Hydrothermal synthesis,crystal structure and physical properties of {[Gd(H2O)4(μ2-C6NO2H5)2Gd(H2O)4](μ3-C6NO2H4)2(ZnCl3)2} · 2H2O · 2Cl

A bimetallic 4f–3d tetranuclear complex {[Gd(H₂O)₄(μ₂-C₆NO₂H₅)₂Gd(H₂O)₄](μ₃-C₆NO₂H₄)₂(ZnCl₃)₂} · 2H₂O · 2Cl (1) has been synthesized via hydrothermal reaction and structurally characterized by single-crystal X-ray diffraction. Complex 1 is characterized by a tetranuclear Gd₂Zn₂ structure with the gadolinium and zinc atoms interconnected by isonicotinic acid ligands. The tetranuclear species of {[Gd(H₂O)₄(μ₂-C₆NO₂H₅)₂Gd(H₂O)₄](μ₃-C₆NO₂H₄)₂(ZnCl₃)₂} link to isolated chlorine ions and water molecules via π?π interactions and hydrogen bonds to yield a 3-D supramolecular framework. Photoluminescent investigation reveals that the title complex displays an emission in ultraviolet region. The solid-state diffuse reflectance spectra of 1 reveal the presence of a sharp optical gap of 3.66 eV.     

Divalent metal complexes of formylhydrazine: Syntheses and crystal structures of M(CH4N2O)2(H2O)2·2NO3 (M = Zn,Co)

The syntheses and crystal structures of Zn(CH₄N₂O)₂(H₂O)₂·2(NO₃) (1) and Co(CH₄N₂O)₂(H₂O)₂·2(NO₃) (2), the first well-characterised metal complexes of formylhydrazine (fh), are described. In both compounds, the fh acts as an N,O-bidentate ligand in a centrosymmetric [M(fh)₂(H₂O)₂]²⁺ cation, with charge balance supplied by nitrate counter ions. The packing for the two compounds are quite different: in 1, chains of [Zn(fh)₂(H₂O)₂]²⁺ units are seen in the triclinic unit cell, whereas in the monoclinic structure of 2, sheets of cations occur. This might arise because the conformations of the five-membered chelate rings for the ligands are slightly different, with that for 2 showing a greater degree of puckering.     

Coordination of cobalt(III), nickel(II), copper(II), palladium(II) and platinum(II) with N-ethyl-N′-(4′-methylthiazol-2′-yl)thiourea (HL)

Coordination complexes of formula [ML₂], [CoL₃], [Pd(HL)Cl₂], [CuLCl(H₂O)] and [CuL₂(H₂O)₂] {L=anion of N-ethyl-N^′-(4^′-methylthiazol-2′-yl)thiourea; M=Pt^II, Pd^II or Ni^II} were prepared and characterized by elemental analyses, magnetic susceptibilities, and by IR, NMR, electronic and mass spectral measurements.     

Synthesis and characterization of sol–gel derived PVA-titanium dioxide (TiO<Subscript>2</Subscript>) nanocomposite

Novel PVA/TiO₂ polymer nanocomposites have been prepared at low temperature via sol–gel route. XRD analysis showed the particles to be elongated along a- and b-direction but contracted along c-direction. PVA-assisted TiO₂ nanocomposite samples dried at a temperature of 35 °C were found to have ~12 nm particle size. It was found that the composite nanoparticles had an increased degree of crystallinity in comparison to pure TiO₂ dried at 80 °C. TEM analysis depicted the formation of highly dense nanorods (and prism)-like structure of increasing length and diameter depending on PVA concentration. Our studies revealed that by increasing the concentration of PVA in TiO₂ the band gap was lowered from 3.55 to 1.65 eV. The photoluminescence studies showed that emission shifts towards higher wavelength (417–457 nm) accompanied by a reduction in impurity centres with increasing concentration of PVA in TiO₂.     

Synthesis and Magnetic Properties of Maghemite (γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) Short-Nanotubes

We report a rational synthesis of maghemite (γ-Fe₂O₃) short-nanotubes (SNTs) by a convenient hydrothermal method and subsequent annealing process. The structure, shape, and magnetic properties of the SNTs were investigated. Room-temperature and low-temperature magnetic measurements show that the as-fabricated γ-Fe₂O₃ SNTs are ferromagnetic, and its coercivity is nonzero when the temperature above blocking temperature (T _B). The hysteresis loop was operated to show that the magnetic properties of γ-Fe₂O₃ SNTs are strongly influenced by the morphology of the crystal. The unique magnetic behaviors were interpreted by the competition of the demagnetization energy of quasi-one-dimensional nanostructures and the magnetocrystalline anisotropy energy of particles in SNTs.     

Fluxional Behavior of <Emphasis Type="Italic">cis</Emphasis>-Fe(DMeOPrPE)<Subscript>2</Subscript>(H)<Subscript>2</Subscript> (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane); Implications for the Pressure Swing Purification of Natural Gas

Materials such as trans-Fe(DMeOPrPE)₂(X)(H₂O)⁺ (DMeOPrPE?=?1,2-[bis(dimethoxypropyl)phosphino]ethane; X?=?Cl or H) show considerable promise as sorbents for the removal of N₂ from natural gas in a pressure swing process. One problem, however, is that in long-term tests these sorbents slowly degrade over a period of many weeks. This study probed the degradation mechanism for the purpose of finding ways to stabilize the sorbents. To investigate the likelihood of degradation initiated by Fe–P bond dissociation, the fluxional behavior of the related cis-Fe(DMeOPrPE)₂(H)₂ complex was investigated by variable temperature ¹P{¹H} NMR spectroscopy. Analysis of the spectra gave the following activation parameters for the fluxional process: ΔH^??=?11.6 kcal/mol and ΔS^??=??9.2 cal/mol K. These results suggest that Fe–P bond dissociation (20–45 kcal/mol) is not occurring in the fluxional process and by implication that Fe–P bond dissociation is not initiating the decomposition of the trans-Fe(DMeOPrPE)₂(X)(H₂O)⁺ sorbents. Consequently, macrocycle ligands may not be the best approach for stabilizing the sorbents, as we have previously proposed. A “tetrahedral jump” mechanism is proposed for the fluxional process in cis-Fe(DMeOPrPE)₂(H)₂.     

Synthesis,crystal structure and dehydration kinetics of NaB(OH)<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O

Sodium metaborate tetrahydrate (NaB(OH)₄·2H₂O) was synthesized by reaction of anhydrous borax (Na₂O·2B₂O₃) with sodium hydroxide (NaOH) under conditions at 90 °C for 150 min. The structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM) and Thermogravimetric (TG) analyses. Moreover, dehydration kinetics of NaB(OH)₄·2H₂O was carried out under non-isothermal conditions and the Coats-Redfern method was applied to analyze the TG data for calculation of activation energies (E _a ) and pre-exponential factors (k _o ) for different heating rates. It was determined that dehydration of sodium metaborate tetrahydrate occurred in five steps. According to the Coats-Redfern non-isothermal model, E _a and k _o were calculated as 50.89 kJ/mol and 26×10⁴ min⁻¹ for region I, 18.51 kJ/mol and 0.87×10³ min⁻¹ for region II, 15.72 kJ/mol and 0.52×10³ min⁻¹ for region III, 4.37 kJ/mol and 0.04×10³ min⁻¹ for region IV and 37.42 kJ/mol and 8.56×10³ min⁻¹ for region V, respectively.     

Synthesis and molecular structure of bis(2-benzoylimino-benzimidazolinato)copper(II)-dimethylformamide — a metal-containing guanidine derivative

Bis(2-benzoylimino-benzimidazolinato)copper(II) (1) as the first neutral chelate of an acylimino-benzimidazoline contains guanidine and amide moieties directly coordinated to a metal atom. The ligands are arranged in trans position. The synthesis of cis-bis(pyridine)bis(N-benzoyl-O-ethyl-N′-m-nitrophenyl-isoureato)nickel(II) (2) is described. The molecular structures of both complexes were determined by X-ray crystal structure analysis.     

A metal complex with a pair of nonlinear N–H—Pd(II) interactions; synthesis and structural characterization of PdCl2(R-Bpeap)2 (Bpeap=6-bromo-2-phenylethylaminopyridine)

Reaction of PdCl₂ with R-(+)-6-bromo-2-phenylethylaminopyridine (R-Bpeap) afforded the title complex PdCl₂(R-Bpeap)₂, which shows a pair of nonlinear N–H—Pd(II) interactions.     

A Michael-type reaction between acrylato ions and ethylenediamine coordinated to Ni(II). Synthesis,crystal structure and magnetic properties of [Ni2(EDDP)2(H2O)2] · 2H2O (H2EDDP = ethylenediamine-N,N-dipropionic acid)

The reaction between NiCO₃ · Ni(OH)₂, acrylic acid and ethylenediamine in a 2:4:1 molar ratio affords the binuclear complex, [Ni₂(EDDP)₂(H₂O)₂] · 2H₂O 1. The organic ligand, EDDP^2? (the dianion of the ethylenediamine-N,N-dipropionic acid ligand), results from the addition of one amine group to the carbon–carbon double bonds of two acrylato ions. The crystal structure of 1 consists of neutral centrosymmetric entities, with the nickel ions connected by two carboxylato groups, each one acting as a monoatomic bridge. The intramolecular Ni?Ni distance is 3.212 Å. The metal ions exhibit an octahedral geometry. The cryomagnetic investigation of 1 reveals an antiferromagnetic coupling of the nickel(II) ions (J = ?21.8 cm^?1, H = ?JS_Ni1S_Ni2).     

Synthesis,characterization and acidochromism of Poly (2-<Emphasis Type="Italic">N,N</Emphasis>–dimethylamino-4,6-Bis (2-thienyl)-pyrimidine)

A new monomer (2-N,N-dimethylamino-4,6-Bis (2-thienyl)–pyrimidine) was synthesized and its homopolymer was successfully prepared by using Ferric trichloride (FeCl₃) as an oxidant. The structure of the polymer and monomer was fully characterized by ¹H–NMR, FTIR, UV-vis, Fluorescent spectroscopy and X-ray diffraction pattern. The polymer gives rise to a band at λ _max = 391 nm. The polymer showed the PL spectrum, gave a peak at 507 nm.We have observed that the polymer was sensitive to inorganic acids and the acidochromism behavior was investigated applying organic acid such as CF₃COOH. The corresponding UV-Vis peaks were observed at 464 nm and 357 nm respectively. X-ray diffraction data shows that polymer has a certain crystallinity. The polymer exhibited an [η] value of 0.26 dLg⁻¹ at 25 °C in H₂SO₄ (w = 98%).     

Synthesis of an osmafuran from photochemical hydrolysis of OsCl2(CHC(PPh3)C(O)-η2-CHCH2)(PPh3)2

The η²-alkene coordinated α,β-unsaturated ketone complex Os(CHC(PPh₃)C(O)-η²-CHCH₂)Cl₂(PPh₃)₂ (3) is very stable even at elevated temperature due to the strong steric hindrance effect of PPh₃ ligands. However, compound 3 in a chloroform solution can be almost quantitatively converted into the corresponding osmafuran [OsCl(CO)(PPh₃)₂(CHC(PPh₃)C(CH₃)O)]Cl (6) via hydrolysis of the η²-coordinated olefin under photochemical conditions. Osmafuran 6 has been characterized by single crystal X-ray diffraction analysis, NMR spectroscopy and elemental analysis data. The UV-induced reaction provides a new highly efficient method for preparation of osmafurans by hydrolysis of η²-α,β-unsaturated ketone complexes.     

Use of HPLC in the identification of cis and trans-diaquabis(2,2′-bipyridine)ruthenium(II) complexes: crystal structure of cis-[Ru(H2O)2(bpy)2](PF6)2

[Ru(H₂O)₂(bpy)₂](PF₆)₂ complex was obtained by reacting HPF₆ in a [Ru(CO₃)(bpy)₂] aqueous solution. The complex can exist as cis and trans isomers and usually has been used in the preparation of several ruthenium–bipyridine species. Despite the possibility to have contamination of a specie in another, there is no analytical control involving the characterization of both complexes. Based on this we have proposed the use of high-performance liquid chromatography (HPLC) as an analytical technique to control the purity of cis and trans isomers. The separation was performed using a CLC-ODS column. The cis isomer eluted at 9.4 min while trans isomer eluted at 4.3 min. In aqueous solution the trans and cis isomer configurations were confirmed by NMR spectra (¹H). The attribution of cis isomer was also made based on the X-ray crystal structure (monoclinic, P2_1/c, a=12.320(2), b=13.852(2), c=34.220(3) Å, β=91.89(1)°, Z=8) which is reported. The six-coordinated ruthenium atom is chelated by two bipyridines and two molecules of H₂O.     

Spectral properties of glass (15Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> · 85GeS<Subscript>2</Subscript>) doped with erbium

For chalcogenide glasses in the system (1 – x)[0.15Ga₂S₃ · 0.85GeS₂] · xEr₂S₃, the absorption and luminescence spectra are investigated and the X-ray diffraction analysis is performed. A small shift in the position of the erbium absorption band with the increase of its content in the glass indicates the decrease of the effective charge on it, while the negligible changes in the angle position of the first sharp diffraction peak points to the constancy of the glass’s intermediate-order parameter. The possibility of describing the dependence of the intensity of erbium luminescence on its concentration using the earlier suggested equation has been discussed.     

Synthesis and properties of hyperbranched aqueous poly(urethane–urea) via A<Subscript>2</Subscript> + bB<Subscript>2</Subscript> approach

Hyperbranched aqueous poly(urethane–urea) (HBAPU) was synthesized via A₂ + bB₂ approach using 2,4-tolylene diisocyanate, polycarbonatediol, dimethylol propionic acid and diethanol amine as materials. The structure of the products were characterized by FT-IR and ¹³C NMR. The results showed that the degree of the branching increased with increasing the molar ratio of the nNCO/nOH. The particle size, thermal and mechanical properties were measured by photon correlation spectroscopy, thermal gravimetric analysis and tensile tests, respectively. The particle size of HBAPU was much smaller than that of linear aqueous polyurethane; thermal stability of HBAPU enhanced with decreasing the molar ratio of nNCO/nOH. The tensile tests revealed that HBAPU exhibited excellent tensile properties and the maximum tensile strength was up to 33 MPa.     

Structure of a catalytically active oxo-centered trinuclear cobalt complex triaqua-(μ<Subscript>3</Subscript>-oxo)-hexa(μ<Subscript>2</Subscript>-pivalato-O,O′)-tricobalt(III)

The structure of a catalytically active oxo-centered trinuclear cobalt complex, namely, [triaqua-(μ₃-oxo)-hexa(μ₂-pivalato-O,O′)-tricobalt(III)]¹⁺ · NO ₃ ^? · 3H₂O, has been determined using X-ray diffraction analysis. The compound crystallizes in the hexagonal crystal system, space group of symmetry P6₃/mmc, with the unit cell parameters a = 12.328(1) Å, c = 22.625(1) Å, V = 2978.1(4) ų, Z = 2, and ρ = 1.075 g/cm³. The final discrepancy factor is R1 = 0.0596 for 589 symmetrically nonequivalent reflections with I ? 2σ(I), wR2 = 0.1612, and GooF = 1.035. The high-symmetry complex [C₃₀H₆₀O₁₆Co₃]¹⁺ with symmetry D _6h and a diameter of ～11 Å is an oxo-centered trinuclear cluster consisting of three symmetrically equivalent Co(III) atoms. Among the oxo-centered trinuclear metal complexes known to date, this complex has the highest symmetry and differs by the presence of two chemically equivalent bridges between the metal atoms. Apart from the two positively charged symmetrically equivalent trinuclear complexes, the unit cell contains two symmetrically equivalent NO ₃ ^? ions (statistically disordered over four positions) and six crystal water molecules.     

Palladium‐Catalyzed Decarboxylative Coupling of α‐ Oxocarboxylic Acids with C(sp2)?H of 2‐Aryloxypyridines

An efficient palladium‐catalyzed decarboxylative ortho‐acylation of 2‐aryloxypyridines with α‐oxocarboxylic acids is described. In this new transformation, the aromatic C(sp²) H bond was successfully acylated to give diverse aromatic ketones regioselectively in moderate to good yields. The pyridine group can be removed easily after the acylation to give the corresponding 2‐hydroxy aromatic ketones.     

The first metal chelate of un-substituted 2,6-pyridine-dicarboxamide (pdcam): synthesis,molecular and crystal structure,and properties of [CuII(pdc)(pdcam)] · 2H2O (pdc = 2,6-pyridine-dicarboxylato(2−) ligand)

The compound (2,6-pyridine-dicarboxamide)(2,6-pyridine-dicarboxylato)copper(II) dihydrate ([Cu(pdc)(pdcam)] · 2H₂O, compound 1) has been synthesised by reaction of Cu₂(CO₃)(OH)₂, H₂pdc acid and pdcam in an aqueous-ethanol medium. The new compound has been characterised by thermal, spectral, magnetic and X-ray diffraction methods. Its crystal consists of a 3D hydrogen bonded network where all N–H(amide) bonds of pdcam act as H-donors for O carboxyl(pdc) or water acceptor atoms. The Cu(II) atom exhibits an elongated octahedral coordination, type 4 + 2. Both pdc and pdcam ligands define a nearly orthogonal dihedral angle (88.4°). The anionic pdc acts as mer-NO₂(equatorial) tridentate ligand, supplying three among the four closest to the metal donor atoms (Cu–N 1.913(2), Cu–O 2.022(2) and 2.055(2) Å). The diamide pdcam ligand displays a mer-N(equatorial) + O₂(apical) role (Cu–N 2.007(2), Cu–O(amide) 2.295(2) and 2.305(2) Å), thus showing a remarkable conformational flexibility.