Slow Magnetic Relaxation and Electron Delocalization in an S = 9/2 Iron(II/III) Complex with Two Crystallographically Inequivalent Iron Sites

The magnetic, electronic, and Mössbauer spectral properties of Fe 2L(µ-OAc)2ClO4, 1, where L is the dianion of the tetraimino-diphenolate macrocyclic ligand, H2L, indicate that 1 is a class III mixed valence iron(II/III) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a [Fe2]V cationic configuration with a St 9/2 ground state. Fits of the dc magnetic susceptibility between 2 and 300K and of the isofield variable-temperature magnetization of 1 yield an isotropic magnetic exchange parameter, J, of -32(2) cm-1 for an electron transfer parameter, B, of 950 cm-1, a zero-field uniaxial D9/2 parameter of -0.9(1) cm-1, and g 1.95(5). In agreement with the presence of uniaxial magnetic anisotropy, ac susceptibility measurements reveal that 1 is a single-molecule magnet at low temperature with a single molecule magnetic effective relaxation barrier, Ueff, of 9.8 cm-1. At 5.25 K the Mössbauer spectra of 1 exhibit two spectral components, assigned to the two crystallographically inequivalent iron sites with a static effective hyperfine field; as the temperature increases from 7 to 310 K, the spectra exhibit increasingly rapid relaxation of the hyperfine field on the iron-57 Larmor precession time of 5 x 10-8 s. A fit of the temperature dependence of the average effective hyperfine field yields |D9/2| 0.9 cm-1. An Arrhenius plot of the logarithm of the relaxation frequency between 5 and 85 K yields a relaxation barrier of 17 cm-1

Bis(3-aminobenzenesulfonato-<i>N</i>)-diaqua-bis(<i>N,N’</i>-dimethylformamide-<i>O</i>)-copper(II)

Reaction of 3-aminobenzenesulfonic acid (HL1) with Cu(NO3)2·2.5H2O in H2O/DMF leads to the formation of the new bis(3-aminobenzenesulfonato-κN)-diaqua-bis(dimethylformamide-κO)-copper(II) complex [Cu(L1)2(DMF)2(H2O)2] (1) (HL1 = 3-aminobenzenesulfonic acid and DMF = N,N-dimethylformamide). Single crystal X-ray analysis reveals that the hexacoordinated copper(II) center adopts a distorted octahedral geometry with trans-oriented two 3-aminobenzenesulfonate ligands (L1−), two water and two dimethylformamide (DMF) molecules. Comparison of its crystal structure with that of the known bis(4-aminobenzenesulfonato-κN)diaquabis(dimethylformamide-κO)-copper(II) complex [Cu(L2)2(DMF)2(H2O)2] (2) (HL2 = 4-aminobenzenesulfonic acid) discloses that 1 and 2 are the isomers with an identical empirical formula (C18H30CuN4O10S2) and equal numbers of same coordinated solvents (DMF and water). H-bonded supramolecular structures and their corresponding topological analyses revealed a 2D with 6-connected hxl/Shubnikov plane net (3,6) for 1 and a 3D with 8-connected bcu; 8/4/c1; sqc3 net for 2, which are completely different

Viscosity B-Coefficients of Tetraalkylammonium Bromides in Dimethyl Sulphoxide Water Mixtures

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Viscosity B-coefficients of tetraalkylammonium iodides, sodium iodide and sodium tetraphenylborate in dimethyl sulphoxide + water mixtures at 298, 308 and 318 K

854-859The relative viscosities of solutions of tetraalkylammonium iodides, R4NI (where R = CH3–, C2H5–, C3H7– and C2H9–) have been measured in dimethyl sulphoxide (DMSO) + water mixtures (20, 40, 60, 80 and 100 wt% of DMSO) at 298, 308 and 318K. The results have been analysed using the Jones-Dole equation and the viscosity B-coefficients have been calculated. The μǂ, Hǂ and TSǂ values of the salts have been determined using the transition state treatment and the temperature coefficient measurements. The ionic B-values and other single ion parameters have been determined using Bu4NBPh4 as the 'reference electrolyte'. The results have been discussed in terms of the structural changes of the solvents and preferential solvation of ions

Catalytic oxidation of cyclohexane with hydrogen peroxide and a tetracopper(II) complex in an ionic liquid

The catalytic peroxidative oxidation (with H2O2) of cyclohexane in an ionic liquid (IL) using the tetracopper(II) complex [(CuL)2(μ4-O,O′,O′′,O′′′-CDC)]2·2H2O [HL = 2-(2-pyridylmethyleneamino)benzenesulfonic acid, CDC = cyclohexane-1,4-dicarboxylate] as a catalyst is reported. Significant improvements on the catalytic performance, in terms of product yield (up to 36%), TON (up to 529), reaction time, selectivity towards cyclohexanone and easy recycling (negligible loss in activity after three consecutive runs), are observed using 1-butyl-3-methylimidazolium hexafluorophosphate as the chosen IL instead of a molecular organic solvent including the commonly used acetonitrile. The catalytic behaviors in the IL and in different molecular solvents are discussed

A sulfonated Schiff base dimethyltin(IV) coordination polymer: synthesis, characterization and application as a catalyst for ultrasound- or microwave-assisted Baeyer–Villiger oxidation under solvent-free conditions

The synthesis and crystal structure of the new dimethyltin(IV) compound [SnMe2(HL)(CH3OH)]n$(0.5nCH3OH) (1) derived from the Schiff base 2-[(2,3-dihydroxyphenyl) methylideneamino]benzenesulfonic acid (H3L) are described. Despite having six potentially donating centres (one imine nitrogen, two phenoxo and three sulfonate oxygen atoms), the monoprotonated dianionic ligand (HL2) behaves as an O,O,O-tridentate chelator. Single crystal X-ray diffraction revealed that 1 is a 1D coordination polymer with every tin(IV) ion bound to two methyl groups, a methanol molecule, two Ophenoxo and one m-Osulfonate atom from HL2. The coordination polymer 1 was applied as a heterogeneous catalyst for the Baeyer–Villiger oxidation of ketones to esters orlactones, using aqueous hydrogen peroxide as oxidant, under ultrasound (US) or microwave (MW) irradiation and solvent- and additive-free conditions. Overall conversions up to 76/82, 98/93, 93/89, 91/94, 83/90, 68/62 and 81/87% under US/MW irradiations were obtained with 3,3-dimethyl-2-butanone, cyclopentanone, 2-methylcyclopentanone, cyclohexanone, 3-methylcyclohexanone, benzophenone and acetophenone, respectively. The catalyst can be recycled up to five cycles without losing appreciable activity.UID/QUI/00100/2013PTDC/QEQERQ/1648/2014PTDC/QEQ-QIN/3967/2014info:eu-repo/semantics/publishedVersio

Sulfonated Schiff base copper(II) complexes as efficient and selective catalysts in alcohol oxidation: syntheses and crystal structures

The reaction between 2-aminobenzenesulfonic acid and 2-hydroxy-3-methoxybenzaldehyde produces the acyclic Schiff base 2-[(2-hydroxy-3-methoxyphenyl) methylideneamino] benzenesulfonic acid (H2L center dot 3H(2)O) (1). In situ reactions of this compound with Cu(II) salts and, eventually, in the presence of pyridine (py) or 2,2'-bipyridine (2,2'-bipy) lead to the formation of the mononuclear complexes [CuL(H2O)(2)] (2) and [CuL(2,2'-bipy)]center dot DMF center dot H2O (3) and the diphenoxo-bridged dicopper compounds [CuL(py)](2) (4) and [CuL(EtOH)](2)center dot 2H(2)O (5). In 2-5 the L-2-ligand acts as a tridentate chelating species by means of one of the O-sulfonate atoms, the O-phenoxo and the N-atoms. The remaining coordination sites are then occupied by H2O (in 2), 2,2'-bipyridine (in 3), pyridine (in 4) or EtOH (in 5). Hydrogen bond interactions resulted in R-2(2) (14) and in R-4(4)(12) graph sets leading to dimeric species (in 2 and 3, respectively), 1D chain associations (in 2 and 5) or a 2D network (1). Complexes 2-5 are applied as selective catalysts for the homogeneous peroxidative (with tert-butylhydroperoxide, TBHP) oxidation of primary and secondary alcohols, under solvent-and additive-free conditions and under low power microwave (MW) irradiation. A quantitative yield of acetophenone was obtained by oxidation of 1-phenylethanol with compound 4 [TOFs up to 7.6 x 10(3) h(-1)] after 20 min of MW irradiation, whereas the oxidation of benzyl alcohol to benzaldehyde is less effective (TOF 992 h(-1)). The selectivity of 4 to oxidize the alcohol relative to the ene function is demonstrated when using cinnamyl alcohol as substrate

Sulfonated schiff base dimeric and polymeric copper(II) complexes: temperature dependent synthesis, crystal structure and catalytic alcohol oxidation studies

Temperature dependent synthesis and crystal structure of the dicopper(II) complex [Cu2(L-jONO0 )2(l- 4,40 -bipy)(DMF)2] (1) and the dicopper(II) based coordination polymer [Cu2(l-L-1jONO0 :2jO)2(l-4, 40 -bipy)]nnH2OnDMF (2) derived from the acyclic Schiff base 2-[(2-hydroxy-3-methoxyphenyl)methylideneamino]benzenesulfonic acid (H2L) are described. Compounds 1 and 2 crystallize in monoclinic P21/n and P21/c systems, respectively. Crystal structure analysis reveals that the coordination polymer 2 consists of a dimeric building block which is comparable to the basic structure of 1. The compounds are isolated from the same reaction mixture but at different reaction temperatures and 1 can be converted into the coordination polymer 2. They were tested as catalysts for (both primary and secondary) alcohols oxidation. They show good catalytic activity for the solvent- and additive-free microwave (MW) assisted peroxidative (with tert-butylhydroperoxide) oxidation of cyclohexanol (up to 85% yield of cyclohexanone) after 30 min of low power MW irradiation. 2info:eu-repo/semantics/publishedVersio

Metal-organic frameworks with pyridyl-based isophthalic acid and their catalytic applications in microwave assisted peroxidative oxidation of alcohols and Henry reaction

Reactions of 5-{(pyridin-4-ylmethyl)amino} isophthalic acid (H(2)L1) with copper(II), zinc(II), and cadmium(II) were studied, and the obtained metal organic frameworks (MOFs) [{Cu(L1)(DMF)}center dot DMF center dot H2O](n) (1), [Zn(L1)(H2O)(n) (2), and [Cd(L1)](n) (3) were characterized by elemental analysis, Fourier transform infrared spectroscopy, and X-ray single-crystal diffraction. As shown by X-ray crystallography, novel hybrid organic inorganic coordination-driven assemblies were obtained which exhibit different two- and three-dimensional (2D and 3D) polymeric architectures. Compounds 1 and 2 have 2D structures, whereas compound 3 features a 3D network type polymer with a dimetallic core acting as a secondary building unit. These frameworks act as heterogeneous polymeric solid catalysts (the most effective one being the copper MOF 1) for solvent-free microwave assisted peroxidative oxidation of primary and secondary alcohols. They also effectively catalyze the nitroaldol (Henry) reaction of different aldehydes with nitroalkanes in water. These MOF-based heterogeneous catalysts can be easily recovered and reused, at least for a few consecutive cycles, without losing activity.info:eu-repo/semantics/publishedVersio

Solvent-free microwave-assisted peroxidative oxidation of alcohols catalyzed by Iron(III)-TEMPO catalytic systems

The iron(III) complexes [H(EtOH)][FeCl2(L)(2)] (1), [H(2)bipy](1/2)[FeCl2(L)(2)].DMF (2) and [FeCl2(L)(2,2'-bipy)] (3) (L = 3-amino-2-pyrazinecarboxylate; H(2)bipy = doubly protonated 4,4'-bipyridine; 2,2'-bipy = 2,2'-bipyridine, DMF = dimethylformamide) have been synthesized and fully characterized by IR, elemental and single-crystal X-ray diffraction analyses, as well as by electrochemical methods. Complexes 1 and 2 have similar mononuclear structures containing different guest molecules (protonated ethanol for 1 and doubly protonated 4,4'-bipyridine for 2) in their lattices, whereas the complex 3 has one 3-amino-2-pyrazinecarboxylate and a 2,2'-bipyridine ligand. They show a high catalytic activity for the low power (10 W) solvent-free microwave assisted peroxidative oxidation of 1-phenylethanol, leading, in the presence of TEMPO, to quantitative yields of acetophenone [TOFs up to 8.1 x 10(3) h(-1), (3)] after 1 h. Moreover, the catalysts are of easy recovery and reused, at least for four consecutive cycles, maintaining 83 % of the initial activity and concomitant rather high selectivity. 3-Amino-2-pyrazinecarboxylic acid is used to synthesize three new iron(III) complexes which act as heterogeneous catalysts for the solvent-free microwave-assisted peroxidative oxidation of 1-phenylethanol