EPR Susceptibility Research Articles

Structural investigation, quantum chemical calculation, energy framework analysis and MIC studies of silver and cobalt complexes of 4-amino-N-(4, 6-dimethyl-2 pyrimidinyl) benzenesulfonamide in presence of secondary ligand

Silver and cobalt complexes of SMZ ligand (SMZ = 4-amino-N-(4, 6-dimethyl-2 pyrimidinyl) benzenesulfonamide) have been synthesized and characterized by elemental, FT-IR and 1H-NMR spectroscopy analysis. Due to the magnetic behaviour of the cobalt complex, it was characterized by EPR and magnetic susceptibility analysis. Single crystal X-ray diffraction (SC-XRD) study reveals the [Ag2(C12H14N4O2S)2(C6H7N), complex-1 crystallizes in orthorhombic space group Pbca, while [{Co(C12H13N4O2S)2(C5H5N)2}.(C5H5N)], complex-2 crystallizes in monoclinic space group C2/c. The SC-XRD analysis shows that silver in complex-1 is four-coordinate exhibiting distorted tetrahedral geometry, while cobalt in complex-2 is coordinated to six nitrogen’s leading to distorted octahedral geometry. Additionally, Hirshfeld surfaces and 2D fingerprint plots analysis shows that the H…H intermolecular contacts are the main contribution to the Hirshfeld surface area displaying values for complex-1 and complex-2 are 59.1% and 50% respectively (%H-H; complex 1 > Complex 2). In 3D energy frameworks analysis, complex-1, has shown the highest dispersion interaction energies than that of complex 2 [dispersion energy; -74.5 kJ mol-1 (complex-1) > -63.4 kJ mol-1 (complex-2)], Moreover, computational studies such as frontier molecular orbital (FMO), natural bond orbital (NBO) and Mulliken population analysis (MPA) were calculated using B3LYP method. Besides, The MIC data against panel of gram-positive and gram-negative organisms confirm that both the metal complexes of SMZ ligand possesses better inhibitory activities than that of SMZ ligand. The MIC data shows the silver complex exhibits comparatively better response towards the panel of the gram positive and gram negative bacteria. Furthermore, the molecular docking study agrees that the binding affinity of the complexes with 1BNA is higher than that of free SMZ ligand.

Synthesis, structural characterization, thermal analysis, DFT, biocidal evaluation and molecular docking studies of amide-based Co(II) complexes.

Many distinct amino acid and aromatic amine-derived transition metal complexes are used as physiologically active compounds. A few Cobalt (II) complexes have been synthesized by reacting cobalt (II) chloride with 1, 8-diaminonapthalene-based tetraamide macrocyclic ligands in an ethanolic media. These synthesized ligands (TAML1-3) and associated Co(II) complexes were fully characterized with various spectroscopic techniques, such as IR, NMR, CHN analysis, EPR, molar conductance, and magnetic susceptibility measurements, TGA, UV-visible spectra, powder X-ray diffraction and DFT analysis. The IR spectra reveal interactions between the core metal atom and ligands through N of 1, 8-diaminonapthalene. The distorted octahedral geometry of synthesized Co(II) macrocyclic complexes were confirmed by ESR, UV-Vis and DFT studies. The synthesized ligands (TAML1-TAML3) and their Co(II) complexes were tested for antimicrobial activity against A. niger, C. albicans, and F. oxysporum in addition to bacteria like S. aureus, B. subtilis, and Gram-negative bacteria like E. coli. The ligand TAML1 and complex [Co(TAML1)Cl2] showed an excellent antibacterial activity. The minimum inhibitory concentration of TAML1 and [Co(TAML1)Cl2] against S. aureus were found to be 7mm and 10mm zone of inhibition at 500ppm, respectively, compared to drug ampicillin (3mm). Additionally, each molecule exhibited notable antioxidant activity. The biological significance of the synthesized compounds was then evaluated by molecular docking experiments with the active site of the receptor protein such as Sars-Cov-2, C. Albicans, X. campestris and E. coli. The molecular docking assisted data strongly correlated to the experimental approach of antimicrobial activity. The online version contains supplementary material available at 10.1007/s11696-023-02843-y.

Synthesis, characterization, structure, in vitro enzymatic activity and sensing aspects of a copper(II) complex stabilized from a naphthaldehyde based Schiff base ligand

A mononuclear copper(II) complex, [CuL(ClO4)(H2O)].THF (1), from a naphthaldehyde based Schiff base probing ligand, 1-(benzothiazol-2-yl-hydrazonomethyl)-napthalen-2-ol (LH), has been prepared and characterized by FT-IR, UV–vis, EPR, CHN analysis, electrical conductivity and magnetic susceptibility measurements. The X-ray crystal structure of 1 has also been determined. In vitro enzymatic activity of LH and 1 on digestive enzymes like amylase, trypsin and lipase has been investigated. Molecular docking studies have also been performed to corroborate this bioactivity. LH displays quenching of fluorescence intensity only upon addition of a Cu2+ ion at 459 nm. Other metal ions under present study, however, offer no influence. The low limit of detection value, 0.35 µM, indicates that LH offers high selectivity towards Cu2+. Calculations at the level of DFT were also undertaken to have an insight into the electronic environment of both LH and 1.

Structural and magnetic characterization of mixed-valence vanadium (IV/V) complex with {(VO)2(µ‒O)}3+ core: Theoretical and experimental insights

Using deprotonated forms of tetradentate phenol amine ligands 2-((((1-methylbenzimidazol-2-yl)methyl)(pyridin-2-ylmethyl)amino)methyl)phenol (HL1), dinuclear vanadium(IV,V) complex of composition [(L1)2(VIVO)(µ-O)(VVO)](ClO4) (1) was synthesized and characterized by X–ray crystallography, UV–Vis, EPR and magnetic susceptibility measurements. Direct current (DC) variable-temperature magnetic susceptibility measurements on polycrystalline sample of 1 were carried out in the temperature range 1.8–300 K. Electron paramagnetic resonance and magnetic studies for 1 demonstrated the complete localization of the single 3d electron on one of vanadium ion and very weak antiferromagnetic interaction between the paramagnetic vanadium(IV) ions in the crystal lattice. The cyclic voltammogram observed with 1, revealed one oxidation process which is tentatively assigned to VIVVV/V2V. [(L1)2(VVO)2(µ-O)](ClO4)2 (2.2.5CH2Cl2) has been synthesized chemically from 1 and were thoroughly characterized by X–ray crystallography, UV–Vis, 51V NMR and IR measurements.

Spin crossover properties of Fe(III) complexes in [Fe (bzacen)(tvp)]BPh4 ·nSolv chain structures: EPR study.

Two types of Fe(III) polynuclear iron(III) 1D-chain coordination compounds of the general formula [Fe (L)(tvp)]BPh4 nSolv, where L = dianion of N,N'-ethylenebis (benzoylacetylacetone)2,2'-imine (bzacen), tvp = 1,2-di(4-pyridyl)ethylene were synthesized and studied by the electron paramagnetic resonance (EPR) and magnetic susceptibility methods in the temperature range (100-300) К. Two types of spin-variable complexes are formed depending on the time of precipitation of the complexes from the same solution leading to differently solvated species. They have different characteristics of the local ligand field and the spin transition behavior. The thermodynamic parameters of spin transitions were determined from the temperature dependence of the EPR signals integral intensity. The energy levels splitting values obtained by analyzing g-factors of low-spin Fe(III) centers evidenced not only on the crucial role of low-symmetry distortions on the principal possibility of spin-crossover processes, but also on the temperature peculiarities of spin transitions.

Structure and magnetic properties of a serendipitously synthesized copper(II) complex: [Cu(3-Br-2-pyone)6](ClO4)2

Hexakis(3-bromo-2(1H)-pyridone)copper(II) perchlorate was prepared. Crystals and powdered bulk samples were characterized using IR, single-crystal and powder X-ray diffraction, combustion analysis, EPR and temperature-dependent magnetic susceptibility data. The complex crystallizes in the triclinic space group P$$\bar{1}$$ and comprises a Jahn–Teller distorted Cu(II)–O6 coordination sphere with the ligands coordinated via the pyridone O-atoms. EPR and variable temperature susceptibility measurements show that the complex is well isolated magnetically in the lattice.

Structural and Biological Properties of a Silver and Cobalt Complexes of Sulfamethazine in Presence of Secondary Ligand: An Experimental and Computational Approach

Silver and cobalt complexes of SMZ ligand [SMZ = 4-amino-N-(4, 6-dimethyl-2 pyrimidinyl) benzenesulfonamide] have been synthesized and characterized by elemental and FT-IR spectroscopy analysis. Due to the magnetic behaviour of the cobalt complex, it was characterized by EPR and magnetic susceptibility analysis. Single crystal X-ray diffraction study reveals the [Ag2(C12H14N4O2S)2(C6H7N)2], complex-1 crystallizes in orthorhombic space group Pbca, while [{Co(C12H13N4O2S)2(C5H5N)2}.(C5H5N)], complex-2 crystallizes in monoclinic space group C2/c. X-ray diffraction analysis revealed that silver in complex-1 is four-coordinate exhibiting distorted tetrahedral geometry, while cobalt in complex-2 is coordinated to six nitrogens leading to distorted octahedral geometry. The molecular structures of the complexes are stabilized by π…π and C–H…π intermolecular interactions. Furthermore, the computational studies such as frontier molecular orbital (FMO), natural bond orbital (NBO) and Mulliken population analysis (MPA) have been measured using DFT/B3LYP method in gaseous phase of the complexes. The visualized and correlated in a novel way through qualitative investigation using Hirshfeld surface and 3D energy frameworks analysis have been performed of the complexes. Additionally, The MIC data against a panel of gram positive and gram negative organisms suggest that both the complexes possess enhanced inhibitory activities than that of free SMZ ligand. Molecular docking investigation specifies that the binding affinity of the complexes with 1BNA is higher than that of free SMZ ligand.

Pyrazine-bridged Cu(ii) chains: diaquabis(n-methyl-2-pyridone)copper(ii) perchlorate complexes.

A family of pyrazine-bridged, linear chain complexes of Cu(ii) of the formula [CuL2(H2O)2(pz)](ClO4)2 [pz = pyrazine; L = n-methyl-2(1H)-pyridone, n = 3 (1), 5 (2), and 6 (3)] has been prepared. Single-crystal X-ray diffraction shows six-coordinate, pyrazine-bridged chains with trans-pairs of ancillary ligands. The substituted pyridine molecules exist in their pyridone tautomers and are coordinated through the carbonyl oxygen atom. The structure is stabilized by intramolecular hydrogen bonds between the pyridone and water molecule, and via hydrogen bonds between the water molecules and perchlorate ions. 2 undergoes a crystallographic phase transition between C2/c (high temperature phase) and P1[combining macron] (low temperature phase). Powder EPR spectra reveal that all complexes are rhombic, although differences between gx and gy can only be seen clearly at Q-band. Variable temperature magnetic susceptibility data show antiferromagnetic interactions and the data were fit to the uniform chain model yielding J/kB = -9.8, -9.2 and -11 K for 1-3 respectively. Attempts to model an interchain interaction strength indicate that the chains are very well isolated.

Copper(II) complexes with isoxazole Schiff bases: Synthesis, spectroscopic investigation, DNA binding and nuclease activities, antioxidant and antimicrobial studies

Three novel Cu(II) complexes 1 [Cu(L1)2], 2 [Cu(L2)2] and 3 [Cu(L3)2], where L1H = 2-((3,4-dimethylisoxazol-5-ylimino)methyl)-6-tert-butylphenol, L2H = 2-((3,4-dimethylisoxazol-5-ylimino)methyl)-4,6-di-tert-butylphenol and L3H = 2-((3,4-dimethylisoxazol-5-ylimino)methyl)-4,6-dibromophenol were synthesized and characterized by elemental analysis, FT-IR, UV–Visible, 1H NMR, 13C NMR, ESI mass, EPR and magnetic susceptibility studies. Based on spectroscopic and analytical data, a square planar geometry is assigned for all complexes. DNA binding and cleavage studies against calf thymus DNA (CT-DNA) and supercoiled pBR322 DNA respectively revealed an intercalative mode of binding and also cleave pBR322 DNA in an efficient manner. The ligands and their complexes were examined for antimicrobial activity against bacterial species E. coli, B. subtilis and fungal species S. rolfsii and M. phaseolina and found that all the Cu(II) complexes show more activity than the free Schiff base ligands. The antioxidant activity of metal complexes have also been determined using DPPH assay and found that the complexes are found to be good free radical scavengers.

Square-planar aminonitronate transition metal complexes (M = CuII, NiII, PdII, and PtII)

Treatment of the aromatic aminonitrones p-RC6H4C(NH2)N+(Me)O− (R=NMe2, Cl) with CuCl2·2H2O, NiCl2·2H2O, β-PdCl2, or cis-[PtCl2(Me2SO)2] in the presence of a base leads to the [M{p-RC6H4C(NH)N+(Me)O−}2] (M=Cu,Ni,Pd) (72–95%) or [Pt{p-RC6H4C(NH)N+(Me)O–}Cl(Me2SO)] (ca. 80%) complexes, respectively. These compounds were characterized by elemental analyses (C, H, N), HRESI+-MS, FTIR, 1H and 13C{1H} NMR, and for the CuII and NiII complexes EPR and magnetic susceptibility. In addition, eight species were studied by single-crystal X-ray diffraction. In the X-ray structures of 2a–d, the hydrogen bonds are responsible for the formation of 1D polymeric chains. These bonds were evaluated by DFT calculations (M06/DZP-DKH level of theory) and topological analysis of the electron density distribution within the formalism of Bader’s theory (QTAIM method). Estimated strengths of these non-covalent interactions are 2.7–4.4kcal/mol.

Intermolecular interactions and spin states of complexes [Fe(3-MeO-Qsal)2]Y (Y = PF6, BF4)

Compounds [Fe(3-MeO-Qsal)2]Y (Y = PF6, BF4) have been prepared by diffusion method and studied in temperature range 5–300 K by EPR and magnetic susceptibility methods. The coexistence of spatially separated high-spin (solvated) and low-spin (unsolvated) fractions in the studied compounds has been established. It has been shown that change in the type of outer-sphere anion leads to change in the character of intermolecular interactions in the high-spin fraction and has no effect on the parameters and character of interactions of paramagnetic centers in the low-spin fraction.

Magnetic properties of composites based on the intercalation of ZnII and CuII bimetallic macrocyclic complexes in the MnPS3 phase

EPR and magnetic susceptibility data of composites based on MnPS3 show the influence of the intercalated species on their magnetic properties.

Synthesis, characterization and magnetic properties of a dinuclear oxidovanadium(IV) complex: Magneto-structural DFT studies on the effects of out-of-plane –OCH3 angle

A new dinuclear oxidovanadium(IV) complex with a symmetric heptadentate N4O3-donor ligand, [V2(O)2L(μ-OCH3)] CH3OH (1), was synthesized and characterized by elemental analysis, spectroscopic methods (FT-IR, UV–Vis and EPR) and single crystal X-ray analysis, where H3L is the Schiff base ligand obtained by the condensation of triethylenetetramine and 5-bromosalicylaldehyde. Single crystal X-ray analysis indicated that the vanadium(IV) ions have distorted octahedral geometry and are connected together by phenoxy and methoxy bridging groups. The EPR and magnetic susceptibility measurements show weak V⋯V antiferromagnetic interactions. The analysis of the magnetic susceptibility data with the Bleaney–Bowers equation gave a value for the magnetic coupling constant of J=−1.60cm−1 (H=−JS1S2). A Broken-Symmetry DFT study also agreed with an intramolecular character of the magnetic coupling giving a comparable value for J and showed an important dependence of the magnetic interaction with the out-of-plane shift of the methyl group of the methoxy bridging group.

Slow Relaxation of Magnetization in an Isostructural Series of Zinc-Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study.

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %.

Oximato-bridged copper(II) compounds: syntheses, molecular structures, magnetic, thermal and spectroscopic properties

Reaction of the Schiff base, 1-(4-methylimidazol-5-yl) phenylhydrazonopropane-2-one oxime (LH), with copper(II) perchlorate hexahydrate and copper(II) nitrate trihydrate in a 1 : 1 M proportion in methanol affords [Cu2L2(H2O)(ClO4)](ClO4) (1) and [Cu2L2(H2O)2](NO3)2] (2) in moderate yields. Both 1 and 2 have been characterized by elemental analysis, ESI-MS, FT-IR, UV–vis absorption spectroscopy, EPR, electric conductivity, and magnetic susceptibility measurements. The X-ray crystal structures of 1·CH3COCH3 and 2 have been determined. Both compounds are dinuclear copper(II) complexes, with each copper μ2-bridged by two oxime ligands in a μ2-η1,η2 fashion. Variable temperature magnetic studies on 1 and 2 show that both compounds are dominated by an antiferromagnetic coupling through the oxime bridges.

Lability of spin state of Fe(III) complexes with tetradentate Schiff’s bases

[FeLX2]Y [L = N,N'-ethylenebis(salicylimine) (salen), N,N'-ethylenebis(acetylacetonylimine) (acen), or N,N'-ethylenebis(3-methyloxysalicylimine) (vanen); X = imidazole or N-methylimidazole; Y = BF4, ClO4, or BPh4] compounds have been prepared and studied by means of EPR and magnetic susceptibility measurements at 5–300 K. It has been shown that the different electron-donating properties of acen and salen planar ligands result in different spin states of Fe(III) ions. Intermolecular π-interactions of the outer-sphere BPh4 ion affect the complexes spin state as well.

Specific features of spin-variable properties of [Fe(acen)pic2]BPh4 · nH2O

The [Fe(acen)pic2]BPh4 · nH2O compound has been synthesized and studied in the temperature interval of 5–300 K by the methods of EPR and magnetic susceptibility. The existence of ferromagnetic interactions between Fe(III) complexes in this compound has been revealed, in contrast to unhydrated [Fe(acen)pic2]BPh4. The reduction in the integrated intensity of the magnetic resonance signal as the temperature decreases below 80 K has been explained by the transition of high-spin ions to the low-spin state. It has been shown that the phase transition temperature in the presence of intermolecular (ferromagnetic) interactions is lower than that in the case of noninteracting centers.

Structural and magnetic studies of the nickel doped CoFe2O4 ferrite nanoparticles synthesized by the chemical co-precipitation method

The physical properties of nickel doped cobalt ferrite nanoparticles NixCo1−xFe2O4 (x=0.5, 0.75, 0.9) derived by the chemical co-precipitation route are characterized by XRD, FTIR, TEM, EPR, search coil and ac susceptibility techniques to develop stable kerosene based ferrofluid. XRD patterns and TEM images confirm the single phase formation of NixCo1-xFe2O4 nanoparticles whose crystallite size increases and lattice parameters decreases with the increase in Ni content. EPR resonance signal peak-to-peak line width and resonance field value decreases with the increase in Ni concentration in these samples. The broad nature of resonance signal is attributed to the ferromagnetic nature of the as-prepared nanoparticles and the increase in super exchange interaction among Ni2+-O-Co2+ facilitate the shifting of resonance value to lower field. The hysteresis loops of these nickel doped cobalt ferrite analogs exhibits highly magnetic nature of these nanoparticles at ambient temperature whose saturation magnetization, coerecivity and remanence magnetization decreases linearly with the increase in Ni-concentration in cobalt ferrite. The magnetic susceptibility with temperature curve shows increasing trend of blocking temperature with rise in nickel ion concentration.

EPR of γ-induced defects and their effects on the photoluminescence in the glasses of the Ag0.05Ga0.05Ge0.95S2–Er2S3 system

Abstract Paramagnetic defects in erbium-doped γ-irradiated chalcogenide glasses were investigated by EPR method. Vacancy nature of defects and the dependence of their concentration on the irradiation dose and erbium content were determined. The measurement of the static magnetization revealed the presence of paramagnetic and ferromagnetic subsystems caused by isolated Er3+ ions and ion clusters, respectively. PL spectra of 4f–4f transitions of Er3+ ions and the radiation mechanism of γ-irradiated glasses were investigated. It was determined that PL intensity depends on the number of radiation induced defects and on the nature of the distribution of erbium which were determined by EPR and magnetic susceptibility.

Structural phase transitions and magnetic and spectroscopic properties of the double perovskites Sr2Co1-xMgxTeO6 (x = 0.1, 0.2 and 0.5).

The structural and magnetic properties of a series of ordered double perovskites with the formula Sr(2)Co(1-x)Mg(x)TeO(6) (x = 0.1, 0.2 and 0.5) are investigated by X-ray diffraction, low temperature neutron diffraction, electron paramagnetic resonance and magnetic susceptibility. The progressive substitution of the paramagnetic Co(2+) high spin ion by the diamagnetic Mg(2+), of about the same size, induces changes in the room temperature crystal structure, from a distorted P2(1)/n phase for the undoped Sr(2)CoTeO(6) oxide to the I4/m of the end member (Sr(2)MgTeO(6)). These perovskites experience structural transitions on heating, the temperature at which the transitions occur being smaller as x increases. The novel approach of mode-crystallography is used for the analysis. All oxides show antiferromagnetic exchange interactions between Co(2+) ions but the long range antiferromagnetic order is not achieved for the phase with x = 0.5. The low temperature neutron diffraction data have been evaluated using a full symmetry analysis. Results are consistent with an unquenched orbital contribution of a high spin Co(2+) ion.