Bridging Nitrate Research Articles

Structure and luminescence of a nitrate-bridged heterotrinuclear Cu2-Pr complex with compartmental Schiff base ligand

A unique heterotrinuclear nitrate-bridged complex of hexanitrate praseodymium(III) and dicopper(II) compartmental species has been synthesized and characterized by X-ray single crystal structure analysis. The structure determination indicates that the dinuclear copper moiety undergoes a tilted deformation (with respect to the dicopper complex) upon connection to the lanthanide species via a rare nitrate bridge. The trinuclear species is highly fluorescent owing to the presence of praseodymium.

Dimerization of Dendrimeric Lanthanide Complexes: Thermodynamic, Thermal, and Liquid-Crystalline Properties

A series of 10 different mesomorphic semidendrimeric tridentate ligands L5-L14 grafted with terminal cyanobiphenyl groups have been synthesized. Upon reaction with Ln(NO(3))(3) (Ln = trivalent lanthanide), the central 2,6-bis(N-ethylbenzimidazol-2-yl)pyridine unit is meridionally tricoordinated to the metal to give rodlike monomeric [Ln(Lk)(NO(3))(3)] and H-shaped dimeric [Ln(2)(Lk)(2)(NO(3))(6)] complexes. For the small Lu(III) cation, the monomeric complexes are quantitatively formed in a noncoordinating CD(2)Cl(2) solution. For larger cations (Ln = Eu, Pr), the thermodynamic equilibrium 2[Ln(Lk)(NO(3))(3)] ↔ [Ln(2)(Lk)(2)(NO(3))(6)] can be evidenced across the complete ligand series. Detailed thermodynamic studies show that the dimeric complexes result from the formation of primary intermetallic nitrate bridges whose strength depends on the metallic size. For each complex, secondary nonspecific interstrand van der Waals interactions produce nonartifactual enthalpy/entropy compensation. In the absence of solvent, only the complexes with the most extended ligands L5 and L6 produce thermotropic mesophases. Layered organizations are dominant (smectic A) with the induction of nematogenic behavior at high temperature when interstrand interactions are modulated by methyl substitutions. Correlations between the trend of dimerization and the sequences of thermotropic mesophases are attempted.

Hexafluorophosphate salts of bis and tetrakis(2,2′-bipyridine)lead(II) complexes

Both bis- and tetrakis-substituted 2,2′-bipyridine complexes of lead(II), [Pb(bpy)2](PF6)2 and [Pb(bpy)4](PF6)2 · bpy, respectively, have been characterized by X-ray crystallography as hexafluorophosphate salts when three equivalents of bipyridine is combined with Pb(NO3)2 in aqueous solution prior to metathesis. The tetrakis-substituted product, [Pb(bpy)4](PF6)2 · bpy, shows an unusual combination of intramolecular and intermolecular π-stacking of two of the bipyridine ligands throughout the crystal. Incomplete metathesis also produces a catenated, mixed-anion complex, [Pb(bpy)2(µ-NO3)](PF6), where the nitrate bridges lead(II) metal centers to form a 1-D coordination polymer. If metathesis is carried out using perchlorate, a known [Pb(bpy)2](ClO4)2 analog is produced along with [bpyH](ClO4), which has not been previously characterized by X-ray crystallography.

Synthesis and crystal structure of two new lead(II) coordination polymers with substituted 2,2′-bipyridine ligands with dicyanamide and nitrate as co-ligands

The two lead(II) coordination polymers [Pb(4,4′-dm-2,2′-bpy)(Dca)(NO 3)] n ( 1) and [Pb(4,4′-dmo-2,2′-bpy)(Dca)(NO 3)] n ( 2) were prepared by treatment of lead(II) nitrate, sodium dicyanamide with 4,4′-dimethyl-2,2′-bipyridine and 4,4′-dimethoxy-2,2′-bipyridine, respectively. Both polymers were characterized by elemental analysis, IR and 1H NMR spectroscopy, thermogravimetric analysis and X-ray crystallography. The coordination polymers can be described as one-dimensional double-chains with Pb(II) centers bridged by Dca and nitrate co-ligands, containing trinuclear rings, [Pb 3(L) 3(NO 3) 2(Dca)], and bridging nitrate and Dca co-ligands in cis and trans positions, respectively. The coordination number of the Pb(II) ions in 1 and 2 is seven, with the PbN 4O 3 coordination polyhedron containing a stereochemically active lone pair of electrons with hemi-directed coordination spheres. The polymer chains form networks via supramolecular interactions that include O⋯O, C H⋯O, C H⋯N interactions, in addition to hydrogen bonding and π–π stacking.

Selective catalytic reduction of NO with NH 3 over manganese substituted iron titanate catalyst: Reaction mechanism and H 2O/SO 2 inhibition mechanism study

Selective catalytic reduction (SCR) of NO with NH 3 over Mn substituted iron titanate catalyst (Fe 0.75Mn 0.25TiO x ) was fully investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy. At relatively low temperatures, both ionic NH 4 + and coordinated NH 3 contributed to the SCR reaction, and both bridging nitrate and monodentate nitrate were confirmed to be the reactive nitrate species. In the SCR reaction condition, surface NH 4NO 3 species was formed as intermediate species and its reactivity was also proved. An NH 3-SCR mechanism over Fe 0.75Mn 0.25TiO x at low temperatures was proposed accordingly, in which the reduction of NH 4NO 3 by NO was possibly the rate-determining step. Due to the mild and reversible inhibition effect of H 2O on NH 3/NO x adsorption, the SCR activity decline in the presence of H 2O was also slight and recoverable; however, the inhibition effect of SO 2 was much more intense and irreversible, because the formation of nitrate species was totally inhibited by the formation of sulfate, resulting in the cut-off of the SCR reaction pathway at low temperatures.

A tetranuclear copper(II) complex with bis( o-aminobenzaldehyde)thiocarbohydrazone

Bis( o-aminobenzaldehyde)thiocarbohydrazone (HL) forms with copper(II) nitrate a tetranuclear complex [Cu 2(L)(NO 3) 3] 2·2H 2O, in which two dinuclear units are joined by nitrate bridges. The dihydrazone ligand behaves ditopically, providing NNS and NNN binding sites, with the four coppers essentially in a square-pyramidal geometry. The tetranuclear molecule displays intramolecular magnetic interactions, with the antiferromagnetic exchange (−2 J = 210(1) cm −1) between the copper(II) ions within each dinuclear moiety dominant over weak interdimer ferromagnetic coupling.

{6,6′-Dimethoxy-2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato-1κ4O1,O1′,O6,O6′:2κ4O1,N,N′,O1′}(ethanol-1κO)-μ-nitrato-1:2κ2O:O′-dinitrato-1κ4O,O′-samarium(III)zinc(II)

In the title heteronuclear ZnII–SmIII complex, [SmZn(C18H18N2O4)(NO3)3(CH3CH2OH)], with the hexa­dentate Schiff base compartmental ligand N,N′-bis­(3-methoxy­salicyl­idene)ethyl­enediamine (H2 L), the SmIII and ZnII ions are triply bridged by two phenolate O atoms from the Schiff base ligand and one nitrate anion. The five-coordinate ZnII ion is in a square-pyramidal geometry formed by the donor centers of two imine N atoms, two phenolate O atoms and one of the bridging nitrate O atoms. The SmIII center is in a ten-fold coordination of O atoms, involving the phenolate O atoms, two meth­oxy O atoms, one ethanol O atom, and two O atoms from two nitrate anions and one from the bridging nitrate anion. In the crystal, inter­molecular O—H⋯O and C—H⋯O inter­actions generate a layer structure extending parallel to (101).

Tetrakis(6-methyl-2,2′-bipyridine)-1κ2N,N′;2κ2N,N′;3κ2N,N′;4κ2N,N′-tetra-μ-nitrato-1:2κ2O:O′;2:3κ3O:O′,O′′;2:3κ3O,O′:O′′;3:4κ2O:O′-tetranitrato-1κ4O,O′;4κ2O,O′-tetralead(II)

In the tetranuclear centrosymmetric title compound, [Pb4(NO3)8(C11H10N2)4], irregular PbN2O5 and PbN2O4 coordination polyhedra occur. The hepta­coordinated lead(II) ion is bonded to two bidentate and one monodentate nitrate ion and one bidentate 6-methyl-2,2′-bipyridine (mbpy) ligand. The six-coordinate lead(II) ion is bonded to one bidentate and two monodentate nitrate anions and one mbpy ligand. In the crystal, bridging nitrate anions lead to infinite chains propagating in [111]. A number of C—H⋯O hydrogen bonds may stabilize the structure.

Lanthanide Complexes with Cucurbit[n]urils (n = 5, 6, 7) and Perrhenate Ligands: New Examples of Encapsulation of Perrhenate Anions

The reaction of lanthanide nitrates with cucurbit[n]urils (CBn, n = 5, 6, 7) under hydrothermal conditions in the presence of perrhenic acid and, for some of them, other reactants such as KNO(3) yielded 14 new complexes which were crystallographically characterized and present some original features. Four of the five complexes with CB5 are capsules closed by a lanthanide ion (Ce, Sm, Gd) on one side and potassium on the other and have an encapsulated bridging nitrate ion, but the fifth is a monodimensional polymer with both bidentate portals of CB5 complexed to ytterbium. All eight CB6 complexes (Ce, Pr, Sm, Gd, Yb, Lu) and the single ytterbium complex of CB7 (the first lanthanide complex of CB7 to be characterized) involve perrhenate encapsulation, in a form which is either bridging the lanthanide ions coordinated at each tridentate portal, or terminal when the CB is bidentate and the cation is further from the portal, or even noncoordinating in one case. The orientation of the cation in the cavity varies depending upon its coordination mode, as well as the nature of the shortest contacts in the cavity. Some original architectures are described, in particular a sinuous chain, ribbonlike assembly in a cerium complex of CB6 and a novel samarium-CB6 sandwich complex. The ubiquitous encapsulation of ReO(4)(-) in CB6 and CB7 may open new perspectives for the investigation of anion complexation by these macrocycles.

IRMPD Spectroscopy of Anionic Group II Metal Nitrate Cluster Ions

Anionic group II metal nitrate clusters of the formula [M(2)(NO(3))(5)](-), where M(2) = Mg(2), MgCa, Ca(2), and Sr(2), are investigated by infrared multiple photon dissociation (IRMPD) spectroscopy to obtain vibrational spectra in the mid-IR region. The IR spectra are dominated by the symmetric and the antisymmetric nitrate stretches, with the latter split into high and low-frequency components due to the distortion of nitrate anion symmetry by interactions with the cation. Density functional theory (DFT) is used to predict geometries and vibrational spectra for comparison to the experimental spectra. Calculations yield two stable isomers: the first one contains two terminal nitrate anions on each cation and a single bridging nitrate ("mono-bridging"), while the second structure features a single terminal nitrate on each cation with three bridging nitrate ligands ("tri-bridging"). The tri-bridging isomer is calculated to be lower in energy than the mono-bridging one for all species. Theoretical spectra of the tri-bridging structure provide a better qualitative match to the experimental infrared spectra of [Mg(2)(NO(3))(5)](-) and [MgCa(NO(3))(5)](-). However, the profile of the low-frequency nu(3) band for the Mg(2) complex suggests a third possible isomer not predicted by theory. The IRMPD spectra of the Ca(2) and Sr(2) complexes are better reconciled by a weighted summation of the spectra of both isomers suggesting that a mixture of structures is present.

Formation of Crystalline Polymers from the Reaction of Amine-Functionalized C60 with Silver Salts

Three new crystalline compounds of Ag(I) with fullerene-containing ligands, the piperidine adduct [C(60)(N(CH(2)CH(2))(2)N)] and the fullero[60]pyrrolidine [C(60)(CH(2)N(CH(3))CH(2))], have been prepared and characterized by X-ray crystallography. The polymeric structure of {[C(60)(N(CH(2)CH(2))(2)N)][Ag(O(2)CCF(3))](2)}.CS(2) consists of linear chains composed of two distinct molecules of the functionalized fullerene, with four Ag(I) ions attached to the four nitrogen atoms and four bridging trifluoroacetate ions. Two of the four Ag(I) ions form eta(2)-bonds to carbon atoms in different regions of the fullerene cage, and there is one close Ag-Ag contact (3.1657(7) A) as well. These chains are further cross-linked by bridging trifluoroacetate ions. The structure of {[C(60)(CH(2)N(CH(3))CH(2))]Ag(NO(3))}.0.25CH(3)OH involves two similar polymeric chains in which Ag(I) ions bind to the nitrogen atom of one N-methyl-3,4-fullero[60]pyrrolidine ligand and to a carbon atom of another N-methyl-3,4-fullero[60]pyrrolidine in eta(1)-fashion for one chain and in distorted eta(2)-fashion in the other. Additionally, each Ag(I) ion is bonded to two oxygen atoms from two bridging nitrate ions. On the other hand, [C(60)(N(CH(2)CH(2))(2)N)](2)Ag(NO(3)).0.5CH(3)OH.CH(2)Cl(2) is a simple coordination complex with two very large ligands attached to Ag(I). Coordination of Ag(I) to C(60) produces much smaller alterations to the fullerene geometry than does coordination of Pt(0)(PPh(3))(2) or Ir(I)(CO)Cl(PPh(3))(2) groups.

Synthesis and spectroscopic studies of mixed-ligand complexes of lead(II) hexafluoroacetylacetonate including the crystal structure of [Pb2(phen)4(hfa)2(𝛍-NO3)2

Four new mixed-ligand complexes of lead(II) hexafluoroacetylacetonate (hfa) were synthesized and characterized by elemental analyses, IR, 1H and 13C NMR spectroscopy. The single-crystal structure of [Pb2(phen)4(hfa)2(μ-NO3)2] (1) shows the complex to be a dimeric unit as a result of nitrate bridging. The coordination number of Pb(II) is eight with four N-donors from a “phen” and four O-donors from the hexafluoroacetylacetonate and nitrate ligands. This dimeric complex is the first fluorine β-diketonate and nitrate mixed-ligand lead(II) complex that has been characterized by X-ray structural analysis. The supramolecular features in this complex are controlled by weak directional intermolecular interactions and aromatic π–π stacking interactions.

Adsorption and reaction of NO 2 on ordered alumina films and mixed baria–alumina nanoparticles: Cooperative versus non-cooperative reaction mechanisms

In order to obtain insights into the mechanism and kinetics of adsorption and reaction of NO 2 on aluminum and barium oxide surfaces, we have performed systematic adsorption experiments on single-crystal-based model materials. As a model surface, we use BaO containing nanoparticles grown by physical vapor deposition (PVD) of Ba under ultrahigh vacuum (UHV) conditions on an ordered Al 2O 3 film on NiAl(110) and subsequent oxidation and annealing. The growth behavior, the morphology and the chemical composition of the three-dimensional mixed barium aluminum oxide particles (BaAl 2 x O 1 + 3 x ) formed via this procedure have previously been characterized by scanning tunneling microscopy (STM) and high-resolution photoelectron spectroscopy (HR-PES). In order to monitor adsorption and reaction processes on these systems, we perform time-resolved infrared reflection absorption spectroscopy (TR-IRAS) during exposure to a molecular beam (MB) of NO 2. In a first step, the interaction of NO 2 with the Al 2O 3/NiAl(110) model support is probed. At 100 K, only molecular adsorption occurs in form of the D 2h dimer (N 2O 4) in all coverage regions from the submonolayer up to multilayers. At 300 K, a slow surface reaction occurs, initially leading to the formation of surface nitrites and, subsequently, of surface nitrates in bridging adsorption geometry. On the BaAl 2 x O 1 + 3 x particles on Al 2O 3/NiAl(110), NO 2 shows a very different and strongly temperature-dependent behavior. At 100 K, molecular adsorption of the D 2h dimer (N 2O 4) is accompanied by a highly efficient reaction channel, leading to the formation of surface nitrites and nitrates. With the surface temperature increasing to 300 K, however, the reaction probability decreases by several orders of magnitude. In contrast to reaction at 100 K, surface nitrites in flat-lying adsorption geometry are the only primary product, indicating a temperature-dependent change in the reaction mechanism from a cooperative to a non-cooperative pathway. With increasing exposure, the nitrite coverage increases and, finally, the surface nitrites are converted into bridging and monodentate surface nitrates. The latter reaction shows a complex kinetics, including an initial induction period. For temperatures of 400 K and above, nitrate formation becomes more efficient, eventually resulting in the formation of ionic nitrates. The vibrational properties of these ionic species sensitively depend on the reaction temperature, indicating the formation of well-defined structures in a narrow temperature interval around 500 K. The mechanism of the NO x storage process and the vibrational assignments of the related surface species are critically discussed on the basis of the present results.

Desorption of Nitric Acid From Boehmite and Gibbsite

Solid-state Fourier transform infrared spectroscopy (FTIR), evolved gas analysis-FTIR (EGA-FTIR), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC) have been used to investigate the desorption of nitric acid from boehmite and from gibbsite. Samples containing between 3 and 36% of adsorbed nitric acid by mass were prepared by placing the mineral in a 70% nitric acid solution or by the adsorption of nitric acid vapors in humid air. FTIR established that water-solvated nitrate was the main species adsorbed on the surface of either mineral under these conditions. The water-solvated nitrate vaporized as nitric acid at approximately 400 K with an enthalpy of desorption of approximately 50 kJ/mol for both surfaces. A second nitric acid desorption occurred at approximately 450 K and had an enthalpy of desorption of 85 kJ/mol (95 kJ/mol) for boehmite (gibbsite). This was assigned as desorption of partially solvated aluminum hydroxylated nitrate. Monodentate and bridging nitrate were also observed on the boehmite. These species desorbed at approximately 725 K as NO2 and O2 with an enthalpy of reaction of approximately 55 kJ/mol of NO2 desorbed.

An in situ Fourier transform infrared study on the mechanism of NO reduction by acetylene over mordenite-based catalysts

Selective catalytic reduction of NO with acetylene (C 2H 2-SCR) over mordenite-based catalysts (HMOR, 0.5% Mo/HMOR and NaMOR) was investigated by in situ Fourier transform infrared spectroscopy. A possible mechanism was proposed to explain catalytic performance of the mordenite-based catalysts in the C 2H 2-SCR: Nitrosonium ions (NO +) and bidentate nitrate are reactive nitric species towards acetylene at 250 °C. Isocyanate species thus formed are then hydrolyzed to acid amide species that are crucial intermediate of the C 2H 2-SCR. Bridging nitrate species become reactive towards the reductant when reaction temperature increased to 300 °C. Molybdenum loading on HMOR zeolite considerably increased the population of bridging nitrate species and therefore enhanced the title reaction above 300 °C.

{μ-6,6′-Dimethoxy-2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}-μ-nitrato-dinitratoholmium(III)zinc(II)

In the title heteronuclear ZnII–HoIII complex (systematic name: {μ-6,6′-dimeth­oxy-2,2′-[ethane-1,2-diylbis(nitrilo­methyl­idyne)]diphenolato-1κ4 O 1,O 1′,O 6,O 6′:2κ4 O 1,N,N′,O 1′)-μ-nitrato-1:2κ2 O:O′-dinitrato-1κ4 O,O′-holmium(III)zinc(II)), [HoZn(C18H18N2O4)(NO3)3], with the hexa­dentate Schiff base compartmental ligand N,N′-bis­(3-methoxy­salicyl­idene)ethyl­enediamine (H2 L), the Ho and Zn atoms are triply bridged by two phenolate O atoms of the Schiff base ligand and one nitrate ion. The five-coordinate Zn atom is in a square-pyramidal geometry with the donor centers of two imine N atoms, two phenolate O atoms and one of the bridging nitrate O atoms. The HoIII center has a ninefold coordination environment of O atoms, involving the phenolate O atoms, two meth­oxy O atoms, two O atoms from two nitrate ions and one from the bridging nitrate ion. Weak inter­molecular C—H⋯O inter­actions generate a two-dimensional double-layer structure.

{μ-6,6′-Dimethoxy-2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}-μ-nitrato-dinitratoterbium(III)zinc(II)

In the title heteronuclear ZnII—TbIII complex (systematic name: {6,6′-dimeth­oxy-2,2′-[ethane-1,2-diylbis(nitrilo­methyl­id­yne)]diphenolato-1κ4 O 6,O 1,O 1′,O 6′}:2κ4 O 1,N,N′,O 1′-μ-nitrato-1:2κ2 O:O′-dinitrato-1κ4 O,O′-terbium(III)zinc(II)), [TbZn(C18H18N2O4)(NO3)3], with the hexa­dentate Schiff base compartmental ligand N,N′-bis­(3-methoxy­salicyl­idene)ethyl­enediamine (H2 L), the Tb and Zn atoms are triply bridged by two phenolate O atoms of the Schiff base ligand and one nitrate ion. The five-coordinate Zn atom is in a square-pyramidal geometry with the donor centers of two imine N atoms, two phenolate O atoms and one of the bridging nitrate O atoms. The TbIII center has a ninefold coordination environment of O atoms, involving the phenolate O atoms, two meth­oxy O atoms, two O atoms from two nitrate ions and one from the bridging nitrate ion. Weak inter­molecular C—H⋯O inter­actions generate a two-dimensional layer structure.

Identifying surface species by vibrational spectroscopy: Bridging vs monodentate nitrates

Identification of surface species by IR spectroscopy is often based on common knowledge, with a clear risk of misassignment. Combining density functional theory (DFT) and IR reflection absorption spectroscopy (IRAS), we investigated surface nitrate formation on BaO/Al 2O 3 thin films. We found that it is not possible to identify coordination geometries of nitrates based solely on their vibrational frequencies. For metal-supported thin films, however, differences in polarization of the NO stretching modes facilitate unambiguous identification. In contrast to traditional assignments, we show that both bridging and monodentate nitrates are formed on BaO, whereas on Al 2O 3 bridging nitrates dominate.

{μ-6,6′-Dimethoxy-2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}-μ-nitrato-dinitratoeuropium(III)zinc(II)

In the title heteronuclear ZnII–EuIII complex [systematic name: {6,6′-dimeth­oxy-2,2′-[ethane-1,2-diylbis(nitrilo­methyl­idyne)]diphenolato-κ4 O 1,O 1′,O 6,O 6′:2κ4 O 1,N,N′,O 1′}-μ-nitrato-1:2κ2 O:O′-dini­trato-1κ4 O,O′-europium(III)zinc(II)], [EuZn(C18H18N2O4)(NO3)3], with the hexa­dentate Schiff base compartmental ligand N,N′-bis­(3-methoxy­salicyl­idene)ethyl­enediamine (H2 L), the Eu and Zn atoms are triply bridged by two phenolate O atoms of the Schiff base ligand and one nitrate ion. The five-coordinate Zn atom is in a square-pyramidal geometry with the donor centers of two imine N atoms, two phenolate O atoms and one of the bridging nitrate O atoms. The EuIII center has a ninefold coordination environment of O atoms, involving the phenol­ate O atoms, two meth­oxy O atoms, two O atoms from two nitrate ions and one from the bridging nitrate ion. Weak inter­molecular C—H⋯O inter­actions generate a two-dimensional double-layer structure.

Poly[μ2-(N-hydroxypyridine-2-carboxamidine)-μ2-nitrato-silver(I)

In the title complex, [Ag(NO3)(C6H7N3O)]n or [Ag(NO3)(pyaoxH2)] (pyaoxH2 is N-hydroxy­pyridine-2-carboxamidine), the Ag+ ion is bridged by the pyaoxH2 ligands and nitrate anions, giving rise to a two-dimensional mol­ecular structure. Each pyaoxH2 ligand coordinates to two Ag+ ions using its pyridyl and carboxamidine N atoms, and the OH and the NH2 groups are uncoordinated. Each nitrate anion uses two O atoms to coordinate to two Ag+ ions. The Ag⋯Ag separation via the pyaoxH2 bridge is 2.869 (1) Å, markedly shorter than that of 6.452 (1) Å via the nitrate bridge. The two-dimensional structure is fishscale-like, and can be described as pyaoxH2-bridged Ag2 nodes that are further linked by nitrate anions. Hydrogen bonding between the amidine groups and the nitrate O atoms connects adjacent layers into a three-dimensional network.