Synthesis and DFT calculations of oxido and phenylimido-rhenium(V) complexes incorporating the N,O donor ligand 2-[(2-hydroxyethylimino)methyl]phenol

The reactions of equimolar amounts of trans-[ReOC1₃(PPh₃)₂] or trans-[Re(NPh)(PPh₃)₂Cl₃] with a Schiff base formed by condensation of 2-hydroxy-4-methoxybenzaldehyde and ethanolamine (H₂L) result in the formation of cis-[ReO(HL)PPh₃Cl₂] (1a) and trans-[Re(NPh)(HL)(PPh₃)Cl₂] (2b), respectively, in good yields. 1a and 2b have been characterized by a range of spectroscopic and analytical techniques. The X-ray crystal structures of 1a and 2b reveal that 1a is an octahedral cis-Cl,Cl oxorhenium(V) complex, while 2b is a trans-Cl,Cl phenylimidorhenium(V) complex. The complexes are weakly emissive at room temperature with quantum yields of 10^?4. Density functional theory calculations of the electronic properties of the complexes were performed and are in agreement with the experimental results. The complexes display quasi-reversible Re(V)/Re(VI) redox couples in acetonitrile. There is reasonable agreement between the experimental and calculated redox potentials of 1a and 2b.     

A new trans-dioxorhenium(V) complex with 4-aminopyridine: synthesis,structure, electrochemical aspects,DFT, and TD-DFT calculations

The reaction of 1?:?4.4?M proportion of cis-[ReO₂I(PPh₃)₂] and 4-aminopyridine (ampy) in acetone–water gives trans-[ReO₂(ampy)₄]I·2H₂O (1a) in 85% yield. 1a has been characterized by C, H, and N microanalyses, FT-IR, UV–vis, ¹H NMR spectroscopy, and molar conductivity. The X-ray crystal structure of 1a reveals an octahedral trans dioxorhenium(V) complex with a “N₄O₂” coordination for rhenium. 1a has an orthorhombic space group C2221 with a?=?17.576(4), b?=?19.370(4), c?=?15.730(4) Å, V?=?5355(2) ų, and Z?=?8. Geometry optimization of the trans-O,O complex, 1a and its cis-O,O analog, 1b performed at the level of density functional theory reveal that 1a is more stable than 1b by 25?kcal M^–1 in the gas phase. The electronic spectrum of 1a was also analyzed at the level of time-dependent density functional theory. Excitation of 1a in methanol at 450?nm leads to a fluorescent emission at 505?nm with a quantum yield (Ф) of 0.04. Electrochemical studies of 1a in acetonitrile show a quasi-reversible Re(V) to Re(VI) oxidation at 0.618?V versus Ag/AgCl. This redox potential matches with the calculated redox potential of 0.621?V versus Ag/AgCl.     

Synthesis,characterization, and antimicrobial activities of a dinuclear copper(II) complex with bis(2-[(2-hydroxy-ethylimino)-methyl]-4,6-diiodo-phenol)

A dinuclear copper(II) complex with a newly synthesized tridentate Schiff-base ligand 2-[(2-hydroxy-ethylimino)-methyl]-4,6-diiodo-phenol (HL), of formula [Cu₂L₂Cl₂?·?C₄H₈O] (1), was prepared. Both the ligand and the complex were characterized by X-ray crystallography, confirming that the Schiff base is tridentate and its dinuclear copper(II) complex is five-coordinate from one nitrogen and two oxygens from L and two chlorides. The complex was assayed for antibacterial (Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter cloacae) activities by the MTT method. Complex 1 exhibited better antimicrobial activity than the ligand.     

Syntheses and crystal structures of two copper(II) complexes derived from 2-bromo-4-chloro-6-[(2-morpholin-4-ylethylimino)methyl]phenol

Two new copper(II) complexes, [CuL₂] (1) and [Cu₂L₂(NCS)₂] · 2CH₃CN (2) (HL = 2-bromo-4-chloro-6-[(2-morpholin-4-ylethylimino)methyl]phenol), have been synthesized and characterized by elemental analyses, infrared spectroscopy, and single-crystal X-ray diffraction. Complex 1 was synthesized by reaction of HL with copper(II) acetate in methanol, while 2 was synthesized by adding ammonium thiocyanate to a methanol/acetonitrile (V : V = 2 : 1) solution of 1. Complex 1 crystallizes in the P2₁/n space group, and the thiocyanato-bridged dinuclear copper(II) complex, 2, crystallizes in the Pbcn space group. The Cu in 1 is four-coordinate square-planar with two imine N and two phenolate O atoms from two Schiff-base ligands. The Cu in 2 is five-coordinate square-pyramidal with NNO donor atoms of one Schiff-base ligand and one N atom of a bridging thiocyanate ligand defining the basal plane, and with one S atom of another bridging thiocyanate ligand occupying the apical position.     

Synthesis,electrochemistry, MO properties,and X-ray diffraction structures of the new redox-active diphosphine ligand 2-(2-thienylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (tbpcd) and the rhenium compound fac-BrRe(CO)3(tbpcd)

Knoevenagel condensation of 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) with thiophene-2-carboxaldehyde furnishes the second-generation unsaturated diphosphine ligand 2-(2-thienylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (1, tbpcd) in high yield. The substitution chemistry of the rhenium compounds BrRe(CO)₅ and BrRe(CO)₃(THF)₂ with tbpcd has been investigated and found to produce fac-BrRe(CO)₃(tbpcd) (2). Compounds 1 and 2 have been isolated and fully characterized in solution by IR and NMR (¹H and ³¹P) spectroscopies, in addition to mass spectrometry, and X-ray crystallography. The redox properties of 1 and 2 have been examined by cyclic voltammetry, and these data are discussed relative to the results obtained from extended Hückel MO calculations and emission spectroscopic studies, as well as related ligand derivatives previously prepared by us. Our data indicate that the lowest excited state in tbpcd and fac-BrRe(CO)₃(tbpcd) arises from a π → π^∗ intraligand (IL) transition confined exclusively to the tbpcd ligand.     

Synthesis,structures, and characterization of copper(II), nickel(II), and cobalt(III) metal complexes derived from an asymmetric bidentate Schiff-base ligand

An asymmetric bidentate Schiff-base ligand (2-hydroxybenzyl-2-furylmethyl)imine (L–OH) was prepared. Three complexes derived from L–OH were synthesized by treating an ethanolic solution of the appropriate ligand with an equimolar amount of metallic salt. Three complexes, Cu₂(L–O^?)₂Cl₂ (1), Ni(L–O^?)₂ (2) and Co(L–O^?)₃ (3), have been structurally characterized through elemental analysis, IR, UV spectra and thermogravimetric analysis. Single crystal X-ray diffraction shows metal ions and ligands reacted with different proportions 1?:?1, 1?:?2 and 1?:?3, respectively, so copper(II), nickel(II), and cobalt(III) have different geometries.     

Experimental and computational studies on a new mixed ligand oxido–rhenium(V) compound

A mixed ligand oxido–rhenium(V) complex, [ReOS₃(HL)]Cl.H₂O ( 1p Cl.H₂O), with 3‐thiopentane‐1,5‐dithiolato (S₃) as a tridentate ligand and imidazolidinethione (HL) as an ancillary monodentate sulfur donor co‐ligand, has been synthesized. 1p Cl.H₂O has been characterized by spectral analyses. The X‐ray crystal structure of 1p Cl.H₂O shows that the complex contains a distorted square‐pyramidal “ReOS₄” core. The structural parameters agree with our optimized structure of 1p ⁺. Subsequently, the optimized structure was used to calculate systematically the relative stabilities of a sequence of oxido–Re(V) and the analogous oxido–Tc(V) complexes just by varying the donor sites (N, S, and O) on the tridentate ligand moiety in 1p ⁺. Electrochemical studies on 1p Cl.H₂O show an oxidative rhenium(VI)/ rhenium(V) couple at 1.561 V versus Ag/AgCl under controlled linear diffusion situation. Vibrational frequencies, electronic structures, and redox potential of 1p ⁺ have been calculated theoretically employing density functional theory (DFT) or time‐dependent‐DFT methods. The experimental findings are in excellent agreement with the computed results. The calculated redox potentials of the investigated oxido–Re(V) complexes and their oxido–Tc(V) counterparts are shown to correlate linearly with their respective chemical potential values.     

Tridentate (NNO) Schiff-base copper(II) complex: synthesis,crystal structure,and magnetic study

A new azido adduct of a tridentate Schiff-base copper(II) complex has been synthesized and characterized structurally and magnetically. X-ray single crystal structure analysis reveals that the asymmetric unit of [Cu₂(L)₂(µ_1,1-N₃)₂][Cu(L)(N₃)] (1) [HL = 1-(N-ortho-hydroxyacetophenimine)-2,2-diethyl-aminoethane] has two independent moieties. One of these forms a dimer, containing end-on azido bridges, with its center of inversion related equivalents. The complex crystallizes in monoclinic space group P₂1/c with a = 10.112(2), b = 31.938(4), c = 9.718(2) Å and β = 95.00(2)°. Variable temperature magnetic susceptibility data show antiferromagnetic interactions between copper(II) centers.     

An integrated experimental and theoretical investigation of the structural and spectroscopic properties of two nickel(II) isothiosemicarbazone complexes

Two nickel(II) isothiosemicarbazone complexes of dianionic 5-bromosalicylaldehyde S-allyl isothiosemicarbazonehydrobromide (H₂L.HBr), [Ni(Im)L] and [Ni(2-MeIm)L] (Im: imidazole, 2-MeIm: 2-methylimidazole), were synthesized and characterized by single crystal X-ray crystallography, ¹H NMR spectrometry, IR, and electronic spectroscopy. The complexes have square-planar geometry and the ligand is coordinated as a dinegative tridentate chelating agent via phenolic oxygen, isothioamide nitrogen, and azomethine nitrogen atoms. To complement the experimental data, density functional theory (DFT) and time-dependent DFT methods were used to validate the structural parameters and infrared and electronic spectra.     

Syntheses and crystal structures of nickel(II), copper(II), and zinc(II) complexes with a biphenyl-bridged bis(pyrrole-2-yl-methyleneamine) ligand

The reactions of nickel(II), copper(II), and zinc(II) acetate salts with a potentially tetradentate biphenyl-bridged bis(pyrrole-2-yl-methyleneamine) ligand yielded three complexes with different coordination geometries. X-ray crystal structural analysis reveals that in the nickel(II) complex each nickel is five-coordinate, distorted trigonal bipyramid. In the copper(II) complex, each copper is four-coordinate, between square planar and tetrahedral. In the zinc(II) complex, each zinc is four-coordinate with a distorted tetrahedral geometry and the molar ratio of the zinc and ligand is 1 : 2.     

Crystal structure of 4,4-bipyridine-containing complexes of copper(II) nitrate with 1-[(2-Hydroxyethylimino)methyl]naphthalen-2-ol and 2-[(2-hydroxyethylimino)methyl]phenol

The crystal structures of (μ-4,4-bipyridine)-di(nitrato-1-[(2-hydroxyethylimino)methyl]naphthalen-2-olocopper (I) and catena-di(μ-4,4’-bipyridine)di(μ-4,4’-bipyridine)-di(nitrato-2-[2-(hydroxyethylimino) methyl]phenolocopper)diaquacopper(II) nitrate (II) were determined. In the crystal of I, each of the two copper atoms coordinates a singly deprotonated tridentate azomethine molecule, a nitrate ion, and bipyridine, which functions as a bridge between the central atoms. The copper coordination polyhedron is a slightly distorted tetragonal pyramid with the base formed by the imine and bipyridine nitrogen atoms and the phenol and alcohol oxygen atoms. The axial site in the pyramid is occupied by the oxygen atom of the monodentate nitrate groups. In the trinuclear structure II with C₂ crystal chemical symmetry, the terminal coordination unit is composed through copper coordination of monodeprotonated 2-[2-(hydroxyethylimino)methyl]phenol, bipyridine, and the nitrate anion. In the crystal, the trinuclear molecules form infinite ribbons along the z axis in which the pyridine molecules perform the bridging function. The central copper atom has an octahedral configuration formed by the nitrogen atoms of four 4,4’-bipyridine molecules and oxygen of two water molecules.     

Synthesis,characterization, X-ray structure and DFT calculation of two Mo(VI) and Ni(II) Schiff-base complexes

In this study, the syntheses of two new Mo(VI) and Ni(II) complexes with H₂L tridentate (ONO) Schiff-base ligand have been described and fully characterized by means of elemental analysis, FT–IR, electronic, ¹H-NMR spectroscopy and single-crystal X-ray diffraction. In both complexes, the Schiff-base completely deprotonates and coordinates to the metal ion as a dianionic tridentate ligand via the donor oxygens and nitrogen atoms. The coordination numbers of Mo(VI) and Ni(II) are six and four, respectively. The DFT-B3LYP/6–31 + G (d,p) and PBEPBE/6–31 + G (d,p) calculations are carried out for the determination of the optimized structures. Frequency calculations and NBO analysis are also performed for characterization. According to the theoretical analysis of the complexes, ligand-to-metal donation is greater than back donation. NBO data revealed that the main contribution of the frontier orbitals belongs to L⁻².     

Electrochemical, EPR and computational results on [Fe2Cp2(CO)2]-based complexes with a bridging hydrocarbyl ligand

The dimetallacyclopentenone complexes [Fe₂Cp₂(CO)(μ−CO){μ−η¹:η³−C_αHC_β(R)C(O)}] (R = CH₂OH, 1a; R = CMe₂OH, 1b; R = Ph, 1c) were prepared by photolytic reaction of [Fe₂Cp₂(CO)₄] with alkyne according to the literature procedure. The X-ray and the electrochemical characterization of 1c are presented. The μ-allenyl compound [Fe₂Cp₂(CO)₂(μ−CO){μ−η¹:η²_α,β−C_αHC_βCMe₂][BF₄] ([2][BF₄]), obtained by reaction of 1b with HBF₄, underwent monoelectron reduction to give a radical species which was detected by EPR at room temperature. The EPR signal has been assigned to [Fe₂Cp₂(CO)₂(μ−CO){μ−η¹:η²_α,β-C_αHC_βCMe₂}], [2]^•. The molecular structures of [2]⁺ and [2]^• were optimized by DFT calculations. The unpaired electron in [2]^• is localized mainly at the metal centers and, coherently, [2]^• does not undergo carbon-carbon dimerization, by contrast with what previously observed for the μ-vinyl radical complex [Fe₂Cp₂(CO)₂(μ−CO){μ−η¹:η²-CHCH(Ph)}]^•, [3]^•. Electron spin density distributions similar to the one of [2]^• were found for the μ-allenyl radical complexes [Fe₂Cp₂(CO)₂(μ-CO){μ-η¹:η²_α,β-C_αHC_βC(R¹)(R²)}]^• (R¹ = R² = H, [4]^•; R¹ = H, R² = Ph, [5]^•; R¹ = R² = Ph, [6]^•).     

Coordination compounds from the planar tridentate Schiff-base ligand 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol (mqmpH) with several transition metal ions: Use of [Fe(mqmp)(CH3OH)Cl2] in the catalytic oxidation of alkanes and alkenes

Four coordination compounds were synthesized in high yields from different transition metal ions (Fe^III, Co^II, and Cu^II) and an in situ generated Schiff-base ligand, i.e. 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol (mqmpH). The compounds were characterized by single-crystal X-ray diffraction, ESI-MS, IR spectroscopy, and ligand-field spectroscopy. The iron(III) complex is an efficient catalyst for the oxidation of alkanes and alkenes, under relatively mild conditions and with dihydrogen peroxide as terminal oxidant.     

A new Schiff-base as fluorescent chemosensor for selective detection of Cr3+: An experimental and theoretical study

A novel Schiff base fluorescent sensor N,N′-bis(salicylidene)-2,6-bis(4-aminophenyl)-4-phenylpyridine (P3) was synthesized through condensation of 2,6-bis(4-aminophenyl)-4-phenylpyridine and 2-hydroxybenzaldehyde. The obtained results from fluorescence analysis revealed that by excess of Cr³⁺ to P3, a remarkable increase was observed in the fluorescent intensity of the Schiff base at 663?nm with the ratio of CH₃CN/H₂O (95/5%), even though the other cations would likely have no impact on the fluorescence intensity. The cause of this trend might be ascribed to the formation of a 1:1 stoichiometric P3-Cr³⁺ complex, confirmed by Job's plot, which is resulted in preventing the photo-induced electron transfer (PET) process. From fluorescence titration, the association constant K_a was gained 2.28?×?10⁵?M^?1 and the limit of detection (LOD) was determined to be 1.3?×?10^?7?M. Furthermore, the optimized structure together with the electronic spectra of the proposed complex was determined by DFT and TDDFT calculations.     

Synthesis,X-ray structure,DFT studies,and catalytic activity of a vanadium(V) complex containing a tridentate Schiff base

Reactions of a solution of NH₄VO₃ in H₂O₂ and water and salicylidene benzoyl hydrazine as a tridentate Schiff base (ONO) afford a six-coordinate V(V) complex [VO(ONO)(OCH₃)(CH₃OH)] with a distorted octahedral configuration. The complexes [VO(ONO)(OCH₃)(CH₃OH)] were isolated as air-stable crystalline solids and fully characterized, including by single-crystal X-ray structure analysis. DFT calculations have been performed to understand the electronic structure of the complex. Vibrational frequencies and maximum absorption wavelengths of the complex theoretically calculated are in good agreement with experimental values. [VO(ONO)(OCH₃)(CH₃OH)] shows efficient oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.     

Synthesis and Crystal Structure of the Copper(II) Complex with N,N'-Cyclohexanebis(3- formyl- 5-tert-butyl-salicylaldimine)

INTRODUCTION Schiff-base complexes are some of the most important stereochemical models in transition metal coordination chemistry, with their ease of preparation and structural variation.[1~4] Metal derivatives of Schiff-base have been studied extensively, and copper(II) and nickel (II) complexes play major roles in both synthetic and structural research. The geometry of the coordination sphere is usually planar in the case of Ni, but of Cu, a tetrahedral distortion is often observed.[…     

5-甲氧基-2-[(E)-(6-甲基吡啶-2-亚氨基)甲基]苯酚的合成与表征

研究了以2-羟基-4-甲氧基苯甲醛和2-氨基-6-甲基吡啶为原料合成新型席夫碱化合物5-甲氧基-2-[(E)-(6-甲基吡啶-2-亚氨基)甲基]苯酚的方法。当2-羟基-4-甲氧基苯甲醛与2-氨基-6-甲基吡啶摩尔比为1∶1.6,反应时间为6 h,反应温度为75℃时,反应产率最高。采用元素分析、UV-Vis、IR、1H NMR、X-射线单晶衍射等方法进行结构表征。该化合物为单斜晶系,空间群P21/c,a=1.1886(3)nm,b=0.65948(16)nm,c=1.6897(4)nm,β=108.505(3)°,V=1.2560(5)nm3,Dc=1.281 g·cm-3,Z=4,F(000)=512,μ=0.087 mm-1,R1=0.0477,wR2=0.1342。通过π···π堆积和分子内氢键O2-H2···N1、C8-H8A···N2形成较稳定的晶体结构,并具有蓝色荧光。     

Synthese und Struktur von [Re(NH)Cl2(PMe2Ph)3][TaCl6] und [(Me2PhP)3Cl2Re≡N]2VOCl2

Synthesis and Structure of [Re(NH)Cl₂(PMe₂Ph)₃][TaCl₆] and [(Me₂PhP)₃Cl₂Re≡N]₂VOCl₂ The products of the reaction of ReNCl₂(PMe₂Ph)₃ with TaCl₅ are dependent on the solvent. In CH₂Cl₂ the solvent protonates the nitrido ligand to yield [Re(NH)Cl₂(PMe₂Ph)₃][TaCl₆] as air-stable, reddish brown needles with the space group P2₁/n and a = 1213.8(3), b = 1358.0(2), c = 2165.9(4) pm, β = 92.88(1)°, Z = 4. The Re atom of the cation exhibits an octahedral coordination with the phosphine ligands in meridional arrangement. The imido ligand is in trans-position to a Cl atom with a distance Re–N = 170.4(4) pm. When the reaction is carried out in toluene the dinuclear nitrido complex [Re(NTaCl₅)Cl₂(PMe₂Ph)₃] is obtained instead. The reaction of ReNCl₂(PMe₂Ph)₃ with VCl₃(THF)₃ in toluene affords the threenuclear complex [Re₂N₂Cl₄(PMe₂Ph)₅]VCl₃, which upon crystallization at air gives air-stable, reddish-brown crystals of [(Me₂PhP)₃Cl₂ReN]₂VOCl₂. They crystallize in the monoclinic space group P2₁ with a = 1519.2(5), b = 1257.1(1), c = 1564.3(6) pm, β = 102.86(2)°, and Z = 2. The threenuclear complex shows an almost linear arrangement Re≡N–V–N≡Re with distances Re–N 171(2) pm and V–N of 209(2) pm.