Electron Spin Resonance Spectral Studies Research Articles

Origin of Intersystem Crossing in Red-Light Absorbing Bodipy Derivatives: Time-Resolved Transient Optical and Electron Paramagnetic Resonance Spectral Studies with Twisted and Planar Compounds.

We studied the intersystem crossing (ISC) property of red-light absorbing heavy atom-free dihydronaphtho[b]-fused Bodipy derivatives (with phenyl group attached at the lower rim via ethylene bridge, taking constrained geometry, i.e., BDP-1 and the half-oxidized product BDP-2) and dispiroflourene[b]-fused Bodipy (BDP-3) that have a twisted π-conjugated framework. BDP-1 and BDP-3 show strong and sharp absorption bands (i.e., ε = 2.0 × 105 M-1 cm-1 at 639 nm, fwhm ∼491 cm-1 for BDP-3). BDP-1 is significantly twisted (φ = 21.6°), while upon mono-oxidation, BDP-2 becomes nearly planar on the oxidized side (φ = 3.5°). Interestingly, BDP-2 showed efficient ISC (triplet state quantum yield, ΦT = 40%) due to S1/T2 state energy matching. Long-lived triplet excited state was observed (τT = 212 μs in solution and 2.4 ms in polymer matrix), and ISC takes 4.0 ns. Differently, twisted BDP-1 gives weak ISC only 5%, ISC takes 7.7 ns, and the triplet state is populated only with addition of ethyl iodide. Time-resolved electron paramagnetic resonance spectra of BDP-1 revealed the coexistence of two triplet states, with drastically different zero-field splitting D parameters of -2047 MHz and -1370 MHz, respectively, along with varying sublevel population ratios. We demonstrate that the ISC is not necessarily enhanced by torsion of the π-conjugation framework; instead, S1/Tn state energy matching is more efficient to induce ISC even in compounds that have planar molecular structures.

Triplet Excited State Mechanistic Study of meso‐Substituted Methylthio Bodipy Derivative: Time‐Resolved Optical and Electron Paramagnetic Resonance Spectral Studies

AbstractUnderstanding the intersystem crossing (ISC) mechanism of organic compounds is essential for designing new triplet photosensitizers. Herein, we investigated the ISC mechanism of a heavy atom‐free Bodipy derivative with thiomethyl substitution (S−BDP). A long‐lived triplet state was observed with nanosecond transient absorption spectroscopy with lifetime of 7.5 ms in a polymer film and 178 μs intrinsic lifetime in fluid solution, much longer as compared with what was previously reported (apparent triplet lifetime=15.5 μs). Femtosecond transient absorption studies retrieved an ISC time constant of ∼3 ns. Time‐resolved electron paramagnetic resonance (TREPR) indicated a special triplet electron spin polarization phase (ESP) pattern (a, e, a, e, a, e) for S−BDP, different from the ESP (e, e, e, a, a, a) typical for the spin‐orbital coupling (SOC) mechanism. This indicates that the electron spin selectivity of the ISC of S−BDP is different from that of the normal SOC effect in iodo‐Bodipy. Simulations of the TREPR spectra give a zero‐field‐splitting D parameter of −2257 MHz, much smaller as compared to the reference 2,6‐diiodo‐Bodipy (D=−4380 MHz). The computed SOC matrix elements (0.28–1.59 cm−1) and energy gaps for the S1/Tn states suggest that the energy matching between the S1 and T2/T3 states (supported by the largest kISC ∼109 s−1) enhances the ISC for this compound.

Synthesis, characterization, molecular docking, DNA cleavage properties, and antimicrobial activity studies of mixed ligand complexes

AbstractCu (II), Ni (II), Co (II), and Mn (II) acetato in addition to Cu (II) chloro and nitrato mixed ligand complexes of 4‐([quinolin‐2‐yl]methyleneamino)‐1,2‐dihydro‐2,3‐dimethyl‐1‐phenylpyrazol‐5‐one (L), as a primary ligand and 2,4‐dihydroxy benzaldehyde (H2L), as a secondary ligand have been isolated. The structural features and geometrical arrangements of the synthesized mixed ligand complexes were identified by elemental analysis, Fourier transform infrared spectroscopy (FT‐IR), conductivity measurements, UV‐Vis spectra, magnetic moment measurements, X‐ray diffraction, and electron spin resonance (ESR) spectral and thermogravimetric techniques studies of the mixed ligand complexes confirming the molar ratio 1:1:1 (primary ligand: M: secondary ligand) for Cu (II), Co (II), Mn (II), and UO2(II) chelates. The spectral techniques also confirmed the metal chelates have the formulae (Cu[H2L][L][X]2), where X = Cl−(1); NO3−(2); and (M[L][HL][OAc])YH2O, where M = Cu (II) (3), Co (II) (4); Y = 1, Mn (II) (5); Y = 1 and UO2(II) (6); Y = 2. The kinetic and thermodynamics parameters of the mixed ligand complexes at different decomposition steps were calculated using Coast‐Redfern and Horowiz‐Metzger methods. Also, the antimicrobial activities of ligands and their mixed ligand complexes were screened by Disc Diffusion method. It was found that all mixed ligand complexes (1–6) have high antibacterial activity againstKlebsiella pneumoniaethan penicillin G. By studying the molecular docking between the quinoline‐2‐carbaldehyde, the ligand and the receptors (Escherichia coli(PDB code: 3t88),Staphylococcus aureus(PDB code: 3q8u), lung cancer (PDB code: 1x2j), and colon cancer (PDB code: 2hq6)), it was found that the ligand is efficient compound for all the receptors than the quinoline‐2‐carbaldehyde. The DNA cleavage properties of the two ligands and their complexes have been investigated by gel electrophoresis and the results showed that complex (1) without H2O2and complex (6) with H2O2exhibited a significant partial oxidative cleavage among other complexes.

CuII{(LISQ)˙-}2] (H2L: thioether-appended o-aminophenol ligand) monocation triggers change in donor site from N2O2 to N2O(2)S and valence-tautomerism.

Using a potentially tridentate o-aminophenol-based redox-active ligand H2L1 (2-[2-(benzylthio)phenylamino]-4,6-di-tert-butylphenol) in its deprotonated form, [Cu(L1)2] has been synthesized and crystallized as [CuII(L1)2]·CH2Cl2 (1·CH2Cl2). A cyclic voltammetry experiment (in CH2Cl2; V vs. SCE (saturated calomel electrode)) on 1·CH2Cl2 exhibits two oxidative (E = 0.20 V (peak-to-peak separation, ΔEp = 100 mV) and E = 0.90 V (ΔEp = 140 mV)) and two reductive (E = -0.52 V (ΔEp = 110 mV) and E = -0.92 V (ΔEp = 120 mV)) responses. Upon oxidation using a stoichiometric amount of [FeIII(η5-C5H5)2](PF6), 1·CH2Cl2 yielded [Cu(L1)2](PF6) (2). Structural analysis (100 K) reveals that 1·CH2Cl2 is a four-coordinate bis(iminosemiquinonato)copper(ii) complex (CuN2O2 coordination), and that the thioethers remain uncoordinated. The twisted geometry of 1 (distorted tetrahedral) results in considerable changes in the electronic structure, compared to well-known square-planar analogues. Crystallographic analysis of 2 both at 100 K and at 293 K reveals that it is effectively a four-coordinate complex with a CuN2OS coordination; however, a substantial interaction with the other phenolate O is observed. The metal-ligand bond distances and metric parameters associated with the o-aminophenolate rings indicate a valence-tautomeric (VT) equilibrium involving monocationic (iminosemiquinonato)(iminoquinone)copper(ii) and bis(iminoquinone)copper(i). Complex 1·CH2Cl2 is a three-spin system and a magnetic study (4-300 K) established that it has a S = 1/2 ground-state, owing to the strong antiferromagnetic coupling between the unpaired spin of the copper(ii) and the iminosemiquinonate(1-) π-radical anion. Electron paramagnetic resonance (EPR) spectral studies corroborate this result. Complex 2 is diamagnetic and the existence of VT in 2 was probed using variable-temperature (248-328 K) 1H NMR and EPR (100-298 K) spectral measurements and X-ray photoelectron spectroscopic studies at 298 K. Remarkably, modification of the well-studied 2-anilino-4,6-di-tert-butylphenol by incorporation of a benzylthioether arm leads to the occurrence of VT in 2. The electronic structure of 1·CH2Cl2 and 2 has been assigned using density functional theory (DFT) calculations at the B3LYP-D3 level of theory. Time-dependent (TD)-DFT calculations have been performed to elucidate the origin of the observed UV-VIS-NIR absorptions.

Synthesis, characterization, fluorescence imaging, and cytotoxicity studies of a uracil‐based azo derivative and its metal complexes

A uracil‐based heterocyclic azo derivative was prepared by coupling diazotized 5‐aminouracil with 2‐naphthol. This ligand, viz., 1‐(2,4‐dioxopyrimidine‐5‐yl)‐azo‐naphth‐2‐ol (HNAP), was used as a precursor for the synthesis of a series of complexes with manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) ions. Various physicochemical measurements UV–Visible, Infrared (IR), 1H NMR, 13C Nuclear Magnetic Resonance (NMR), and electron spin resonance (ESR) spectral studies were employed to characterize the ligand and the metal complexes. The ligand showed good selectivity toward Mn2+ over the other metal ions with a detection limit of 1.36 μM. This probe was used for the confocal fluorescence imaging of Mn2+ ions in Michigan Cancer Foundation‐7 (MCF‐7) cells. The ligand and the metal complexes were tested for their cytotoxicity on the MCF‐7 cell line. It was observed that complexation of HNAP with the metal ions exhibited a promising cytotoxicity.

General Strategy for Enhancing Electrochemiluminescence of Semiconductor Nanocrystals by Hydrogen Peroxide and Potassium Persulfate as Dual Coreactants.

Semiconductor nanocrystals usually suffer from weak electrogenerated chemiluminescence (ECL) emissions compared with conventional organic emitters. In this work, we propose, for the first time, a very convenient but effective way to greatly enhance ECL emission of semiconductor TiO2 nanotubes (NTs) by H2O2 and K2S2O8 as dual coreactants, generating ECL emission ca. 6.3 and 107 times stronger than that of K2S2O8 or H2O2 as an individual coreactant, respectively. Scanning electron microscopy, X-ray diffraction, and electron paramagnetic resonance spectral studies were carried out to investigate the ECL enhancement mechanism. The ECL enhancement of TiO2 NTs by the K2S2O8-H2O2 system was supposed to originate from the coordination of H2O2 to the TiO2 surface and the synergy effect between H2O2 and K2S2O8 in the ECL process. The coordination of H2O2 to the surface of TiO2 could stabilize the electrogenerated coreactant-related radical OH(•) (hydroxyl radical), which could obviously promote the amount of sulfate radical anion (SO4(•-)) near the electrode surface by inducing decomposition of K2S2O8 into SO4(•-) or inhibiting the consumption of SO4(•-) by its reaction with H2O. The holes (h(+)) released from SO4(•-) were injected into the valence band of TiO2, resulting in more TiO2(+), which combined with the electrons coming from the conduction band with an enhanced light emission. Moreover, this enhancement effect was also applicable to ECL of a CdS nanocrystal film on a glass carbon electrode, with ca. 2.74- and 148.3-fold enhanced ECL intensity correspondingly, indicating wide applications in the development of semiconductor nanocrystal-based ECL biosensors.

Iodophenol blue-enhanced luminol chemiluminescence and its application to hydrogen peroxide and glucose detection

In this study, we found that iodophenol blue can enhance the weak chemiluminescence (CL) of luminol–H2O2 system. With the aid of CL spectral, electron spin resonance (ESR) spectral measurements and studies on the effects of various free radical scavengers on the iodophenol blue-enhanced luminol–H2O2 system, we speculated that iodophenol blue may react with H2O2 and oxygen to produce oxidizing radical species such as OH• and O2•− resulting the formation of 1O2. The generated 1O2 may react with luminol anion generating an unstable endoperoxide and subsequent 3-aminophthalate* (3-APA*). When the excited-state 3-APA returned to the ground-state, an enhanced CL was observed. Based on the H2O2 concentration dependence of the catalytic activity of iodophenol blue, a cheap, simple, sensitive CL assay for the determination of H2O2 was established. Under the optimum experimental conditions, a linear relationship between the relative CL intensity and H2O2 concentration in the range of 0.025–10μM was obtained. As low as 14nM H2O2 can be sensitively detected by using the proposed method. The relative standard deviation for 5, 1 and 0.25μM H2O2 was 2.58%, 5.16% and 4.66%, respectively. By combining the glucose oxidase (GOx)-catalyzed oxidation reaction, CL detection of glucose was realized. The linear range of glucose detection was 0.1–30μM with a detection limit of 0.06μM. The proposed method has been applied to the detection of glucose in diluted serum.

Antibacterial, antifungal and in vitro antileukaemia activity of metal complexes with thiosemicarbazones.

1-phenyl-3-methyl-4-benzoyl-5-pyrazolone 4-ethyl-thiosemicarbazone (HL) and its copper(II), vanadium(V) and nickel(II) complexes: [Cu(L)(Cl)]·C2H5OH·(1), [Cu(L)2]·H2O (2), [Cu(L)(Br)]·H2O·CH3OH (3), [Cu(L)(NO3)]·2C2H5OH (4), [VO2(L)]·2H2O (5), [Ni(L)2]·H2O (6), were synthesized and characterized. The ligand has been characterized by elemental analyses, IR, 1H NMR and 13C NMR spectroscopy. The tridentate nature of the ligand is evident from the IR spectra. The copper(II), vanadium(V) and nickel(II) complexes have been characterized by different physico-chemical techniques such as molar conductivity, magnetic susceptibility measurements and electronic, infrared and electron paramagnetic resonance spectral studies. The structures of the ligand and its copper(II) (2, 4), and vanadium(V) (5) complexes have been determined by single-crystal X-ray diffraction. The composition of the coordination polyhedron of the central atom in 2, 4 and 5 is different. The tetrahedral coordination geometry of Cu was found in complex 2 while in complex 4, it is square planar, in complex 5 the coordination polyhedron of the central ion is distorted square pyramid. The in vitro antibacterial activity of the complexes against Escherichia coli, Salmonella abony, Staphylococcus aureus, Bacillus cereus and the antifungal activity against Candida albicans strains was higher for the metal complexes than for free ligand. The effect of the free ligand and its metal complexes on the proliferation of HL-60 cells was tested.

Oxidovanadium(IV) complexes involving dehydroacetic acid and β-diketones of bioinorganic and medicinal relevance: Their synthesis, characterization, thermal behavior and DFT aspects

Six new mixed-ligand complexes of oxidovanadium(IV) of the general composition [VO(dha)(L)(H2O)], where dhaH=dehydroacetic acid, LH=β-diketones, viz., acetoacetanilide (aaaH), o-acetoacetotoluidide (o-aatdH), o-acetoacetanisidide (o-aansH), acetylacetone (acacH), methyl acetoacetate (macacH) or ethyl acetoacetate (eacacH) have been synthesized by the reaction of VOSO4⋅5H2O and the ligands given above in aqueous-ethanol medium. The resulting complexes have been characterized on the basis of elemental analyses, vanadium determination, molar conductance and magnetic measurements, mass spectrometry, thermogravimetric analysis, infrared and electron spin resonance spectral studies. The thermal decomposition processes of two representative complexes are discussed and the order of reaction (n) and the activation energy (Ea) for the particular decomposition steps have been calculated from thermogravimetric (TG) curve. Geometry optimizations were performed with the Gaussian 09 software package by using density functional theory (DFT) methods with Becke-3–Lee–Yang–Parr (B3LYP) hybrid exchange–correlation functional and the standard LANL2MB basis set for dhaH and its complex [VO(dha)(acac)(H2O)]. Molecular surface electrostatic potentials (MSEP), vibrational frequency calculations, bond lengths, bond angles, dihedral angles, natural population analysis and calculations of molecular energies, HOMO and LUMO were made. No imaginary frequency was found in the optimized model compounds and hence ensures that the molecule is in the lowest point of the potential energy surface, that is, a energy minimum. Finally calculated results were applied to simulated Infrared spectra of the title compound which show good agreement with observed spectra. Based on experimental and theoretical data, suitable trans-octahedral structures have been proposed for these complexes.

Carbon Nitride Quantum Dots: A Novel Chemiluminescence System for Selective Detection of Free Chlorine in Water

A facile one-step microwave-assisted approach for the preparation of strong fluorescent carbon nitride quantum dots (g-CNQDs) by using guanidine hydrochloride and EDTA as the precursors was developed. Strong chemiluminescence (CL) emission was observed when NaClO was injected into the prepared g-CNQDs, and a novel CL system for direct detection of free chlorine was established. Free residual chlorine in water was sensitively detected with a detection limit of 0.01 μM and had a very wide detection range of 0.02 to 10 μM. On the basis of CL spectral, UV-visible absorption spectral, and electron spin resonance (ESR) spectral studies, as well as investigations on the effects of various free radical scavengers, a possible CL mechanism was proposed. It was suggested that the radiative recombination of oxidant-injected holes and electrons in the g-CNQDs accounted for the CL emission. Meanwhile, (1)O2 on the surface of g-CNQDs, generated from some reactive oxygen species in the g-CNQDs-NaClO system, could transfer energy to g-CNQDs and thus further enhance the CL emission. The CL system is highly sensitive and differentiable, opening a new field for the development of novel CL-emitting species, but also expanding the conventional optical utilizations of g-CNQDs.

Synthesis, spectral characterization and biological activity studies of transition metal complexes of Schiff base ligand containing indole moiety

A new series of transition metal complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), with a tridentate (oxygen nitrogen nitrogen) ligand 3,5-dimethyl-N′-[(1E)-1′-pyridin-2′-ylethylidene]-1H-indole-2-carbohydrazide (L) have been synthesized and characterized on the basis of analytical, magnetic susceptibility, infra red, nuclear magnetic resonance, fast atom bombardment-mass, electron paramagnetic resonance spectral studies, X-ray powder diffraction and UV-visible spectral data. Based on analytical and molar conductance data, the complexes may be formulated as [M(L)2]·(H2O)n, where M˭ Co, Cu and Ni and [M(L)Cl2].(H2O)n, where M=Zn, Cd and Hg. The spectral studies revealed that, an octahedral geometry for Co(II), Ni(II) and Cu(II) complexes, whereas square pyramidal geometry for Zn(II), Cd(II) and Hg(II) complexes. The ligand and its Co(II) complex have been characterized by X-ray powder diffraction studies. The ligand and its complexes were tested for their antibacterial activity against Escher...

Synthesis, Structure, and Electrochemistry of Sm-Modified LiMn2O4 Cathode Materials for Lithium-Ion Batteries

Spinel lithium manganese oxide and a series of Sm/LiMn2O4 spinels with different Sm additive contents (x = 0.02%, 0.05%) were prepared for the first time via a coprecipitation method for rechargeable lithium-ion batteries. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive analysis of x-rays (EDAX), infrared (IR), and electron spin resonance spectral studies as well as various electrochemical measurements were used to examine the structural and electrochemical characteristics of LiMn2−xSmxO4 (x = 0.00%, 0.02%, 0.05%). XRD and SEM studies confirmed the nano materials size for all prepared spinels. From cyclic voltammetry studies, in terms of peak splitting, electrochemical active surface area, and intensity of the peaks, the LiMn1.98Sm0.02O4 sample possesses better electrochemical performance compared with the LiMn1.95Sm0.05O4 sample. Hence, limited addition of a rare-earth dopant is preferable to obtain better efficiency. Direct-current (DC) electrical conductivity measurements indicated that these samples are semiconducting and their activation energies decrease with increasing rare-earth Sm3+ content.

Synthesis, characterization, and solid state electrical conductivity of coordination polymers with copper and zinc

Heterobimetallic complexes [Cu x Zn1− x (dadb) · yH2O] n {where dadb = 2,5-diamino-3,6-dichloro-1,4-benzoquinone (1); x = 1 (2), 0.5 (4), 0.25 (5), 0.125 (6), 0.0625 (7), and 0 (3); y = 2; n = degree of polymerization} were synthesized and characterized. All metal complexes are stable at room temperature but weakly absorb moisture on exposure to air. Monometallic 2 exhibits subnormal magnetic moment whereas 3 exhibits diamagnetism. Heterobimetallic complexes exhibit normal magnetic moments. Heterobimetallic complexes are characterized from powder X-ray diffraction, thermal analysis, and electron spin resonance (ESR) spectral studies. Delocalization of unpaired electron from metal to ligand has been inferred from ESR and natural bond orbital (NBO) analysis. Greater delocalization of unpaired electron of Cu(II) on ligand of 4 as compared to that of 2 is reflected from NBO analysis. Heterobimetallic complexes show higher conductivity than monometallic complexes; all the complexes exhibit semiconductor behavior.

Infrared and electron spin resonance spectral studies of some copper purine and pyrimidine complexes

Copper guanine and barbital complexes were prepared and characterized by elemental analyses and spectral measurements. The data typified the formation of stoichiometries 1:1 (M:L) with possible Cu–Cu interaction “association”. The complexes are with different geometries: square planar, square pyramidal and tetrahedral. The mode of bonding was identified by IR spectra. EPR spectra of the powdered complexes were recorded at X band at the room temperature. Different ESR parameters were calculated and discussed: g//, g⊥, A//, 〈g〉, G, F, K, α2. Molecular modeling techniques and quantum chemical methods have been performed for copper complexes to correlate the chemical structures of the complexes with their physical molecular properties. Bond lengths, bond orders, bond angles, dihedral angles, close contact, dipole moment (μ), sum of the total negative charge (STNC), electronegativity (χ), chemical potential (Pi), global hardness (η), softness (σ), the highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO) and the energy gap (ΔE) were calculated using PM3 semi-empirical and Molecular Mechanics (MM+) methods. The study displays a good correlation between the theoretical and experimental data which confirms the reliability of the quantum chemical methods.

Electron spin resonance and optical absorption spectroscopic studies of Cu2+ ions in aluminium lead borate glasses

Electron Spin Resonance and optical absorption spectral studies of Cu2+ ions in 5 Al2O3+75 B2O3+(20-z) PbO+z CuO (where z=0.1–1.5mol.% of CuO) glasses have been reported. The EPR spectra of all the glasses show resonance signals characteristic of Cu2+ ions at both room and low temperatures. The number of spins and Gibbs energy were calculated at different concentrations and temperatures. From the plot of the ratio of logarithmic number of spins and absolute temperature and the reciprocal of absolute temperature, the entropy and enthalpy have been evaluated. The optical absorption spectra of all the glasses exhibit three bands and these bands have been assigned to 2B1g→2Eg, 2B1g→2B2g, and 2B1g→2A1g transitions in the decreasing order of energy. It is for the first time to observe three optical absorption bands for Cu2+ ions in oxide glasses. Such type of results is due to excellent sample preparation. From the EPR and optical absorption spectroscopies data, the molecular orbital coefficients have been evaluated.

Examples of Reductive Azo Cleavage and Oxidative Azo Bond Formation on Re2(CO)10 Template: Isolation and Characterization of Re(III) Complexes of New Azo-Aromatic Ligands

A new example of simultaneous reductive azo bond cleavage and oxidative azo bond formation in an azo-aromatic ligand is introduced. The chemical transformation is achieved by the reaction of Re(2)(CO)(10) with the ligand 2-[(2-N-Arylamino)phenylazo]pyridine (HL(1)). A new and unexpected mononuclear rhenium complex [Re(L(1))(L(3))] (1) was isolated from the above reaction. The new azo-aromatic ligand, H(2)L(3) (H(2)L(3) = 2, 2'-dianilinoazobenzene) is formed in situ from HL(1). A similar reaction of Re(2)(CO)(10) and a closely related azo-ligand, 2,4-ditert-butyl-6-(pyridin-2-ylazo)-phenol (HL(2)), resulted in a seven coordinated compound [Re(L(2)){(L(4))(•-)}(2)] (2; HL(4) = 2-amino-4,6-ditert-butyl-phenol) via reductive cleavage of the azo bond. The complexes have been characterized by using a host of physical methods: X-ray crystallography, nuclear magnetic resonance (NMR), cyclic voltammetry, ultraviolet-visible (UV-vis), electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT). The experimental structures are well reproduced by density functional theory calculations and support the overall electronic structures of the above compounds. Complex 1 is a closed shell singlet, while complex 2 exemplifies a singlet diradical complex where the two partially oxidized aminophenoleto ligands are coupled to each other, yielding the observed diamagnetic ground state. Complexes 1 and 2 showed two successive one-electron redox responses. EPR spectral studies in corroboration with DFT results indicated that all of the redox processes occur at the ligand center without affecting the trivalent state of the metal ion.

Synthesis and spectroscopic studies of biologically active tetraazamacrocyclic complexes of Mn(II), Co(II), Ni(II), Pd(II) and Pt(II)

Complexes of Mn(II), Co(II), Ni(II), Pd(II) and Pt(II) were synthesized with the macrocyclic ligand, i.e., 2,3,9,10-tetraketo-1,4,8,11-tetraazacycoletradecane. The ligand was prepared by the [2 + 2] condensation of diethyloxalate and 1,3-diamino propane and characterized by elemental analysis, mass, IR and 1H NMR spectral studies. All the complexes were characterized by elemental analysis, molar conductance, magnetic susceptibility measurements, IR, electronic and electron paramagnetic resonance spectral studies. The molar conductance measurements of Mn(II), Co(II) and Ni(II) complexes in DMF correspond to non electrolyte nature, whereas Pd(II) and Pt(II) complexes are 1:2 electrolyte. On the basis of spectral studies an octahedral geometry has been assigned for Mn(II), Co(II) and Ni(II) complexes, whereas square planar geometry assigned for Pd(II) and Pt(II). In vitro the ligand and its metal complexes were evaluated against plant pathogenic fungi (Fusarium odum, Aspergillus niger and Rhizoctonia bataticola) and some compounds found to be more active as commercially available fungicide like Chlorothalonil.

Synthesis, characterization, and 3D-molecular modeling and analysis of some copper(II) chelates in O, N-donor coordination pattern involving Schiff bases derived from 4-butyryl-3-methyl-1-phenyl-2-pyrazolin-5-one and some sulfa drugs

The synthesis of five new chelates of copper(II) of the general formula[Cu(LH)2(Cl)2], where LH=N-(4′-butyrylidine-3′-methyl-1′-phenyl-2′-pyrazolin-5′-one)sulfamethoxazole (bumphp-smzH, I), N-(4′-butyrylidine-3′-methyl-1′-phenyl-2′-pyrazolin-5′-one)sulfadimidine (bumphp-sdmH, II), N-(4′-butyrylidine-3′-methyl-1′-phenyl-2′-pyrazolin-5′-one)sulfanilamide (bumphp-snmH, III), N-(4′-butyrylidine-3′-methyl-1′-phenyl-2′-pyrazolin-5′-one)sulfamoxole (bumphp-smlH, IV) or N-(4′-butyrylidine-3′-methyl-1’-phenyl-2′-pyrazolin-5′-one)sulfaguanidine (bumphp-sgdH, V) has been carried out. The complexes have been characterized by elemental analyses, copper determination, molar conductance, magnetic and decomposition temperature measurements, electron spin resonance, thermogravimetry, infrared, and electronic spectral studies. A trans octahedral structure has been proposed for these complexes. The 3D molecular modeling and analysis for bond lengths and bond angles have also been carried out for one of the representative compound,[Cu(bumphp-snmH)2(Cl)2] (3) to substantiate the proposed structure.

Spectroscopy, Electrochemistry, and Structure of 3d-Transition Metal Complexes of Thiosemicarbazones with Quinoline Core: Evaluation of Antimicrobial Property

ABSTRACT A series of Co(II), Ni(II), Cu(II), and Zn(II) complexes of quinoline-thiosemicarbazones was prepared. The Schiff base ligands that provide N, O, and S donor atoms for ligation are synthesized by the condensation of 2-hydroxy-3-formylquinoline with substituted thiosemicarbazides in ethanol. The ligands and complexes are characterized by elemental analysis, infrared, 1H NMR, UV-Vis, fast atom bombardment (FAB) mass spectroscopy, and electron spin resonance (ESR) spectral studies followed by magnetic susceptibility and conductivity measurements. The ligand-to-metal ratio is found to be 1:1 and 2:2 for the complexes of L1H2 and L2H2, respectively. All the complexes are found to have octahedral geometry except [CuL1H(H2O)Cl], which exhibits a square pyramidal structure. All the complexes are nonelectrolytic in nature and the electrochemical behavior of complexes is dealt with briefly. Further ligands and complexes were evaluated for their antimicrobial activity against bacteria Escherichia coli and Pseudomonas aeruginosa and fungi Aspergillus niger and Cladosporidium.

EPR and optical absorption studies on manganese ion doped in mixed alkali cadmium phosphate glasses

Electron paramagnetic resonance (EPR) spectra of Mn(II) ions in cadmium phosphate glasses are presented with mixed alkali variation as xLi2O + (20 - x) Na2O + 20 CdO + 59.5 P2O5 + 0.5 MnO glass system with 5 ≤ x ≤ 15 mol%. The EPR spectra of Mn(II) ions doped samples exhibit a sextet centered at g = 2·0. The optical absorption spectrum at room temperature shows three bands for Mn(II) ions in octahedral symmetry. The crystal field (Dq) and Racah parameters (B and C) are evaluated. From EPR and optical spectral studies reveals the nature of the bonding is dominantly ionic and its site symmetry is octahedral. At equal composition of alkali content, i.e. for x = 10 the glass system shows the mixed alkali effect.