4-[(E)-(2,4-Difluoro­phen­yl)(hydroxy­imino)meth­yl]piperidinium picrate

The title compound, C12H15F2N2O+·C6H2N3O7 −, a picrate salt of 4-[(E)-(2,4-difluoro­phen­yl)(hydroxy­imino)meth­yl]piper­idine, crystallizes with two independent mol­ecules in a cation–anion pair in the asymmetric unit. In the cation, a methyl group is tris­ubstituted by hydroxy­imino, piperidin-4-yl and 2,4-difluoro­phenyl groups, the latter of which contains an F atom disordered over two positions in the ring [occupancy ratio 0.631 (4):0.369 (4)]. The mean plane of the hydr­oxy group is in a synclinical conformation nearly orthogonal [N—C—C—C = 72.44 (19)°] to the mean plane of the piperidine ring, which adopts a slightly distorted chair conformation. The dihedral angle between the mean plane of the 2,4-difluoro­phenyl and piperidin-4-yl groups is 60.2 (3)°. In the picrate anion, the mean planes of the two o-NO2 and single p-NO2 groups adopt twist angles of 5.7 (2), 25.3 (7) and 8.3 (6)°, respectively, with the attached planar benzene ring. The dihedral angle between the mean planes of the benzene ring in the picrate anion and those in the hydroxy­imino, piperidin-4-yl and 2,4-difluoro­phenyl groups in the cation are 84.9 (7), 78.9 (4) and 65.1 (1)°, respectively. Extensive hydrogen-bond inter­actions occur between the cation–anion pair, which help to establish the crystal packing in the unit cell. This includes dual three-center hydrogen bonds with the piperidin-4-yl group, the phenolate and o-NO2 O atoms of the picrate anion at different positions in the unit cell, which form separate N—H⋯(O,O) bifurcated inter­molecular hydrogen-bond inter­actions. Also, the hydr­oxy group forms a separate hydrogen bond with a nearby piperidin-4-yl N atom, thus providing two groups of hydrogen bonds, which form an infinite two-dimensional network along (011)

Selective sorption of oxygen and nitrous oxide by an electron donor-incorporated flexible coordination network

Incorporating strong electron donor functionality into flexible coordination networks is intriguing for sorption applications due to a built-in mechanism for electron-withdrawing guests. Here we report a 2D flexible porous coordination network, [Ni₂(4, 4′-bipyridine)(VTTF)₂]n(1) (where H₂VTTF = 2, 2′-[1, 2-bis(4-benzoic acid)-1, 2ethanediylidene]bis-1, 3-benzodithiole), which exhibits large structural deformation from the as-synthesized or open phase (1α) into the closed phase (1β) after guest removal, as demonstrated by X-ray and electron diffraction. Interestingly, upon exposure to electron-withdrawing species, 1β reversibly undergoes guest accommodation transitions; 1α⊃O₂ (90 K) and 1α⊃N₂O (185 K). Moreover, the 1β phase showed exclusive O₂ sorption over other gases (N₂, Ar, and CO) at 120 K. The phase transformations between the 1α and 1β phases under these gases were carefully investigated by in-situ X-ray diffraction, in-situ spectroscopic studies, and DFT calculations, validating that the unusual sorption was attributed to the combination of flexible frameworks and VTTF (electron-donor) that induces strong interactions with electron-withdrawing species

Crystal Structure of 2′,3′-Di-O-Acetyl-5′-Deoxy-5-Fluorocytidine with N–H···(O,F) Proton Donor Bifurcated and (C,N)–H···O Bifurcated Acceptor Dual Three-Center Hydrogen Bond Configurations

The title compound, C13H16O6N3F, features a central furan ring containing four carbon atom chiral centers with a 4-amino-5-fluoro-2-oxopyrimidine group, two acetyl groups and a methyl group bonded at the 2,3,4,5 positions, each in an absolute R configuration (2R,3R,4R,5R). It crystallizes in the monoclinic space group C2 with unit cell parameters a = 14.5341(3), b = 7.26230(10), c = 16.2197(3) Å, β = 116.607(2)°, Z = 4. An extensive array of intra and inter molecular hydrogen bond interactions dominate crystal packing in the unit cell highlighted by a relatively rare three-center proton-bifurcated donor N–H···(O,F) hydrogen bond interaction in cooperation with a second, (C,N)–H···O bifurcated acceptor three-center hydrogen bond in a supportive fashion. Additional weak Cg π-ring inter molecular interactions between a fluorine atom and the 4-amino-5-fluoro-2-oxopyrimidine ring in concert with multiple donor and acceptor hydrogen bonds significantly influence the bond distances, bond angles and torsion angles of the deoxy-5-fluorocytidine group. Comparison to a MOPAC computational calculation provides support to these observations

Intermolecularly associated carbolylic acid dimers in the supramolecular assembly of 1,4-benzodioxane 2-carboxylic acid

The title compound, C9H8O4, (I), crystallizes in the monoclinic space group P 21/c with unit cell parameters a = 7.3380(5) angstrom, b = 9.3790(7) angstrom, c = 12.3172(9) angstrom, beta = 90.687(7)degrees, Z = 4. The molecule consists of a benzene ring fused to a 1,4 dioxane ring in a half-chair conformation with a carboxylic acid group bonded at the dioxane 2-position. The carboxylic acid group forms a classic O-H center dot center dot center dot O hydrogen bonded dimer with an O center dot center dot center dot O distance of 2.6292(12) angstrom in a R-2(2) (8) graph-set motif which links the molecules into pairs around inversion centers in a supramolecular assembly in the unit cell. The dihedral angle between the mean planes of the R-2(2) (8) graph-set motif's of two adjacent dimers in the unit cell is 75.7(5)degrees. The mean plane of an R-2(2) (8) graph-set motif makes an angle of 88.4(5)degrees with the mean plane of the benzene ring in the same dimer and 13.1(2)degrees or 13.4(7)degrees with the mean plane of a benzene ring from an adjacent dimer. Additional weak Cg pi-ring intermolecular interactions significantly influence the bond distances, bond angles and torsion angles of the dioxane ring and attached carboxyl group. Comparison to a MOPAC AM1computational calculation provides support to these observations

Crystal structure of abacavir hemisulfate: a nucleoside analog reverse transcriptase inhibitor

The title compound, Abacavir hemisulfate Systematic name: {(1S,4R)-4-2-amino-6-(cyclopropylamino)- 9H-purin-9-yl]cyclopentene}-1-methanol hemisulfate, C14H19N6O+](2) SO42-, (I), crystallizes in the monoclinic space group C2 with unit cell parameters a = 18.7498(7), b = 8.3577(5), c = 13.2563(5), angstrom, beta = 130.575(3)degrees, Z = 2. In the asymmetric unit, the compound crystallizes with two C14H19N6O+ cations and one SO42- anion connected by strong intermolecular N-H center dot center dot center dot O hydrogen bond interactions between two of these C14H19N6O+ cations. Additional strong O-H center dot center dot center dot O hydrogen bond intermolecular interactions are observed between the C14H19N6O+ and SO42-, cation-anion, units, respectively. The C14H19N6O+](2) SO42- units link themselves into an infinite O-H center dot center dot center dot O-H center dot center dot center dot O-H one dimensional chain diagonally along the 101] plane of the unit cell. The dihedral angle between the mean planes of the 5-membered imidazole ring fused to the 6-membered pyrimidine ring is 2.6(8)degrees making it a nonplanar purin-9-yl ring. The dihedral angle between the mean planes of the imidazole and pyrimidine rings with those of the cyclopropane and cyclopentene rings are 63.3(7)degrees, 61.2(2)degrees and 63.2(2)degrees, 63.87 degrees, respectively. Intermolecular O-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen bond interactions influence the cyclopropane twist angle and therefore play a role in stabilizing crystal packing in the unit cell. The geometries of the C14H19N6O+, SO42-, cation-anion pair, were optimized means of density functional theory (DFT) molecular orbital theoretical calculation at the B3-LYP/6-311 + G(d,p) level and compared to the crystallographic results providing support for these observations

Crystal structure of 3-oxo-4-aza-5-alpha-androstone-17 beta-tert-butyl carboxamide with an o center dot center dot center dot h-(c,n) acceptor four-center hydrogen bond

The title compound, C23H38N2O2, is the saturated form of a modified steroid derivative Finasteride, containing a delta-lactamide ring, fused to successive cyclohexane and cyclopentane rings which contain a tert-butylamide residue. It crystallizes in the monoclinic space group C2 with unit cell parameters a = 9.99450(10), b = 7.67870(10), c = 28.4954(3), angstrom, beta = 93.8706(10)degrees, Z = 4. Crystal packing effects are influenced by intermolecular hydrogen bond interactions dominated by an acceptor O center dot center dot center dot H-(C,N) four-center hydrogen bond interaction around the keto oxygen atom from the delta-lactamide ring in the asymmetric unit. Intramolecular three-center C-H center dot center dot center dot O hydrogen bonds around the tert-butylamide oxygen atom appear to have little effect on crystal packing. A comparison of the geometric parameters of the asymmetric unit (a 5 alpha isomer) is made and with a solvated analog compound (a 5 beta isomer) and some solvated Finasteride compounds which differ only in the unsaturation of the C1=C2 bond in the delta-lactamide ring. The dihedral angle between the mean planes of the fused delta-lactamide and cyclohexane rings is 2.5(8)degrees which differs significantly from the 74.8(8) and 76.1(9)degrees values observed in the solvated analog compound and with its geometry optimized (MOPAC) computed structure, respectively

Crystal structure of a second polymorph of gabapentin hydrochloride hemihydrate with a three-center bifurcated hydrogen bond

Gabapentin hydrochloride hemihydrate, a derivative of Gabapentin or 1-(aminomethyl) cyclohexaneacetic acid; Gpn, C6H17NO2], is a salt of C9H18NO2 (+) Cl- 0.5 H2O, which crystallizes in the monoclinic space group I 2/a with unit cell parameters a = 13.2467(3), b = 6.5552(2), c = 26.0094(8)angstrom, beta = 96.561(3)degrees, Z = 8. The crystal structure and bonding network is compared to its isostructural and previously reported polymorphic derivative, Gpn hydrochloride hemihydrate C9H17NO2 HCl 1/2 H2O]. Both of these derivatives exhibit extensive inter and intra molecular hydrogen bonding networks between the NH3 (+) group and neighboring Cl-, water and carboxyl oxygen atoms as well as similar interactions between the chloride anion and nearby water and carboxyl oxygen atoms. A unique and relatively rare three-center hydrogen bond configuration (with a bifurcated chlorine Cl-center dot center dot center dot H-(N,O) and Cl-center dot center dot center dot H-O acceptor hydrogen bonds) as well as N-H center dot center dot center dot O donor hydrogen bonds can be seen linking the molecules into chains along the 1 0 1] plane of the unit cell