Synthesis,structure, and properties of a pentanuclear cobalt(III) coordination cluster

The synthesis, X-ray structure and properties of a pentanuclear cobalt(III) coordination cluster [{L(O₂CCH₃)Co₂O(OCH₃)₂}₂Co](ClO₄)₃ (1) (L^? = 2,6-bis((3-aminopropylimino)methyl)-4-methylphenolate) are described. The dinucleating L^? is coordinated with two cobalt(III) centers to form the {L(O₂CCH₃)Co₂O(OCH₃)₂} unit, where each metal center is in a distorted octahedral N₂O₄ environment. The oxo and the methoxo ligands of these two dinuclear units assemble a distorted octahedral O₆ coordination sphere around the central cobalt(III). Elemental analysis and spectroscopic (IR, NMR, UV–vis, and HRMS) features are consistent with the pentanuclear structure of the complex. The diamagnetic complex is a 1?:?3 electrolyte in solution. It is redox-active and displays a metal-centered reduction at E_1/2 = ?0.04 V (vs. Ag/AgCl).     

Synthesis and physicochemical studies on Co(III) complexes

Complexes of Co(III) with 2-hydroxyacetophenone-thiosemicarbazone, 2-hydroxy-3-methylacetophenonethiosemicarbazone and 2-hydroxy-4-methyl-acetophenonethiosemicarbazone, and the addition complexes of 2-hydroxy-acetophenone thiosemicarbazone with ammonia, pyridine, aniline,o-toluidine,m-toluidine andp-toluidine have been synthesized and characterized on the basis of their conductivities, electronic and infrared spectral data. All complexes are low-spin octahedral in nature. Various parameters have been obtained using ligand field theory.     

Effect of substituents on the photoluminescence performance of Ir(III) complexes: Synthesis, electrochemistry and photophysical properties

We have prepared and characterized a series of substituted imidazole ligands namely dmmppi, dmmpfpi, dmdmppi and dmdmpfpi. These compounds will readily undergo cyclometalation with iridium trichloride and form di-irrido and the six coordinated iridium(III) dopants of the substituted imidazole ligands. They emit green colour both in solid and in solution phase. The peak emission wavelength of the dopants (λ_max = 428–497 nm) can be finely tuned depending upon the electronic properties of the phenyl, fluorophyenyl, methoxy phenyl and dimethoxyphenyl substituents as well as their positions in the imidazole ring. These iridium complexes namely Ir(dmmppi)₂(pic) 1a, Ir(dmmpfpi)₂(pic) 1b, Ir(dmdmppi)₂(pic) 1c and Ir(dmdmpfpi)₂(pic) 1d were characterized by ¹H NMR, MS and elemental analysis. All these iridium complexes 1a–1d show unusual high HOMO levels (E_HOMO = 5.21–5.41 eV) and high phosphorescence. These complexes emit green light with exceedingly high efficiency.     

Synthesis,X-ray crystal structure,and electrochemistry of polynuclear azido-bridged manganese(III) and copper(II) Schiff base complexes

New azido-bridged [Mn^III(salabza)(μ-1,3-N₃)]_n (1), and [Cu^II₄(salabza)₂(μ-1,1-N₃)₂(N₃)₂(HOCH₃)₂],(2) complexes with an unsymmetrical Schiff base ligand, {H₂salabza = N,N’-bis(salicylidene)-2-aminobenzylamine}, have been synthesized, characterized by spectroscopic and electrochemical methods, and their crystal structures have been determined by X-ray diffraction. In complex 1, each manganese(III) atom is coordinated with N₂O₂ donor atoms from salabza and two adjacent Mn(III) centers are linked by an end-to-end (EE) azide bridge to form a helical polymeric chain with octahedral geometry around the Mn(III) centers. Complex 2 is a centrosymmetric tetranuclear compound containing two types of Cu(II) centers with square pyramidal geometry. Each terminal copper atom is surrounded by N₂O₂ atoms of a salabza ligand, and the oxygen atom of the methanol molecule. Each central copper(II) ion is coordinated with two phenoxo oxygen atoms from one salabza, one terminal azido, and two end-on (EO) bridging azido ligands. The central copper(II) ions are linked to each other by the two end-on (EO) azido groups.     

Mononuclear gallium(III) complexes based on salicylaldoximes: Synthesis,structure and spectroscopic characterization

The reactions of Ga(acac)₃ with salicylaldoxime (saoH₂) and methyl-salicylaldoxime (Me-saoH₂) in dichloromethane/hexane afforded the complexes [Ga(acac)(saoH)₂] (1) and [Ga(acac)₃][Ga(acac)(MesaoH)₂] (2), respectively, in high yields. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Both complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded by two bidentate chelate R-saoH⁻ and one bidentate chelate acac⁻ ligands. A [Ga(acac)₃] moiety has co-crystallized along with the methylsalicylaldoximato complex. Characteristic IR as well as NMR data are discussed in terms of the nature of bonding in the structures of the two complexes. ¹H and ¹³C NMR data in CDCl₃ indicate that the salicylaldoximato complexes isomerize in solution.     

Pentacyanido(L)ferrate(III) complexes: Crystal structures, electrochemical and DFT studies (L = pyrazine, 4,4′-bipyridine, azide)

The crystal structures of two pentacyanido(L) ferrate(III) complexes, [P(C₆H₅)₄]₂[Fe(CN)₅(prz)]·4H₂O 1, [P(C₆H₅)₄]₂[Fe(CN)₅(4,4′-bipy)]·3H₂O 2, have been solved. Within the two complex anions the iron atoms are hexacoordinated by five cyanido ligands, the sixth position being occupied by the nitrogen atom arising from pyrazine and, respectively, 4,4′-bipyridine. The electrochemical properties of compounds 1, 2 and of the azido derivative, (Ph₄As)₂[Na(H₂O)₄][Fe(CN)₅(N₃)] 3, have been investigated by cyclic voltammetry. A relatively complicated redox behavior of these complexes was found, due especially to the electron transfer involving the central metallic ion that changes reversibly its oxidation state (Fe^III/Fe^II redox site) and also to the coligand (4,4′-bipyridine, pyrazine or azide) which intervenes in a distinct electron transfer. The experimental data have been rationalized through DFT calculations.     

Synthesis,structures and properties of cobalt(III) and iron(III) complexes with a new triazamacrocycle, 1,4-diacetate-1,4,7-triazacyclodecane

A new bidisplaced acetate functionalized pendant arm derivative, 1,4-diacetate-1,4,7-triazacyclodecane (L) and its corresponding Co(III), Fe(III) complexes [CoLCl] (1) and [FeLCl]₂ · 3H₂O (2) were synthesized and characterized by elemental analysis, IR spectra,UV–Vis spectra, HNMR, MS, XPRD, TGA and single-crystal X-ray diffraction analysis. The crystal structure shows the metal ions in the complexes have similar coordination six-coordinate, by three nitrogens and two oxygens of the chelate ligand, and a chloride. Through calculation of the twist angle, we discover 1 forms a distorted octahedral geometry while 2 forms a distorted-prismatic geometry. In 2, there are abundant hydrogen bonds between the oxygen atoms of water and the nitrogens and oxygens of the ligand, resulting in a two-dimensional supramolecular network with a regular triatomic water cluster. The thermal gravimetric analyses of the two complexes are also given.     

Synthesis,crystal structure,and antibacterial activity of mononuclear nickel(II) and cobalt(III) Schiff-base complexes

Four new mononuclear complexes, [Ni(L¹)(NCS)₂] (1), [Ni(L²)(NCS)₂] (2), [Co(L¹)(N₃)₂]ClO₄ (3), and [Co(L²)(N₃)₂]ClO₄ (4), where L¹ and L² are N,N′-bis[(pyridin-2-yl)methylidene]butane-1,4-diamine and N,N′-bis[(pyridin-2-yl)benzylidene]butane-1,4-diamine, respectively, have been prepared. The syntheses have been achieved by reaction of the respective metal perchlorate with the tetradentate Schiff bases, L¹ and L², in presence of thiocyanate (for 1 and 2) or azide (for 3 and 4). The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 are distorted octahedral geometries. The antibacterial activity of all the complexes and their constituent Schiff bases have been tested against Gram-positive and Gram-negative bacteria.     

Synthesis and structure of N-salicylidene-o-aminophenolato gallium(III) complexes

The reactions of Ga(acac)₃ with N-salicylidene-o-aminophenol (saphH₂) and its 5-methyl (5MesaphH₂) and 5-bromo (5BrsaphH₂) derivatives in alcohols afforded the complexes [Ga(acac)(saph)(EtOH)] (1), [Ga(acac)(5Mesaph)(MeOH)] (2) and [Ga(acac)(5Brsaph)(EtOH)] (3), respectively, in good yields. The crystal structures of 1 and 2 have been solved by single-crystal X-ray crystallography. All three complexes are mononuclear with the Ga^III atoms being surrounded by a dianionic tridentate Schiff base ligand, one bidentate acac⁻ ligand and a terminal alcohol molecule. Characteristic IR data are discussed in terms of the nature of bonding and the structures of the three complexes.     

Synthesis,crystal structures and properties of five-coordinate Schiff-base Zn(II) complexes

Five-coordinate Schiff-base Zn complexes (1,2-cyclohexanediamino-N,N′-bis(salicylidene)) zinc-pyridine 1 and (1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)) zinc-pyridine 2 were synthesized and the structures of 1 and 2 have been determined by single-crystal X-ray analysis. All Zn atoms are five-coordinate in both structures. Both complexes exhibit interesting structures based on intermolecular π–π stacking and hydrogen bond interactions. Complex 1 has a one-dimensional molecular chain structure via π–π stacking interaction, while complex 2 has an interesting lattice structure (with cavities with dimensions 10.9?×?6.9?Å) formed through intermolecular π–π stacking and hydrogen bond interactions. 1 and 2 are compared and characterized by MS, elemental analysis, IR, UV-Vis and Photoluminescence (PL). Fluorescence spectra show that the maximal emission wavelength of 1 and 2 are 454?nm, and 480?nm, respectively, upon radiation by UV light. Cyclic voltammetry performed on 1 and 2 indicate a dependence of the cathodic potentials upon conformational and electronic effects. Electronic spectral properties of 1 and 2 were studied by TD-DFT methods. The fluorescent emission of these complexes originates from ligand-centred π–π? transitions. The Zn (II) centres play a key role in enhancing the fluorescent emission of the ligands.     

Benign synthesis of carboxamide ligands,H2Me2bqb and H2Me2bpb. Preparation,characterization and electrochemistry of Ni(II) complexes: The crystal structure of [Ni(Me2bqb)]

A novel and highly efficient approach for the synthesis of H₂Me₂bqb and H₂Me₂bpb using ionic liquid as an environmentally benign reaction medium has been developed, eliminating the need for the pyridine as a toxic solvent. The Ni(II) complex of the dianionic ligand Me₂bqb²⁻, [Me₂bqb²⁻ = 1,2-bis(quinoline-2-carboxamide)-4,5-dimethyl-benzene dianion], has been synthesized and characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structure of [Ni(Me₂bqb)] (1), has been determined by X-ray crystallography. The complex exhibits distorted square-planar NiN₄ coordination geometry with two short and two long Ni–N bonds (Ni–N ∼1.85 and ∼1.96 Å, respectively). The electrochemical behavior of [Ni(Me₂bqb)] (1), has been studied by cyclic voltammetry and compared with the analogous complex, [Ni(Me₂bpb)] (2).     

Synthesis, reaction and structure of a series of chromium(III) complexes containing oxalate ligand

A series of chromium(III) complexes [Cr(bipy)(HC₂O₄)₂]Cl·3H₂O (1), [Cr(phen)(HC₂O₄)₂]Cl·3H₂O (2), [Cr(phen)₂(C₂O₄)]ClO₄ (3), [Cr₂(bipy)₄(C₂O₄)](SO₄)·(bipy)_0.5·H₂O (4) and [Mn(phen)₂(H₂O)₂]₂[Cr(phen)(C₂O₄)₂]₃ClO₄·14H₂O (5) were synthesized (bipy=4,4′-bipyridine, phen=1,10-phenanthroline), while the crystal structures of 1 and 3–5 have been determined by X-ray analysis. 1 and 3 are mononuclear complexes, 4 contains binuclear chromium(III) ions and 5 is a 3D supromolecule formed by complicated hydrogen bonding. 1–3 are potential molecular bricks of chromium(III) building blocks for synthesis heterometallic complexes. When we use these molecular bricks as ligands to react with other metal salts, unexpected complexes 4 and 5 are isolated in water solution. The synthesis conditions and reaction results are also discussed.     

Rhodium(III) and iridium(III) complexes of thioarylazoimidazoles: Synthesis,structure, spectral characterization,electrochemistry and DFT calculation

[M(SRaaiNR′)Cl₃] (M = Rh(III), Ir(III) and SRaaiNR′ = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) complexes are described in this article. The single crystal X-ray structure of one of the complexes, [Rh(SMeaaiNEt)Cl₃] (3b), shows a tridentate chelation of SMeaaiNEt via N(imidazole), N(azo) and S(thioether) donor centres. Spectral characterization has been done by IR, UV–Vis and ¹H NMR data. The electronic structure, redox properties and spectra are well supported by DFT and TDDFT computation on the complexes.     

Synthesis,characterization and catalytic activity of halo-methyl-bis(salicylaldehyde)ethylenediamine cobalt(II) complexes

The synthesis, characterization and catalytic activity of a series of tetra-halo-dimethyl salen and di-halo-tetramethyl-salen ligands are reported in this paper: α,α′-dimethyl-Salen (dMeSalen) (L¹); 3,3′,5,5′-tetrachloro-α,α′-dimethyl-Salen, (tCldMeSalen) (L²); 3,3′-dibromo-5,5′-dichloro-α,α′-dimethyl-Salen, (dCldBrdMeSalen) (L³); 3,3′,5,5′-tetrabromo-α,α′-dimethyl-Salen, (tBrdMeSalen) (L⁴); 3,3′,5,5′-tetraiodo-α,α′-dimethyl-salen, (tIdMeSalen) (L⁵); 3,3′-dichloro-5,5′,α,α′-tetramethyl-Salen (dCltMeSalen) (L⁶); 3,3′-dibromo-5,5′,α,α′-tetramethyl-Salen (dBrtMeSalen) (L⁷); and 3,3′-diiodo-5,5′,α,α′-tetramethyl-Salen (dItMeSalen) (L⁸) (Salen = bis(salicylaldehyde)ethylenediamine). Upon reaction with Co(II) ions, these ligands form complexes with square planar geometry that have been characterized by elemental analysis, cyclic voltammetry, UV–Vis, IR and EPR spectroscopies. In the presence of pyridine the obtained Co(II) complexes were found able to bind reversibly O₂, which was shown by EPR spectroscopy and cyclic voltammetry. They were also found able to catalyze the oxidation of 2,6-di-tert-butylphenol (DtBuP) (9) with formation of 2,6-di-tert-butyl-1,4-benzoquinone (DtBuQ) (10) and 2,6,2′,6′-tetra-tert-butyl-1,1′-diphenobenzoquinone (TtBuDQ) (11). These properties are first influenced by the coordination of pyridine in axial position of the Co(II) ion that causes an increase of the electronic density on the cobalt ion and as a consequence a decrease in the E_1/2 value and an increase of the reducing power of the Co(II) complex. It is noteworthy that, under those conditions the complexes also show a remarkable quasi-reversible behaviour. Second, complex properties are also influenced by the substituents (methyl and halogen) grafted on the aromatic ring and on the azomethynic groups. The donating methyl substituent on the azomethynic groups causes a decrease in the E_1/2 value, whereas the halogen substituents on the aromatic rings have two effects: a mesomeric donating effect that tends to lower the redox potential of the complex, and a steric effect that tends to decrease the conjugation of the ligand and then to increase the redox potential of the Co(II) complex. In pyridine, the steric effect predominates, which causes both an increase of the redox potential and a decrease of the selectivity of the oxidation of phenol 9. As a result of all these effects, it then appears that the best catalysts to realize the selective oxidation of 2,6-di-tert-butyl-phenol (9) by O₂ are the Co complexes of ligands bearing CH₃ donating substituents, Co(dMeSalen) 1 (2CH₃ substituents), and Co-di-halo-tetra-methyl-salen complexes 6, 7 and 8 (4CH₃ substituents), in the presence of pyridine.     

DNA binding and cleavage properties of certain ethylenediamine cobalt(III) complexes of modified 1,10-phenanthrolines

Two complexes of the type [Co(en)₂IP]³⁺ (IP = imidazo[4,5-f][1,10]-phenanthroline) and [Co(en)₂PIP]³⁺ (PIP = 2-phenylimidazo[4,5-f][1,10]-phenanthroline) have been synthesized and characterized by UV–VIS, IR and¹H NMR spectral methods. Absorption spectroscopy, emission spectroscopy, viscosity measurements and DNA melting techniques have been used to investigate the binding of these two complexes with calf thymus DNA and photocleavage studies have been used to investigate the binding of these complexes with plasmid DNA. The spectroscopic studies together with viscosity measurements and DNA melting studies support that complexes 1 and 2 bind to CT DNA(=calf thymus DNA) by an intercalation mode via IP or PIP into the base pairs of DNA. Complex 2 binds more avidly to CT DNA than 1, which is consistent with the extended planar ring π system of PIP. Noticeably, the two complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.     

Synthesis,crystal structure,and electrochemistry of [Co{(Me-sal)2dien}(N3)] and [Co{(Me-sal)2dpt}(N3)]

The structure, spectroscopic, and electrochemical properties of [Co{(Me-sal)₂dien}(N₃)] and [Co{(Me-sal)₂dpt}(N₃)], where (Me-sal)₂dien = 2,2′-[1,1′-(3-azapentane-1,5-diyldinitrilo)diethylidyne] diphenolate and (Me-sal)₂dpt = 2,2′-[1,1′-(4-azapentane-1,7-diyldinitrilo)diethylidyne] diphenolate, have been investigated. These complexes have been characterized by elemental analyses, IR, UV–Vis, and ¹H-NMR spectroscopy. The crystal structures of these complexes have been determined by X-ray diffraction. Complex 1 crystallizes in the triclinic space group P 1, with a = 7.8443(4) Å, b = 11.0660(5) Å, c = 11.6216(6) Å, α = 73.360(1)°, β = 76.965(1)°, γ = 84.436(1)° and Z = 2. Complex 2 crystallizes in the monoclinic space group P2₁/n, with a = 12.1985(13) Å, b = 10.9332(12) Å, c = 15.2808(16) Å, β = 76.965(1)° and Z = 4. The coordination geometry around cobalt(III) in both complexes is a distorted octahedron. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile indicates that the first reduction corresponding to Co^III–Co^II is electrochemically irreversible, accompanied by dissociation of the axial Co–N(N₃) bond. The second reduction step of Co(II/I) leads to decomposition of the complex. These observations are rationalized based on the structure-function relations.     

Syntheses,crystal structures,and antibacterial activities of two cobalt(III) complexes

Syntheses, structures, and antimicrobial activities of cobalt(III) complexes with two tetradentate Schiff-base ligands, (BA)₂en?=?bis(benzoylacetone)ethylenediimine dianion and (acac)₂en?=?bis(acetylacetone)ethylenediimine dianion, and two axial pyridines (py) have been investigated. These complexes were characterized by FT-IR, ¹H-NMR, UV-Vis spectroscopy, and elemental analysis. The crystal structures of the complexes were determined by X-ray crystallography. Single-crystal X-ray diffraction analyses revealed that both complexes have distorted octahedral environments, Schiff-base ligand coordinates cobalt in four equatorial positions, and the two axial positions are occupied by pyridines. The pyridines and Schiff-base ligands are involved in N–H···O hydrogen bonds with perchlorate. Biological activities of the ligands and metal complexes have been studied on Staphylococcus aureus, Escherichia coli, and Bacillus subtilis by the well diffusion method. The activity data show the metal complexes to be more potent than the parent ligand against two bacterial species.     

Synthesis,structural characterization,and antibacterial activity of mononuclear cobalt(III) azido complexes of two pentadentate Schiff bases derived from 2-hydroxynaphthaldehyde

The structural, spectroscopic, and electrochemical properties of [Co{(naph)₂dien}(N₃)] and [Co{(naph)₂dpt}(N₃)], where (naph)₂dien?=?bis-(2-hydroxy-1-naphthaldimine)-N-diethylenetriaminedianion and (naph)₂dpt?=?bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriaminedianion have been investigated. These complexes are characterized by elemental analyses, IR, and UV–Vis spectroscopy. The crystal structures of these complexes have been determined by X-ray diffraction. The geometry around cobalt is distorted octahedral. The electrochemical behavior of these complexes in acetonitrile solution was also investigated. Both complexes show an irreversible Co^III–Co^II reduction at ca. ?0.8?V, accompanied by dissociation of the axial Co^II–N₃ bond. The in vitro antibacterial activities of these complexes were tested against Staphylococcus aureus and Bacillus licheniformis.     

Ketiminate supported aluminum(III) complexes: Synthesis, characterization and reactivity

The reaction of LLi, (L = [RNC(Me)CHC(Me) = O] (R = C₂H₄NEt₂)), with AlCl₃ at −78 °C forms the mono-ketiminate product, LAlCl₂, 1, while the same reaction at 0 °C affords the bis-ketiminate complex, [{(LH)₂AlCl}(Cl₂)], 2, Reduction of 1 with Li^o, K^o or Mg^o yielded an unusual dimeric aluminum(III) species, [L′AlCl]₂, 3, where C-C coupling of the ligand backbone is observed.