Crystallographic,spectroscopic and electrochemical characterization of pyridine adducts of magnesium(II) and zinc(II) porphine complexes

A new purification method of magnesium(II) and zinc(II) porphine complexes (MgP and ZnP, respectively) by crystallization of their respective pyridine adducts is described. Pure MgP and ZnP can be regenerated by removal of the coordinated pyridine ligands by heating at 200 °C under vacuum. X-ray crystallographic structures of the pyridine adducts are presented for the first time. NMR analyses of the adducts reveal the coordination of two pyridine molecules. Electrochemical as well as UV-vis absorption spectroscopy analyses in DMF of MgP·(Py)₂, ZnP·(Py)₂, MgP and ZnP indicate that pyridine adducts are totally dissociated. Besides, oxidation peaks of these complexes are totally irreversible, revealing a high reactivity of the oxidized species. Electrolyses at the first oxidation potential lead to the formation of the meso-meso (ZnP)₂ and (MgP)₂ dimers, oligomers and polymers on the electrode surface, as attested by MALDI-TOF mass spectrometry and UV-vis absorption spectroscopy analyses of the crude solution.     

The equilibrium constants of cadmium(II)-, lead(II)-, magnesium(II)-, and zinc(II)-alpha,beta,gamma,delta-tetrakis(1-methylpyridinium-4-yl)porphine complexes

The equilibrium constants of alpha,beta,gamma,delta-tetrakis(1-methylpyridinium-4-yl)porphine (TMPyP) complexes of cadmium(II), lead(II), magnesium(II), and zinc(II) were spectrophotometrically determined using the absorption spectra at the Soret band and the fluorescence spectra. The values of the following constants at 25 degrees C and ionic strength 0.1M were evaluated: K(PbP) = 10(-8.07 +/- 0.09), K(CdP) = 10(-7.68 +/- 0.03), K(ZnP) = 10(1.72 +/- 0.08), and K(MgP) = 10(-7.40 +/- 0.08) by the acid hydrolysis reaction of the TMPyP-metal complex at various pHs; K(PbP) = 10(-7.80 +/- 0.04) and K(CdP) = 10(-7.38 +/- 0.04) were determined by the ligand exchange reaction between TMPyP and nitrilotriacetic acid.     

Direct synthesis of magnesium porphine via 1-formyldipyrromethane

The reaction of 1-formyldipyrromethane (100 mM) in toluene at 115 degrees C containing DBU (10 mol equiv) and MgBr2 (3 mol equiv) in the presence of air affords the magnesium chelate Mg(II) porphine in 30-40% yield. The advantages of the new method include simplicity, high concentration, chromatography-free purification, gram-scale synthesis, and avoidance of the poorly soluble free base porphine. Mg(II) porphine exhibits good solubility in common organic solvents and is a valuable core scaffold for derivatization.     

Aggregation of meso-tetra-(p-sulphonatophenyl)porphine and its cu(II) and zn(II) complexes in aqueous solution

The aggregation of meso-tetra(p-sulphonatophenyl)porphine, an analytical reagent for the determination of metals at low concentration, has been studied over a wide concentration range by both spectrophotometric and (1)H NMR methods. Up to a concentration of about 3 x 10(-4)M, the experimental data were satisfactorily accounted for by a monomer-dimer equilibrium. At higher concentrations, the best fit of the chemical shift data required postulation of a tetramer. Analysis of the experimental data for the Zn(II) complex indicated the occurrence of dimerization at higher concentrations.     

Electrochemical studies of mercury(II)

The reduction of Hg²⁺ is studied by linear sweep voltammetry, rotated disk electrode voltammetry, and chronoamperometry in a non-complexing medium at a vitreous carbon electrode (VCE). At the VCE which is completely free of any mercury deposit, the reduction of Hg²⁺ is found to be of first order, involving two electrons and reversible at slow sweep rates. When the VCE is partially covered with mercury droplets, the reduction mechanism is different and occurs in two steps. At the most active sites on the VCE where mercury droplets are formed during a previous cathodic sweep, Hg²⁺ undergoes disproportionation to Hg₂²⁺ which is subsequently reduced to Hg. The second step involves the simple two-electron, diffusion-controlled reduction of Hg²⁺ to Hg at the bare electrode surface.     

Iron(II) and magnesium(II) porphyrin acid solvolysis reactions

Rate = k(M-P)(H⁺)² for a Mg²⁺ and Fe²⁺ water soluble porphyrin acid solvolysis reaction. Such rates parallel Buchler's stability index, S_i, and the kinetic stability to acid solvolysis of 2+ metal ions is Ni>Cu>Co>Zn>Fe>Mn>Mg>Cd.     

Crystal structure of magnesium(II) diaquatetracarbamidenitrate

Magnesium(II) diaquatetracarbamidenitrate nitrate was structurally studied. Crystals of composition [Mg(H₂O)₂(ur)₄](NO₃)₂ (I) are monoclinic, Z = 2, P2₁/n, a = 6.449(1) Å, b = 17.670(2) Å, c = 7.578(1) Å; β = 91.637(2)°. In the structure of complex I, the central magnesium atom has octahedral geometry: the four carbamide molecules are in equatorial positions, and water molecules occupy axial positions.     

Electrochemical solid-phase nanoextraction of copper(II) on a magnesium oxinate-modified carbon paste electrode by cyclic voltammetry

Solid-phase nanoextraction is a sample preparation technique, which combines nanotechnology with analytical chemistry, and brings analytical chemistry to a higher level, particularly for complex system analysis. This paper describes a typical example of electrochemical solid-phase nanoextraction and electrochemical detection. Trace amounts of copper (5.0?×?10^?13?mol/L) were extracted by electrochemical solid-phase nanoextraction on to the magnesium oxinate nanoparticle-modified carbon paste electrode surface in a pH?7.2 phosphate buffer system at ?0.50 V for 100 s. The extraction is achieved by the cation exchange between copper(II) in the aqueous solution and magnesium(II) from the magnesium oxinate nanoparticles on the electrode surface. The extracted copper shows an irreversible anodic peak at about 0.2 V (vs. saturated calomel electrode). The peak current is proportional to the scan rate, which shows this to be a surface-controlled process. The oxidation peak current is proportional to the logarithm of the copper concentration in the range 5.0?×?10^?13?～?5.0?×?10^?7?M with a slope of 2.215. This powerful method uses the carbon paste electrode to combine extraction with electrochemical analysis.     

Transmetalation of (octaphenyltetraazaporphyrinato)magnesium(II) with manganese(II) chloride in dimethylformamide

The reaction of (octaphenyltetraazaporphyrinato)magnesium(II) with manganese(II) chloride in dimethylformamide gave (chloro)(octaphenyltetraazaporphyrinato)manganese(III). Reactions of the latter with nitrogen-containing bases were studied. The kinetic parameters of the transmetalation of (octaphenyltetraazaporphyrinato) magnesium(II) with MnCl₂ in dimethylformamide at 323, 333, and 343 K were determined, and a probable reaction mechanism was proposed.     

Electrochemical reduction of copper(II) galacturonate

The complexes formed in the interaction between copper(II) anda-andβ-galacturonic acid, in the pH range 2.5–11.0, have been investigated by means of d.c. polarography and cyclic voltammetry. Witha-galacturonic acid, no complex is formed with copper up to pH 6. Between pH 6 and about 9.5, a complex is formed in solution. Above pH 9.5, the complex appears to break up releasing the ligand. In the case of β-galacturanic acid, no complex is formed until pH 3.5, and persists in solution up to a pH of about 9.5. A second complex forms above pH 6.9 and co-exists with the first complex up to pH 9.5. The complexes formed with both forms of galacturonic acid were studied and the stability constant of the coppera-galacturonate determined.     

Electrochemical synthesis of copper(II) carboxylates

A number of copper(II) carboxylates have been synthesized by anodic oxidation of copper. The reactions were found to proceed with current efficiencies of 0.95 to 1.00 eq./Faraday. Reaction products have been characterized by infrared spectral studies and analysis of copper.     

Why magnesium is five‐coordinate in methanol(phthalocyaninato)magnesium(II)

The square‐pyramidal Mg center in the title compound, [Mg(C₃₂H₁₆N₈)(CH₄O)], is five‐coordinate due to the formation of back‐to‐back π–π dimers that saturate the vacant apical site of the metal coordination sphere. Each complex is a member of a back‐to‐back and a face‐to‐face dimer; the latter are tethered by two strong O—H⋯N hydrogen bonds. The dimers form columns that likely determine the solid‐state packing. The phthalocyaninate ligands are essentially planar, with a slight `hat visor' conformation character.     

Fluorescent magnesium(II) coordination polymeric hydrogel

A pH and mechano-responsive coordination polymeric gel was developed without the use of long chain hydrophobic groups. The hydrogel was synthesised by reacting the aqueous solution of Mg2+ with the basic aqueous solution of N-(7-hydroxyl-4-methyl-8-coumarinyl)-alanine. The gelation is attributed to the self-aggregation of 1D coordination polymers to form 3D nanostructures through non-covalent interactions to entrap water molecules. The freeze-dried hydrogel exhibits a fibrillar network structure with a uniform ribbon shape. UV/vis absorption studies illustrate that the hydrogel displays a typical pi-pi* transition. The fluorescence intensity of the hydrogel is enhanced drastically with a longer lifetime upon gel formation. Mechanical analysis including dynamic oscillation on shear, steady shear and creep (retardation-relaxation) testing have been performed to elucidate the supramolecular nature of the 3D assembly. Together with the viscoelastic properties and biocompatibility, the Mg2+ hydrogel may find utility as a novel soft material in biomedical applications.     

Electrochemical route to Co(II) polyporphine

Journal of Solid State Electrochemistry - Novel synthetic route towards electroactive films of Co(II) polyporphine has been elaborated. It is based on the electrochemical transformation of the...     

Electrochemical processes of meso-tetrakis (4-sulfonatophenyl) porphine at a silver electrode studied by surface-enhanced resonance raman spectroscopy

The potential dependence of surface-enhanced resonance Roman spectra of meso-tetrakis (4-sulfonatophenyl) porphine (TSPP) in 0.05 M H₂SO₄ reveals two electrochemical processes at a silver electrode surface. One which begins around ?0.3 V is interpreted as dissociation of aggregated TSPP to monomers. The other which occurs near ?0.4 V is ascribed to a partial Ag incorporation of TSPP molecules.     

Electrochemical investigations of cationictrans-haloarylisocyanidebis(tertiaryphosphino)platinum (II) complexes

Summary The electrochemical behaviour of a series of cationic platinum(II) isocyanide complexes has been studied in acetonitrile. All the tested compounds are oxidized at a platinum electrode via a two-electron process and reduced at a platinum or mercury electrode via two successive one-electron steps. The anodic step involves the formation of platinum(IV) complexes. The main reduction product formed in correspondence to the first cathodic process is a stable dimer platinum(I) containing bridging isocyanide ligands. Platinum(0) species are formed in the subsequent reduction step.