Synthesis,structural characterization and catalytic potential of oxidovanadium(IV) and dioxidovanadium(V) complexes with thiazole-derived NNN-donor ligand

Reaction between the tridentate NNN donor ligand, (E)-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)benzo[d]thiazole (HL), and V₂O₅ in ethanol gave a new vanadium(V) complex, [VO₂L] (1), while the similar reaction by using [V^IVO(acac)₂] as the metal source gave two different types of crystals related to compounds [VO₂L] (1) and [V^IVO(acac)L] (2). The molecular structures of the complexes were determined by single-crystal X-ray diffraction and spectroscopic characterization was carried out by means of FT-IR, UV–vis and NMR experiments as well as elemental analysis. The oxidovanadium(IV) and dioxidovanadium(V) species were used as catalyst precursors for olefin oxidation in the presence of hydrogen peroxide (H₂O₂) as an oxidant. Under similar experimental conditions, the presence of 1 resulted in higher oxidation conversion than 2.     

Sol–Gel Approach to Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> Phosphor from Single Alkoxide Precursors

Syntheses and characterizations of sol–gel precursors of Sr₂CeO₄ were carried out. Each molecular precursor, [Sr₂Ce(OCH₂CH₂OCH₃)₈] (1), [Sr₂Ce(OⁱPr)₈] (2) and [Sr₂Ce₂(OⁱPr)₁₂(ⁱPrOH)₄] (3) was prepared from mixtures of Sr complexes and cerium(IV) alkoxides. The molecular structure of 3 showed that [CeO₆] octahedra are connected with distorted [SrO₆] octahedra by sharing edges with oxo bridges. X-ray powder diffraction patterns and spectrofluorometry were used to determine the evolution of structure from the precursor molecules to the luminescent oxides. The luminescent strontium cerium oxides were derived at relatively mild reaction conditions (700 °C for 1 h), and complete conversion was observed at 1000 °C for 1 h from these precursors. Comparing the spectra of the oxides derived from 2 and 3, the emission intensity of the oxide derived from 2 is much stronger.     

A mechanistic study of the H/D exchange reactions of protonated arginine and arginine-containing Di- and tripeptides

The gas-phase H/D exchange reactions of arginine (R) and arginine-containing di- and tri-peptide (gly-arg (GR), arg-gly (RG), gly-gly-arg (GGR), gly-arg-gly (GRG) and arg-gly-gly (RGG)) [M+H]⁺ ions with deuterated ammonia (ND₃) were investigated by using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR), ion mobility-mass spectrometry (IM-MS), ab initio and density functional theory-based molecular orbital calculations and molecular modeling. Three exchanges are observed for arginine and arginine-containing tri-peptide [M+H]⁺ ions, whereas the di-peptide [M+H]⁺ ions undergo a single H/D exchange. In addition, C-terminal methylation blocks H/D exchange of arginine and the arginine-containing peptide [M+H]⁺ ions, and a single H/D exchange is observed for N-terminal acetylated arginine [M+H]⁺ ions. A general mechanism for H/D exchange involving a collision complex that is best described as a “solvated salt-bridge” structure is proposed.     

Preparation and X-Ray Study of Inclusion Complexes of (4Z,5E)-Pyrimidine-2,4,5,6(1 H,3H)-Tetraone 4,5-Dioxime and the Product of Its Cyclization, (1,2,5)-Oxadiazolo(3,4-d)-Pyrimidine-5,7(4 H,6H)-Dione with Two 18-Membered Macrocycles

The novel dioxime, (4Z,5E)-pyrimidine-2,4,5,6(1H,3H)-tetraone 4,5-dioxime (H₂-PTD) was obtained by the interaction of 6-amino-5-nitrosopyrimidine-2,4(1H,3H)-dione with hydroxylamine hydrochloride. X-ray structural analysis determined the 4Z,5E-configuration of the corresponding monoanion, pyrimidine-2,6(1H,3H)-dione-4-iminole-5-iminolate in the inclusion complexes with diazonia-18-crown-6 (1,4,10,13-tetraoxa-7,16-diazoniacyclooctadecane) (H₂-DA18C6)²⁺ (complex (1), stoichiometry 2 : 1), and its ammonium salt in the complex with the cis-syn-cis isomer of dicyclohexano-18-crown-6(DCHA) (cis-syn-cis-2,5,8,15,18,21-hexaoxatricyclo (20.4.0.0^9,14)hexacosane) (complex (2), stoichiometry 1 : 1). X-ray data were also obtained for the complex of the product of (H₂-PTD) cyclization, (1,2,5)-oxadiazolo(3,4-d)pyrimidine-5,7(4H,6H)-dione (OPD) with diaqua diaza-18-crown-6 (complex (3), stoichiometry 2 : 2 : 1).In (1) the (H-PTD)^- anions are joined into dimers through the bifurcated OH...N and OH...O hydrogen bonds and alternate with diazonia-18-crown-6 cations in the chains sustained by the NH(crown) ... O and NH(crown) ...N interactions. The chains are further combined into the 3D network via NH...O(crown) hydrogen bonds. In (2) the self-complementarity of the (H-PTD)^- anions facilitates their assembly into the chain via OH...N, NH...O and OH...O interactions. The ammonium cations bridge each anion and the DCHA macrocycle with the formation of a ribbon developed along the [101] direction in the unit cell. Ternary complex (3) is built of the neutral species, diaza-18-crown-6, water molecules and dimers of OPD alternated in the chains and held together by OH...O and NH...O hydrogen bonds.     

OH−-induced β-elimination reactions with 1-(2-Xethyl)-4-nitrobenzene substrates in solvent mixture H2O/CH3CN and H2O/DMSO: Reactivity and mechanism

The behaviour of 1-(2-bromoethyl) 4-nitrobenzene (1), N,N,N-triethyl-2-(4-nitrophenyl)ethanaminium bromide (2) and N,N-diethyl-N-[2-(4-nitrophenyl)ethyl]octan-1-aminium bromide (3) in the OH⁻-induced elimination reactions with formation of 1-nitro-4-vinylbenzene in mixtures of DMSO/H₂O or CH₃CN/H₂O has been investigated. With all three substrates an increase in dipolar aprotic solvent content implies a limited increase of the second-order rate constant k _OH up to ≅605, and then an exponential increase is observed. The variation of activation parameters ΔH ^# and dGS ^#, measured in DMSO/H₂O mixtures, is parallel for 1 and 2. This similar behaviour of 1 and 2 with respect to variation in solvent composition is evidence that it is not possible to use this technique of solvent effect for the mechanistic diagnosis of elimination reactions.     

Synthesis,structure, and magnetic properties of lanthanide ferrocenoylacetonates with nitrate and 2,2′-bipyridine ligands

Ferrocenoylacetonate complexes of several lanthanides, [Ln(fca)₂(NO₃)(bpy)]·nMeC₆H₅ (Ln = Sm (1), Dy (3), Er (4), Yb (5), n = 1; Eu (2), n = 0.5; fca = FcC(O)CHC(O)Me; bpy = 2,2′-bipyridine), were synthesized and characterized by X-ray single-crystal analysis. Complexes 1, 4, and 5 are isostructural; 2 has a similar molecular structure with cis-disposition of fca ligands. The molecular structure of 3 is different, with trans-disposition of the fca ligands. Crystal lattices of the complexes are stabilized by π-stacking interactions. The Ln³⁺ ions in the complexes are eight-coordinate. According to mass spectroscopic data, the complexes are unstable in the gas phase. Magnetic properties of 2 and 4 were studied in a DC field; for 4, AC studies were also carried out. The values of spin-orbital parameters obtained using two estimation methods for 2 are in satisfactory agreement. Slow relaxation of the magnetization was found for the Er complex.     

Thermochemistry of europium and dithiocarbamate complex Eu(C5H8NS2)3(C12H8N2)

A solid complex Eu(C₅H₈NS₂)₃(C₁₂H₈N₂) has been obtained from reaction of hydrous europium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen⋅H₂O) in absolute ethanol. IR spectrum of the complex indicated that Eu³⁺ in the complex coordinated with sulfur atoms from the APDC and nitrogen atoms from the o-phen. TG-DTG investigation provided the evidence that the title complex was decomposed into EuS. The enthalpy change of the reaction of formation of the complex in ethanol, Δ_r H _m ^θ(l), as –22.214±0.081 kJ mol^–1, and the molar heat capacity of the complex, c _m, as 61.676±0.651 J mol^–1 K^–1, at 298.15 K were determined by an RD-496 III type microcalorimeter. The enthalpy change of the reaction of formation of the complex in solid, Δ_r H _m ^θ(s), was calculated as 54.527±0.314 kJ mol^–1 through a thermochemistry cycle. Based on the thermodynamics and kinetics on the reaction of formation of the complex in ethanol at different temperatures, fundamental parameters, including the activation enthalpy (ΔH _≠ ^θ), the activation entropy (ΔS _≠ ^θ), the activation free energy (ΔG _≠ ^θ), the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A) and the reaction order (n), were obtained. The constant-volume combustion energy of the complex, Δ_c U, was determined as –16937.88±9.79 kJ mol^–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_c H _m ^θ, and standard enthalpy of formation, Δ_f H _m ^θ, were calculated to be –16953.37±9.79 and –1708.23±10.69 kJ mol^–1, respectively.     

New complexes of fullerences C60 and C70 with CoII and MnII tetraphenylporphyrinates and their ESR study

Complexes of fullerenes C₆₀ and C₇₀ with cobalt(II) and manganese(II) tetraphenylporphyrinates of compositions Mn(TPP)·(C₆₀)₂(CS₂)_1.5 (1), Mn(TPP)·C₇₀(CS₂) _x , wherex<=1.25 (2), Co(TPP)·C₆₀(CS₂)_0.5 (3), and Co(TPP)·C₇₀(CS₂) _x , wherex<0.25 (4), were synthesized and studied by ESR spectroscopy. At 77 K, complexes1 and2 have singlet ESR spectra characteristic of the low-spin (S=1/2) state of Mn^II, withg=2.002 and linewidths of 250 G and 300 G, respectively, and differing significantly from that of the initial Mn^II(TPP) (g ₁=5.9 andg=2.0,S=5/2). The spectra of complexes1 and2 exposed to oxygen exhibit hyperfine structure due to interaction with⁵⁵Mn and¹⁴N nuclei. The ESR spectra of complexes3 and4 are asymmetric (<g>=2.4, ΔH _pp=(500–600) G), which is due to the overlap of parallel and perpendicular spectral components. The absence of ESR signals from C₆₀ ^.− and C₇₀ ^.− radical anions makes it possible to conclude that the formation of complexes1–4 is not accompanied by electron transfer from Co(TPP) and Mn(TPP) to fullerences C₆₀ and C₇₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 722–725, April, 1999.     

Supramolecular architectures with ladder and lamellar topologies using metal-ligand coordination units via C–H···Cl and O–H···Cl hydrogen bonding

New Mn^II/Cu^II/Zn^II complexes [(L¹)MnCl₂] (1), [(L²)CuCl₂]·0.5H₂O (2) and [(L²)ZnCl(H₂O)][ClO₄] (3), containing (2-pyridyl)alkylamine ligands, N-methyl-N,N-bis(2-pyridylmethyl)amine (L¹) and methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine (L²), have been prepared and characterized, including X-ray crystallography. The most striking feature of the structures of these complexes is the formation of molecular ladder and lamellar topology through the crystal packing arrangement, determined by both strong O–H···Cl and weak (however, multiple) C–H···Cl hydrogen-bonding interactions, to maintain the neutral/cationic metal-ligand coordination units linked to each other. In 3, additional secondary interactions are observed involving coordinated solvent and the counter-ion. The results presented here demonstrate that (i) the choice of organic ligands to provide flexibility and inherent potential to participate in hydrogen-bonding interactions, (ii) the coordination geometry preferences of metal ions, (iii) the number of metal-bound chloride ion and (iv) the presence of solvent/counter-anion have a great influence on supramolecular network topology.     

Studies on synthesis, characterization and thermochemistry of Mg2[B2O4(OH)2]·H2O

A new magnesium borate Mg₂[B₂O₄(OH)₂]·H₂O has been synthesized by the method of phase transformation of double salt at hydrothermal condition and characterized by XRD, IR, TG and DSC. The enthalpy of solution of Mg₂[B₂O₄(OH)₂]·H₂O in 0.9764 mol L^–1 HCl was determined. With the incorporation of the enthalpies of solution of H₃BO₃ in HCl (aq), of MgO in (HCl+H₃BO₃) (aq), and the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of –(3185.78±1.91) kJ mol^–1 of Mg₂[B₂O₄(OH)₂]·H₂O was obtained.This revised version was published online in November 2005 with corrections to the Cover Date.     

Green and efficient synthesis of 1H-indazolo[1,2-b] phthalazine-1,6,11(13H)-triones using ZrO(NO3)2.2H2O as a novel catalyst and theoretical study of synthesized compounds

The one-pot three-component synthesis for the preparation of 1H-indazolo[1,2-b] phthalazine-1,6,11(13H)-triones through condensation of phthalimide, hydrazine monohydrate, dimedone, and aromatic aldehydes in the presence of a novel catalytic amount of ZrO(NO₃)₂.2H₂O at reflux conditions in water has been reported. Quantum theoretical calculations for the three structures of compounds ( 5a , 5b , and 5c ) were performed using the G3MP2, LC-ωPBE, MP2, and B3LYP methods with the 6-311 + G** basis set. After optimizing the structures, geometric parameters were obtained and experimental measurements were compared with the calculated data. The structures of the products were confirmed by IR, ¹H NMR, ¹³C NMR, and elemental analysis. IR spectra data and ¹H NMR and ¹³C NMR chemical shifts computations of the 1H-indazolo[1,2-b]phthalazine-1,6,11(13H)-trione derivatives in the ground state were calculated. Frontier molecular orbitals, total density of states, thermodynamic parameters, and molecular electrostatic potentials of the title compounds were investigated by theoretical calculations. Molecular properties such as the ionization potential (I), electron affinity (A), chemical hardness (η), electronic chemical potential (μ), and electrophilicity (ω) were investigated for the structures. Consequently, there was an excellent agreement between experimental and theoretical results.     

Preparation and characterization of four polymeric metal complexes based on the flexible ligand 1H-1,2,4-triazole-1-propionic acid in different conformations

Three 2-D layered coordination polymers with (4,4) topology, {[Cu(trzp)₂(H₂O)]·1.18H₂O} _n (1), {[Co(trzp)₂(H₂O)₂]·2H₂O} _n (2), and {[Cd(trzp)₂(H₂O)]·2H₂O} _n (3), have been synthesized with the flexible, bifunctional ligand 1H-1,2,4-triazole-1-propionate (trzp^?) as a two-connected bridge. In addition, a complicated 3-D MOF [Ag₃(trzp)₂(NO₃)] _n (4) has been obtained with the help of Ag?Ag interactions and trzp^? as a four-connected linker. Htrzp and 1–4 have been characterized by single-crystal X-ray diffraction, elemental analysis, and infrared spectroscopy. The structural analysis showed that Htrzp has a gauche conformation in the solid state. However, both gauche and trans conformers of trzp^? are observed in the crystals of 1; only one conformer of trzp^? exists in the other three compounds (trans conformation in 2 and 3, and gauche conformation in 4). The thermal behaviors of 1–4 have been examined by thermal gravimetric analysis under nitrogen, which revealed that metal cyanide salts M(CN) _n (M?=?Cu(II), Co(II), Cd(II), and Ag(I), n?=?1 or 2) may be an intermediate pyrolytic decomposition product of the corresponding compounds.     

Synthesis, Structure, and 31P NMR of Sulfur/Oxygen-Bridged Incomplete Cubane-Type Molybdenum and Tungsten Clusters with Triphenylphosphine Ligands

Sulfur/oxygen-bridged incomplete cubane-type triphenylphosphine molybdenum and tungsten-clusters [Mo₃S₄Cl₄(H₂O)₂(PPh₃)₃]·3THF (1A), [Mo₃S₄Cl₄(H₂O)₂(PPh₃)₃]·2THF (2A), [Mo₃OS₃Cl₄(H₂O)₂(PPh₃)₃]·2THF (1B), and [W₃S₄Cl₄(H₂O)₂(PPh₃)₃]·2THF (1C) were prepared from the corresponding aqua clusters and PPh₃ in THF/MeOH. On recrystallization from THF, procedures with and without addition of hexane to the solution gave 1A and 2A, respectively, while the procedures gave no effect on the formation of 1B and 1C. Crystallographic results obtained are as follows: 1A: monoclinic, P2₁/n, a=17.141(4) Å, b=22.579(5) Å, c=19.069(4) Å, =96.18(2)°, V=7337(3) ų, Z=4, R(R _w)=0.078(0.102); 1C: monoclinic, P2 ₁/c, a=12.635(1) Å, b=20.216(4) Å, c=27.815(3) Å, =96.16(1)°, V=7062(2) ų, Z=4, R(R _w)=0.071(0.083). If the phenyl groups are ignored, the molecule [Mo₃S₄Cl₄(H₂O)₂(PPh₃)₃] in 2A has idealized CS symmetry with the mirror plane perpendicular to the plane determined by the metal atoms, while the molecule in 1A does not have the symmetry. The tungsten compound 1C is isomorphous with the molybdenum compound 2A. ³¹P NMR spectra of 1A, 2A, and 1C were obtained and compared with similar clusters with dmpe (1,2-bis(dimethylphosphino)ethane) ligands.     

Gold(III)pentafluorophenylarylazoimidazole: Synthesis and spectral (H, C, COSY, HMQC NMR) characterisation

Reaction of [Au^III(C₆F₅)₃(tht)] with RaaiR′ in dichloromethane medium leads to [Au^III(C₆F₅)₃ (RaaiR′)] [RaaiR′=p-R-C₆H₄-N=N-C₃H₂-NN-l-R′, (1-3), R = H (a), Me (b), Cl (c) and R′= Me (1), CH₂CH₃ (2), CH₂Ph (3), tht is tetrahydrothiophen]. The nine new complexes are characterised by ES/MS as well as FAB, IR and multinuclear NMR (¹H,¹³C,¹⁹F) spectroscopic studies. In addition to dimensional NMR studies as¹H,¹H COSY and¹H¹³C HMQC permit complete assignment of the complexes in the solution phase.     

Kinetics of oxidation of hydroquinone to <Emphasis Type="Italic">p</Emphasis>-benzoquinone catalyzed by microporous metal-organic frameworks M<Subscript>3</Subscript>(BTC)<Subscript>2</Subscript> [M = copper(II), cobalt(II), or nickel(II); BTC = benzene-1,3,5-tricarboxylate] using molecular oxygen

The kinetics of oxidation of hydroquinone (H₂Q) to p-benzoquinone (Q) catalyzed by microporous metal-organic frameworks (MOFs) using molecular oxygen has been investigated. MOF catalysts with different metals and pore sizes, i.e. M₃(BTC)₂(H₂O) _x (M = Cu^II (1), Co^II (2), or Ni^II (3); BTC = benzene-1,3,5-tricarboxylate; x = 3 for MOF 1 and 12 for 2 and 3), were used to catalyze the oxidation reaction. The apparent first-order reaction rate constant increased with increasing temperature, molar ratio of catalyst/H₂Q, and pH of the medium. A kinetic model for the heterogeneous catalysis is proposed, and the apparent activation energy (E _a), the association constants between the hydroquinone and the catalyst (K _s), and the first-order rate constants for product formation in the MOF channels (k _N) were calculated.     

Three 4-connected nickel coordination polymers affording a 3-D CdSO4 network and two 2-D (4,4) networks

The self-assembly reaction of 1,4-bis(1,2,4-triazol-1-yl)butane (btb) and Ni(II) salts gives three coordination polymers {[Ni(btb)₂(NCS)₂]?·?H₂O} _n (1), [Ni(btb)₂(NCO)₂] _n (2), and [Ni(btb)₂Cl₂] _n (3). Compound 1 is comprised of a twofold interpenetrating 4-connected 6⁵?·?8-CdSO₄ 3-D coordination network. Compounds 2 and 3 are neutral 2-D (4,4) networks with the ABAB?···?and ABCABC?···?stacking modes, respectively. The thermal stabilities of 1–3 were investigated.     

Crystal structures,electrochemical properties,antioxidant screening and in vitro cytotoxic studies on four novel Cu(II) complexes of bidentate Schiff base ligands derived from 2-methoxyethylamine

Four novel Schiff base ligands and their copper(II) complexes, [Cu(L¹)₂] (1), [Cu(L²)₂] (2), [Cu(L³)₂] (3), and [Cu(L⁴)₂] (4), were synthesized and characterized by elemental analyses, FT-IR, and UV–Vis spectroscopy. The ligands were synthesized from the condensation of 2-methoxyethylamine with various salicylaldehyde derivatives (x-salicylaldehyde for HLⁿ, x = H (n = 1), 5-Br (n = 2), 3-OMe (n = 3), and 4-OMe (n = 4)). The molecular structures of 1, 2, and 3 were determined by the single crystal X-ray diffraction technique. The redox behavior studies of the complexes in acetonitrile display the electronic effects of the groups on the redox potential. The antioxidant activity of the Schiff base ligands and their Cu(II) complexes was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method and FRAP assay. Furthermore, the in vitro anticancer activity of compounds was screened, including MTT and migration assays against gastric cancer cell line (MKN-45). The results show that all ligands and complexes have antioxidant and anticancer activity in a concentration-dependent way.     

QSAR based modeling on a series of α-hydroxy amides as a novel class of bradykinin B1 selective antagonists

G-protein coupled receptors like Bradykinin (BK) B₁ represent a potential treatment route for chronic pain and inflammation. Quantitative structure activity relationship has been performed on a series of α-hydroxy amides as a novel class of bradykinin B₁ selective antagonists, using different physicochemical parameters along with appropriate indicator variables. It has been found that physicochemical parameters such as connectivity indices ³χ, ⁴χ and ⁵χ, molecular weight, molar refractivity, density along with indicator variables are significantly correlated with activity. In this paper best results were obtained by using multiple regression analysis. Different models were generated with high values of R² and low values of PRESS/SSY ratio. The significant equations were statistically tested by using leave one out (LOO) technique and cross validation methods.     

Cadmium(II) complexes with phosphine tellurides: synthesis and multinuclear (31P, 125Te,and 113Cd) NMR characterization in solution

New cadmium(II) complexes with phosphine telluride ligands of the type CdX₂(R₃PTe)_n [X?=?ClO₄^?, n?=?4: R?=?n-Bu (1), Me₂?N (2), C₅H₁₀?N (3), C₄H₈?N (4) or OC₄H₈?N (5); X?=?Cl^–, n?=?2: R?=?n-Bu (6), Me₂?N (7), C₅H₁₀?N (8), C₄H₈?N (9) or OC₄H₈?N (10)] have been synthesized and characterized by elemental analyses, IR and multinuclear (³¹P, ¹²⁵Te, and ¹¹³Cd) NMR spectroscopy. In particular, the solution structures of these complexes were confirmed by ¹¹³Cd NMR at low temperature, which displays a quintuplet for each of the perchlorate complexes and a triplet for each of the chloride complexes due to coupling with four and two equivalent phosphorus atoms, respectively, indicating a four-coordinate tetrahedral geometry for the metal center. These multiplet features were further accompanied by one bond Te–Cd couplings, clearly showing that the ligand is coordinated to the metal through tellurium. The results are discussed and compared with those obtained for closely related phosphine chalcogenide analogs.