Quinquedentate Schiff Base Research Articles

Oxidative Cleavage of DNA by Transition Metal Complexes: Synthesis, Spectral Characterization and DNA Interactions of Copper(II) Complexes with Quinquedentate Schiff Base Ligands

Oxidative Cleavage of DNA by Transition Metal Complexes: Synthesis, Spectral Characterization and DNA Interactions of Copper(II) Complexes with Quinquedentate Schiff Base Ligands

Mono-, di- and tri-nuclear manganese(II) complexes derived from a quinquedentate ligand: Superoxide dismutase and catalase mimetic studies

In this study, three manganese complexes [Mn(H2L)Cl2]·MeOH, [Mn3(L)2(OAc)2(MeOH)2]·2MeOH and [Mn2Ca(L)2(OAc)2(MeOH)2]·2MeOH derived from a quinquedentate Schiff base ligand (H2L) were synthesised and characterised by the spectroscopic and analytic methods. Molecular structures of the complexes were determined by single crystal X-ray diffraction studies. In mononuclear complex [Mn(H2L)Cl2]·MeOH, the Mn(II) ions are seven-coordinate pentagonal bipyramidal geometry with two chloride ions at the axial positions. The trinuclear complex [Mn3(L)2(OAc)2(MeOH)2]·2MeOH consists of two mononuclear units linked by a central Mn(II) ion. The calcium containing complex [Mn2Ca(L)2(OAc)2(MeOH)2]·2MeOH contains two mononuclear units bridged by a six-coordinate Ca(II) ion. The superoxide dismutase (SOD activities of the structurally complexes were evaluated and the mononuclear complex [Mn(H2L)Cl2]·MeOH showed the greatest SOD activity with an IC50 value of 0.95μM which gives a calculated kcat value of 1.67×106M−1s−1. Finally, the ability of the complexes to disproportionate H2O2 in the presence of base was tested by measuring the rate of oxygen evolution at room temperature. The trinuclear [Mn3(L)2(OAc)2(MeOH)2]·2MeOH complex is the most efficient complex catalase mimic of the tested complexes with the fastest rate 5.33ml/s.

Constructing octa- and hexadecanuclear manganese clusters from tetrahedral MnIII3MnII cores bridged by quinquedentate Schiff base and versatile azide groups

Reactions of MnX(2) meltsalt (X = Cl and ClO(4)) and a quinquedentate Schiff base ligand together with its coligand azides in MeOH produced the unprecedented assembly of novel octa- and hexadecanuclear manganese clusters containing two and four alternant tetrahedral Mn(III)(3)Mn(II) cores bridged by Schiff base ligands and versatile azides groups. The magnetic measurements on both compounds indicate dominant antiferromagnetic interactions between the metal centers. This synthetic approach may suggest a promising pathway to the design of novel Schiff base-based polynuclear manganese clusters and novel magnetic materials.

Biological and spectral studies of transition metal complexes with a quinquedentate Schiff base, 2,6-diacetylpyridine bis(thiocarbohydrazone)

Manganese(II), cobalt(II), and copper(II) complexes with a quinquedentate Schiff base, 2,6-diacetylpyridine bis(thiocarbohydrazone), have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibility, and IR, 1H NMR, 13C NMR, mass (for ligand), UV and Electron Paramagnetic Resonance spectroscopies. The complexes are [M(L)X]X, where M=Mn(II), Co(II), and Cu(II), L = 2,6-diacetylpyridine bis(thiocarbohydrazone), and X= and Oac−. The ligand with five coordination sites forms six-coordinate complexes with octahedral geometry for manganese(II), whereas the cobalt(II) and copper(II) complexes were of tetragonal geometry. The A iso values, nephelauxetic parameter (β), and orbital reduction factor (k) indicate the covalent nature of the metal–ligand bond. The compounds have been screened for their antipathogenic activities against Alternaria brassicae, Aspergillus niger, Fusarium oxysporum, Xanthomonas compestris, and Pseudomonas aeruginosa.

Manganese(III,IV) and Manganese(III) Oxide Clusters Trapped by Copper(II) Complexes

Reactions of quinquedentate Schiff base ligands with Mn and Cu ions afforded icosa- and hexadecanuclear mixed-metal clusters in which dinuclear CuII complexes trapped oxo-bridged [MnIII8MnIV4O12] and [MnIII6O6] cores, respectively. Maximum entropy method analysis for synchrotron X-ray diffraction data was used to determine the oxidation states of the Mn ions.

Magnetic Properties of Iron(III) Complexes with Photoisomerizable Ligands

Abstract New spin-crossover Iron(III) complexes [Fe(salten)(trans-stpy)]BPh4·(CH3)2CO·0.5H2O 1 and [Fe(salten)(cis-stpy)]BPh42 with cis-trans photoisomerizable ligands have been synthesized and characterized, where trans-stpy is trans-4-styrylpyridine and cis-stpy cis-4-styrylpyridine, and salten denotes bis(3-salicylideneaminopropyl)amine, which is a quinquedentate Schiff base derived from the condensation of salicylaldehyde and di(3-aminopropyl)amine. The data of the variable-temperature magnetic susceptibility measurements for the complexes show that 1 and 2 exhibit spin-crossover phenomena in a solid. The spin-state transition temperature of 1 is lower than that of 2. The temperature dependencies of the Mössbauer spectra for the complexes also provide evidence that spin-state transitions between the high- and low-spin states take place, and that the rates of the spin interexchange at 298 K are faster than the inverse of the lifetime (1×10-7 s) of the Mössbauer nucleus. A temperature dependence of the UV-visible spectra suggesting spin-equilibrium in acetonitrile solution was obtained. The X-ray diffraction structures of single crystals of 1 and 2 were determined. Crystal data for 1: C60H61N4O3.5FeB, space group P1 (#2), Z = 2, a = 14.83(1), b = 17.98(1), c = 11.31(2) Å, α = 103.71(8), β = 110.60(8), γ = 94.31(7)°, V = 2702(5) Å3, R = 14.0%, Rw = 17.2%. Crystal data for 2: C57H54N4O2FeB, space group P21/n (#14), Z = 4, a = 14.823(9), b = 17.417(7), c = 18.37(1) Å, β = 95.331(8)°, V = 4722(3) Å3. The coordination cores of both complexes have trans coordination in oxygen atoms. Although light irradiation to 1 in acetonitrile brings about isomerization from trans- to cis- of styrylpyridine, the change in the spin-state of the complexes is not clear.

Mössbauer and magnetic studies on the spin states of mono- and binuclear iron(III) complexes with quinquedentate ligand methyl-substituted pyridine and bridged by pyrazine or bis(pyridine) compounds

Mono- and binuclear iron(III) complexes with the general formula [FeXL] and [LFe-Y-FeL](BPh4)2 have been prepared and their spin states of the iron atom in the complexes has been investigated by means of the temperature-dependent Mossbauer spectroscopy and magnetic measurements, where X is a methyl-substituted pyridine, L denotes a quinquedentate Schiff-base derived from salicylaldehyde with N-(2-aminoethyl)-1,3-propanediamine and Y denotes bridged ligands such as pyrazine(pyr), 4,4′-pyridine(bpy), 4,4′-vinylenepyridine(vipy). On the basis of the Mossbauer and magnetic data, it was concluded that the spintransition characteristics depends on the methyl substituent of pyridine and the bridged ligand.

Synthesis and Mossbauer Spectra Studies of Mono‐Binuclear Iron(III) Complexes with a Quinquedentate Ligand Derived from Saucylaldehyeds and Diethylenetriamine

AbstractMono‐ and bi‐nuclear iron(III) complexes of general formula [FeXL] and [LFe‐Y‐FeL](Bph4)2 have been prepared, and their spin state of iron atom in the complexes has been studied by means of the temperature dependence of the Mössbauer spectra, electronic spectra and magnetic measurement, where X is a mono‐ dentate ligand such as Cl‐, NCS‐, NCO‐, N3‐, pyridine and L denotes a quinquedentate Schiff base derived from salicylaldehyde and diethylenetriamine, and Y denotes bridged ligand such as pyrazine(pyr), 4,4′‐bipyridine(bpy) and 4,4′‐vinylenebipyridine(vibpy). On the basis of the Mössbauer and magnetic data, it was concluded that these complexes were all the high‐spin (S = 5/2) slate. The effect of gamma ray irradiation for these complexes has been discussed.

Synthesis, characterization and electrochemical studies on technetium(V) and rhenium(V) oxo-complexes with N, N′-2-hydroxypropane-1,3-bis(salicylideneimine)

Ligand-exchange reactions of potential quinquedentate Schiff base ligands derived from salicylaldehyde and 1,3-diamino-2-hydroxypropane (H 3L) with [MOCl 4] − (M = Tc and Re) have been investigated. The complexes [MOCl 2(ROH)(H 2L·HCl)] ( I) (R = Me, Et), [ReOCl(HL)] ( II) and μ-O[MO(HL)] 2 ( III) were synthesized and characterized by the usual physicochemical measurements. Cyclic voltammetries for both III complexes reveal two separate and single-electron redox processes. The crystal structure of μ-O[TcO(HL)] 2 was determined by single-crystal X-ray diffraction methods. Crystals are monoclinic, space group P2 1/ c, with a = 9.423(6), b = 19.666(9), c = 22.785(11) Å, β = 99.41(4)° and Z = 4. X-ray diffraction provides 2842 observed reflections (up to θ = 40°) and the structure has been refined by full-matrix least-squares methods to R = 0.10. The ‘dimeric’ structure of μ-O[TcO(HL)] 2 consists of two distorted octahedral TcO(HL) moieties bridged by an oxygen atom which occupies the sixth coordination site of each moiety with the TcOTc angle nearly linear (173°).

The Synthesis and Characterization of Manganese(III) Complexes with the General Formula of [Mn(X)(L)]n+ (n=0, 1) (X=Cl−, N3−, Pyridine, N-Methylimidazole, L=N,N′-[(Methylimino)bis(trimethylene)]bis[salicylideneaminate]: The X-Ray Crystal Structure of [Mn(N-MeIm)(L)][BPh4

Abstract A series of manganese(III) complexes with the general formula of [Mn(X)(L)]n+ (n=0, 1) have been prepared and characterized, where X=Cl−, N3−, pyridine, N-methylimidazole, and L=quinquedentate Schiff base ligand N,N′-(methynmmo)bis(trimethylene)]bis[salicylideneaminate]. The X-ray analysis of [Mn(N-MeIm)(L)][BPh4] confirmed that the coordination geometry of the manganese(III) ion is a tetragonal bipyramid in which two axial positions are occupied by a central amine nitrogen atom N(3) and an imidazole nitrogen atom N(4), with elongated bond distances of Mn–N(3)=2.388(6) Å and Mn–N(4)=2.251(6) Å.

Studies on spin-equilibrium iron(III) complexes. Part 1. Syntheses and magnetic properties of a new family of spin cross-over iron(III) complexes with a unidentate ligand over a wide range of the spectrochemical series and a quinquedentate ligand derived from salicylaldehyde and di(3-aminopropyl)amine. X-Ray crystal structure of [4-azaheptamethylene-1,7-bis(salicylideneiminato)](4-methylpyridine)iron(III) tetraphenylboratet

Iron(III) complexes of general formula [Fe(X)L]n+(n= 0 or 1) have been prepared and characterized, where X is a unidentate ligand such as Cl–, N3–, NCO–, CN–, pyridine (py), 3-methylpyridine (3Me-py), 4-methylpyridine (4Me-py), 4-aminopyridine (apy), 3,4- dimethylpyridine (3,4Me,-py), imidazole (Him), N-methylimidazole (mim), or 2- methylimidazole (2Me-im), and L denotes a quinquedentate Schiff base derived from salicylaldehyde and di(3-aminopropyl)amine. On the basis of the cryomagnetic data, these complexes can be classified into three groups: high spin (S=5//2) for X = Cl, N3, Him, mim; low spin (S=5//2) for X = CN; spin cross-over (S =½⇌S=5//2) for X = py, 3Me-py, 4Me-py, 3,4Me2-py, 2Me-im. This indicates that the spin state for the series of complexes depends predominantly on the order in the spectrochemical series of the ligand X. The magnetic moments for the spin cross-over complexes increased gradually with increase of the temperature and showed no thermal hysteresis, indicating that the present complexes are of continuous spin-transition type. The spin cross-over complexes showed a thermochromism both in the solids and solutions, changing colour from dark violet to blue green, with decreasing temperature, and the thermochromism was studied by the temperature dependence of the electronic spectra in dichloromethane solution. The temperature dependence of the Mossbauer spectra for [Fe(2Me-im)L]BPh4 and [Fe(4Me-py)L]BPh4 has also provided evidence that the spin transition between the high- and low-spin states takes place and that the rate of spin interexchange is as fast as the inverse of the lifetime (1 × 10–7 s) of the Mossbauer nucleus. One of the complexes, [Fe(4Me-py)L] BPh4, was also subjected to a single-crystal X-ray analysis. The result verified the detailed structure in which the iron(III) atom assumes a pseudo-octahedral co-ordination geometry with a trans geometry for the two salicylideneiminate moieties, and the two axial positions are occupied by the secondary amine nitrogen of the di(3-aminopropyI)amine moiety of L and the nitrogen atom of the 4-methylpyridine ligand.