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Heterocyclic compounds play a critical role in medicinal chemistry, and many available drugs contain heterocyclic rings. A six-membered heterocyclic compound, pyridine, showed various applications, including being an important solvent, reagent, and precursor in agrochemicals and pharmaceuticals. Due to the increase in drug resistance, there is an apparent medical need to develop new antiviral agents. Various derivatives of pyridine scaffold display broad biological activities such as anti-microbial, antiviral, antioxidant, anti-diabetic, anti-cancer, anti-malarial, analgesic, and antiinflammatory activities. Furthermore, they display psychopharmacological, antagonistic, anti-amoebic agents, and anti-thrombic activities. Due to the high importance of pyridine derivatives, in the present review, we tried to collect and classify many pyridine derivatives based on their structures from 2000 to 2020. Pyridine derivatives were classified into two general categories, including pyridine containing heterocycles and pyridine fused rings. The structure-activity relationship (SAR) and the action mechanism of derivatives were also investigated. According to the recent studies, these derivatives exhibited good antiviral activity against different types of viruses such as the human immunodeficiency viruses (HIV), the hepatitis C virus (HCV), the hepatitis B virus (HBV), respiratory syncytial virus (RSV), and cytomegalovirus (CMV). These derivatives inhibited viral application with different action mechanism such as RT inhibition, polymerase inhibition, inhibition of RNase H activity, inhibition of maturation, inhibition of the viral thymidine kinase, AAK1 (Adaptor-Associated Kinase 1) inhibition, GAK (Cyclin G-associated kinase) inhibition, inhibition of post-integrational event, inhibition of HDAC6, CCR5 antagonistic activity, DNA and RNA replication inhibition, gene expression inhibition, cellular NF-jB signaling pathway and neuraminidase (NA) inhibition, protein synthesis inhibition, and generally inhibition of viral replication cycle. This paper summarized the past and present results about the discovery of novel lead compounds with good antiviral activity. Studies exhibited that almost all of the evaluations were performed by way of in vitro testing. It is necessary to investigate in vivo and clinical testing for better evaluations in the future. We believe that pyridine derivatives can be used as promising antiviral agents and more broad investigations in this field need to be performed.

The enthalpies of sublimation of five substituted pyridine N-oxides were determined by the Knudsen effusion method with mass spectrometric control of the vapor composition within the framework of the second law of thermodynamics. The sublimation enthalpy of mono-substituted compounds 4-X-PyO depends on the nature of the substituent X and increases in the order CH3→NO2→OCH3. A difference is noted in the nature of dissociative ionization of disubstituted derivatives 2-CH3-4-NO2PyO and 3-CH3-4-NO2PyO. The relationship between the packing of molecules in crystals and the ΔH°subl values is considered.

The aim of the Research. To identify morphological changes in Tetrahymena pyriformis W infusoria under the acute exposure to plant growth regulators (PGR) — derivatives of pyridine-N-oxide and compare them to functional disorders of cells. Materials and Methods. In the research we used the 2-methylpyridine-N-oxide, 2,6-dimethylpyridine-N-oxide and their complexes with organic acids (succinic, maleic) or metal salts (ZnCl2, ZnI 2, CoCl2, MnCl2) (a total of 15 substances), synthesized at the Institute of Bioorganic chemistry and Petrochemistry, NAS, Ukraine. Studies were performed on Tetrahymena pyriformis W infusoria in isotoxic doses — at the level of toxic concentrations — LC50, LC16 and inactive concentrations (LC0). Morphological changes in cells of infusoria were assessed visually with the use of a light microscope. Structural changes in infusoria were compared to functional changes in cells (motor activity and energy state) obtained under the same experiment. Results and Conclusions. It is demonstrated that 2-methylpyridine-N-oxide, 2,6-dimethylpyridine-N-oxide and their complexes with organic acids (succinic, maleic) or metal salts (ZnCl2, ZnI2, CoCl 2, MnCl2) cause functional and morphostructural changes in infusoria, the extent of which depends on the current concentration. Morphostructural changes in infusoria under the influence of the studied PGRs are characterized by a change of shape, growth of the contractile vacuole, vesiculation, damage to the integrity of the cytoplasmic membrane, emission of cytoplasm and structural elements of cells into the nutrient medium. Complexes of methyl derivatives of pyridine-N-oxide with metal salts in the studied concentrations reduce speed and increase energy expenditure on movement, cause changes in behavioural reactions and structure of cells to a greater extent than 2-methylpyridine-N-oxide, 2,6-dimethylpyridine-N-oxide and their complexes with organic acids. Both functional and morphological changes in infusoria are more evident under the influence of studied PGR occurring at concentrations corresponding to LC50. At lower concentrations the changes in the functional activity of infusoria were observed. Comparison of the obtained functional and morphostructural indicators of the state of infusoria shows that complexes of methyl derivatives of Pyridine-N-oxide with metal salts have more toxic effects on infusoria than complexes of methyl derivatives of pyridine-N-oxide with organic acids. Reduced motor activity and an increase in energy consumption per a unit of a path of motion, together with the morphological changes of cell structure, are the indicators of toxicity of xenobiotics for infusoria and criteria for assessing their viability. Key Words: methyl derivatives of Pyridine-N-oxide, Tetrahymena pyriformis W, morphofunctional changes.

A depsipeptidic analogue of FE399 was efficiently synthesized mainly through macrolactamization using 2-methyl-6-nitrobenzoic anhydride (MNBA), and a detailed investigation of the desired 16-membered macrolactam core of FE399 was performed. It was determined that the combination of MNBA and a catalytic amount of 4-(dimethylamino)pyridine N-oxide exhibits much higher activity than that of conventionally used coupling reagents such as hexafluorophosphate azabenzotriazole tetramethyl uronium and benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate.

Herein, we demonstrate that 2-difluoromethylpyridine is a bioisosteric replacement of pyridine-N-oxide. Using the quorum sensing inhibitor 4NPO as a model compound, a library of 2-difluoromethylpyridine derivatives was designed, synthesized, and evaluated toward quorum sensing activity, biofilm formation, anti-violacein activity, and protease activity. As a result, compounds 1 (IC(50) of 35 ± 1.12 μM), 5 (IC(50) of 19 ± 1.01 μM), and 6 (IC(50) of 27 ± 0.67 μM) showed a similar or better activity in comparison to 4NPO (IC(50) of 33 ± 1.12 μM) in a quorum sensing system of Pseudomonas aeruginosa. In addition, compounds 1, 5, 6, and 4NPO showed good antibiofilm biomass of Pseudomonas aeruginosa and reduced violacein production in Chromobacterium violaceum. In terms of protease activity, compounds 1, 5, and 6 showed significant activity compared to 4NPO. Overall, the replacement of pyridine-N-oxide by 2-difluoromethylpyridine enhances the activity of the model compound, which could open a new path for bioisosteric replacement in drug discovery and development.

The extraction of microamounts of REE(III), U(VI), and Th(IV) from HClO4 solutions with solutions of 2,6-bis(diphenylphosphorylmethyl) pyridine N-oxide (I) in 1,2-dichloroethane was studied depending on the HClO4 concentration in the equilibrium aqueous phase. The stoichiometry of the extracted complexes was determined. It was shown that compound I extracts REE(III), U(VI), and Th(IV) from dilute HClO4 solutions with much higher efficiency than from HNO3 solutions. With an increase in the concentration of acids, the magnitude of the “perchlorate” effect upon extraction of REE(III) and U(VI) decreases, and Th(IV) is extracted by compound I from HClO4 solutions with lower efficiency than from HNO3 solutions.

Direct activation of O–H bond in water via hydrogen atom transfer (HAT) reactions is a challenge because of its high bond dissociation energy. In this work, a strong hydrogen atom abstracting reage...

Reaction of copper(II) perchlorate with pyrazine and pyridine-N-oxide produced the coordination polymer catena-[diaqua-μ-pyrazine-bis(pyridine-N-oxide)copper(II)] perchlorate (1) which was characterized by single-crystal X-ray diffraction, EPR and variable temperature magnetic susceptibility measurements. The compound forms well-isolated linear chains, bridged by pyrazine. EPR studies show a rhombic structure with gave = 2.15. The magnetic data are well described by the uniform Heisenberg chain model giving J/kB = −9.6(1) K and show no signs of inter-chain interactions down to 1.8 K [H = −JΣS1S2]. In the course of the synthesis, the related [tetrakis(pyridine-N-oxide)copper(II)] perchlorate complex (2) was also isolated. X-Ray studies confirm the identity of the compound in comparison to the previous literature. EPR studies indicate a rhombic structure, similar to 1, but variable temperature magnetic susceptibility data show no significant magnetic exchange in agreement with the absence of a superexchange pathway in the crystal.

New dipyridylpyrrole N-oxide ligands HL1 and HL2 are designed and synthesized via oxidation of 2-(5-(pyridin-2-yl)-1H-pyrrol-2-yl)pyridine (Hdpp) by using 3-chloroperbenzoic acid (m-CPBA) in CH2Cl2. The treatment of ZnEt2 with two equiv. of HL1 and HL2 affords [Zn(L1)2] and [Zn(L2)2] in medium yield, respectively. These ligands and zinc complexes are fully characterized by NMR, IR, UV-vis and ESI-MS spectroscopy and X-ray diffraction analysis. The structure of HL1 and HL2 shows a planar geometry. The intramolecular hydrogen-bond interactions between the imino hydrogen and N-oxide oxygen atom are observed. In [Zn(L1)2] and [Zn(L2)2], two ligands chelate to the zinc metal with a cross perpendicular geometry. The zinc complexes were employed as a highly efficient catalyst for the thiol-Michael addition of thiols to α,β-unsaturated ketones in EtOH at room temperature. The loading of the catalyst is lowered to 0.01 mol%. The catalytic mechanism was proposed based on NMR and ESI-MS experiments.

Five [PSiP]-pincer iron hydrides 1-5, [(2-Ph2PC6H4)2HSiFe(H)(PMe3)2 (1), (2-Ph2PC6H4)2MeSiFe(H)(PMe3)2 (2), (2-Ph2PC6H4)2PhSiFe(H)(PMe3)2 (3), (2-(iPr)2PC6H4)2HSiFe(H)(PMe3) (4), and (2-(iPr)2PC6H4)2MeSiFe(H)(PMe3)2 (5)], were used as catalysts to study the effects of pyridine N-oxide and the electronic properties of [PSiP]-ligands on the catalytic hydrosilylation of carbonyl compounds. It was proved for the first time that this catalytic process could be promoted with pyridine N-oxide as the initiator at 30 °C because the addition of pyridine N-oxide is beneficial for the formation of an unsaturated hydrido iron complex, which is the key intermediate in the catalytic mechanism. Complex 4 as the best catalyst shows excellent catalytic performance. Among the five complexes, complex 3 was new and the molecular structure of complex 3 was determined by single crystal X-ray diffraction. A proposed mechanism was discussed.

Rapid capture of 129 I with high volatility and toxicity in the environment has attracted much attention. Herein we reported a firstly synthesized nonporous material: pyridine N-oxides (NTPO and ATPO) as iodine adsorbent. Both of NTPO and ATPO exhibit remarkable performance on the adsorption of iodine in aqueous solution, vapor state and organic solvents. Upon the capture of iodine, pyridine N-oxides were transformed to binary cocrystals combined with the pyridine N-oxides and iodine which is driven by halogen bond between iodine and oxygen atoms. Moreover, pyridine N-oxides shows high chemical, thermal and moisture stability.

International audience; In the context of bioinspired OAT catalysis, we developed a tetradentate dipyrrinpyridine ligand, a hybrid of hemic and non-hemic models. The catalytic activity of the iron(iii) derivative was investigated in the presence of iodosylbenzene. Unexpectedly, MS, EPR, Mossbauer, UV-visible and FTIR spectroscopic signatures supported by DFT calculations provide convincing evidence for the involvement of a relevant Fe-III-O-N-Py active intermediate.

A rhodium-catalyzed Suzuki–Miyaura coupling reaction via C(O)-C bond activation to form 2-benzoylpyridine N-oxide derivatives is reported. Both the C(O)–C(sp2) and C(O)–C(sp3) bond could be activated during the reaction with yields up to 92%. The N-oxide moiety could be employed as a traceless directing group, leading to free pyridine ketones.

A study of the strong N-X⋅⋅⋅- O-N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N-halosaccharins and pyridine N-oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from -47.5 to -120.3 kJ mol-1 ; the strongest N-I⋅⋅⋅- O-N+ XBs approaching those of 3-center-4-electron [N-I-N]+ halogen-bonded systems (ca. 160 kJ mol-1 ). 1 H NMR association constants (KXB ) determined in CDCl3 and [D6 ]acetone vary from 2.0×100 to >108 m-1 and correlate well with the calculated donor×acceptor complexation enthalpies found between -38.4 and -77.5 kJ mol-1 . In X-ray crystal structures, the N-iodosaccharin-PyNO complexes manifest short interaction ratios (RXB ) between 0.65-0.67 for the N-I⋅⋅⋅- O-N+ halogen bond.

The synthesis and crystal structures of four dimeric complexes composed of manganese(II) dibromide, a pyridine N-oxide and solvent mol­ecules are reported. The pyridine N--oxide, 2-methyl­pyridine N-oxide, 3-methyl­pyridine N-oxide, and 4-methyl­pyridine N-oxide complexes all form similar structures with slight differences owing to the substituent group effects., Four manganese(II) bromide coordination complexes have been prepared with four pyridine N-oxides, viz. pyridine N-oxide (PNO), 2-methyl­pyridine N-oxide (2MePNO), 3-methyl­pyridine N-oxide (3MePNO), and 4-methyl­pyridine N-oxide (4MePNO). The compounds are bis­(μ-pyridine N-oxide)bis­[aqua­dibromido­(pyridine N-oxide)manganese(II)], [Mn2Br4(C5H5NO)4(H2O)2] (I), bis­(μ-2-methyl­pyridine N-oxide)bis­[di­aqua­dibromido­manganese(II)]–2-methyl­pyridine N-oxide (1/2), [Mn2Br4(C6H7NO)2(H2O)4]·2C6H7NO (II), bis­(μ-3-methyl­pyridine N-oxide)bis­[aqua­dibromido­(3-methyl­pyridine N-oxide)manganese(II)], [Mn2Br4(C6H7NO)4(H2O)2] (III), and bis­(μ-4-methyl­pyridine N-oxide)bis­[di­bromido­methanol(4-methyl­pyridine 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-octa­hedral 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 mol­ecule of solvation. Compounds I, III and IV exhibit the same arrangement of mol­ecules around each manganese atom, ligated by two bromide ions, oxygen atoms of two PNO ligands and one solvent mol­ecule, whereas in compound II each manganese atom is ligated by two bromide ions, one O atom of a PNO ligand and two water mol­ecules with a second PNO mol­ecule inter­acting with the complex via hydrogen bonding through the bound water mol­ecules. 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.

One of the major problems in the household machine laundry process is dyes bleeding from coloured garments and then the re-depositing on lighter-coloured garments in the same wash load. Thus it creates staining on the light coloured cloth and also colour loss on the dark coloured cloth. Numerous attempts made to solve the issue but none of the remedies are completely successful. Improper loading of high quantity of dye transfer inhibitor (DTI) polymer also had severe negative effect on coloured garment in terms of colour striping, patchy and unsightly appearance. In this research, the amine based aromatic dye transfer inhibitor polymers pyridine N-oxide (PNO), used for the analysis. The performance of the polymer was optimized for better dye transfer inhibition property in the ‘in wash’ liquor against reactive dye. The findings of the research indicate that the performance pyridine N-oxide against reactive dye was excellent over the commercial DTI polymer polyvinylpyrrolidone (PVP). The addition of detergent diminishes the properties of the PVP, but the PNO overcomes that issues and acts well in presence of maximum quantity of the detergent. The research work optimized the amount of DTI polymer required for a single wash load, as 0.25 g. The level of detergent preferably 10 g/l and the pH value of 8. The findings revealed that the PNO polymer performs excellent against all the commercial dyes and also it is noted that the polymer overcomes the shortfalls of commercially available DTI polymers like PVP.

Fe3O4 nanoparticles were prepared from a salt comprising a tetrachloroferrate anion and a methyltrioctylammonium cation in toluene using ethylenediamine as a reductant and pyridine-N-oxide as an oxygen donor and an oxidant. The X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy showed that the product was Fe3O4. Water content measurement with a Karl Fischer moisture meter showed the presence of only a small amount of water in the present system, indicating a limited contribution of water to the formation of Fe3O4 nanoparticles. The Fe3O4 nanoparticle size based on transmission electron microscopy (TEM) observation was approximately 10–30 nm, a result consistent with the crystallite diameter estimated by Scherrer's equation (15.7 nm). A possible reaction mechanism involves the reduction of Fe3+ to Fe2+ by ethylenediamine, coordination of both ethylenediamine and pyridine-N-oxide to Fe2+, and oxidation of a part of Fe2+, leading to a mixed-valence iron-oxygen network, which was a precursor of Fe3O4 nanoparticles. As concerns magnetic properties, saturation magnetization of the product was 57 emu g−1. Both the coercivity and remanent magnetization were nearly zero and the similar decreases in magnetization were observed above the blocking temperature in the zero-field-cooled and field-cooled curves, results indicating the formation of superparamagnetic Fe3O4 nanoparticles.

A photocatalyzed ortho-alkylation of pyridine N-oxide with ynamides and arylacetylenes has been developed, which yields a series of α-(2-pyridinyl) benzyl amides/ketones. Mechanistic studies, including electrochemical studies, radical-trapping experiments, and Stern-Volmer fluorescence quenching studies demonstrate that pyridine N-oxide serves as both a redox auxiliary and radical acceptor to achieve the mild photocatalytic single-electron oxidation of carbon-carbon triple bonds with the generation of a cationic vinyl radical intermediate.

The paper reports the generation of a carbon-center radical (R•) from an alkyl iodide (R-I) via a halogen bonding catalysis using pyridine N-oxide (PO) catalysts. The use of this catalysis in organocatalyzed living radical polymerization was systematically studied over a series of substituted POs. A more electron-donating substitute led to a higher catalytic activity, as experimentally observed and theoretically supported by DFT (density functional theory) calculation. Notably, the polymerization was induced and controlled not only by thermal heating but also by photoirradiation. The polymerization was compatible with several functional monomers and afforded block copolymers. MOE (Min. of Education, S’pore) Accepted version

Substituted benzimidazoles were obtained from o-phenylenediamine and organic halides in solvent-free medium. The procedure involves pyridine N-oxide as mild oxidizing agent. The benzimidazoles were prepared without the separation of the intermediates. The absence of catalysts and good yields are important benefits of the method.

Catalytically active chiral π-conjugated polymers (poly-1(NO)r) bearing pyridine N-oxide pendants were synthesized by ternary copolymerization of a d-glucose-bound diethynyl compound with two types of thieno[3,4-b]thiophene comonomer, one of which contained a pyridine N-oxide group. When the pyridine N-oxide content in the copolymer was 10 mol% (poly-1(NO)0.10), the polymer backbone formed a one-handed helical structure in acetonitrile. Pyridine N-oxide pendants arranged inside the helical cavity of poly-1(NO)0.10 exhibited catalytic activity for the asymmetric allylation of benzaldehydes, producing the corresponding allyl alcohols with up to 43% ee.

A series of dinuclear lanthanide complexes bridged by three pyridine-N-oxide (PyNO) ligands with formula [Dy2(hfac)6(4-cpyNO)3]·4H2O (Dy1), [Gd2(hfac)6(4-cpyNO)3]·4H2O (Gd1), [Dy2(hfac)6(4-mepyNO)3] (Dy2), [Gd2(hfac)6(4-mepyNO)3] (Gd2) (hfac− = hexafluoroacetylacetonate, 4-cpyNO = 4-cyanopyridine N-oxide, 4-mepyNO = 4-Methylpyridine N-oxide), and series of dinuclear lanthanide complexes bridged by two PyNO ligands with formula [Dy2(hfac)6(4-cpyNO)2] (Dy3), [Y2(hfac)6(4-cpyNO)2] (Y1), [Gd2(hfac)6(4-cpyNO)2] (Gd3), [Dy2(hfac)6(4-mepyNO)2] (Dy4), [Y2(hfac)6(4-mepyNO)2] (Y2), [Gd2(hfac)6(4-mepyNO)2] (Gd4), were structurally and magnetically characterized. The crystal structures revealed that pyridine-N-oxide serves as an effective bridge to link two Ln(III) centers, and periphery β-diketonate ligands complete the coordination sphere. The number of PyNO bridge can be rationally controlled by the stoichiometric ratio of reagents, which leads to different local coordination models and intramolecular Ln-Ln distances. Furthermore, elaborate modulation on the strength of magnetic coupling transmitted by PyNO bridge was successfully carried out by introducing electron-donating or -withdrawing substituents on the bridge ligand backbone. Magnetic measurements revealed that complex Dy3 displayed significant double zero-field slow magnetic relaxation process, while Dy1 and Dy2 showed field-induced SMM behavior. Significantly enhanced SMMs performance was observed in Dy4 with a hysteresis temperature of 2.5 K. The distinct slow magnetic relaxation behaviors were strongly related to their different individual Dy(III) ion magnetic anisotropy and Dy(III)-Dy(III) coupling, which were further confirmed by ab initio calculation.

An improved, safe, and scalable isolation process for (substituted) pyridine and quinoline N-oxides in quantitative yields along with high purities using the m-CPBA–NH3(g) system is described. The safety was assessed by reaction calorimetry and differential scanning calorimetry studies for possible hazards during the conversion and isolation steps. Careful interpretation of the data substantiated the safety and scalability. The process flow is simplified to meet the industrial requirements of safety, cost-effectiveness, and utility minimization. The reaction was safely demonstrated at a 2.5 kg scale.

Photoinduced electron transfer (PET) with the formation of stable radicals plays an importance role in many areas. However, the discovery of new photoresponsive moieties is still a challenge. In this work, pyridine N-oxide group itself was demonstrated to possess photoinduced electron transfer (PET) property for the first time. The radical of 4-phenyl-pyridine-N-oxide (ppno), generated by PET from oxygen atom to 4-phenyl-pyridine part, remained stable in dark in air at least for two weeks. [ZnCl2(ppno)2], one ppno-based novel crystalline coordination compound, has two electron donors, chlorine and oxygen atoms. In particular, experimental and theoretical calculation results showed that oxygen atoms in [ZnCl2(ppno)2] have dual actions. Firstly, oxygen atom as electron-withdrawing group increased the electron accepting ability of 4-phenyl-pyridine. Then, oxygen atoms themselves are rich in electrons and can act as electron donors. This is exactly why the performance of PET and radical yield and stability of [ZnCl2(ppno)2] much better than ppno. Thus, pyridine N-oxide group as an effective photoresponsive functional motif, whether by interspersion or by coordination, could construct various novel photoresponsive materials.

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-[aquamanganese(II)]-μ2-acetato-μ-(pyridine N-oxide)-manganese(II)-μ3-acetato-μ2-acetato-μ-(pyridine N-oxide)-[aquamanganese(II)]-di-μ2-acetato], [Mn4(CH3COO)8(C5H5NO)2(H2O)2] n , (I), catena-poly[[manganese(II)]-μ3-acetato-μ2-acetato-μ-(2-methylpyridine N-oxide)-[aquamanganese(II)]-di-μ2-acetato-manganese(II)-di-μ2-acetato-μ3-acetato-[aquamanganese(II)]-μ2-acetato-μ-(2-methylpyridine N-oxide)], [Mn4(CH3COO)8(C6H7NO)2(H2O)2] n , (II), and catena-poly[[manganese(II)-di-μ2-acetato-μ-(4-methylpyridine 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-octahedral six-coordinate manganese(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-methylpyridine N-oxide (2MePNO), or 4-methylpyridine 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 molecule forms bridging hydrogen bonds between two neighboring acetates. In compound (III) a water molecule of solvation is found in the lattice, not bound to the metal ion but hydrogen bonding to a bridging acetate.

A facile synthesis of a series of pyrimidinone derivatives from the reaction of benzyl halides, (1-bromoethyl)benzene and urea in the presence of pyridine N-oxide (PNO) under solvent-free conditions is described. This transformation presumeably occurs via oxidation/cross-aldol condensation/Michael addition/intra molecular cyclization, domino sequence, involving the formation of one C–C bond and two C–N bonds in a single step. Pyridine N-oxide (PNO) has been demonstrated to be efficient and mild reagent for the one-pot synthesis of 4,6-diarylpyrimidin-2(1H)-ones (DAPMs) from a variety of benzyl halides and (1-bromoethyl)benzene instead of benzaldehydes and acetophenone respectively with short reaction times and excellent yields.

Three M(II)-coordination polymers (M Zn(II), Mn(II)) were synthesized based on a pyridine N-oxide bridging ligand 3,5-bis(4-carboxylphenyl)-pyridine N-oxide (L1). Compounds 1–3 all have novel complicated structures. Compound 1 (Zn(L1)2(H2O)2) and 2 (Zn2(L1)2(H2O)2) are two single crystals obtained in “one pot” and 1 features 1D double chains motif and 2 features 3D network structure. Compound 3 shows 3D network structure with triangular tunnels. The thermogravimetric analyses and photoluminescence properties were also used to investigate the title compounds.

The extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO3 solutions in the form of complexes with 2,6-bis(diphenylphosphorylmethyl)pyridine N-oxide (I) was studied in relation to the kind of organic diluent and to the HNO3 concentration in the equilibrium aqueous phase. The stoichiometry of the extractable complexes was determined. With respect to the ability to extract Th(IV) and REE(III), compound I considerably surpasses tetraphenylmethylenediphosphine dioxide and tetraalkyl-substituted analogs of I.

The trans–cis- and cis–trans-isomerization of styryl derivatives of heterocyclic N-oxides in acetonitrile and ethanol is studied. The isomerization quantum yields and spectral characteristics of the cis-form of the investigated N-oxides are determined. No thermally induced cis–trans-conversion is detected.

The data on the kinetics of the reaction between hexachlorocyclotriphosphazatriene (the phosphazene) with pyridine N-oxide in mixed organic solvents in the presence of water are presented. The reaction of the phosphazene with pyridine N-oxide leads to the formation of the onium salt. It has been found that water catalyzes this reaction, the catalytic action resulting from the solvation of the polar transition state due to the formation of the phosphazene complex with hydrogen bonding, thus facilitating the rupture of the phosphorus bond with the leaving anion.

Four different coordination compounds have been synthesized and structurally characterized in the reaction of aqueous solution of Mn(NO3)2 with pyridine-N-oxide co-ligands in the presence of KNCS, namely: [Mn(2-methylpyridine-N-oxide)(NCS)2]n (1); [Mn(3-methylpyridine-N-oxide)2(NCS)2]n (2), [Mn(4-methylpyridine-N-oxide)2(NCS)2(H2O)2] (3) and [Mn(4-cyanopyridine-N-oxide)2(NCS)2(H2O)]2 (4). Single crystal X-ray crystallography revealed the polymeric nature of the complexes as 2-D and 1-D for 1 and 2, respectively, with doubly μ(N,S) isothiocyanato bridging and μ(O,O) bridging methylpyridine-N-oxide ligands. The metal centers in the dinuclear complex 4 are linked by doubly μ(N,S) isothiocyanato bridges, whereas only terminal ligands are observed in the mononuclear complex 3. The magnetic properties of the complexes 1, 2 and 4 were investigated over the temperature range 2–300 K.