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.     

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.     

ϵ‐RbCuCl3, a new polymorph of rubidium copper trichloride: synthesis,structure and structural complexity

A novel polymorph of RbCuCl₃ (rubidium copper trichloride), denoted ϵ‐RbCuCl₃, has been prepared by chemical vapour transport (CVT) from a mixture of CuO, CuCl₂, SeO₂ and RbCl. The new polymorph crystallizes in the orthorhombic space group C222₁. The crystal structure is based on an octahedral framework of the 4H perovskite type. The Rb⁺ and Cl⁻ ions form a four‐layer closest‐packing array with an ABCB sequence. The Cu²⁺ cations reside in octahedral cavities with a typical [4 + 2]‐Jahn–Teller‐distorted coordination, forming four short and two long Cu—Cl bonds. ϵ‐RbCuCl₃ is the most structurally complex and most dense among all currently known RbCuCl₃ polymorphs, which allows us to suggest that it is a high‐pressure phase, which is unstable under ambient conditions.     

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.     

Chlorido(2,3,7,8,12,13,17,18‐octaethylporphyrinato)iron(III): a new triclinic polymorph of Fe(OEP)Cl

The previous structure determination of the title compound, [Fe(C₃₆H₄₄N₄)Cl], was of a monoclinic polymorph [Senge (2005). Acta Cryst. E 61 , m399–m400]. The crystal structure of a new triclinic polymorph has been determined based on single‐crystal X‐ray diffraction data collected at 100 K. The asymmetric unit contains one molecule of the high‐spin square‐pyramidal iron(III) porphyrinate. The structure exhibits distinct nonstatistical alternative positions for most atoms and was consequently modeled as a whole‐molecule disorder. The compound is characterized by an average Fe—N bond length of 2.065 (2) Å, an Fe—Cl bond length of 2.225 (4) Å, and the iron(III) cation displaced by 0.494 (4) Å from the plane of the 24‐atom porphyrinate core, essentially the same as in the previously determined polymorph. Common features of the porphyrin plane–plane stacking involve two types of synthons, each of which can be further stabilized with additional H...Cl interactions to the axial chloride ligand, exhibiting concerted interactions of H atoms from the ethyl groups with the π‐cloud electron density of adjacent molecules; the shortest methylene H‐atom contacts are in the range 2.75–2.91 Å, resulting in plane–plane separations of 3.407 (4) and 3.416 (4) Å, and the shortest methyl H‐atom contacts are 2.56–2.95 Å, resulting in plane–plane separations of 4.900 (5) and 4.909 (5) Å in the monoclinic polymorph. The plane‐to‐plane stacking synthons in the triclinic polymorph are similar, but at greater distances; the shortest methylene H‐atom contacts are 2.86–2.94 Å, resulting in plane–plane separations of 3.45 (2) and 3.45 (3) Å, and the shortest methyl H‐atom contacts are 2.89–3.20 Å, resulting in plane–plane separations of 5.081 (13) and 5.134 (13) Å, consistent with the density of the triclinic polymorph being 1.5% lower, suggesting lesser packing efficiency and lower stability in the triclinic polymorph. The major molecular differences found in the polymorphs is in three different orientations of the ethyl‐group side chains on the periphery of the porphyrin core.     

Structural and computational analysis of intermolecular interactions in a new 2‐thiouracil polymorph

The crystallization and characterization of a new polymorph of 2‐thiouracil by single‐crystal X‐ray diffraction, Hirshfeld surface analysis and periodic density functional theory (DFT) calculations are described. The previously published polymorph (A ) crystallizes in the triclinic space group P , while that described herein (B ) crystallizes in the monoclinic space group P 2₁/c . Periodic DFT calculations showed that the energies of polymorphs A and B , compared to the gas‐phase geometry, were −108.8 and −29.4 kJ mol⁻¹, respectively. The two polymorphs have different intermolecular contacts that were analyzed and are discussed in detail. Significant differences in the molecular structure were found only in the bond lengths and angles involving heteroatoms that are involved in hydrogen bonds. Decomposition of the Hirshfeld fingerprint plots revealed that O…H and S…H contacts cover over 50% of the noncovalent contacts in both of the polymorphs; however, they are quite different in strength. Hydrogen bonds of the N—H…O and N—H…S types were found in polymorph A , whereas in polymorph B , only those of the N—H…O type are present, resulting in a different packing in the unit cell. QTAIM (quantum theory of atoms in molecules) computational analysis showed that the interaction energies for these weak‐to‐medium strength hydrogen bonds with a noncovalent or mixed interaction character were estimated to fall within the ranges 5.4–10.2 and 4.9–9.2 kJ mol⁻¹ for polymorphs A and B , respectively. Also, the NCI (noncovalent interaction) plots revealed weak stacking interactions. The interaction energies for these interactions were in the ranges 3.5–4.1 and 3.1–5.5 kJ mol⁻¹ for polymorphs A and B , respectively, as shown by QTAIM analysis.     

A novel and facile one‐pot synthesis of pyridylselenium compounds through selective bromine–magnesium exchange with isopropylmagnesium halide

One‐pot synthesis of various unsymmetrical 2‐bromo‐5‐pyridylselenium compounds has been carried out under non‐cryogenic conditions by selective single bromine–magnesium exchange of 2,5‐dibromopyridine using isopropylmagnesium chloride. This exchange gives 2‐bromo‐5‐pyridylmagnesium chloride, which upon the insertion of elemental selenium followed by the treatment with alkyl halide gives the title compounds in good yield. This exchange has also been extended towards bromine–magnesium exchange of 2‐bromopyridine for the improved synthesis of 2‐pyridylselenium compounds. The molecular structure of 2‐bromo‐5‐selenopyridyltribromomethane has been examined by single crystal X‐ray diffraction. This compound crystallizes in the monoclinic space group P2₁/n. From the molecular structure it was found that intermolecular BrBr, NSe and SeBr interactions control its crystal packing. Copyright © 2005 John Wiley & Sons, Ltd.     

Exploring new species on the [H,S, Se,Cl] potential energy surface

This investigation is concerned with the characterization of seleno‐sulfide‐halogen model systems, the isomerization processes, and the dissociation into diatomic fragment channels on the [H, S, Se, Cl] potential energy surface. Structural, energetic, and vibrational data were obtained at the CCSD(T) and MP2 levels of theory with the series of correlation consistent basis sets and extrapolated to the complete basis set (CBS) limit. For the frequencies, additional computations were performed to include the contribution of anharmonic effects, and for the determination of the heats of formation, important corrections incorporating core‐valence correlation effects and relativistic effects (scalar and spin‐orbit) were taken into account. CCSD(T)/CBS relative stability (kcal mol^?1) follows the order: HSSeCl (0.0), HSeSCl (8.80), SSeHCl (23.52), and SeSHCl (25.87). The cis‐rotational barrier for the two lowest isomers is practically identical (10.14 and 10.09 kcal mol^?1), whereas for the trans barrier, we obtained 9.25 (HSSeCl) and 8.45 (HSeSCl) kcal mol^?1. Dissociation of HSSeCl (HSeSCl) into HS (HSe) + SeCl (SCl) requires 59.70 (56.30) kcal mol^?1. For the most stable isomer, we predict a value of the heat of formation at 298.15 K of 2.53 kcal mol^?1. One of the outcomes of this research is that the MP2 results are consistent with those of CCSD(T). The MP2 method turns out to be a reliable alternative for a first exploration of larger catenated species, although it accounts for a lesser fraction of correlation effects. © 2012 Wiley Periodicals, Inc.     

The structural properties of a noncentrosymmetric polymorph of 4‐aminobenzoic acid

The crystal structure of a polymorph of 4‐aminobenzoic acid (PABA), C₇H₇NO₂, at 100 K is noncentrosymmetric, as opposed to centrosymmetric in the structures of the other known polymorphs. The two crystallographically independent PABA molecules form pseudocentrosymmetric O—H...O hydrogen‐bonded dimers that are further linked by N—H...O hydrogen bonds into a three‐dimensional network. The benzene rings stack in the b direction. The CO₂ moieties are bent out slightly from the benzene ring plane.     

The Structure of the Pyridine Complex of p-tetrakis(phenylazo)-tetra-hydroxythiacalix[4]arene

p-Tetrakis(phenylazo)-tetra-hydroxythiacalix[4]arene shows complexing properties with neutral molecules. A complex with pyridine was crystallized and the crystal structure determined. The crystals are monoclinic, space group C2/c, a = 49.953(10), b = 21.566(4), c = 23.448(5) Å, = 105.12(3)°, V = 24386(8) Å ³, Z = 16. Two macrocycles are positioned in such a way that they form a cavity where two pyridine molecules are encapsulated giving a 2:2 endocomplex. 5.5 other pyridine molecules are trapped between the macrocycles, two of them giving H-bonds with the calixarenes.     

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.     

The influence of the type of halogen substituent and its position on the molecular conformation,intermolecular interactions and crystal packing for a series of 1‐benzoyl‐3‐(halogenophenyl)thioureas

By the reaction of benzoyl chloride, potassium isothiocyanate and the appropriate halogenoaniline, i.e. 2/3/4‐(bromo/iodo)aniline, we have obtained five new 1‐benzoyl‐3‐(halogenophenyl)thioureas, namely, 1‐benzoyl‐3‐(2‐bromophenyl)thiourea and 1‐benzoyl‐3‐(3‐bromophenyl)thiourea, C₁₄H₁₁BrN₂OS, and 1‐benzoyl‐3‐(2‐iodophenyl)thiourea, 1‐benzoyl‐3‐(3‐iodophenyl)thiourea and 1‐benzoyl‐3‐(4‐iodophenyl)thiourea, C₁₄H₁₁IN₂OS. Structural and conformational features of the compounds have been analyzed using X‐ray diffraction and theoretical calculations. The novel compounds were characterized by solid‐state IR and ¹H/¹³C NMR spectroscopy. The conformations and intermolecular interactions, such as hydrogen bonds, π–π and S(6)…π stacking, and X…O (X = I or Br), I…S and I…π, have been examined and rationalized, together with four analogous compounds described previously in the literature. The set of nine compounds was chosen to examine how a change of the halogen atom and its position on the phenyl ring affects the molecular and crystal structures.     

Twinning in 5‐fluorosalicylic acid: description of a new polymorph

The crystal structure of 5‐fluorosalicylic acid is known from the literature [Choudhury & Guru Row (2004). Acta Cryst. E 60 , o1595–o1597] as crystallizing in the monoclinic crystal system with space‐group setting P2₁/n and with one molecule in the asymmetric unit (polymorph I). We describe here a new polymorph which is again monoclinic but with different unit‐cell parameters (polymorph II). Polymorph II has two molecules in the asymmetric unit. Its structure was modelled as a twin, with a pseudo‐orthorhombic C‐centred twin cell.     

Crystallographic report: A new polymorph for bis[bis(N,N‐dibenzyldithiocarbamato)cadmium(II)]

The title compound is a centrosymmetric dimer with each cadmium in a distorted CdS₅ square pyramidal geometry. The Cd–S bond distances range from 2.5626(11) to 2.8459(11) Å. Copyright © 2004 John Wiley & Sons, Ltd.     

Conformational polymorphs of 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole

The dipharmacophore compound 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole, C₁₂H₁₁N₅O, was studied on the assumption of its potential biological activity. Two polymorphic forms differ in both their molecular and crystal structures. The monoclinic polymorphic form was crystallized from more volatile solvents and contains a conformer with a higher relative energy. The basic molecule forms an abundance of interactions with relatively close energies. The orthorhombic polymorph was crystallized very slowly from isoamyl alcohol and contains a conformer with a much lower energy. The basic molecule forms two strong interactions and a large number of weak interactions. Stacking interactions of the `head‐to‐head' type in the monoclinic structure and of the `head‐to‐tail' type in the orthorhombic structure proved to be the strongest and form stacked columns in the two polymorphs. The main structural motif of the monoclinic structure is a double column where two stacked columns interact through weak C—H…N hydrogen bonds and dispersive interactions. In the orthorhombic structure, a single stacked column is the main structural motif. Periodic calculations confirmed that the orthorhombic structure obtained by slow evaporation has a lower lattice energy (0.97 kcal mol^?1) compared to the monoclinic structure.     

A new semiconducting quaternary mixed halogenide: pentathallium dimercury pentabromide tetraiodide,Tl5Hg2Br5I4

A novel quaternary mixed halogenide, Tl₅Hg₂Br₅I₄, was synthesized by fusion of thallium bromide and mercury iodide in a 5:2 molar ratio. The crystal structure of Tl₅Hg₂Br₅I₄ represents a new series of composite structures described by the general formula nTlBr*mTl₂[HgBr₂I₂]; in this case, n = 4 and m = 8. Electronic structure calculations indicate that the title compound is a semiconductor.     

Synthesis and characterization of N,N‐diethyldithiocarbamate complexes of 2‐alkoxycarbonylethyltin trichloride

N,N‐Diethyldithiocarbamate complexes of 2‐alkoxycarbonylethyltin trichloride, ROCOCH₂CH₂ SnCl_3?x[S₂CNEt₂]_x (R = CH₃ ( a ); CH₃CH₂ ( b ); CH₂?CHCH₂ ( c ); CH₃CH₂CH₂ ( d ); CH₃CH₂CH₂CH₂ ( e ); x = 1 ( 1 ), 2 ( 2 )) were synthesized and characterized by means of elemental analysis, IR, and NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. The crystal structure of 1b (i.e. R = CH₃CH₂, x = 1) was determined and shows that the tin atom adopts a distorted octahedral geometry with both a five‐membered chelate ring, formed via carbonyl coordination to tin, and a four‐membered chelate ring, formed by the bidentate dithiocarbamate. The spectral data and ab initio calculations indicate that intramolecular carbonyl‐oxygen to tin coordination in 1a–1e persists, but not in 2a–2e , owing to the preference of the dithiocarbamate ligands to chelate the tin centre. Copyright © 2005 John Wiley & Sons, Ltd.     

A new crystalline form of αβ‐d‐lactose prepared by oven drying a concentrated aqueous solution of d‐lactose

A new crystalline form of αβ‐d ‐lactose (C₁₂H₂₂O₁₁) has been prepared by the rapid drying of an approximately 40% w/v syrup of d ‐lactose. Initially identified from its novel powder X‐ray diffraction pattern, the monoclinic crystal structure was solved from a microcrystal recovered from the generally polycrystalline mixed‐phase residue obtained at the end of the drying step. This is the second crystalline form of αβ‐d ‐lactose to be identified and it has a high degree of structural three‐dimensional similarity to the previously identified triclinic form.     

Crystallographic report: A polymorph of undecasodium decatrimethylsilanolate hydroxide: [Na11(OSiMe3)10(OH)]

The title compound is a polymorph of [Na₁₁(OSiMe₃)₁₀(OH)] and was crystallized from a toluene solution containing NaOSiMe₃ and water. The molecular structure is best described as being composed of two subunits, a square antiprism built from eight sodium atoms and an Na₄O₄ heterocubane, both sharing a sodium atom. Copyright © 2004 John Wiley & Sons, Ltd.     

The enhancing effects of molecule X (X = PH2Cl,SHCl, ClCl) on chalcogen–chalcogen interactions in cyclic trimers Y···Y···X (Y = SHCl,SeHCl)

The enhancing effects of molecule X (X = PH₂Cl, SHCl, ClCl) on S···S and Se···Se chalcogen–chalcogen bonds in the cyclic trimers SHCl···SHCl···X and SeHCl···SeHCl···X were investigated by calculations at the MP2/aug‐cc‐pVTZ level. When molecule X is added to the dimer SHCl···SHCl (SeHCl···SeHCl), cyclic trimers are formed. Compared with the dimer, all the cyclic trimers have shorter S···S (Se···Se) lengths, greater electron densities, negative three‐body interaction energies, and larger second‐order perturbation energies. These results indicate that the addition of molecule X strengthens the original S···S (Se···Se) bond. For the SHCl···SHCl···X cyclic trimers, the S···S bond is strongest in SHCl···SHCl···PH₂Cl, weaker in SHCl···SHCl···SHCl, and weakest in SHCl···SHCl···ClCl. This same trend is observed for the Se···Se bond in SeHCl···SeHCl···X. This means that PH₂Cl provides the greatest enhancement to the S···S (Se···Se) interaction.