Oxido- and Dioxidovanadium(V) Complexes with O-vanillin Semicarbazone: Synthesis and Crystal Structure

Two vanadium(V) complexes comprising VO3+ and VO2+ cores with o-vanillin semicarbazone (H2L) have been synthesized and characterized by IR, NMR spectroscopies and single-crystal X-ray diffraction study. The coordination polyhedra are a O5N distorted octahedron in the mono-oxidovanadium complex [VO(HL)(EtO)(EtOH)0.6(H2O)0.4][VO(HL)(SO4)(EtO)]•0.4EtOH (1) and a O4N square-pyramid in the dioxidovanadium compound [VO2(HL)]•2H2O (2)

NICKEL(III) COMPLEX DERIVED FROM 2-HYDROXY-3-METHOXYBENZALDEHYDE SEMICARBAZONE AND 2,2’-BIPYRIDINE

An ONO tridentate semicarbazone Schiff base and a bidentate dipyridyl ligand give a nickel(II) dimer, where atom centers are bridged by phenolate oxygen donors

New Cyanido-Bridged Heterometallic 3d-4f 1D Coordination Polymers: Synthesis, Crystal Structures and Magnetic Properties

Three new 1D cyanido-bridged 3d-4f coordination polymers, {[Gd(L)(H2O)2Fe(CN)6]·H2O}n (1GdFe), {[Dy(L)(H2O)2Fe(CN)6]·3H2O}n (2DyFe), and {[Dy(L)(H2O)2Co(CN)6]·H2O}n (3DyCo), were assembled following the building-block approach (L = pentadentate bis-semicarbazone ligand resulting from the condensation reaction between 2,6-diacetyl-pyridine and semicarbazide). The crystal structures consist of crenel-like LnIII-MIII alternate chains, with the LnIII ions connected by the hexacyanido metalloligands through two cis cyanido groups. The magnetic properties of the three complexes have been investigated. Field-induced slow relaxation of the magnetization was observed for compounds 2DyFe and 3DyCo. Compound 3DyCo is a new example of chain of Single Ion Magnets

Crystal structure and NMR spectroscopic characterization of 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide

The solid-state structure of a symmetrical carbohydrazone, namely 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide was determined by X-ray single crystal diffraction method. Compound 1 crystallizes in the monoclinic space group P21/n with unit cell parameters a= 10.1198(6), b= 22.7847(11), c= 15.1738(10) Å, β= 100.458(6)°, Z= 4, V= 3440.6(3) Å3, R1= 0.0540. Crystal structure of 1 is defined by two crystallographic independent molecules, which are bonded via N–H···O hydrogen bond. The organic molecules are as keto tautomers with respect to the carbamide fragment, and adopt the anti conformation. 1D and 2D NMR experiments have argued on the presence of the title compound in DMSO-d6 solution mostly as keto tautomer in syn conformation, and enol-imino form when considering o-vanillin residue

SYNTHESIS, CHARACTERIZATION AND CRYSTAL STRUCTURE OF BIS-(2-HYDROXYBENZALDEHYDE)DIAMINOGUANIZONE

The new ligand, bis(2-hydroxybenzaldehyde)diaminoguanizone (1) has been synthesized and characterized by elemental analysis, IR and 1H NMR spectroscopies. The crystal structure of the compound was determined by X-ray diffraction. The ligand C15H15N5O2·C2H5OH crystallizes in the monoclinic space group P21/c with unit cell parameters a = 8.9102(3), b = 10.0357(3), c = 19.7618(6) Å, β = 98.385(2)°, Z = 4, V = 1748.21(9) Å3, R1 = 0.040. The amino form of the ligand adopts a planar conformation stabilized by two intramolecular hydrogen bonds of the type O–H···N, in which the H atoms of the central amino group are directed to the lone-pair regions of the azomethine nitrogen atoms

Copper(II) complexes with 1,5-bis(2-hydroxybenzaldehyde) carbohydrazone

The acid–base properties of 1,5-bis(2-hydroxybenzaldehyde)carbohydrazone (H4L) and its thioanalogue 1,5-bis(2-hydroxybenzaldehyde)thiocarbohydrazone (H4LS) have been studied experimentally by pH-potentiometry and UV–Vis spectrophotometry and theoretically by using DFT methods. Copper(II) complexes [Cu2(HL)(DMSO)2(H2O)]NO3·H2O (1), [{Cu2(HL)(DMF)(H2O)}n][{Cu2(HL)(DMF)NO3}n](NO3)n (2), [Cu2(HL)(DMF)2(H2O)]HSO4·H2O (3), [Cu2(HL)(DMF)2(H2O)][Cu2(HL)(SO4)(H2O)(DMF)2]·2H2O (4) and [Cu4(HL)2(HSO4)(DMF)2]HSO4 (5), where H4L = 1,5-bis(2-hydroxybenzaldehyde)carbohydrazone, have been synthesised. Complexes 1–3 have been characterised by elemental analysis, IR spectroscopy, ESI mass spectrometry, cyclic voltammetry, magnetic susceptibility measurements and X-ray diffraction, while 4 and 5 only by X-ray crystallography. X-ray diffraction revealed that the ditopic triply deprotonated ligand possesses two binding sites able to accommodate transition metal ions, namely ONN and ONO. Magnetic measurements showed antiferromagnetic interactions between copper(II) centres

Vanadium(V) complexes with substituted 1,5-bis(2- hydroxybenzaldehyde)carbohydrazones and their use as catalyst precursors in oxidation of cyclohexane

Six dinuclear vanadium(V) complexes have been synthesized: NH4[(VO2)(2)((LH)-L-H)] (NH4[1]), NH4[(VO2)(2)((LH)-L-tBu)] (NH4[2]), NH4[(VO2)(2)((LH)-L-Cl)] (NH4[3]), [(VO2)(2)(VO) ((LH)-L-H) (CH3O)] (4), [(VO2) (VO) (t-BuLH) (C2H5O)] (5), and [ (VO2) (VO) (Cl-LH) (CH3O)(CH3OH/H2O)] (6) (where (LH4)-L-H = 1,5-bis(2-hydroxybenzaldehyde)carb ohydrazon e, t-BuLH4 = 1,5-bis(3,5-di-tert-butyl-2-hydroxybenzaldehyde) carbohydrazone, and (LH4)-L-cl = 1,5-bis(3,5-dichloro-2-hydroxybenzaldehyde)carbohydrazone). The structures of NH4[1] and 4-6 have been determined by X-ray diffraction (XRD) analysis. In all complexes, the triply deprotonated ligand accommodates two V ions, using two different binding sites ONN and ONO separated by a diazine unit -N-N-. In two pockets of NH4[1], two identical VO2+ entities are present, whereas, in those of 4-6, two different VO2+ and VO3+ are bound. The highest oxidation state of V ions was corroborated by X-ray data, indicating the presence of alkoxido ligand bound to VO3+ in 4-6, charge density measurements on 4, magnetic susceptibility, NMR spectroscopy, spectroelectrochemistry, and density functional theory (DFT) calculations. All four complexes characterized by XRD form dimeric associates in the solid state, which, however, do not remain intact in solution. Compounds NH4[1], NH4[2], and 4-6 were applied as alternative selective homogeneous catalysts for the industrially significant oxidation of cyclohexane to cyclohexanol and cyclohexanone. The peroxidative (with tert-butyl hydroperoxide, TBHP) oxidation of cyclohexane was performed under solvent -free and additive -free conditions and under low-power microwave (MW) irradiation. Cyclohexanol and cyclohexanone were the only products obtained (high selectivity), after 1.5 h of MW irradiation. Theoretical calculations suggest a key mechanistic role played by the carbohydrazone ligand, which can undergo reduction, instead of the metal itself, to form an active reduced form of the catalyst.PTDC/QEQERQ/1648/2014PTDC/QEQ-QIN/3967/2014info:eu-repo/semantics/publishedVersio

Vanadium(V) Complexes with Substituted 1,5-bis(2-hydroxybenzaldehyde)carbohydrazones and Their Use As Catalyst Precursors in Oxidation of Cyclohexane

Six dinuclear vanadium­(V) complexes have been synthesized: NH₄[(VO₂)₂(^HLH)] (NH₄[<b>1</b>]), NH₄[(VO₂)₂(^{<i>t</i>‑Bu}LH)] (NH₄[<b>2</b>]), NH₄[(VO₂)₂(^ClLH)] (NH₄[<b>3</b>]), [(VO₂)­(VO)­(^HLH)­(CH₃O)] (<b>4</b>), [(VO₂)­(VO)­(^{<i>t</i>‑Bu}LH)­(C₂H₅O)] (<b>5</b>), and [(VO₂)­(VO)­(^ClLH)­(CH₃O)­(CH₃OH/H₂O)] (<b>6</b>) (where ^HLH₄ = 1,5-bis­(2-hydroxybenzaldehyde)­carbohydrazone, ^{<i>t</i>‑Bu}LH₄ = 1,5-bis­(3,5-di-<i>tert</i>-butyl-2-hydroxybenzaldehyde)­carbohydrazone, and ^ClLH₄ = 1,5-bis­(3,5-dichloro-2-hydroxybenzaldehyde)­carbohydrazone). The structures of NH₄[<b>1</b>] and <b>4</b>–<b>6</b> have been determined by X-ray diffraction (XRD) analysis. In all complexes, the triply deprotonated ligand accommodates two V ions, using two different binding sites ONN and ONO separated by a diazine unit −N–N–. In two pockets of NH₄[<b>1</b>], two identical VO₂⁺ entities are present, whereas, in those of <b>4</b>–<b>6</b>, two different VO₂⁺ and VO³⁺ are bound. The highest oxidation state of V ions was corroborated by X-ray data, indicating the presence of alkoxido ligand bound to VO³⁺ in <b>4</b>–<b>6</b>, charge density measurements on <b>4</b>, magnetic susceptibility, NMR spectroscopy, spectroelectrochemistry, and density functional theory (DFT) calculations. All four complexes characterized by XRD form dimeric associates in the solid state, which, however, do not remain intact in solution. Compounds NH₄[<b>1</b>], NH₄[<b>2</b>], and <b>4</b>–<b>6</b> were applied as alternative selective homogeneous catalysts for the industrially significant oxidation of cyclohexane to cyclohexanol and cyclohexanone. The peroxidative (with <i>tert</i>-butyl hydroperoxide, TBHP) oxidation of cyclohexane was performed under solvent-free and additive-free conditions and under low-power microwave (MW) irradiation. Cyclohexanol and cyclohexanone were the only products obtained (high selectivity), after 1.5 h of MW irradiation. Theoretical calculations suggest a key mechanistic role played by the carbohydrazone ligand, which can undergo reduction, instead of the metal itself, to form an active reduced form of the catalyst

Vanadium(V) Complexes with Substituted 1,5-bis(2-hydroxybenzaldehyde)carbohydrazones and Their Use As Catalyst Precursors in Oxidation of Cyclohexane

Six dinuclear vanadium­(V) complexes have been synthesized: NH₄[(VO₂)₂(^HLH)] (NH₄[<b>1</b>]), NH₄[(VO₂)₂(^{<i>t</i>‑Bu}LH)] (NH₄[<b>2</b>]), NH₄[(VO₂)₂(^ClLH)] (NH₄[<b>3</b>]), [(VO₂)­(VO)­(^HLH)­(CH₃O)] (<b>4</b>), [(VO₂)­(VO)­(^{<i>t</i>‑Bu}LH)­(C₂H₅O)] (<b>5</b>), and [(VO₂)­(VO)­(^ClLH)­(CH₃O)­(CH₃OH/H₂O)] (<b>6</b>) (where ^HLH₄ = 1,5-bis­(2-hydroxybenzaldehyde)­carbohydrazone, ^{<i>t</i>‑Bu}LH₄ = 1,5-bis­(3,5-di-<i>tert</i>-butyl-2-hydroxybenzaldehyde)­carbohydrazone, and ^ClLH₄ = 1,5-bis­(3,5-dichloro-2-hydroxybenzaldehyde)­carbohydrazone). The structures of NH₄[<b>1</b>] and <b>4</b>–<b>6</b> have been determined by X-ray diffraction (XRD) analysis. In all complexes, the triply deprotonated ligand accommodates two V ions, using two different binding sites ONN and ONO separated by a diazine unit −N–N–. In two pockets of NH₄[<b>1</b>], two identical VO₂⁺ entities are present, whereas, in those of <b>4</b>–<b>6</b>, two different VO₂⁺ and VO³⁺ are bound. The highest oxidation state of V ions was corroborated by X-ray data, indicating the presence of alkoxido ligand bound to VO³⁺ in <b>4</b>–<b>6</b>, charge density measurements on <b>4</b>, magnetic susceptibility, NMR spectroscopy, spectroelectrochemistry, and density functional theory (DFT) calculations. All four complexes characterized by XRD form dimeric associates in the solid state, which, however, do not remain intact in solution. Compounds NH₄[<b>1</b>], NH₄[<b>2</b>], and <b>4</b>–<b>6</b> were applied as alternative selective homogeneous catalysts for the industrially significant oxidation of cyclohexane to cyclohexanol and cyclohexanone. The peroxidative (with <i>tert</i>-butyl hydroperoxide, TBHP) oxidation of cyclohexane was performed under solvent-free and additive-free conditions and under low-power microwave (MW) irradiation. Cyclohexanol and cyclohexanone were the only products obtained (high selectivity), after 1.5 h of MW irradiation. Theoretical calculations suggest a key mechanistic role played by the carbohydrazone ligand, which can undergo reduction, instead of the metal itself, to form an active reduced form of the catalyst