An X-ray photoelectron spectroscopic study of some copper(II) tetraaza complexes

A selected series of copper(II) tetraaza complexes, involving open-chain and macrocyclic ligands, has been studied by X-ray photoelectron spectroscopy. The binding energy data obtained are interpreted in terms of the structures of these complexes with particular reference to the existence of π-electron delocalisation over metal and ligand, peripheral ring substituents, cation-anion interaction and hydration water. It is apparent that the degree of cation-anion interaction and photoreduction is a function of the existing experimental conditions.     

Ligation of alkoxymethylimidazoles towards cadmium(II) and zinc(II). X-ray,spectroscopic, thermal and potentiometric investigation

The stability constants and structure of the complexes of Cd^II and Zn^II with 1-ethoxymethylimidazole (ExMeIm), 1-propoxymethylimidazole (PxMeIm), 1-ethoxymethyl-2-methylimidazole (ExMe-2-MeIm) and 1-propoxymethyl-2-methylimidazole (PxMe-2-MeIm) in aqueous solution have been determined by potentiometric methods. Zn^II form both tetrahedral and octahedral species with the cited ligands according to the configurational equilibrium type: octahedron tetrahedron, but Cd^II prefers octahedral coordination of alkoxymethylimidazole complexes in aqueous solution. Retention of the six-coordination form of Cd^II has also been confirmed by the data obtained for two novel compounds which have been synthesized in the solid state. The crystal and molecular structure of [Cd(ExMeIm)₄(NO₃)₂] (1) has been determined by X-ray diffraction. The coordination geometry around the Cd^II ion can be considered as slightly distorted tetragonal bipyramidal (CdN₄O₂). Additionally, another six-coordinate Cd^II compound with ethoxymethyl-2-methylimidazole [Cd(ExMe-2-MeIm)₄(H₂O)](NO₃)₂ (2) has been characterized by spectroscopic (i.r., far i.r., Raman) ES–MS and t.g.a. methods.     

Ligation properties of 2-acetyl-2-thiazoline semicarbazone (ATsc): Isolation, spectroscopic and X-ray study of ATsc and its Cu(II) and Ni(II) complexes

A new ligand, 2-acetyl-2-thiazoline semicarbazone (ATsc), has been prepared and characterized by a variety of physico-chemical techniques. Likewise, the metal complexes [CuCl₂(ATsc)] and [Ni(ATsc)₂](NO₃)₂ · H₂O have been isolated and characterized through elemental analysis, IR, UV–Vis–NIR diffuse reflectance and magnetic susceptibility, as well as, in the case of the copper complex, by means of EPR. Moreover, the structures have been determined by X-ray diffraction. In both complexes the Schiff base acts as a tridentate ligand through N(1), N(2) and O atoms, making two five-membered chelate rings. The copper complex consists of monomeric molecules in which the copper atom is five coordinated in a distorted square-pyramidal geometry, with one ATsc and two chlorine ligands. The complex cation of nickel possesses approximately a non-crystallographic C₂ symmetry. The environment around the nickel atom may be described as a distorted octahedral geometry with the metallic atom coordinated to two ATsc ligands.     

'Double redox-activity' in azobenzene-quinonoid palladium(II) complexes: a combined structural, electrochemical and spectroscopic study

Reactions of [(az(-H))Pd(μ-Cl)(2)Pd(az(-H))] (az = azobenzene) with the zwitterionic, p-benzoquinonemonoimine-type ligands 4-(n-butylamino)-6(n-butylimino)-3-oxocyclohexa-1,4-dien-1-olate (Q(1)) or 4-(isopropylamino)-6(isopropylimino)-3-oxocyclohexa-1,4-dien-1-olate) (Q(2)) in the presence of a base leads to the formation of the mononuclear complexes [(az(-H))Pd(Q(1)(-H))] (1) and [(az(-H))Pd(Q(2)(-H))] (2) respectively. Structural characterization of 2 shows an almost square planar coordination geometry around the Pd(II) centre, a short Pd-C bond, a slight elongation of the N=N double bond of the az(-H) ligand and localization of the double bonds within the Q(2)(-H) ligand. Additionally, intermolecular N-H-O interactions exist between the uncoordinated N-H and O groups of two different molecules. Cyclic voltammetry of the complexes reveals an irreversible oxidation and two reversible reduction processes. A combination of electrochemical and UV-vis-NIR and EPR spectroelectrochemical studies are used to show that both coordinated ligands participate successively in the redox processes, thus revealing their non-innocent character.     

Synthesis,spectroscopic study,X-ray diffraction,and comparative antimicrobial study of Schiff bases based on o-toluidine and their Co(II) complexes

Schiff bases are versatile compounds for the design of the ternary complex. An experiment has been made to synthesize two novel complexes of Co(II). Here, The primary ligand, L₁ was prepared by the condensation reaction of o-toluidine with 3-formyl chromone or o-toluidine with 3- methylquinolinecarbaldehyde and the secondary ligand which was 8-Hydroxyquinoline. These potent complexes were prepared by condensation of primary and secondary ligands with Cobalt salt. The reaction was performed through the conventional reflux method. The newly synthesized chromone and quinoline derived novel compounds are proposed to have significant antimicrobial activity against selective strains of bacteria and fungi. This can be great opportunity for researchers and the use of biological applications of the synthesized novel compounds can be a part of unique field of research for the future to be focus. Chromone derivative has great biological diversity in the medicinal and pharmaceutical fields. Along with these compounds, quinoline derivatives also have antibacterial, and antifungal activities. The synthesized ligand and complex were characterized by elemental analysis, molecular weight determination, magnetic moment measurement, melting point determination, spectral analysis (IR, UV–Vis, ¹H NMR, Mass, etc.), and X-ray diffraction. The synthesized complexes were paramagnetic and non-electrolytic in nature. The Uv–Vis, FTIR, NMR, and Mass spectra suggest the octahedral geometry of the complexes. The synthesized compounds were further evaluated for biological studies against selected bacterial and fungal strains. It has been observed that the antimicrobial activity of most of the complexes are better than that of ligands.     

Nickel(II)-dppa-arylazoimidazole complexes: Synthesis and detailed spectroscopic study

The reaction of [Ni(dppa)(Cl)₂] or [Ni(dppa)(Br)₂] with AgOTf gives [Ni(dppa)(OTf)₂], which then form [Ni(dppa)(RaaiR)](OSO₂CF₃)₂ under the action of arylazoimidazole(RaaiR) in a dichloromethane medium [RaaiR′ = p-R-C₆H₄-N=N-C₃H₂-NN-1-R′, (I–III), abbreviated as N,N′-chelating agent, where N(imidazole) and N(azo) represent N and N’, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (I), CH₂CH₃ (II), CH₂Ph (III), OSO₂CF₃ is the triflate anion]. The ¹H NMR spectral measurements suggest that a bound azoimine is responsible for a number of signals of phenyl protons in the aromatic region. The molecules of the complexes contain a number of different carbon atoms which gives a number of different peaks in the ¹³C (¹H) NMR spectrum. The text was submitted by the author in English. The text was submitted by the author in English.     

Thermal,spectroscopic, X-ray powder diffraction,and structural studies on a new Cd(II) mixed-ligand coordination polymer

A new coordination polymer derived from Cd(II) with both rigid and flexible spacer ligands trans-1,2-bis(4-pyridyl)ethane (bpa) and 4,4′-bipyridine (4, 4′-bipy), {[Cd(μ-bpa)(4, 4′-bipy)₂(H₂O)₂] · (ClO₄)₂} _n has been synthesized and characterized by elemental analysis, IR-, ¹H NMR spectroscopy and studied by thermal analyses as well as X-ray crystallography. The single crystal X-ray analysis shows that the complex is a 1-D polymer as a result of bridging 1,3-di(4-pyridyl)propane (bpa). The 1-D chains are further self-assembled into a 3-D network via hydrogen bonding and π–π stacking. In this structure the perchlorates fill the voids. Thermal studies of this polymer show step to step separating of ligands and counter ion at different temperatures.     

Cu(II)-intercalated muscovite: An infrared spectroscopic study

Diffuse reflectance infrared spectroscopy (DRIFT) has proved to be a useful tool for the investigation of migration paths of intercalated metal cations within the layered structure of phyllosilicates like muscovite. While the fixation of small cations like lithium or copper in clay minerals and their migration paths have been studied extensively, they never have been reported for muscovite. Therefore, the aim of this study was to investigate the effects of a treatment with a supersaturated Cu-nitrate solution on the structure of muscovite. Additional X-ray diffractometric (XRD) data showed the formation of new d(0 0 l) and d(0 0 2) peaks, and thus proved that the new cations already were intercalated into the muscovite interlayers, although the concentration of the original interlayer cation potassium was nearly not affected. This suggested the simultaneous occurrence of both potassium and copper in the interlayers, resulting in an expansion along the c-axis and in a decrease of the a and b parameters. The spectroscopic investigations proved a migration of the cations deep into the tetrahedral sheets. As all bands which can be assigned to vibrations of the octahedral sheet (e.g. at 713 or 903 cm⁻¹) were strongly affected by the treatment, a fixation of Cu close to the OH-groups of the octahedral sheets was suggested.     

Synthesis,characterization and spectroscopic studies of a new ligand [N′-(2-methoxybenzoyl)hydrazinecarbodithioate] ethyl ester and its Mn(II) and Cd(II) complexes: X-ray structural study of Mn(II) complex

A new dithioligand [N′-(2-methoxybenzoyl)hydrazinecarbodithioate] ethyl ester (H₂mbhce, 1) formed complexes [M(Hmbhce)₂]_n {M = Mn(II), Cd(II)} which have been characterized with the help of elemental analyses, magnetic susceptibility measurements, IR, UV–Vis, ¹H and ¹³C NMR and mass spectrometry. [Mn(Hmbhce)₂]_n (2) crystallized in monoclinic system with space group P₂₁/n. In the polymeric structure of 2, the ligand acts as an uninegative tridentate N(1), O(1), S(3) donor and forms a five membered chelate ring with N(1), C(2) and O(1). The intermediate bond lengths (between single and double bond distances) O(1)–C(2) = 1.241(3), N(2)–C(2) = 1.325(3), N(1)–N(2) = 1.393(2), N(1)–C(8) = 1.311(3) ? and C(8)–S(3) = 1.704(2) Å suggest considerable delocalization of charge which develops slightly aromatic character in the chelate ring.     

Copper(II) complexes with derivatives of salen and tetrahydrosalen: a spectroscopic, electrochemical and structural study

Salen type complexes, CuL, the corresponding tetrahydrosalen type complexes, Cu[H₄]L, and N,N′-dimethylated tetrahydrosalen type complexes, Cu[H₂Me₂]L, were investigated using cyclic voltammetry, and electronic and ESR spectroscopy. In addition, the analogous copper(II) complexes with a derivative of the tetradentate ligand ‘salphen’ [salphen=H₂salphen=N,N′-disalicylidene-1,2-diaminobenzene] were studied. Solutions of CuL, Cu[H₄]L and Cu[H₂Me₂]L are air-stable at ambient temperature, except for the complex Cu(^tBu, Me)[H₄]salphen [H₂(^tBu, Me)[H₄]salphen=N,N′-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)-1,2-diaminobenzene]. Cu(^tBu, Me)[H₄]salphen interacts with dioxygen and the ligand is oxidatively dehydrogenated (–CH₂–NH–→–C=N–) to form Cu(^tBu, Me)[H₂]salphen and finally, in the presence of base, Cu(^tBu, Me)salphen. X-ray structure analysis of Cu(^tBu, Me)[H₂Me₂]salen confirms a slightly tetrahedrally distorted planar geometry of the CuN₂O₂ coordination core. The complexes were subjected to spectrophotometric titration with pyridine, to determine the equilibrium constants for adduct formation. It was found that the metal center in the complexes studied is only of weak Lewis acidity. In dichlormethane, the oxidation Cu(II)/Cu(III) is quasireversible for the CuL type complexes, but irreversible for the Cu[H₄]L and Cu[H₂Me₂]L type. A poorly defined wave was observed for the irreversible reduction Cu(II)/Cu(I) at potentials less than −1.0 V. The ESR spectra of CuL at both 77 K and room temperature reveal that very well resolved lines can be attributed to the interaction of an unpaired electron spin with the copper nuclear spin, ¹⁴N donor nuclei and to a distant interaction with two equivalent protons [A^Cu(iso)≈253 MHz, A^N(iso)≈43 MHz, A^N(iso)≈20 MHz]. These protons are attached to the carbon atoms adjacent to the ¹⁴N nuclei. In contrast to CuL, the number of lines in the spectra of the complexes Cu[H₄]L and Cu[H₂Me₂]L is greatly reduced. At room temperature, only a quintet with a considerably smaller nitrogen shf splitting constant [A^N(iso)≈27 MHz] is observed. Both factors, planarity and conjugation, are thus essential for the observation of distant hydrogen shf splitting in CuL. Due to the C=N bond hydrogenation, the coordination polyhedra of the complexes Cu[H₄]L and Cu[H₂Me₂]L is more flexible and more sensitive to ligand modification than that of CuL. The electron-withdrawing effect of the phenyl ring of the phenylenediamine bridge is reflected in a reduction of the copper hyperfine coupling constants in Cu(^tBu, Me)[H₄]salphen and Cu(^tBu, Me)[H₂Me₂]salphen complexes [A^Cu(iso)≈215 MHz].     

Dithizone and its oxidation products: a DFT, spectroscopic, and X-ray structural study

Air oxidation of ortho-fluorodithizone resulted in the first X-ray resolved structure of a disulfide of dithizone, validating the last outstanding X-ray structure in the oxidation of dithizone, H(2)Dz, which proceeds via the disulfide, (HDz)(2), to the deprotonated dehydrodithizone tetrazolium salt, Dz. Density functional theory calculations established the energetically favored tautomers along the entire pathway; in gas phase and in polar as well as nonpolar solvent environments. DFT calculations using the classic pure OLYP and PW91, or the newer B3LYP hybrid functional, as well as MP2 calculations, yielded the lowest energy structures in agreement with corresponding experimental X-ray crystallographic results. Atomic charge distribution patterns confirmed the cyclization reaction pathway and crystal packing of Dz. Time dependent DFT for the first time gave satisfactory explanation for the solvatochromic properties of dithizone, pointing to different tautomers that give rise to the observed orange color in methanol and green in dichloromethane. Concentratochromism of H(2)Dz was observed in methanol. Computed orbitals and oscillators are in close agreement with UV-visible spectroscopic experimental results.     

Copper(II) binding modes in the prion octapeptide PHGGGWGQ: a spectroscopic and voltammetric study

The N-terminal octapeptide repeat region of human prion protein (PrPc) is known to bind Cu(II). To investigate the binding modes of copper in PrPc, an octapeptide Ac-PHGGGWGQ-NH2 (1), which corresponds to an octa-repeat sequence, and a tetrapeptide Ac-HGGG-NH2 (2) have been synthesised. The copper(II) complexes formed with 1 and 2 have been studied by circular dichroism (CD) and electron spin resonance (ESR) spectroscopy. Both peptides form 1:1 complexes with Cu(II) at neutral and basic pH. CD, ESR and visible absorption spectra suggest a similar co-ordination sphere of the metal ion in both peptides, which at neutral pH consists of a square pyramidal geometry with three peptidic nitrogens and the imidazole nitrogen as donor atoms. Cyclic voltammetric measurements were used to confirm the geometrical features of these copper(II) complexes: the observation of negative redox potentials are in good agreement with the inferred geometry. All these results taken together suggest that peptide 1 provides a single metal binding site to which copper(II) binds strongly at neutral and basic pH and that the binding of the metal induces the formation of a stiffened structure in the HGGG peptide fragment.     

Synthesis,spectroscopic and X-ray structural studies of mercury(II) halide complexes of 4-methoxybenzoylmethylenetriphenylphosphorane

The reactions of the title ylide {(C₆H₅)₃PCHCOC₆H₄OCH₃)} (MBPPY) with mercury(II) chloride and mercury(II) bromide in equimolar ratios using methanol as the solvent produces crystals of [(MBPPY) · HgCl₂]₂ (1) and [(MBPPY) · HgBr₂]₂ (2), respectively. Single crystal X-ray analyses reveal the presence of centrosymmetric dimeric structures containing the ylide and HgX₂ (X = Cl or Br) in both cases. The IR and NMR data of the product [(MBPPY) · HgI₂]₂ (3), formed by the reaction of mercury(II) iodide with the same ylide, are similar to those of 1 and 2. Analytical data indicate a 1:1 stoichiometry between the ylide and Hg(II) halide in each of the three products.     

Cu(II), Ni(II), and Hg(II) thiocyanate complexes incorporating 4,5-diazafluoren-9-one: synthesis,spectroscopic characterization,X-ray studies,and magnetic properties

This article presents a combined experimental and computational study of the complexes [Cu(dafone)₂(SCN)₂] (1), [Ni(dafone)₂(SCN)₂] (2) and [Hg(dafone)(SCN)₂] (3), where dafone stands for 4,5-diazafluoren-9-one. The compounds have been studied by IR, UV–Vis spectroscopy, and single crystal X-ray diffraction. The electronic structures of these complexes have been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of 1, 2, and 3 have been calculated with the time-dependent DFT method, and their UV–Vis spectra have been discussed on this basis.     

Copper(II) complexes of new biomimetic polydentate amide ligands: a spectroscopic study

Complexes of Cu(II) with N,N'-bis(3-carboxy-1-oxopropanyl)-1,2-ethylenediamine(C(10)H(16)N(2)O(6),L(1)), N,N'-bis(3-carboxy-1-oxopropanyl)-1,2-phenylenediamine(C(14)H(16)N(2)O(6),L(2)), N,N'-bis(2-carboxy-1-oxophenelenyl)-1,2-phenylenediamine(C(22)H(16)N(2)O(6),L(3)) and N,N'-bis(3-carboxy-1-oxoprop-2-enyl)-1,2-phenylenediamine(C(14)H(12)N(2)O(6),L(4)) have been prepared and characterised by elemental analyses, vibrational spectra, magnetic susceptibility measurements, ligand field spectra, EPR spectra, thermal studies and X-ray diffraction spectra. Vibrational spectra indicate coordination of amide and carboxylate oxygens of the ligands giving a MO(4) square planar chromophore. Ligand field and EPR spectra support square planar geometry around Cu(II). [Cu(L(1))] complex has the maximum activation energy and [Cu(L(3))] complex has the minimum activation energy.     

Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.     

Novel thiocyanate complexes of cadmium(II) - Synthesis, spectroscopic characterization, X-ray studies and DFT calculations

Three novel thiocyanate cadmium(II) compounds [Cd(ind)₂(SCN)₂]_n (1), [Cd(dpa)Cl(SCN)]_n (2) and [Cd(terpy)(SCN)₂] (3) were synthesized and characterized by spectroscopic and crystallographic methods. Thiocyanate ions of 1 act as bridging ligands generating a one-dimensional chain constructed of Cd(SCN)₂Cd units and expanding along the crystallographic direction [1 0 0]. The Cd(II) ions of 2 are bridged by alternating di-μ-Cl and di-μ_1,3-NCS bridges to one-dimensional chain running along the crystallographic direction [0 1 0]. [Cd(terpy)(SCN)₂] (3) is a square pyramidal mononuclear compound.The fluorescence properties of the complexes 1 and 2 were examined in solid state, whereas fluorescence spectra of 3 were recorded in both solid state and solution. All they were compared with the fluorescence properties of the free ligands. Additionally, the electronic spectrum of 3 were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.     

Palladium(II)-dppe-arylazoimidazole complexes: Synthesis,and spectroscopic characterization

Reaction of [Pd(dppe)Cl₂/Br₂] with AgOTf in a dichloromethane medium followed by ligand addition led to [Pd(dppe)(OSO₂CF₃)₂] and then [Pd(dppe)(RaaiR)](OSO₂CF₃)₂ [RaaiR′ = p-R-C₆H₄-N=N-C₃H₂-NN-1-R′, (1–3), abbreviated as a N,N′-chelator, where N(imidazole) and N(azo) are represented by N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), OSO₂CF₃ is the triflate anion, dppe = 1,2-bis-(diphenylphosphinoethane)]. ³¹P “¹H” NMR confirmed that due to the two phosphorus atom interaction in the azoimine symmetrical environment one sharp peak was formed. The ¹H NMR spectral measurements suggest that azo-imine link with lot of phenyl protons in the aromatic region. ¹³C (¹H) NMR spectrum, ¹H, ¹H COSY and ¹H, ¹³C HMQC spectrum assign the solution structure and stereo-retentive conformation in each complex.