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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.

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.

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.

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.

Three different coordination polymeric compounds have been synthesized and structurally characterized in the reaction of aqueous solution of Mn(NO3)2·4H2O with methylpyridine-N-oxide co-ligands (Mepy-N-oxide) in the presence of NaN3 depending on the position of the methyl group in Mepy-N-oxide namely: [Mn(μ(O,O)-2-Mepy-N-oxide)(μ1,3-N3)2]n (1), catena-{[Mn(μ1,1-N3)2(H2O)2](3-Mepy-N-oxide)2} (2) and [Mn3(μ1,1-N3)2(μ1,3-N3)4(μ(O,O)-4-Mepy-N-oxide)2(H2O)2]n (3). Single crystal X-ray crystallography revealed the polymeric nature of the complexes as 2D, 1D and 3D networks, respectively with a doubly end-to-end (EE) azide bridging and μ(O,O) bridging 2-Mepy-N-oxide in 1, and a doubly end-on (EO) azide bridging in 2. In complex 3 within the trinuclear subunit the three Mn(II) atoms are bridged via EO azido groups and μ(O,O) bridging 4-Mepy-N-oxide molecules and the trinuclear subunits are connected further by EE azido bridges to generate the 3D network structure. The magnetic properties of the three complexes were investigated over the temperature range 2–300 K. Complex 2, as far as we know, is the first Mn(II) uniform 1D compound with double EO azido bridges which shows antiferromagnetic coupling. The fit of the magnetic data by using the appropriate equation derived from the Hamiltonian H = −∑JSi·Si+1 gives the best fit parameters J = −3.55(1) cm−1, g = 2.044(1).

Group 12 halides and 2,2′-dithiobis(pyridine N-oxide) (dtpo) form the crystalline the 1D coordination polymers [ZnX2(μ-dtpo-κ2O:O′)]n [X = Cl (1), Br (2), I (3)], [Cd3(μ-Cl)4Cl2(μ-dtpo-κ2O:O′)2(CH3OH)2]n (4), [(CdBr2)2(μ3-dtpo-κ3O,O:O′)2(H2O)2]n (5), and [(CdI2)2(μ-dtpo-κ2O:O′)3]n (6) in methanol. The compounds were structurally characterized by single-crystal X-ray analysis. Compounds 1–3 represent an isomorphous series of single-stranded coordination polymers, whereas the CdII derivatives are structurally diverse. The metal nodes in 4 and 5 are trinuclear and dinuclear cadmium clusters, respectively. In 4 and 5, the metal nodes are linked into double-stranded 1D coordination polymers by two dtpo bridging ligands. Compound 6 contains mononuclear CdI2 units as nodes and can be viewed as an alternating copolymer of CdI2(μ-dtpo-κ2O:O′)2 and CdI2(μ-dtpo-κ2O:O′) entities. Owing to the disulfide moiety, the dtpo bridging ligand inevitably exhibits an axially chiral angular structure. The dtpo ligand adopts various coordination modes through the pyridine N-oxide oxygen atoms.

In contrast to the general tendency that six coordinate iron(iii) porphyrin complexes with neutral oxygen ligands adopt a high-spin state in a wide range of temperature, some complexes with substituted pyridine N-oxides have exhibited spin-crossover from high-spin to low-spin states with decreasing temperature both in solution and in the solid state.

The title compound, [HgI2(C10H8N2O2S2)] n , a one-dimensional coordination polymer with HgI2 units and 2,2′-dithiobis(pyridine N-oxide) spacer ligands in an alternating fashion, forms helical chains running along the b axis in the crystal. Within a single coordination polymer strand, the axially chiral 2,2′-dithiobis(pyridine N-oxide) ligands are homochiral, but the enantiomeric conformation is present in adjacent strands. Within a coordination polymer strand, the iodido ligands point towards the centroids of the aromatic rings of the pyridine N-oxide moieties in the coordination sphere of HgII. Moreover, intra-strand C—H...O and C—H...I interactions, and inter-strand short S...I and S...O contacts are observed.

While six-coordinate iron(III) porphyrin complexes with pyridine N-oxides as axial ligands have been studied as they exhibit rare spin-crossover behavior, studies of five-coordinate iron(III) porphyrin complexes including neutral axial ligands are rare. A five-coordinate pyridine N-oxide–5,10,15,20-tetraphenylporphyrinate–iron(III) complex, namely (pyridine N-oxide-κO)(5,10,15,20-tetraphenylporphinato-κ4 N,N′,N′′,N′′′)iron(III) hexafluoroantimonate(V) dichloromethane disolvate, [Fe(C44H28N4)(C5H5NO)][SbF6]·2CH2Cl2, was isolated and its crystal structure determined in the space group P\overline{1}. The porphyrin core is moderately saddled and the Fe—O—N bond angle is 122.08 (13)°. The average Fe—N bond length is 2.03 Å and the Fe—ONC5H5 bond length is 1.9500 (14) Å. This complex provides a rare example of a five-coordinate iron(III) porphyrin complex that is coordinated to a neutral organic ligand through an O-monodentate binding mode.

In the title hydrate, water mol­ecules and N-oxide groups of the main mol­ecule form supra­molecular chains based on R(10) ring motifs., In the title compound, also known as 3,5-lutidine N-oxide dihydrate, C7H9NO·2H2O, the N—O bond is weakened due to the involvement of the O atom as an acceptor of hydrogen bonds from the two water mol­ecules of crystallization present in the asymmetric unit. Fused R 3 5(10) ring motifs based on O—H⋯O hydrogen bonds form chains in the [010] direction, which are further connected by weak C—H⋯O inter­molecular contacts. As a result, the lutidine mol­ecules are stacked in an efficient manner, with π–π contacts characterized by a short separation of 3.569 (1) Å between the benzene rings.

The synthesis and structural characterization of six new d10 Cd(II) and Zn(II) thiocyanato complexes with pyridine-N-oxide compounds: the polymeric catena-[Cd(μ2-2-picoline-N-oxide)(μN,S-NCS)2] (1), catena-[Cd(μ2-3-picoline-N-oxide)(μN,S-NCS)2] (2), catena-[Cd(4-nitropyridine-N-oxide)2(μN,S-NCS)2] (3), the dinuclear [Cd(4-cyanopyridine-N-oxide)2(μN,S-NCS)(NCS)(H2O)]2 (4) and the mononuclear complexes [Zn(2-picoline-N-oxide)2(NCS)2(H2O)] (5) and [Zn(4-cyanopyridine-N-oxide)2(NCS)2(H2O)] (6) are reported. Single crystal X-ray crystallography revealed the 2D polymeric nature in complexes 1 and 2, the 1D chain in 3 and the dimeric structure in complex 4 with the doubly-bridged Cd(μN,S-NCS)2Cd moiety. Five-coordinate monomeric Zn(II) complexes were obtained in 5 and 6, where the thiocyanto ligands are acting as monodentate N-bonded. The emission spectral properties of the six complexes were investigated. Very strong enhancing fluorescence intensity was observed in complex 3.

The synthesis and structural characterization of two new polymeric zinc(II) azido complexes with pyridine- N -oxide derivative co-ligands, namely catena- [Zn(4-methylpyridine- N -oxide)(μ 1,1 –N 3 ) 2 ] ( 1 ) and catena- {[Zn 2 (μ 2 -isonicotinato- N -oxide) 2 (μ 1,1 –N 3 ) 2 (H 2 O) 3 ](H 2 O)} ( 2 ) are reported. Single crystal structure determination revealed the penta-coordinated geometry of the Zn(II) centers in the polymeric chains of 1 with di-EO azido bridging mode, whereas five and six coordination modes around Zn(II) centers are observed in complex 2 , and the 1D system is formed via alternating single EO-azide and μ(O,O′)-bridging carboxylate group of the isonicotinato- N -oxide molecules. The solid state luminescence properties of 1 were examined.

Aromatic N-oxides interact with Cmethyl-resorcinarene resulting in marked changes in the conformation of the host resorcinarene. In the solid state, 2- and 3-methylpyridine N-oxides form pseudo-capsular 2 : 2 endo host-guest complexes with Cmethyl-resorcinarene stabilized by C-H⋯π interactions. The Cmethyl-resorcinarene·2-methylpyridine N-oxide complex has a C4v crown conformation, while the Cmethyl-resorcinarene·3-methylpyridine N-oxide complex has a slightly open C2v boat conformation. On the contrary, other para-substituted and benzo-fused pyridine N-oxides form only exo complexes with Cmethyl-resorcinarene. In the exo complexes, the asymmetry of the guest, conformational flexibility and preferred inter-host hydrogen bonding of Cmethyl-resorcinarenes exclude endo complexation. All the exo complexes form robust 1-D hydrogen bonded chains between the host hydroxyl groups assisted by the guest N-O groups, resulting in a C2v boat conformation.

As an extension of our interest in pyridine-N-oxide-dicarboxylic acids, we report the design and synthesis of a 2D coordination polymer {[Cu(Hpydco)2]·2H2O}n (1) based on the pyridine-N-oxide-2,5-dicarboxylic acid ligand (H2pydco). Compound 1 was characterized using infrared spectroscopy, CHN-elemental analyses, TGA and single crystal X-ray diffraction (SCXD). Structural analysis showed that this compound is a two-dimensional coordination polymer created by four-connected nodes defined by the copper ion and bridging Hpydco–ligands which created regular tetragons. In the packing, hydrogen bonds connect adjacent 2D sheets to extend the structure into a 3D architecture. Since H2pydco and pyridine-2,5-dicarboxylic acid have similar frameworks, we also highlight some areas of current interest in their coordination behavior by surveying reported structures (Cambridge Structural Database (CSD)) and have investigated the influence of the N-oxide moiety on the coordination mode(s) in the crystal lattice. Finally, DFT calculations have been used to compare H2pydco and pyridine-2,5-dicarboxylic acid ligands and their ability to interact with Cu(II).

In the title co-crystal, C10H8N2O2S2·H2O2, both molecules are generated by crystallographic twofold symmetry; the dihedral angle between the pyridine rings is 101.16 (9)°. In the crystal, the components are linked by O—H...O hydrogen bonds to generate [010] chains of alternating 2,2′-dithiobis(pyridineN-oxide) and hydrogen peroxide molecules. The structure was refined as a two-component inversion twin.

In the title compound, C5H3ClN2O3 (systematic name: 2-chloro-4-nitropyridin-1-ium-1-olate), the nitro group is essentially coplanar with the aromatic ring, with a twist angle of 6.48 (8)°. The molecular packing exhibits a herringbone pattern with the zigzag running along the b axis; here, there are no short contacts, hydrogen bonds, or π–π interactions.

A strategy for threading an axle having a hydrogen bond acceptor unit in the cavity of a C3v symmetric amido-amine macrobicycle is investigated. The macrobicycle acts as a wheel in its neutral as well as triprotonated states to form threaded architectures with a pyridine N-oxide derivative. The negative oxygen dipole of the axle is capable of [2]pseudorotaxane formation in two different orientations with the wheel in its neutral and triprotonated states.

Pyridine and 2-picolinic acid N-oxides form 2 : 2 and 2 : 1 ligand : metal (L : M) discrete L2M2 and polymeric complexes with CuCl2 and Cu(NO3)2, respectively, with copper(ii) salts. The N-oxides also form 1 : 1 host-guest complexes with methylresorcinarene. In combination, the three components form a unique 2 : 2 : 1 host-ligand-metal complex. The methylresorcinarene acts as a reaction vessel/protecting group to control the coordination of copper(ii) from cis-see-saw to trans-square planar, and from octahedral to square planar coordination geometry. These processes were studied in solution and in the solid state via(1)H NMR spectroscopy and single crystal X-ray diffraction.

New cationic silver-containing ionic liquids were synthesized and used as non-aqueous electrolytes for the electrodeposition of silver layers. In the liquid state of these ionic liquids, a silver (I) cation is coordinated by pyridine-N-oxide (py-O) ligands in a 1 : 3 metal-to-ligand ratio, although in some cases a different stoichiometry of the silver center crystallized out. As anions, bis(trifluoromethanesulfonyl)imide (Tf₂N), trifluoromethanesulfonate (OTf), methanesulfonate (OMs) and nitrate were used, yielding compounds with the formulae [Ag(py-O)₃][Tf₂N], [Ag(py-O)₃][OTf], [Ag(py-O)₃][OMs] and [Ag(py-O)₃][NO₃], respectively. The compounds were characterized by CHN analysis, FTIR, NMR, DSC, TGA and the electrodeposition of silver was investigated by cyclic voltammetry, linear potential scans, scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). With the exception of [Ag(py-O)₃][Tf₂N], which melts at 108 °C, all the silver(I) compounds have a melting point below 80 °C and were tested as electrolytes for silver electrodeposition. Interestingly, very high current densities were observed at a potential of −0.5 V vs. Ag/Ag⁺ for the compounds with fluorine-free anions, i.e. [Ag(py-O)₂][NO₃] (current density of −10 A dm¯²) and [Ag(py-O)₃][OMs] (−6.5 A dm¯²). The maximum current density of the compound with the fluorinated anion trifluoromethanesulfonate, [Ag(py-O)₃][OTf], was much lower: −2.5 A dm¯² at −0.5 V vs. Ag/Ag⁺. Addition of an excess of ligand to [Ag(py-O)₃][OTf] resulted in the formation of the room-temperature ionic liquid [Ag(py-O)₆][OTf]. A current density of −5 A dm¯² was observed at −0.5 V vs. Ag/Ag⁺ for this low viscous silver salt. The crystal structures of several silver complexes could be determined by X-ray diffraction, and it was found that several of them had a stoichiometry different from the 1 : 3 metal-to-ligand ratio used in their synthesis. This indicates that the compounds form crystals with a composition different from that of the molten state. The electrochemical properties were measured in the liquid state, where the metal-to-ligand ratio was 1 : 3. Single crystal X-ray diffraction measurements showed that silver(I) is six coordinate in [Ag(py-O)₃][Tf₂N] and [Ag(py-O)₃][OTf], while it is five coordinate in the other complexes. In [Ag₃(py-O)₈][OTf]₃, there are two different coordination environments for silver ions: six coordinate central silver ions and five coordinate for the outer silver ions. In some of the silver(I) complexes, silver–silver interactions were observed in the solid state. Poster presentation by Jeroen Sniekers ispartof: Dalton Transactions vol:43 issue:4 pages:1589-1598 ispartof: location:Tallinn (Estonia) status: published

Two new polymeric complexes of cadmium(II) and manganese(II) with Pyridine- N -oxide (pyo) mediated by thiocyanate and dicyanamide (dca) anions have been synthesized and characterized by X-ray single crystal structure analysis. The structural analyses reveal that complexes [Cd(pyo) 2 (SCN) 2 ] n ( 1 ) and [Mn(pyo) 2 (dca) 2 ] n ( 2 ) [where, pyo = pyridine- N -oxide; dca = dicyanamide] are 2D coordination polymers. In complex 1 hexa-coordinated Cd(II) centers posses distorted octahedral coordination environments. Each Cd(II) is coordinated by four SCN - in end to end fashion forming a zigzag chain and two pyo monodentate ligands bridge two adjacent Cd(II) centers leading to a two-dimensional sheet structure. In complex 2 hexa-coordinated Mn(II) centers posses octahedral coordination environments. The coordination polymer constitute a 2D polymeric sheet and has a (4, 4) grid network architecture Successive stacking of coordination polymeric sheets are enforced by inter layer OH⋯O and OH⋯N hydrogen bonding. The luminescence properties of these two polynuclear complexes in solid state were studied and complex 1 exhibits higher luminescence intensity than 2 .

To understand how deuterium and fluorine substituents influence the supramolecular architecture of pyridine N-oxide crystals, the crystal structure of 3-fluoropyridine N-oxide (PNO-3F) was determined and the crystal packing motives of non-deuterated pyridine-N-oxide (PNO), partial-deuterated pyridine-N-oxide (PNO-D) and PNO-3F were analyzed based on ab initio quantum-chemical calculations of the intermolecular interaction energy, using the MP2/6-311G(d,p) method. The appearance of the weak-directing substituents deuterium and fluorine leads to significant changes in the crystal organization of the isotropic packing of PNO molecules.

To “mark” the nitrogen atoms in phenyl-(2-pyridyl)-(3-pyridyl)-(4-pyridyl)methane (1), we have synthesized the corresponding tris(pyridine N-oxide) 2 by oxidation of 1 with m-chloroperbenzoic acid. The nitrogen atoms of 2 are unequivocally determined by the X-ray crystal analysis of a single crystal of rac-2 whereas the nitrogen atoms cannot be assigned at all in the case of rac-1. N-Oxide 2 can be resolved by chiral high-performance liquid chromatography under similar conditions to those used for the resolution of 1. The calculated circular dichroism (CD) curve for (R)-1 on the basis of time-dependent density functional theory reproduces the experimental spectra very well to suggest that the second-eluted fraction ([CD(+)283]-2) is the R isomer, namely (R)-[CD(+)283]-2. The independent absolute configuration determinations for 1 and 2 are in keeping with the chemical correlation between the two compounds by oxidation of (R)-2 into (R)-1. Chirality 2011. © 2011 Wiley-Liss, Inc.

Two new complexes, [Cu(bppdo)(Hbppdo)(CH3CN)3][PW12O40]·CH3CN·0.5H2O (1) and [Co(2,2′-bpdo)3]2[PWVWVI11O40]·CH3CN·2H2O (2) (bppdo = 1,3-bis(4-pyridyl)propane-N,N′-dioxide, 2,2′-bpdo = 2,2′-bipyridine-N,N′-dioxide), have been synthesized by layering MHPW12O40 salts (M = Cu2+ for 1 and Co2+ for 2) on the organic bppdo (for 1) or 2,2′-bpdo (for 2) ligands with the mixed media of acetonitrile and water at room temperature. Both complexes were fully characterized by elemental analyses, TG analyses, IR, UV–Vis, cyclic voltammetry and single-crystal X-ray diffraction. Both crystal structures exhibit the new polyoxometalate (POM)-templated supramolecular network arrays. The “host” supramolecular networks with large pores are composed of the [Cu(bppdo)(Hbppdo)(CH3CN)3] ring-connected-ring chains for 1 and the [Co(2,2′-bpdo)3] windstick-type units for 2. The “guest” Keggin-type polyoxoanions are located in the pores and dispersed between two organic layers in both complexes. Electrochemical properties of 1 and 2 were investigated and both compounds show the electrocatalytic activity towards the reduction of nitrite.

A number of 15 new solvates containing pyridine-N-oxide of the general formula M(C5H5NO)mn+ (anion)n− is reported. In these compounds M = Li, Na, Mg, Ca, Sr, Ba, Mn, Fe, Co, Cu, Zn, Cd, Pb, and Tl, n = 1-3, m = 3-8, and the anions are ClO4− and BF4−. The compounds are identified by chemical analysis and by means of physical measurements. The shift towards lower wave numbers in the N-O stretching frequency of the complexes is discussed. Far-infrared spectra in the region 700-200 cm−1 have also been investigated. A correlation between νNO and νMO is reported. Ligand-field spectra for the transition-metal solvates of Co(II) and Ni(II) have been re-investigated. New values for Dq and B are reported, and the ligand is placed in the spectrochemical and nephelauxetic series. The Mossbauer spectrum of Fe(C5H5NO)6(ClO4)2 is discussed. Electron paramagnetic resonance spectra of the solvates of Mn(II), Ni(II), and Cu(II) have been investigated. No static Jahn-Teller distortion of the species Cu(C5H5NO)62+ is observed at room temperature. Pyridine-N-oxide is concluded to be a rather strong ligand, as reflected by the facts that preparation of metal solvates is often possible from the hydrated metal salts without dehydration, and the rather high values of Dq/B calculated from the spectra of the cobalt(II) and nickel(II) solvates.

A simple method for synthesis of manganese(II) coordination polymers with different benzoate ligands and pyridine N-oxide having general composition [Mn(RC6H4CO2)2(PyO)] n is presented (where PyO = pyridine N-oxide and R = H, 1a; R = 4-NO2, 1b; R = 4-Cl, 1c; R = 4-OH, 1d; R = 2-NO2, 1e). All these polymers are characterized by X-ray crystallography and other spectroscopic techniques. The coordination polymers have similar structures, but the positions of the manganese atoms differ. For example, 1c is highly symmetric and a mirror plane exists between each manganese site (2/m). In 1d, the manganese centers are related by an inversion center (−1) whereas in 1e the manganese centers are related by C1 rotation (1). Reaction of manganese(II) acetate tetrahydrate with 4-chlorobenzoic acid and PyO upon crystallization from methanol/pyridine gave crystals of coordination polymer 1c along with aqua-bis-pyridine bis-4-chlorobenzoato manganese(II) (2). The structure of 2 also determined by single-crystal X-ray diffr...

Upon combining porphyrin based tectons bearing at the 5,10 meso positions either two pyridine or two pyridine N-oxide groups, with Cd2+ or Cu2+, four ribbon-type 1-D networks were obtained and structurally characterised in the crystalline phase by X-ray diffraction methods. Although, based on tecton’s structural features, the formation of ribbon-type architectures could be anticipated, their deformation, resulting from the geometry of the connecting metal centres as well as the packing forces in the solid state, could not be predicted.

The crystal structure of the compound (C5H7N2O)·(C6H4NO3)·H2O (1) consisting of 2-amino-3-hydroxypyridium, isoniconate-N-oxide and lattice water was characterized by single-crystal X-ray diffraction analysis: monoclinic, P21/c, a = 9.6905(8), b = 6.0040(4), c = 21.039(2) A, β = 101.062(8)°, V = 1201.34(18) A3, Z = 4. In 1, the deprotonated isoniconate-N-oxide, the protonated 2-amino-3-hydroxypyridium and the lattice water are linked by a series of classical hydrogen bonds to form 2-D layer. Then, these 2-D sheets assemble to a 3-D network via weak hydrogen bonds.

In the title compound, C5H4BrNO, there are two molecules in the asymmetric unit that are related by a pseudo-inversion center. The two independent molecules 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 theb-axis direction. The least-squares plane containing the rings of both asymmetric molecules and the plane containing the symmetrically related molecules make a plane–plane angle of 66.69 (10)°, which makes the bend of the herringbone pattern. The bromo group on one molecule points to the bromo group on the neighboring molecule, with a Br...Br intermolecular distance of 4.0408 (16) Å. The herringbone layer-to-layer distance is 3.431 (4) Å with a shift of 1.742 (7) Å. There are no short contacts, hydrogen bonds, or π–π interactions.

Two Co2+ metal-organic framework materials, constructed from a combination of 1,4-benzenedicarboxylate (BDC) and either 2,2′-dipyridyl-N-oxide (DPNO) or 2,2′-dipyridyl-N,N′-dioxide (DPNDO), are synthesized under solvothermal reaction conditions, and their structures solved by single crystal X-ray diffraction. Both have three-dimensional structures that contain octahedral Co2+ centers with μ2-(η2)-BDC, and bidentate DPNO or DPNDO coligands that bridge pairs of metal centers but do not contribute toward the overall connectivity of the framework. Co3(BDC)3(DPNO)2 contains trimers of trans corner-shared Co-centered octahedra with one type of bridging BDC ligand forming terminal edges of the trimers, bridging to neighboring trimer units, and a second type, bridging pairs of metals and also connecting neighboring trimers. Co2(BDC)2(DPNDO) is constructed from one-dimensional inorganic chains consisting of cis- and trans-corner shared Co2+-centered octahedra. The DPNDO ligand is bis-bidentate, forming the edges of one type of octahedron and the trans corners of the second type, with the coordination for both octahedra completed by bridging BDC linkers, which in turn connect the inorganic chains to yield a three-dimensional structure. Thermogravimetric analysis shows both materials contain trapped solvent, and while Co3(BDC)3(DPNO)2 is unstable with respect to solvent loss, Co2(BDC)2(DPNDO), and its magnesium analogue, can be desolvated to yield permanently porous materials that show thermal stability up to 300 °C. For Co2(BDC)2(DPNDO), gas adsorption studies show permanent microporosity with moderate uptake of small gas molecules (N2, CO2, CH4, and C2H6), supported by Grand Canonical Monte Carlo calculations based on the assumption of rigid crystal structures, while gravimetric analysis shows rapid and reversible methanol adsorption at ambient pressure for both the Co and Mg analogues of the framework.

The title three-component cocrystal, C6F3I3·2C5H5NO·H2O, has been prepared as a strong candidate for multiple I⋯O interactions. Its crystal structure is compared with its 1:1 close relative, C6F3I3·C5H5NO [Aakeröy et al. (2014a ). CrystEngComm, 16, 28-31]. The 1,3,5-trifluoro-2,4,6-triiodobenzene and water species both have crystallographic twofold axial symmetry. The main synthon in both structures is the π-π stacking of benzene rings, complemented by a number of O-H⋯O, C-F⋯π and, fundamentally, C-I⋯O interactions. As expected, the latter are among the strongest and more directional interactions of the sort reported in the literature, confirming that pyridine N-oxide is an eager acceptor. On the other hand, the structure presents only two of these contacts per 1,3,5-trifluoro-2,4,6-triiodobenzene molecule instead of the expected three. Possible reasons for this limitation are analyzed. Fil: Raffo, Pablo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Cukiernik, Fabio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Baggio, Ricardo Fortunato. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina

The absolute configuration of the resolved axially chiral pyridine- N -oxide derivative, (±)- trans -2,6-di- ortho -tolyl-3,4,5-trimethylpyridine- N -oxide, has been determined by VCD and ECD analyses supported by TD-DFT calculations carried out at different levels of theory. DFT calculations confirmed that in spite of the two biaryl axes, the compound is conformationally less flexible and the major conformer is stabilized by two weak hydrogen bonds formed between the hydrogen of the methyl group of the tolyl moieties and the nitroxide oxygen. The experimental VCD spectra of this compound and the previously studied (±)-2,6-di-sec-butyl-4-methylpyridine-N-oxide with two stereogenic centers were compared in the frequency range 1200–1300 cm −1 . A (+,−,+)/(−,+,−) pattern of bands was observed in both cases. By replacing the sec -butyl moieties with tolyl ones, the VCD peaks shifted toward higher frequencies and the intensities were increased.

The new ligand 4′-(4‴-pyridyl-N-oxide)-2,2′:6′,2″-terpyridine (pyNoxterpy) and its homoleptic iron(II) complex have been synthesised, and structural and spectroscopic studies have been carried out. The obtained results have been compared with the reported data for the parent ligand 4′-(4‴-pyridyl)-2,2′:6′,2″-terpyridine (pyterpy) and its homoleptic iron(II) complex. Significant differences between the spectral and electrochemical properties of the metal complexes have been found, derived from the changes in the electronic properties of the coordinated ligands.

Solid equimolar complexes of pyridine, 2-picoline, and 2,6-lutidine N-oxides with iodine are studied. External pressure can induce a first-order phase transition in the latter complex. The solid-phase dipole moments of neighboring molecules of complexes have an antiparallel orientation, and much high-polarity intermediates are formed in certain cases. The mechanism of the solid-phase dielectric relaxation at radio frequencies involves activated translations both of these associates and of free polar molecules. The mechanism of electrical conductivity is primarily electronic in the solid phase and primarily ionic in melt. More mobile in most crystal phases are holes, and electron-hole pairs is generated by long-wave intracomplex transitions.

We determined crystal structures of [(PyO)D][AuCl4], [(PyO)4D3][AuCl4]3 and [(PyO)3D2][AuCl4]2 (PyO: pyridine N-oxide) at room temperature (1/1, 4/3 and 3/2 D-salts, respectively). The powder X-ray diffraction patterns of these salts (D-salts) were identical to those of the corresponding ones having normal hydrogen (H-salts) unlike the case of [(PyO)2D/H][AuCl4]. In the crystals of the 4/3 and 3/2 salts, there exist not only the monomer-type protonic adducts of PyO, but also dimer-type adducts in which two PyO units are bridged by a proton. A few types of aggregation of AuCl4 units (sheet and ribbons) were found in these crystals. The variety in the aggregation motif of the anion and that in the structure of the cation seem to be related to the presence of the various salts having several base-to-acid ratios. The isotope effect on the preparation of the salts is discussed. 35Cl NQR and phase transitions of these compounds are also reported.

Molybdenum complexes of 3,6-di-tert-butylcatechol have been prepared from the reaction between [Mo(CO)6] and 3,6-di-tert-butyl-1,2-benzoquinone. A putative "[MoO(3,6-DBCat)2]" monomer is assumed to form initially by reaction with trace quantities of oxygen. Condensation of the reaction mixture leads to the formation of oligomeric products, including the [{MoO(3,6-DBCat)2}4] chiral square isolated by chromatographic separation. Molybdenum centers at the corner of the square are bridged by oxo ligands centered along edges. Four-fold and inversion crystallographic symmetry gives tetramers as either or isomers, and the crystal structure consists of parallel columns of squares with the same chirality. Addition of O-Subst (O-Subst = dmso, pyridine N-oxide, triphenylarsine oxide) ligands to [MoO(3,6-DBCat)2] occurs selectively to give cis-[MoO(O-Subst)(3,6-DBCat)2] products. All three addition complexes are fluxional in solution. The temperature-dependent stereodymanic behavior of [MoO(dmso)(3,6-DBCat)2] has been shown to occur via a trigonal prismatic intermediate (Bailar twist) that conserves the cis disposition of oxo and dmso ligands. Electrochemical and chemical reduction reactions have been investigated for [MoO(dmso)(3,6-DBCat)2] with interest in displacement of SMe2 with formation of cis-[MoO2(3,6-DBCat)2]2-. Cyclic voltammetry shows an irreversible two-electron reduction for the complex at -0.852 V (vs Fc/Fc+). Chemical reduction using CoCp2 was observed to give a product with an electronic spectrum that is generally associated with cis-[MoO2(Cat)2]2- complexes. Structural characterization revealed that the product was [CoCp2][MoO(3,6-DBCat)2], possibly formed as the product of dmso displacement upon one-electron reduction of [MoO(dmso)(3,6-DBCat)2]. (Less)

The interaction of pyridine-N-oxide (pyNO) and 3-picoline-N-oxide (3picNO) with zinc(II) and cadmium(II) azides afforded complexes with empirical formulae Zn(N3)2(pyNO)(H2O)2, Zn(N3)2(3picNO)2(H2O)2 and Cd(N3)2(3picNO)2(H2O)2. The IR spectra of these complexes are measured and discussed. X-Ray single crystal diffraction showed for the first complex, which should be formulated as {[Zn(N3)2(H2O)2](pyNO)}n, to consist of 1D chains of trans-[Zn(N3)2(H2O)2]n, double end-on (μ-1,1) azido bridges and noncoordinated pyNO molecules. The other two complexes are isomorphous containing 1D trans-[M(N3)2(H2O)2]n, double (μ-1,1) azido bridges, and hydrogen bonded noncoordinated 3picNO molecules. Each pyridine-N-oxide molecule forms three hydrogen bonds, whereas the 3-picoline-N-oxides form two hydrogen bonds. The metal centers exhibit distorted octahedral geometry.

A tridentate ligand (Hpoxap=2-(o-hydroxyphenyliminomethyl)pyridine N-oxide) has been synthesised by the Schiff condensation of 2-pyridinecarboxaldehyde N-oxide with 2-aminophenol. A series of copper(II) complexes with this ONO-donor ligand has been prepared and their spectroscopic properties (electron, vibration, ESR) were studied. The structures for two complexes have been determined by X-ray analysis. The structure of [Cu(poxap)(OAc)] consists of isolated neutral molecules in which the copper(II) atom is situated in a slightly distorted square-planar surrounding. The structure of [Cu(poxap)(H2O)(NO3)] consists of neutral molecules which are interconnected by hydrogen bonds giving rise to a ladder structure of copper(II) ions with two different Cu⋯Cu distances of 5.27 and 7.41 A. The copper atoms are in a slightly distorted square-pyramidal environment with the tridentate ligand poxap− and the water molecule in the basal plane; the apical position being occupied by an oxygen atom of the nitrate anion. Magnetic susceptibility studies were undertaken and these confirm predominantly a dimeric character of the complex.

A new complex of hexa(isothicyanato)chromate(III) hydro-bis(pyridine N-oxide) [(PyО)2H]3[Cr(NCS)6] was synthesized and studied by X-ray diffraction analysis. The coordination polyhedra of Cr atoms are the perfect octahedra that form the layered structure. Molecules of pyridine N-oxide form bimolecular cationic associates that compensate the charge on the complex anions. The crystals are triclinic: a = 11.559(2) A; b = 12.644(3) A; c = 16,110(4) A; α = 90.02(2)°; β = 95.15(2)°; γ = 98.23(2)°; V = 2320.6(9) A3; ρcalcd = 1.394 g/cm3. Z = 2, space group P1¯.

International audience; We report the synthesis of a cyclen-based ligand (4,10-bis[(1-oxidopyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid=L1) containing two acetate and two 2-methylpyridine N-oxide arms anchored on the nitrogen atoms of the cyclen platform, which has been designed for stable complexation of lanthanide(III) ions in aqueous solution. Relaxometric studies suggest that the thermodynamic stability and kinetic inertness of the Gd(III) complex may be sufficient for biological applications. A detailed structural study of the complexes by (1) H NMR spectroscopy and DFT calculations indicates that they adopt an anti-Δ(λλλλ) conformation in aqueous solution, that is, an anti-square antiprismatic (anti-SAP) isomeric form, as demonstrated by analysis of the (1) H NMR paramagnetic shifts induced by Yb(III) . The water-exchange rate of the Gd(III) complex is ${k{{298\hfill \atop {\rm ex}\hfill}}}$=6.7×10(6) s(-1) , about a quarter of that for the mono-oxidopyridine analogue, but still about 50 % higher than the ${k{{298\hfill \atop {\rm ex}\hfill}}}$ of GdDOTA (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The 2-methylpyridine N-oxide chromophores can be used to sensitize a wide range of Ln(III) ions emitting in both the visible (Eu(III) and Tb(III) ) and NIR (Pr(III) , Nd(III) , Ho(III) , Yb(III) ) spectral regions. The emission quantum yield determined for the Yb(III) complex (${Q{{{\rm L}\hfill \atop {\rm Yb}\hfill}}}$=7.3(1)×10(-3) ) is among the highest ever reported for complexes of this metal ion in aqueous solution. The sensitization ability of the ligand, together with the spectroscopic and relaxometric properties of its complexes, constitute a useful step forward on the way to efficient dual probes for optical imaging (OI) and MRI.

An improved crystal structure of the title compound, C6H6N2O3, is reported. The structure, previously solved [Liet al.(1987).Jiegou Huaxue (Chin. J. Struct. Chem.),6, 20–24] in the orthorhombic space groupPca21and refined toR= 0.067, has been solved in the orthorhombic space groupPbcmwith data of enhanced quality, giving an improved structure (R= 0.0485). The molecule adopts a planar conformation with all atoms lying on a mirror plane. The crystal structure is composed of molecular sheets extending parallel to theabplane and connectedviaC—H...O contacts involving ring H atoms and O atoms of theN-oxide and nitro groups, while van der Waals forces consolidate the stacking of the layers.

C 12 H 20 N 6 NiO 6 S 2 or NiL 2 (SCN) 2 ](NH 4 ) 2 .2H 2 O, where L is 2-hydroxy-pyridine-N-oxide, has been prepared and characterized using elemental analyses, IR, UV and visible spectrometry, magnetic moment measurements, thermal analyses and single crystal X-ray analyis. The results indicate that the complex reacts as a bidentate ligand and is bound to the metal ion via the two oxygen atoms of the ligand (HL). The activation energies, ∆ E*, entropies ∆S*, enthalpies ∆H* and order of reactions have been derived from differential thermogravimetric (DTA) curves. Based on inhibition zone diameter measurements, the complex exhibited significant antibacterial activity against both Staphylococcus aureus and Escherichia coli. It also exhibited significant antifungal activity against Candida albicans, but no activity was found against Aspergillus flavus . The crystal structure of the Ni(II) complex [C 12 H 20 N 6 Ni O 6 S 2 ], Mr = 467.17, was determined from Cu Kα X-ray diffraction data, λ = 1.54178 A, at 100 K using direct methods. The crystals are monoclinic, space group P2 1 /n with Z = 4 and a = 8.9893(2) A, b = 17.6680(5) A, c = 12.5665(3) A, β = 108.609(1)°. In parallel with this study corresponding results were derived for the crystal structure determined independently from synchrotron X-ray diffraction data, λ = 0.61990 A, at 100 K. The unit cell parameters derived in this experiment are a = 9.000(2) A, b = 17.700(4) A, c = 12.590(3) A, β = 108.61(3)°. Both studies show 4 O and 2 N atoms coordinating Ni in a distorted octahedral arrangement. Each of the Ni 2-hydroxy-pyridinium-N-oxide moieties is highly planar and the S=C=N-Ni ligands are approximately linear. The crystal structure is characterised by a number of strong hydrogen bonds.

The Schiff condensation of the 2-pyridinecarboxaldehyde N-oxide with 2-aminophenol yielded a tridentate ligand, abbreviated as Hpoxap. This ligand is a base of a series of mononuclear complexes [M(poxap)2] and trinuclear complexes of the type [M(poxap)MX4M(poxap)], where X is an acetate or chloro bridge. The X-ray structure of the complex [Zn(poxap)Zn(OAc)4Zn(poxap)]·H2O has been determined: this complex forms a pair of distortion isomers differing slightly in bond lengths and bond angles within the chromophores. The copper(II) doping gave mixed crystals suitable for the ESR spectroscopy (g‖=2.282, g⊥=2.016, A‖=135 G, A⊥=26 G). The magnetic susceptibility of an analogous [Cu(poxap)CuCl4Cu(poxap)] trinuclear complex at low temperature indicates a slight antiferromagnetic interaction (JCuCu/hc=−5.2 cm−1, gCu=2.285).

The condensation reaction of 2-pyridinecarboxaldehyde N-oxide with ethylenediamine yields the tetradentate ligand L1=poxen. Hydrogenation then produces tetrahydropoxen, L2=H4-poxen, which has been isolated in a free form. Several metal complexes of the formula [M(H4-poxen)](ClO4)2·nH2O have been prepared (M=Mn, Cu and Zn) and investigated. The X-ray structure of [Cu(H4-poxen)H2O](ClO4)2·H2O shows that the copper atom is pentacoordinate, the poxen ligand forming a base of the tetragonal pyramid; the aqua ligand is situated in the apical position inside the cavity formed by the ligand arms. In contrast, in the case of [Co(poxen)H2O](ClO4)2, the apical aqua ligand is situated outside the ‘cavity’ formed by the dehydrogenated ligand arms.

Rare earth picrates addition compounds with 2,2′-dithiobis(pyridine-N-oxide) (dithio) were synthesized and characterized. CHN analysis suggest a general formula Ln(pic) 3 ·1.5dithio·4H 2 O (Ln = La, Nd, Eu, Dy, Ho). IR spectra indicate: (a) the presence of water molecules; (b) the presence of picrate in bidentade form; and (c) a bond of dithio to the RE through NO groups. Parameters, calculated from Nd absorption spectra at room temperature are in agreement with a small covalent character of the Ln:L interaction. Thermogravimetric data under N 2 and air atmospheres, show that: (a) the water molecules loss is the first decomposition step (up to 453 K); (b) the residue, at ca. 1173 K, is essentially Ln 2 O 3 .

Twenty one ternary complexes of lanthanide with 3,5-di-tert-butyl-gamma-resorcylic acid (L) and seven different substituted pyridine-N-oxides (L1-7), with compositions of REL3L21-7. nH(2)O (RE=Nd, Gd, Er; L-1=4-picoline-N-oxide; L-2=4-phenyl-pyridine-N-oxide; L-3=pyridine-N-Oxide; L-4=3-picoline-N-oxide; L-5 =quinoline-N-oxide; L-6=iso-quinoline-N-oxide; L-7=4-methoxyl-pyridine-N-oxide; n=0, 1, 2, 5), were synthesized and characterized by means of elemental analysis, electrical conductivity, thermal analysis and IR spectra. The novel crystal structure of ErL3L23.(EtOH) has been determined by a single-crystal X-ray diffraction method. It shows that each erbium ion is linked to three 3,5-di-tert-butyl-gamma-resorcylic acid ions through two different types of dentation modes in which only the carboxylate oxygen atoms participate. The coordination geometries of erbium ion can be described as a distorted octa-coordinated bicapped trigonal prism. (C) 1999 Elsevier Science Ltd. All rights reserved.

The crystal and molecular structure of (C 5 H 5 NO) 2 ·HClO 4 has been determined at room temperature by X-ray diffraction. The compound crystallizes in the monoclinic C2/c space group with a =10.597(3), b =8.919(2), c =13.716(2) A and β =103.99(2)°. The unit cell contains four ClO 4 anions and four homoconjugated cations. The proton in the symmetric hydrogen-bond has been located on the two-fold axis and the O⋯H + ·⋯O bridge has the following geometry: O⋯O=2.429(4) A and + ⋯O=176(1)°. The structure of the title complex has also been analyzed by the HF/6-31G(d,p), PM3 and SAM1 methods. In the calculations, the hydrogen-bonded proton is located asymmetrically in the bridge and the pyridine rings are not equivalent. The distances between the proton and the Cl atom of the perchlorate ion are: 4.18 and 4.74 A (crystal), 3.98 A (PM3), 5.07 A (HF) and 9.23 A (SAM1). The results of 1 H NMR studies have revealed no pyridine ring reorientations, which means that in the time scale of this method the cation is rigid. The solid state FTIR spectrum of the complex shows a broad absorption extending from ca. 1700 down to 400 cm −1 , due to the H-bond vibration. This absorption is absent in Raman and inelastic neutron scattering spectra. The frequencies of the skeletal vibrations are also analyzed.

The asymmetric unit of the title compound, C21H16N4O4·4CH3OH, consists of a quarter molecule of tetrakis(1-oxidopyridin-2-yl)methane and one methanol solvent molecule. In the crystal, the pyridineN-oxide derivative is located about a fourfold rotoinversion axis and exhibitsS4symmetry along thecaxis. An intermolecular O—H...O hydrogen bond is observed between the O atom of the pyridineN-oxide and the OH group of the methanol. An intermolecular C—H...O bond is also observed between adjacent pyridineN-oxide rings.

X-ray structures are reported for Cu(poph)Cl 2 , [Cu(pxo)Cl 2 ] 2 and the new complex [Cu(pxo)(pxo-H)Cl] 2 (poph = 2-pyridinecarboxaldehyde 1-oxide 2′-pyridinylhydrazone; pxo = 2-acetylpyridine 1-oxide oxime), and correlated with magnetic properties. The complex Cu(poph)Cl 2 has a monomeric square pyramidal structure. The ligand coordinates to the basal plane as an ONN tridentate, and two coordinated chlorides complete the five-coordination. The apical chloride in each complex is hydrogen-bonded to the hydrazine hydrogen in an adjacent Cu(poph)Cl 2 species. This produces a centrosymmetric, hydrogen-bonded dimeric arrangement. The complex [Cu(pxo)Cl 2 ] 2 has a dimeric N -oxide-bridged structure, involving square pyramidal coordination. Planar coordination is produced by an ON-bonded pxo ligand and two chlorides. Each planar ‘Cu(pxo)Cl 2 ’ entity is linked by an apical out-of-plane N -oxide bridging bond to another equivalent entity. The new complexes Cu(pxo)(pxo-H)Hal (Hal = Cl, Br) are reported. The complex [Cu(pxo)(pxo-H)Cl] 2 has a six-coordinate dimeric N -oxide-bridged structure. A new mode of coordination by pxo has been identified in which neutral and deprotonated pxo molecules are hydrogen-bonded together, producing planar N 2 O 2 coordination. Each five-coordinate ‘Cu(pxo)(pxo-H)Cl’ entity is linked by an apical out-of-plane N -oxide bridging bond to another equivalent entity.

International audience; Centro-symmetric dinuclear complexes of formula [Ln(tta)(3)(L)](2)*xCH(2)Cl(2), (tta(-) = 2-thenoyltrifluoroacetonate anion, x = 0.5 for Ln = Eu (1a), Tb (3), and Dy (4) and x = 0 for Ln = Eu (1b) and Nd (2)) have been synthesized using the tetrathiafulvalene-3-pyridine-N-oxide as a bridging ligand (L). X-ray structures have shown the formation of channels with CH(2)Cl(2) solvent inside. 1 is stable with both filled channels (at 150 K) and empty channels (at room temperature). The Dy(III) analogue displays a complex butterfly like hysteresis loop at 1.5 K. Photophysical properties of the coordination complexes have been studied by solution and solid-state absorption spectroscopy. Time-dependent density functional theory (TD-DFT) calculations have been carried out on the diamagnetic Y(III) derivative to shed light on the absorption spectrum. For 2, the excitation of the charge transfer transitions induces line shape emission in the near-infrared spectral range assigned to (4)F(3/2) → (4)I(9/2), (4)F(3/2) → (4)I(11/2), and (4)F(3/2) → (4)I(13/2) neodymium centered transitions. The reversible redox-activity of the ligand L makes possible an original sensitization process involving a ligand centered charge separation followed by energy transfer to the Nd(III) ion upon recombination.