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.

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.

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.

Synthesis, stereochemical characterization, and antimicrobial evaluation of a potentially nonnephrotoxic 3'-C-acethydrazide puromycin analog.

Puromycin is a peptidyl nucleoside endowed with significant antibiotic and anticancer properties, but also with an unfortunate nephrotoxic character that has hampered its use as a chemotherapeutic agent. Since hydrolysis of puromycin's amide to puromycin aminonucleoside is the first metabolic step leading to nephrotoxicity, we designed a 3'-C-hydrazide analog where the nitrogen and carbon functionality around the amide carbonyl of puromycin are inverted. The title compound, synthesized in 11 steps from D-xylose, cannot be metabolized to the nephrotoxic aminonucleoside. Evaluation of the title compound on Staphylococcus epidermidis and multi-drug resistance Staphylococcus aureus did not show significant antimicrobial activity up to a 400 µM concentration.

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.

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°.