Tautomeric polymorphism of the neuroactive inhibitor kynurenic acid.

Kynurenic acid (KYN; systematic name: 4-hydroxyquinoline-2-carboxylic acid, C10H7NO3) displays a therapeutic effect in the treatment of some neurological diseases and is used as a broad-spectrum neuroprotective agent. However, it is understudied with respect to its solid-state chemistry and only one crystal form (α-KYN·H2O) has been reported up to now. Therefore, an attempt to synthesize alternative solid-state forms of KYN was undertaken and six new species were obtained: five solvates and one salt. One of them is a new polymorph, ß-KYN·H2O, of the already known KYN monohydrate. All crystal species were further studied by single-crystal and powder X-ray diffraction, thermal and spectroscopic methods. In addition to the above methods, differential scanning calorimetry (DSC), in-situ variable-temperature powder X-ray diffraction and Raman microscopy were applied to characterize the phase behaviour of the new forms. All the compounds display a zwitterionic form of KYN and two different enol-keto tautomers are observed depending on the crystallization solvent used.

The role of different nonspecific interactions and halogen contacts in the crystal structure organization of 5-chloroisatoic anhydride.

The crystal structure of 6-chloro-2,4-dihydro-1H-3,1-benzoxazine-2,4-dione (5-chloroisatoic anhydride), C8H4ClNO3, has been determined and analysed in terms of connectivity and packing patterns. The compound crystallizes in the noncentrosymmetric space group Pna21 with one molecule in the asymmetric unit. The role of different weak interactions is discussed with respect to three-dimensional network organization. Molecules are extended into one-dimensional helical arrangements, making use of N-H...O hydrogen bonds and π-π interactions. The helices are further organized into monolayers via weak C-H...O and lone pair-π interactions, and the monolayers are packed into a noncentrosymmetric three-dimensional architecture by C-Cl...π interactions and C-H...Cl and Cl...Cl contacts. A Hirshfeld surface (HS) analysis was carried out and two-dimensional (2D) fingerprint plots were generated to visualize the intermolecular interactions and to provide quantitative data for their relative contributions. In addition, tests of the antimicrobial activity and in vitro cytotoxity effects against fitoblast L929 were performed and are discussed.

Synthesis, structural characterization and computational studies of catena-poly[chlorido[µ3-(pyridin-1-ium-3-yl)phosphonato-κ3O:O':O'']zinc(II)].

Coordination polymers are constructed from two basic components, namely metal ions, or metal-ion clusters, and bridging organic ligands. Their structures may also contain other auxiliary components, such as blocking ligands, counter-ions and nonbonding guest or template molecules. The choice or design of a suitable linker is essential. The new title zinc(II) coordination polymer, [Zn(C5H5NO3P)Cl]n, has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction and vibrational spectroscopy (FT-IR and FT-Raman). Additionally, computational methods have been applied to derive quantitative information about interactions present in the solid state. The compound crystallizes in the monoclinic space group C2/c. The four-coordinated ZnII cation is in a distorted tetrahedral environment, formed by three phosphonate O atoms from three different (pyridin-1-ium-3-yl)phosphonate ligands and one chloride anion. The ZnII ions are extended by phosphonate ligands to generate a ladder chain along the [001] direction. Adjacent ladders are held together via N-H...O hydrogen bonds and offset face-to-face π-π stacking interactions, forming a three-dimensional supramolecular network with channels. As calculated, the interaction energy between the neighbouring ladders is -115.2 kJ mol-1. In turn, the cohesive energy evaluated per asymmetric unit-equivalent fragment of a polymeric chain in the crystal structure is -205.4 kJ mol-1. This latter value reflects the numerous hydrogen bonds stabilizing the three-dimensional packing of the coordination chains.

New polymorphs of an old drug: conformational and synthon polymorphism of 5-nitrofurazone.

Two new polymorphic forms of 5-nitrofurazone (5-nitro-2-furaldehyde semicarbazone) have been synthesized and structurally characterized by single-crystal and powder X-ray diffraction methods, vibrational spectroscopy (FT-IR and temperature Raman), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Hirshfeld surface analysis. The compound crystallizes in three different polymorphic forms P21/a (polymorph α), P21 (polymorph ß) and P21/c (polymorph γ), the crystal structures of two of which (polymorphs ß and γ) represent new structure determinations. The solid-state molecular organization in the three crystal forms is analyzed and discussed in terms of molecular conformation, crystal packing and hydrogen-bonded networks. All three crystals are formed from trans geometrical isomers, but the molecular conformation of the α-polymorph is syn-anti-anti-anti, while that of ß- and γ-polymorphs is syn-anti-syn-syn. As a consequence of this the hydrogen-bond donor and acceptor sites of the molecules are oriented differently, which in turn results in different hydrogen-bond connectivity and packing patterns.

The supramolecular architecture of tris(naphthalene-1,5-diaminium) bis(5-aminonaphthalen-1-aminium) octakis[hydrogen (5-carboxypyridin-3-yl)phosphonate].

The asymmetric unit of the title compound, 3C(10)H(12)N(2)(2+)·2C(10)H(11)N(2)(+)·8C(6)H(5)NO(5)P(-), contains one and a half naphthalene-1,5-diaminium cations, in which the half-molecule has inversion symmetry, one 5-aminonaphthalen-1-aminium cation and four hydrogen (5-carboxypyridin-3-yl)phosphonate anions. The crystal structure is layered and consists of hydrogen-bonded anionic monolayers between which the cations are arranged. The acid monoanions are organized into one-dimensional chains along the [101] direction via hydrogen bonds established between the phosphonate sites. (C)O-H···N(py) hydrogen bonds (py is pyridine) crosslink the chains to form an undulating (010) monolayer. The cations serve both to balance the charge of the anionic network and to connect neighbouring layers via multiple hydrogen bonds to form a three-dimensional supramolecular architecture.

Poly[aqua[µ3-(pyridin-1-ium-3,5-diyl)diphosphonato-κ3O:O':O''][µ2-(pyridin-1-ium-3,5-diyl)diphosphonato-κ2O:O']calcium(II)].

The rigid organic ligand (pyridine-3,5-diyl)diphosphonic acid has been used to create the title novel three-dimensional coordination polymer, [Ca(C(5)H(6)NO(6)P(2))(2)(H(2)O)](n). The six-coordinate calcium ion is in a distorted octahedral environment, formed by five phosphonate O atoms from five different (pyridin-1-ium-3,5-diyl)diphosphonate ligands, two of which are unique, and one water O atom. Two crystallographically independent acid monoanions, L1 and L2, serve to link metal centres using two different coordination modes, viz. η(2)µ(2) and η(3)µ(3), respectively. The latter ligand, L2, forms a strongly undulated two-dimensional framework parallel to the crystallographic bc plane, whereas the former ligand, L1, is utilized in the formation of one-dimensional helical chains in the [010] direction. The two sublattices of L1 and L2 interweave at the Ca(2+) ions to form a three-dimensional framework. In addition, multiple O-H···O and N-H···O hydrogen bonds stabilize the three-dimensional coordination network. Topologically, the three-dimensional framework can be simplified as a very unusual (2,3,5)-connected three-nodal net represented by the Schläfli symbol (4·8(2))(4·8(8)·10)(8).

Hexaaquacobalt(II) bis[hydrogen bis(4-carboxyphenylphosphonate)] dihydrate.

The Co(II) ion in the title complex salt, [Co(H(2)O)(6)](C(14)H(13)O(10)P(2))(2)·2H(2)O or [Co(H(2)O)(6)][H(C(7)H(6)O(5)P)(2)]·2H(2)O, resides on an inversion centre and exhibits an octahedral environment formed by six aqua ligands. Two unique acid residues share an H atom between their phosphonate groups, forming a complex monoanion with a very short (P)O···H···O(P) hydrogen bond of 2.435 (2) Å. The crystal structure is layered and consists of thick organic bilayers with hydrated metal [Co(H(2)O)(6)](2+) ions arranged between them. The interior of the bilayer is occupied by the aromatic portions of the complex monoanions and the carboxyl groups, which form hydrogen-bonded R(2)(2)(8) ring motifs. The phosphonate groups are arranged outwards in order to form the hydrogen-bonded surfaces of the bilayer. Electrostatic and multiple hydrogen-bond interactions, established between the coordination and solvent water molecules and the phosphonate O atoms, hold neighbouring bilayers together.

Solid-state molecular organization and solution behavior of methane-1,1-diphosphonic acid derivatives of heterocyclic amines: the role of the topochemical ring modification and the intramolecular hydrogen bonds in monosubstituted piperid-1-ylmethane-1,1-diphosphonic acids.

The crystal structures of 3-methylpiperid-1-ylmethane-1,1-diphosphonic (2), 4-methylpiperid-1-ylmethane-1,1-diphosphonic (3), 2-ethylpiperid-1-ylmethane-1,1-diphosphonic (4), and 2-methylpiperid-1-ylmethane-1,1-diphosphonic (5) acids have been determined and are discussed with respect to their molecular organization and crystal-packing preferences. The chair conformation, predominant also in solution, favors equatorial positioning of the bulky substituents of the heterocyclic N and C atoms. The molecular geometry also provides access to intramolecular hydrogen-bond formation between the axial protons located on the nitrogen atoms, as well as the carbon atoms closest to it, and phosphonic/phosphonate oxygen atoms. The molecules preferably arrange in monolayers, observed in all crystals with an exception of 3. The layers are held in place in the third direction through van der Waals interactions. The analysis of two-dimensional hydrogen-bonded networks is concentrated on revealing how the substituent's topology of the molecule affects the solid-state organization in well-defined structures and is aimed at unraveling the consequences and the possible conformational changes by stepwise network disruption upon crystal dissolution in water. The solution NMR studies are focused on revealing the role that the topochemistry of the substituent plays for the stereodynamics in 2-5. It is demonstrated that in contrast to piperid-1-ylmethane-1,1-diphosphonic acid (1), in which the ring inversion/rotation around the C-N bond concerted with the N-H...O hydrogen-bond breaking/formation process leads to a mixture of two interconverting conformers, the concerted N-H...O breaking/rotation/N-H...O formation process in 2 and 3 allows for a predominance of one conformer in solution. However, placement of a substituent at 2-position in the ring hampers the rotation around the C-N bond; this makes 4 and 5 significantly less flexible relative to compounds 1-3. In addition, both compounds 4 and 5 are proved to exist as a mixture of two conformers, the equilibrium of which in acidic solution is shifted towards the conformer found in solid state. In alkaline solutions of 4 and 5, the equilibrium is shifted towards the conformer that is forced by the flipping of the heterocyclic ring. These results correlate well with recently documented differences in the biological potency of this group of compounds.

Polymeric sodium 3,5-dicarboxybenzenesulfonate-urea-water (1/1/1).

In the title compound, poly[sodium-mu(4)-3,5-dicarboxybenzenesulfonato-kappa4O:O':O":O"'-mu(2)-urea-kappa2O:N] monohydrate], [[Na(C8H5O7S)(CH4N2O)] x H2O]n, the organic anions are arranged almost vertically within (001) monolayers, with the sulfonate and carboxylic acid groups pointing into the interlayer region. The inversion-related aromatic rings of the anions inside the layers are arrayed via offset face-to-face interactions into molecular stacks along the crystallographic a axis. The 'up' and 'down' arrangement of the aromatic portions makes both faces of the layers ionic and hydrophilic, whereas the interiors of the layers are primarily hydrophobic. The interleaving of the anions is such that the carboxylic acid groups are oriented more toward the interior than are the sulfonate groups. The aromatic rings in neighbouring layers are arranged in a herring-bone fashion. The coordination sphere of the Na+ ions contains two sulfonate and two carboxylic acid O atoms, from a total of four different acid anions belonging to two neighbouring anionic monolayers. The urea molecules are positioned between translation-related anionic stacks inside the (001) layers, serving a triple function, viz. they fill in the large meshes (empty cavities) formed within the anionic-cationic network, and they provide additional Na+ coordination and hydrogen-bond sites.