III), sulfapyridine dioxane solvate, sulfapyridine tetrahydrofuran solvate and sulfapyridine piperidine solvate, all at 173 K

J. Pratt, J. Hutchinson and C. L. Klein Stevens

The X-ray crystal structures of solvates of sulfapyridine have been determined to be conformational polymorphs. 4-Amino-N-(1,2-dihydropyridin-2-ylidene)benzenesulfonamide (polymorph III), C₁₁H₁₁N₃O₂S, (1), 4-amino-N-(1,2-dihydropyridin-2-ylidene)benzenesulfonamide 1,3-dioxane monosolvate, C₁₁H₁₁N₃O₂S·C₄H₈O₂, (2), and 4-amino-N-(1,2-dihydropyridin-2-ylidene)benzenesulfonamide tetrahydrofuran monosolvate, C₁₁H₁₁N₃O₂S·C₄H₈O, (3), crystallized as the imide form, while piperidin-1-ium 4-amino-N-(pyridin-2-yl)benzenesulfonamidate, C₅H₁₂N⁺·C₁₁H₁₀N₃O₂S^-, (4), crystallized as the piperidinium salt. The tetrahydrofuran and dioxane solvent molecules in their respective structures were disordered and were refined using a disorder model. Three-dimensional hydrogen-bonding networks exist in all structures between at least one sulfone O atom and the aniline N atom.

Two polymorphs of N¹,N⁴-bis(5-hydroxypenta-1,3-diynyl)-N¹,N⁴-diphenylbenzene-1,4-diamine

H. Tabata, N. Kubo and T. Okuno

The title compound, C₂₈H₂₀N₂O₂, forms two conformational polymorphs, (I) and (II), where the molecular structures are similar except for the orientation of the two hydroxy groups. In (I), which was obtained by slow evaporation from chloroform, the two hydroxy groups have an anti conformation. The molecules form a sheet structure within the ac plane, where the hydroxy groups form zigzag hydrogen bonds. In (II), which was obtained by slow evaporation from acetonitrile, the two hydroxy groups have a syn conformation. The molecules form a double-sheet structure within the ab plane, where the hydroxy groups form 4-helix hydrogen bonds.

Polymorphs of anhydrous theophylline: stable form IV consists of dimer pairs and metastable form I consists of hydrogen-bonded chains

D. Khamar, R. G. Pritchard, I. J. Bradshaw, G. A. Hutcheon and L. Seton

The structure of a previously unreported polymorph of anhydrous theophylline (1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione), C₇H₈N₄O₂, has been determined at 100 K and shown to have monoclinic symmetry with Z' = 2. The structure is named form IV and experimental observation indicates that this is the stable form of the material. The molecular packing consists of discrete hydrogen-bonded dimers similar to that observed in the monohydrate structure. The structure of form I has also been determined and consists of hydrogen-bonded chains.