Structure and properties of cobalt(III) porphyrinate molecular complexes

By combined calculation and spectral methods the structure and properties of the molecular complexes of cobaltoctaalkylporphyrin in benzene were studied. Geometric and energy characteristics of the optimized molecules of cobalt porphyrinate and its molecular complexes were calculated. Their stability and degree of deformation were evaluated. It was established that the process of axial coordination is accompanied by the reduction of cobalt. Interrelation between the stability of the cobalt porphyrinate complexes and the nature of the base was noted. A change in the degree of deformation of the porphyrin ligand in the course of reaction was shown. Correlations between the calculation data and the value of the equilibrium constant of the axial coordination reaction were obtained.     

Interaction of cobalt(III) polypyridyl complexes containing asymmetric ligands with DNA

Four asymmetric cobalt(III) complexes, [Co(bpy)₂(aip)]³⁺, [Co(bpy)₂(pyip)]³⁺, [Co(phen)₂(aip)]³⁺, and [Co(phen)₂(pyip)]³⁺ (bpy = 2,2,bipyridine, phen = 1,10-phenathroline), (pyip = 2-(1-pyrenyl)-1H-imidazo[4,5-f][phen], (aip = 2-(9-anthryl)-1H-imidazo[4,5,-f][phen], have been synthesized and characterized. Their interaction with calf thymus DNA (CT-DNA) was investigated by physico-chemical methods and photocleavage. The size and shape of the ligands have a marked effect on the DNA-binding affinity of the complexes. Irradiation of pBR322 DNA with these novel cobalt(III) complexes results in nicking of the plasmid DNA. Toxicity and induced cell death investigations revealed that the complexes of pyip had higher toxicity than those of aip. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

N-monoaryldithiocarbamate cobalt(III) complexes(1)

Summary Diamagnetic cobalt(III) complexes of the type (RHNCS₂)₃Co [R = Ph, XC₆H₄ (X=p-Me,p-OMe,p-Cl,p-Br andp-I) and 2,4-Me₂C₆H₃] have been synthesised by reaction of the corresponding dithiocarbamate ammonium salts and hexaaquocobalt(II) chloride. Ligand field parameters calculated from visible spectral data indicate strong covalent character for the Co-S bond. The i.r. spectral data reveal that the CN bond in these dithiocarbamates has less double bond character compared to the corresponding dialkyldithiocarbamates.     

Racemic iron(III) and cobalt(III) complexes containing a new pentadentate "helmet" phthalocyaninato ligand

Solvothermal reactions of iron(II) acetate tetrahydrate and cobalt(II) acetate tetrahydrate with 1,2-dicyanobenzene in methanol solution result in the formation of racemic six-coordinate iron(III) and cobalt(III) complexes, respectively, with a new bicyclic pentadentate 14,28-[1,3-diiminoisoindolinato]phthalocyaninato ligand.     

Cleavage by halogens of carboncobalt bonds in organometallic complexes of cobalt(III) : II. Organobis(dimethylglyoximato)cobalt(III) complexes

The reaction between organocobaloximes and ICl in chloroform has been studied. In absence of an excess of added chloride ion the reaction is electrophilic in character; in presence of an excess of chloride ion both oxidative dealkylation and radical attack can occur.     

Bacterial activity of cobalt(III) complexes. Part IV: Diethylenetriaminemonoacetatocobalt(III) complexes

Summary The activities of the diethylenetriaminemonoacetatocobalt(III) complexes, [Co(en)(DTMA)]I₂, [CoX₂(DTMA)] and [CoCO₃(DTMA)]·H₂O (DTMA=diethylenetriaminemonoacetato or formally 3-amino-3, 6-diazaoctanato; en=ethylenediamine, X=Cl^–, NO ₂ ^– , NCS^–) were studied onEscherichia coli B growing in a minimal glucose medium in both lag- and log-phases. Activities decrease in the order: [Co(NCS)₂(DTMA)]> [Co(NO₂)₂(DTMA)]>[Co(en)(DTMA)]I₂>[CoCl₂(DTMA)] >[CoCO₃(DTMA)]·H₂O. The antagonistic activities of the complexes were also studied.     

Photocleavage of lysozyme by cobalt(III) complexes

Photochemical reagents that cleave proteins at specific sites (photoproteases) are useful for studying protein structure and protein-ligand interactions. PolyammineCo(III) complexes are tested here as photochemical probes to cleave proteins. Irradiation of a mixture of lysozyme, a model protein, and polyammineCo(III) complexes resulted in the facile cleavage of the peptide backbone. Photocleavage yielded two fragments of molecular weights 10.6 and 3.7 kDa, and these masses sum to the molecular mass of lysozyme (14.3 kDa). No cleavage was detected in the absence of the metal complex, in the dark, or upon irradiation at wavelengths of >420 nm. The photocleavage yield increased with irradiation time and with the concentrations of the metal complex and the protein. N-terminal sequencing of the 10.6 kDa fragment indicated residues that are identical to the N-terminus of lysozyme, and sequencing of the 3.7 kDa fragment indicated Val-Ala-Trp-Arg, an internal sequence of lysozyme. From the known primary sequence of lysozyme and the sequencing data, the cleavage site was assigned to Trp108-Val109. Molecular modeling indicates that the observed cleavage site is within few angstroms from the proposed metal binding site at Glu35-Asp52. This is the first report of the successful photocleavage of proteins, with high selectivity, by transition metal complexes. This novel observation can facilitate the rational design of transition metal complexes for the photochemical footprinting of metal binding sites on proteins.     

Dinuclear cyano complexes of cobalt(III) and Iron(III) containing noninnocent 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene bridging ligands

Two new dinucleating ligands 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene, H(4)(tpb), and 1,2,4,5-tetrakis(4-tert-butyl-2-pyridinecarboxamido)benzene, H(4)(tbpb), have been synthesized, and the following dinuclear cyano complexes of cobalt(III) and iron(III) have been isolated: Na(2)[Co(III)(2)(tpb)(CN)(4)] (1); [N(n-Bu)(4)](2)[Co(III)(2)(tbpb)(CN)(4)] (2); [Co(III)(2)(tbpb(ox2))(CN)(4)] (3); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(N(3))(4)] (4); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(CN)(4)] (5); [N(n-Bu)(4)](2)[Fe(III)(2)(tbpb)(CN)(4)] (6). Complexes 2-4 and 6 have been structurally characterized by X-ray crystallography at 100 K. From electrochemical and spectroscopic (UV-vis, IR, EPR, M?ssbauer) and magnetochemical investigations it is established that the coordinated central 1,2,4,5-tetraamidobenzene entity in the cyano complexes can be oxidized in two successive one-electron steps yielding paramagnetic (tbpb(ox1))(3)(-) and diamagnetic (tbpb(ox2))(2)(-) anions. Thus, complex 6 exists in five characterized oxidation levels: [Fe(III)(2)(tbpb(ox2))(CN)(4)](0) (S = 0); [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Fe(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Fe(III)Fe(II)(tbpb)(CN)(4)](3)(-) (S = (1)/(2)); [Fe(II)(2)(tbpb)(CN)(4)](4)(-) (S = 0). The iron(II) and (III) ions are always low-spin configurated. The electronic structure of the paramagnetic iron(III) ions and the exchange interaction of the three-spin system [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) are characterized in detail. Similarly, for 2 three oxidation levels have been identified and fully characterized: [Co(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Co(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Co(III)(2)(tbpb(ox2))(CN)(4)](0). The crystal structures of 2 and 3 clearly show that the two electron oxidation of 2 yielding 3 affects only the central tetraamidobenzene part of the ligand.     

Simple and mixed complexes of cobalt(II) and cobalt(III) ions

Summary Bivalent and trivalent cobalt complexes with 1-(2-pyridylazo)-2-naphthol (PAN), PAN+1, 10-phenanthroline and PAN+2, 2-bipyridyl were prepared and characterized by physico-chemical and magnetic measurements. The spectral studies suggest that PAN behaves as a bidentate ligand and is coordinated to metal ions through oxygen and (pyridine) nitrogen, whereas 1, 10-phenanthroline and 2, 2-bipyridyl are coordinated through (pyridine) nitrogen. The tentative (M–O) and (M–N) band assignments in the lower i.r. region, and magnetic moment data favour four coordination for the complexes studied.     

Trans-bis(dimethylglyoximato) cobalt(III) complexes containing imidazole and thiocyanate as axial ligands

Imidazole(Im), benzimidazole(BzIm), morpholine (Morph) and their derivatives react with Co(CNS)₂ and dimethylglyoxime(DH₂) in ethanolic medium in presence of air to form a number of new cobalt(III) complexes of the type trans-[Co(DH)₂(L)(SCN)], which are characterised on the basis of electronic and IR spectra, NMR (¹H and ¹³C) and mass spectra as well as thermogravimetric (TG-DTA) and conductance measurements. The thiocyanate groups are S-bonded. The NMR observations suggest that in solution these compounds exist as mixtures of the neutral species [Co(DH)₂(L)(SCN)] and the salt [Co(DH)₂(SCN)₂]^? [Co(DH)₂(L)₂]⁺. The mass spectra does not show the molecular ion peak of the complex. The TG-DTA measurements show that the thermolysis of these complexes proceeds through polymeric intermediates giving CO₃O₄ as the end product.     

Trans-bis(difluoroborondimethylglyoximato) cobalt(III) complexes containing imidazole and chloride or thiocyanate as axial ligands

Halo- and pseudohalocobaloxime complexes [Co(DH)₂(Im)(X)] (X = Cl or CNS), containing imidazole (Im) or its derivatives, interact with BF₃·Et₂O to form a series of cobalt(III) complexes, [Co(DBF₂)₂(Im)(X)], that contain a 14-membered macrocyclic ligand. These light coloured microcrystalline solid complexes, stable under ordinary conditions, were characterized on the basis of elemental analyses, conductivity measurements, electronic, IR, NMR and mass spectra, and thermogravimetric and cyclic voltammetric studies, and are shown to posses a six-coordinated trans-octahedral configuration. The mass spectra do not reveal any molecular-ion peak whereas the results of thermolyses reveal the decreased stability of these complexes compared to the corresponding cobaloximes and yield polymeric intermediates, and finally forming Co₃O₄ as the end product. Cyclic voltammetric studies show four reductive waves and an oxidative wave, confirming an oxidation number of III for the central cobalt atom.     

Synthesis and characterization of cobalt(III) tetraaza macrocyclic complexes containing chloro and azido ligands

The complexes [Co(L)Cl₂]Cl · 4H₂O (1) and [Co(L)(N₃)₂]N₃ · 2H₂O (2) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0^1.18,0^7.12]docosane) have been synthesized, and structurally characterized by X-ray crystallography, spectroscopy and cyclic voltammetry. The crystal structure of (1) is centrosymmetric and the cobalt(III) atom has an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two chloride ligands. The cobalt(III) ion in (2) is coordinated to four nitrogen atoms from the macrocycle, and two azide ligands in an octahedral environment, which forms the 1D polymer through hydrogen bonding contacts involving the cation, azide anion and solvent water molecules. Electronic spectra of the complexes also exhibit a low-spin octahedral environment. Cyclic voltammetry of the complexes undergoes a one-electron wave corresponding to Co(III)/Co(II) processes. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the axial ligands.     

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.