Comparison of N···I and N···O Halogen Bonds in Organoiodine Cocrystals of Heterocyclic Aromatic Diazine Mono-N-oxides.

A series of cocrystals of halogen bond donors 1,4-diiodotetrafluorobenzene (p-F4DIB) and tetraiodoethylene (TIE) with five aromatic heterocyclic diazine mono-N-oxides based on pyrazine, tetramethylpyrazine, quinoxaline, phenazine, and pyrimidine as halogen bonding acceptors were studied. Structural analysis of the mono-N-oxides allows comparison of the competitive occurrence of N···I vs O···I interactions and the relative strength and directionality of these two types of interactions. Of the aromatic heterocyclic diazine mono-N-oxide organoiodine cocrystals examined, six exhibited 1:1 stoichiometry, forming chains that utilized both N···I and O···I interactions. Two cocrystals presented 1:1 stoichiometry with exclusive O···I interactions. Two cocrystals displayed a 2:1 stoichiometry-one characterized solely by O···I interactions and the other solely by N···I interactions. We have also compared these interactions to those present in the corresponding diazines, some of which we report here and some which have been previously reported. In addition, a computational analysis using density functional theory (M062X/def2-SVPD) was performed on these two systems and has been compared to the experimental results. The calculated complex formation energies were, on average, 4.7 kJ/mol lower for the I···O halogen bonding interaction as compared to the corresponding N···I interaction. The average I···O interaction distances were calculated to be 0.15 Å shorter than the corresponding I···N interactions.

1-(Pyrrolidin-1-yl)ethan-1-iminium chloride.

The title compound, C6H13N2 +·Cl-, is as an amidinium salt that was isolated as unexpected product from the reaction between aceto-nitrile, chloro-form and pyrrolidine under refluxing conditions. The packing features two N-H⋯Cl hydrogen bonds to generate centrosymmetric tetra-mers (two cations and two anions) and van der Waals inter-actions.

1,2,3-Triazoles: Controlled Switches in Logic Gate Applications.

A 1,2,3-triazole-based chemosensor is used for selective switching in logic gate operations through colorimetric and fluorometric response mechanisms. The molecular probe synthesized via "click chemistry" resulted in a non-fluorescent 1,4-diaryl-1,2,3-triazole with a phenol moiety (PTP). However, upon sensing fluoride, it TURNS ON the molecule's fluorescence. The TURN-OFF order occurs through fluorescence quenching of the sensor when metal ions, e.g., Cu2+, and Zn2+, are added to the PTP-fluoride ensemble. A detailed characterization using Nuclear Magnetic Resonance (NMR) spectroscopy in a sequential titration study substantiated the photophysical characteristics of PTP through UV-Vis absorption and fluorescence profiles. A combination of fluorescence OFF-ON-OFF sequences provides evidence of 1,2,3-triazoles being controlled switches applicable to multimodal logic operations. The "INH" gate was constructed based on the fluorescence output of PTP when the inputs are F- and Zn2+. The "IMP" and "OR" gates were created on the colorimetric output responses using the probe's absorption with multiple inputs (F- and Zn2+ or Cu2+). The PTP sensor is the best example of the "Write-Read-Erase-Read" mimic.

1-(Hex-5-en-1-yl)-4-{[3-methyl-2,3-di-hydro-1,3-benzo-thia-zol-2-yl-idene]meth-yl}quinolin-1-ium iodide monohydrate.

The title thia-zole orange derivative, bearing an alkene substituent, crystallized as a monohydrate of its iodide salt, namely, (Z)-1-(hex-5-en-1-yl)-4-{[3-methyl-2,3-di-hydro-1,3-benzo-thia-zol-2-yl-idene]meth-yl}quinolin-1-ium iodide monohydrate, C24H25N2S+·I-·H2O. The packing features aromatic π-stacking and van der Waals inter-actions. The water mol-ecule of crystallization inter-acts with the cation and anion via O-H⋯N and O-H⋯I hydrogen bonds, respectively.

Crystal structures of three zinc(II) halide coordination complexes with quinoline N-oxide.

The reaction of one equivalent of zinc(II) halide with two equivalents of quinoline N-oxide (QNO) in methanol yields compounds as ZnX 2(QNO)2, where X = Cl (I), Br (II) and I (III), namely, di-chlorido-bis-(quinoline N-oxide-κO)zinc(II), [ZnCl2(C9H7NO)2], di-bromido-bis-(quinoline N-oxide-κO)zinc(II), [ZnBr2(C9H7NO)2], and di-iodido-bis-(quinoline N-oxide-κO)zinc(II) [ZnI2(C9H7NO)2]. In all three complexes, Zn cations are coordinated by two QNO ligands bound through the oxygen atoms and two halide atoms, with X-Zn-X bond angles ca 20° wider than the O-Zn-O, giving rise to a distorted tetra-hedral geometry. Crystals of (II) and (III) are isostructural and both show pairwise π-stacking of QNO ligands and weak C-H⋯X hydrogen bonds, while (I) packs differently, with a shorter C-H⋯Cl bond and without π-stacking.

Crystal structures and Hirshfeld surface analysis of 5-amino-1-(4-meth-oxy-phen-yl)pyrazole-4-carb-ox-ylic acid and 5-amino-3-(4-meth-oxy-phen-yl)isoxazole.

The title compounds, C11H11N3O3, (I), and C10H10N2O2, (II), are commercially available and were crystallized from ethyl acetate solution. The dihedral angle between the pyrazole and phenyl rings in (I) is 52.34 (7)° and the equivalent angle between the isoxazole and phenyl rings in (II) is 7.30 (13)°. In the crystal of (I), the mol-ecules form carb-oxy-lic acid inversion dimers with an R(8) ring motif via pairwise O-H⋯O hydrogen bonds. In the crystal of (II), the mol-ecules are linked via N-H⋯N hydrogen bonds forming chains propagating along [010] with a C(5) motif. A weak N-H⋯π inter-action also features in the packing of (II). Hirshfeld surface analysis was used to explore the inter-molecular contacts in the crystals of both title compounds: the most important contacts for (I) are H⋯H (41.5%) and O⋯H/H⋯O (22.4%). For (II), the most significant contact percentages are H⋯H (36.1%) followed by C⋯H/H⋯C (31.3%).

Di-µ-benzoato-di-µ-ethano-lato-tetra-kis-[µ3-5-(hy-droxy-meth-yl)-2-methyl-4-(oxidometh-yl)pyridin-1-ium-3-olato]tetra-kis-[µ3-5-(hy-droxy-meth-yl)-2-methyl-4-(oxidometh-yl)pyridin-3-olato]di-µ3-oxido-hepta-manganese(II,III) ethanol octa-solvate.

Our work in the area of synthesis of polynuclear manganese complexes and their magnetic properties led to the synthesis and crystallization of the title compound, [Mn7(C8H9NO3)4(C8H10NO3)4(C2H5O)2(C7H5O2)2O2]·8C2H5OH. Herein, we report the molecular and crystal structure of the title compound, which was synthesized by the reaction of Mn(C6H5COO)2 with pyridoxine (PNH2, C8H11NO3) followed by the addition of tetra-methyl-ammonium hydroxide (TMAOH). The core of this centrosymmetric complex is a cage-like structure consisting of six MnIII ions and one MnII ion bound together through Mn-O bonds. The compound crystallizes in hydrogen-bonded layers formed by O-H⋯N hydrogen bonds involving the aromatic amine group of the ligand PN2- with the neighboring O atoms from the PNH- ligand. The crystal structure has large voids present in which highly disordered solvent mol-ecules (ethanol) sit. A solvent mask was calculated and 181 electrons were found in a volume of 843 Å3 in one void per triclinic unit cell. This is consistent with the presence of seven ethanol mol-ecules per formula unit, which accounts for 182 electrons per unit cell. Additionally, one ethanol mol-ecule was found to be ordered in the crystal.

Rationally designed phenanthrene derivatized triazole as a dual chemosensor for fluoride and copper recognition.

A 1,2,3-triazole chemosensor containing phenanthrene and phenol moieties (PhTP) was efficiently synthesized via copper (I)-catalyzed azide-alkyne cycloaddition, "click chemistry". PhTP is a dual analyte sensor for fluoride and copper (II) ions in homogeneous medium. Deprotonation of the phenolic OH proton by the fluoride ion is responsible for a change in fluorescence color from blue (PhTP) to yellowish-orange (PhTP-fluoride adduct), while a charge transfer between the triazole nitrogen of the chemosensor and Cu2+ revealed a turn-off fluorescence output. The detection capability of PhTP was analyzed with a series of anions (F-, Cl-, Br-, I-, H2PO4-, ClO4-, OAc-, BF4-) and cations (Fe3+, Fe2+, Cu2+, Ag+, Cr3+, Al3+, Co2+, Ni2+, Cd2+, Zn2+). With anions, competitive fluorescence responses under UV lamp were observed for acetate and dihydrogen phosphate anions, but maximum response from fluoride ion was substantiated from steady state absorption and fluorescence experiments. With cations, PhTP displayed a selective and sensitive recognition towards Cu2+ ion through spectral modulation in absorption spectroscopy and a turn-off fluorescence response. Nuclear magnetic resonance (NMR) spectroscopic titration studies supported the results obtained through photophysical studies and provided evidence for the ion-binding sites on the probe.

3-(4-Iodo-phen-yl)-2,3-di-hydro-1H-benzo[f]chromen-1-one.

In the title compound, C19H13IO2, the dihedral angle between the naphthyl ring system and the pendant iodo-phenyl ring is 72.48 (11)°. In the crystal, C-H⋯π inter-actions and I⋯O [3.293 (2) Å] halogen bonds are observed, which combine to generate a herringbone packing motif.

Ethyl 1H-indole-2-carboxyl-ate.

Our work in the area of synthesis of tris indole compounds as a potential chelator led to the synthesis and crystallization of ethyl 1H-indole-2-carboxyl-ate, C11H11NO2, an indole that was synthesized by the thionyl chloride reaction of 1H-indole-2-carb-oxy-lic acid, followed by dissolution in ethanol. The mol-ecular packing exhibits a herringbone pattern with the zigzag running along the b-axis direction; the compound crystallizes as a hydrogen-bonded dimer resulting from O⋯H-N hydrogen bonds, between the indole N-H group and the keto oxygen atom, which build centrosymmetric R 2 2(10) ring motifs in the crystal.

Pyridine-4-carboxamidoxime N-oxide.

Our work in the area of synthesis of metal-organic frameworks (MOFs) based on organic N-oxides led to the crystallization of pyridine-4-carboxamidoxime N-oxide. Herein we report the first crystal structure of the title compound, C6H7N3O2 [systematic name: (Z)-4-(N'-hy-droxy-carbamimido-yl)pyridine N-oxide]. The hy-droxy-carbamimidoyl group is essentially coplanar with the aromatic ring, r.m.s.d. = 0.112 Å. The compound crystallizes in hydrogen-bonding layers built from the formation of strong O-H⋯O hydrogen bonds between the oxime oxygen atom and the oxygen atom of the N-oxide, and the formation of N-H⋯O hydrogen bonds between one amine nitro-gen atom and the N-oxide oxygen atom. These combined build R 3 4(24) ring motifs in the crystal. The crystal structure has no π-π inter-actions.

Crystal structures of four dimeric manganese(II) bromide coordination complexes with various derivatives of pyridine N-oxide.

Four manganese(II) bromide coordination complexes have been prepared with four pyridine N-oxides, viz. pyridine N-oxide (PNO), 2-methyl-pyridine N-oxide (2MePNO), 3-methyl-pyridine N-oxide (3MePNO), and 4-methyl-pyridine N-oxide (4MePNO). The compounds are bis-(µ-pyridine N-oxide)bis-[aqua-dibromido-(pyridine N-oxide)manganese(II)], [Mn2Br4(C5H5NO)4(H2O)2] (I), bis-(µ-2-methyl-pyridine N-oxide)bis-[di-aqua-dibromido-manganese(II)]-2-methyl-pyridine N-oxide (1/2), [Mn2Br4(C6H7NO)2(H2O)4]·2C6H7NO (II), bis-(µ-3-methyl-pyridine N-oxide)bis-[aqua-dibromido-(3-methyl-pyridine N-oxide)manganese(II)], [Mn2Br4(C6H7NO)4(H2O)2] (III), and bis-(µ-4-methyl-pyridine N-oxide)bis-[di-bromido-methanol(4-methyl-pyridine N-oxide)manganese(II)], [Mn2Br4(C6H7NO)4(CH3OH)2] (IV). All the compounds have one unique MnII atom and form a dimeric complex that contains two MnII atoms related by a crystallographic inversion center. Pseudo-octa-hedral six-coordinate manganese(II) centers are found in all four compounds. All four compounds form dimers of Mn atoms bridged by the oxygen atom of the PNO ligand. Compounds I, II and III exhibit a bound water of solvation, whereas compound IV contains a bound methanol mol-ecule of solvation. Compounds I, III and IV exhibit the same arrangement of mol-ecules around each manganese atom, ligated by two bromide ions, oxygen atoms of two PNO ligands and one solvent mol-ecule, whereas in compound II each manganese atom is ligated by two bromide ions, one O atom of a PNO ligand and two water mol-ecules with a second PNO mol-ecule inter-acting with the complex via hydrogen bonding through the bound water mol-ecules. All of the compounds form extended hydrogen-bonding networks, and compounds I, II, and IV exhibit offset π-stacking between PNO ligands of neighboring dimers.

Structures of substituted pyridine N-oxide with manganese(II) acetate.

Manganese(II) acetate coordination polymers have been prepared with three derivatives of pyridine N-oxide. The compounds are catena-poly[manganese(II)-µ3-acetato-di-µ2-acetato-[aqua-manganese(II)]-µ2-acetato-µ-(pyridine N-oxide)-manganese(II)-µ3-acetato-µ2-acetato-µ-(pyridine N-oxide)-[aqua-manganese(II)]-di-µ2-acetato], [Mn4(CH3COO)8(C5H5NO)2(H2O)2] n , (I), catena-poly[[manganese(II)]-µ3-acetato-µ2-acetato-µ-(2-methyl-pyridine N-oxide)-[aqua-manganese(II)]-di-µ2-acetato-manganese(II)-di-µ2-acetato-µ3-acetato-[aqua-manganese(II)]-µ2-acetato-µ-(2-methyl-pyridine N-oxide)], [Mn4(CH3COO)8(C6H7NO)2(H2O)2] n , (II), and catena-poly[[manganese(II)-di-µ2-acetato-µ-(4-methyl-pyridine N-oxide)] monohydrate], {[Mn(CH3COO)2(C6H7NO)]·H2O} n , (III). Compounds (I) and (II) both have three unique Mn atoms; in both compounds two of them sit on a crystallographic inversion center while the third is on a general position. In compound (III), the single unique Mn atom sits on a general position. Pseudo-octa-hedral six-coordinate mangan-ese(II) centers are found in all compounds. All of the compounds form chains of Mn atoms bridged by acetate ions and the oxygen atom of the N-oxide in pyridine N-oxide (PNO), 2-methyl-pyridine N-oxide (2MePNO), or 4-methyl-pyridine N-oxide (4MePNO). Compound (I) and (II) both exhibit a bound water of solvation. In (I), the water hydrogen bonds to a nearby acetate whereas in (II) the water mol-ecule forms bridging hydrogen bonds between two neighboring acetates. In compound (III) a water mol-ecule of solvation is found in the lattice, not bound to the metal ion but hydrogen bonding to a bridging acetate.

Manganese(II) chloride complexes with pyridine N-oxide (PNO) derivatives and their solid-state structures.

Three manganese(II) N-oxide complexes have been synthesized from the reaction of manganese(II) chloride with either pyridine N-oxide (PNO), 2-methyl-pyridine N-oxide (2MePNO) or 3-methyl-pyridine N-oxide (3MePNO). The compounds were synthesized from methano-lic solutions of MnCl2·4H2O and the respective N-oxide, and subsequently characterized structurally by single-crystal X-ray diffraction. The compounds are catena-poly[[aqua-chlorido-manganese(II)]-di-µ-chlorido-[aqua-chlorido-manganese(II)]-bis-(µ-pyridine N-oxide)], [MnCl2(C5H5NO)(H2O)] n or [MnCl2(PNO)(H2O)] n (I), catena-poly[[aqua-chlorido-man-gan-ese(II)]-di-µ-chlorido-[aqua-chlorido-manganese(II)]-bis-(µ-2-methyl-pyridine N-oxide)], [MnCl2(C6H7NO)(H2O)] n or [MnCl2(2MePNO)(H2O)] n (II), and bis-(µ-3-methyl-pyridine N-oxide)bis-[di-aqua-dichlorido-manganese(II)], [Mn2Cl4(C6H7NO)2(H2O)4] or [MnCl2(3MePNO)(H2O)2]2 (III). The MnII atoms are found in pseudo-octa-hedral environments for each of the three complexes. Compound I forms a coordination polymer with alternating pairs of bridging N-oxide and chloride ligands. The coordination environment is defined by two PNO bridging O atoms, two chloride bridging atoms, a terminal chloride, and a terminal water. Compound II also forms a coordination polymer with a similar metal cation; however, the coordination polymer is bridged between MnII atoms by both a single chloride and 2MePNO. The distorted octahedrally coordinated metal cation is defined by two bridging 2MePNO trans to each other, two chlorides, also trans to one another in the equatorial (polymeric) plane, and a terminal chloride and terminal water. Finally, complex III forms a dimer with two bridging 3MePNOs, two terminal chlorides and two terminal waters forming the six-coordinate metal environment. All three compounds exhibit hydrogen bonding between the coordinating water(s) and terminal chlorides.

Crystal structure of (E)-2-[(2-bromopyridin-3-yl)methyl-idene]-6-meth-oxy-3,4-di-hydro-naphthalen-1(2H)-one and 3-[(E)-(6-meth-oxy-1-oxo-1,2,3,4-tetra-hydro-naphthalen-2-ylidene)meth-yl]pyridin-2(1H)-one.

The title compounds C17H14BrNO2, (I), and C17H15NO3, (II), were obtained from the reaction of 6-meth-oxy-3,4-di-hydro-2H-naphthalen-1-one and 2-bromo-nicotinaldehyde in ethanol. Compound (I) was the expected product and compound (II) was the oxidation product from air exposure. In the crystal structure of compound (I), there are no short contacts or hydrogen bonds. The structure does display π-π inter-actions between adjacent benzene rings and adjacent pyridyl rings. Compound (II) contains two independent mol-ecules, A and B, in the asymmetric unit; both are non-planar, the dihedral angles between the meth-oxy-benzene and 1H-pyridin-2-one mean planes being 35.07 (9)° in A and 35.28 (9)°in B. In each mol-ecule, the 1H-pyridin-2-one unit participates in inter-molecular N-H⋯O hydrogen bonding to another mol-ecule of the same type (A to A or B to B). The structure also displays π-π inter-actions between the pyridyl and the benzene rings of non-equivalent mol-ecules (viz., A to B and B to A).

Crystal structure of (E)-1-(3-chloro-phen-yl)-3-(furan-2-yl)prop-2-en-1-one.

The title compound, C13H9ClO2, exhibits a non-planar geometry; the furan ring being inclined to the benzene ring by 50.52 (16)°. In the crystal, mol-ecules stack along the a axis; however, there are no significant inter-molecular inter-actions present.

Crystal structure of 2,6-di-chloro-4-nitro-pyridine N-oxide.

In the title compound, C5H2Cl2N2O3, the nitro group is essentially coplanar with the aromatic ring, with a twist angle of 4.00 (6)° and a fold angle of 2.28 (17)°. The crystal structure exhibits a herringbone pattern with the zigzag running along the b axis. The herringbone layer-to-layer distance is 3.0075 (15) Å, with a shift of 5.150 (4) Å. Neighboring mol-ecules are tilted at a 57.83 (4)° (ring-to-ring) angle with each other. The nitro group on one mol-ecule points to the N-oxide group on the neighboring one, with an inter-molecular O⋯N(nitro) distance of 3.1725 (13) Å.

Crystal structure of 3-bromo-pyridine N-oxide.

In the title compound, C5H4BrNO, there are two mol-ecules in the asymmetric unit that are related by a pseudo-inversion center. The two independent mol-ecules are approximately planar, with an observed (ring-ring) angle of 5.49 (13)°. The crystal structure exhibits a herringbone pattern with the zigzag running along the b-axis direction. The least-squares plane containing the rings of both asymmetric molecules and the plane containing the symmetrically related mol-ecules make a plane-plane angle of 66.69 (10)°, which makes the bend of the herringbone pattern. The bromo group on one mol-ecule points to the bromo group on the neighboring mol-ecule, with a Br⋯Br inter-molecular distance of 4.0408 (16) Å. The herringbone layer-to-layer distance is 3.431 (4) Šwith a shift of 1.742 (7) Å. There are no short contacts, hydrogen bonds, or π-π inter-actions.

Isolation of 3-amino-4-nitro-benzyl acetate: evidence of an undisclosed impurity in 5-amino-2-nitro-benzoic acid.

Yellow crystals of the title compound 3-amino-4-nitro-benzyl acetate, C9H10N2O4, were isolated from the reaction of acetic anhydride with (5-amino-2-nitro-phen-yl)methanol, prepared from reduction of commerically available 5-amino-2-nitro-benzoic acid with borane-THF. The mol-ecule is essentially planar (r.m.s. deviation = 0.028 Å). The mol-ecules are linked by inter-molecular N-H⋯O hydrogen-bonding inter-actions between the carbonyl and amine groups, forming a zigzag chain along the b-axis direction lying in a plane parallel to (-102). The chains are stacked along the c axis by π-π inter-actions [centroid-centroid distances = 3.6240 (3) and 3.5855 (4) Å]. A strong intra-molecular N-H⋯O hydrogen-bonding inter-action is observed between the nitro group and the amine group [2.660 (2) Å].

A square-planar hydrated cationic tetrakis(methimazole)gold(III) complex.

The cationic pseudo-square-planar complex tetrakis(1-methyl-2,3-dihydro-1H-imidazole-2-thione-κS)gold(III) trichloride sesquihydrate, [Au(C4H6N2S)4]Cl3·1.5H2O, was isolated as dark-red crystals from the reaction of chloroauric acid trihydrate (HAuCl4·3H2O) with four equivalents of methimazole in methanol. The Au(III) atoms reside at the corners of the unit cell on an inversion center and are bound by the S atoms of four methimazole ligands in a planar arrangement, with S-Au-S bond angles of approximately 90°.