Direct electrosynthesis of Cu,Cd, Zn complexes of piroxicam (4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide-1,1,-dioxide) and isoxicam (4-hydroxy-2-methyl-N-(5-methyl-3-isoxazolyl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide) in nonaqueous media by in-situ generation of supporting electrolyte

The direct electrosynthesis of Cu, Cd and Zn complexes of the anti-inflammatory drugs piroxicam (4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide-1,1,-dioxide=H-pir) and isoxicam (4-hydroxy-2-methyl-N-(5-methyl-3-isoxazolyl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide=H-isox) was accomplished by electrochemical dissolution of sacrificial metallic anodes in an acetonitrile solution of the ligand. The chemical and electrochemical in-situ generation of supporting electrolyte was used as a means to obtain pure coordination compounds without the use of supporting electrolytes such as tetraalkylammonium or lithium salts in nonaqueous media. Characterization of the complexes obtained by direct synthesis and comparison with those obtained by traditional synthesis shows that a new copper–piroxicam complex was synthesized.     

A Multi-Technique Investigation of the Complex Formation Equilibria between Bis-Deferiprone Derivatives and Oxidovanadium (IV)

The increasing biomedical interest in high-stability oxidovanadium(IV) complexes with hydroxypyridinone ligands leads us to investigate the complex formation equilibria of V^IVO²⁺ ion with a tetradentate ligand, named KC21, which contains two 3-hydroxy-1,2-dimethylpyridin-4(1H)-one (deferiprone) moieties, and with the simple bidentate ligand that constitutes the basic unit of KC21, for comparison, named L5. These equilibrium studies were conducted with joined potentiometric–spectrophotometric titrations, and the results were substantiated with EPR measurements at variable pH values. This multi-technique study gave evidence of the formation of an extremely stable 1:1 complex between KC21 and oxidovanadium(IV) at a physiological pH, which could find promising pharmacological applications.     

Tetraaqua-bis(3-hydroxy-4-nitrobenzoato) Co(II) and Ni(II) complexes and diaqua-bis(2-hydroxy-4-methoxybenzoato) Zn(II) complex: crystal structure and thorough metal-coordination investigation

Reactions of Co(II) and Ni(II) salts with the monosodium salt of 3-hydroxy-4-nitrobenzoic acid (3) in aqueous solution resulted in isomorphous covalent complexes 3C and 3D, of centrosymmetric geometries. In similar conditions, 2-hydroxy-4-methoxybenzoic acid (5) led to the covalent Zn(II) complex 5A, exhibiting a marked dissymmetric geometry. The present crystallographic data with structural data for a series of closely related metal complexes previously reported allow a tentative rationalization of the solid-state architecture of such complexes. The dissymmetry in 5A was interpreted on the basis of a mixed (monodentate and bidentate) metal-ligation mode and a pyramidal coordination at the metal.     

New lipophilic 3-hydroxy-4-pyridinonate iron(III) complexes: synthesis and EXAFS structural characterisation

New tris-iron(III) chelates of 3-hydroxy-4-pyridinone ligands derived from maltol (3-hydroxy-2-methyl-4-pyrone) or ethylmaltol (2-ethyl-3-hydroxy-4-pyrone), including a variety of N-aryl (phenyl, 4'-tolyl, 4'-(n-butyl)phenyl, 4'-(n-hexyl)phenyl) and N-benzyl (4'-methylbenzyl, 4'-fluorobenzyl and 4'-(trifluoromethyl)benzylamine) substituents on the nitrogen atom of the pyridinone ring, have been prepared. Characterization by C,H,N elemental analysis and thermogravimetric measurements indicates that most of the complexes are obtained as hydrates of general formula ML3.xH2O. Structural characterization of these difficult to crystallize lipophilic complexes has been achieved by EXAFS spectroscopy. Solutions of iron(III) complexes of maltol, ethylmaltol, 1,2-dimethyl-3-hydroxy-4-pyridinone and 1-phenyl-2-methyl-3-hydroxy-4-pyridinone in methanol-water mixtures were also examined by EXAFS. Distances from the central atom to ligand atoms, within 6 A of the metal, have been determined in the solid and solution samples and the results show that the structure observed in the powder is maintained in solution. The local structure around the metal centre, bond distances and bond angles, does not change significantly with variable lipophilicity, thus indicating that ligands may be tailored according to specific needs without altering their chelation properties. EXAFS data analysis for this set of tris-iron(III) compounds illustrates the important contribution of both intra-ligand and inter-ligand multiple scattering pathways through the metal centre to a peak observed in the FT spectrum at twice the metal ligand distance (approximately 4 A). The present results demonstrate that EXAFS features at twice the metal-ligand distance are valuable in the assignment of molecular geometry and that location of hydration water molecules, by EXAFS analysis, is limited by the geometry of the complexes, in particular for those in which ligands containing phenyl rings are present.     

Solubilities of iron(III) complexes of 3-hydroxy-2-ethyl-4-pyranone and of 3-hydroxy-1,2-dimethyl-4-pyridinone in aqueous salt solutions

Solubilities are reported for the tris-ligand–iron(III) complexes of 3-hydroxy-2-ethyl-4-pyranone and of 3-hydroxy-1,2-dimethyl-4-pyridinone in aqueous solutions of alkali halides and of ammonium and tetraalkylammonium bromides. The Setchenow coefficients estimated from salt effects on solubilities for these complexes are compared with those for other inorganic complexes.     

3d Metal complexes with 2-hydroxy-3-methoxybenzaliminopropyl and 4-hydroxy-3-methoxybenzaliminopropyl immobilized on aerosil as catalysts of ozone decomposition

The composition and structure of M(II) (Mn, Co, Cu) complexes with Schiff bases (L1 = 2-hydroxy-3-methoxybenzaliminopropyl, L2 = 4-hydroxy-3-methoxybenzaliminopropyl) immobilized on Aerosil and their catalytic activity in ozone decomposition were studied. The formation of pseudotetrahedral bisligand complexes M(L1)₂ and pseudooctahedral complexes M(L2)₂ on the modified surface of Aerosil was confirmed by IR and ESR spectroscopy and by diffuse reflectance spectroscopy (DSR). The catalytic activity of isostructural complexes in ozone decomposition varies in the order Mn > Co > Cu, and M(L₂)₂ complexes are more active than M(L1)₂.     

Binuclear copper(II) complexes with acyldihydrazones of 4-formyl-5-hydroxy-3-methyl-1-phenylpyrazoles

The synthesis of copper(II) binuclear complexes with acyldihydrazones of saturated carboxylic acids and 4-formyl-5-hydroxy-3-methyl-1-phenylpyrazoles in which the coordination polyhedra are connected by polymethylene chains of different length (two to five units) is described. The complexes were studied by chemical and thermal analysis, IR spectroscopy, and EPR. The molecular and crystal structure of the copper(II) complex with glutaric acid and 1-(4′-chlorophenyl)-4-formyl-5-hydroxy-3-methylpyrazole acyldihydrazone (H₄L) described as [Cu₂L·2Py] · Py · 4H₂O was determined by X-ray diffraction. The crystals are orthorhombic: a = 24.789(7) Å, b = 39.319(9) Å, c = 4.6336(14) Å, space group Pnma, Z = 4. The number of symmetrically unrelated reflections is 4716, R = 0.0606, R _w = 0.1307. The central atoms are separated by a chain of eight σ bonds and are located at a distance of 8.939 Å. The copper coordination polyhedron is a square. A specific feature of the crystal structure is the stacking interaction involving chelate rings and the pyrazole ring, resulting in stacks of molecular complexes. The EPR spectrum of a solution of the complex based on the acyldihydrazone of succinic acid and 4-formyl-5-hydroxy-3-methyl-1-phenylpyrazole recorded at room temperature exhibits seven HFS lines with an intensity ratio of 1: 2: 3: 4: 3: 2: 1 and a constant of 33.3 G as a result of exchange coupling of the unpaired electrons to the two equivalent copper nuclei. An increase in the length of the polymethylene chain to 3–5 units or introduction of the para-chlorine atom into the benzene ring hampers the exchange interactions, and the EPR spectrum shows a signal of four HFS lines with a constant of 55–70 G typical of monomeric copper(II) complexes.     

Spectroscopic and potentiometric characterization of oxovanadium(IV) complexes formed by 3-hydroxy-4-pyridinones. Rationalization of the influence of basicity and electronic structure of the ligand on the properties of V(IV)O species in aqueous solution

Aqueous solution studies regarding the identification and characterization of complexes formed by the VIVO ion and 11 3-hydroxy-4-pyridinone derivatives have been performed using EPR and UV/vis spectroscopic techniques. For the three ligands (HL) adequately soluble in water (1-methyl-3-hydroxy-4-pyridinone, 1-methyl-2-ethyl-3-hydroxy-4-pyridinone, and 1,2-diethyl-3-hydroxy-4-pyridinone), potentiometric titrations were performed; the results are consistent with the formation of [V(IV)OL]+, [V(IV)OL2], [V(IV)OL2H(-1)]-, [(V(IV)O)2L2H(-2)], and [V(IV)L3]+ species. Bis chelated complexes are characterized by a cis-trans isomerism, the trans isomer being strongly favored with respect to the cis arrangement. Tris chelated non-oxo V(IV) species were prepared in CH3COOH; their spectroscopic features point to a d(z2) ground state and a geometry intermediate between an octahedron and a trigonal prism, related to the steric requirements of the substituent on the carbon atom in position 2 of the pyridinone ring. Four new solid derivatives, [V(IV)O(1,2-diethyl-3-hydroxy-4-pyridinonato)2], [V(IV)O(1-(p-tolyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], [V(IV)O(1-(p-(n-butyl)phenyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], and [V(IV)O(1-(p-(n-hexyl)phenyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], were isolated and characterized; they exhibited a five-coordinate geometry close to square-pyramid. A criterion for establishing the degree of distortion toward the trigonal-bipyramid on the basis of the electronic absorption spectra is provided. Relationships between the pKa of the -OH group in position 3 of the ring and (i) log K of mono and bis chelated complexes, (ii) pK of the water molecule in cis-[V(IV)OL2(H2O)], (iii) log K of tris chelated species [V(IV)L3]+, and (iv) 51V hyperfine coupling constant (Az) have been established and discussed for a number of pyrone, pyridinone, and catechol ligands. The results are rationalized by assuming for pyridinones an electronic structure intermediate between that of pyrones and catechols. The relationships are valuable to the understanding of the behavior of VIVO species in aqueous solution.     

Optical resolution of racemic 4-hydroxy-3-isobornyl-5-methylbenzaldehyde

Racemic 4-hydroxy-3-isobornyl-5-methylbenzaldehyde was separated into particular enantiomers via transformation into diastereoisomeric Schiff bases by reaction with (R)-1-phenylethanamine. The absolute configuration of the products was determined on the basis of the X-ray diffraction data for camphanate derived from one enantiomer of 4-hydroxy-3-isobornyl-5-methylbenzaldehyde.     

DFT studies, vibrational spectra and conformational stability of 4-hydroxy-3-methylacetophenone and 4-hydroxy-3-methoxyacetophenone

The FT-IR and FT-Raman spectra of 4-hydroxy-3-methylacetophenone (HMA) and 4-hydroxy-3-methoxyacetophenone (HMOA) have been recorded. The total energy calculations of HMA and HMOA were tried for various possible conformers. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G** methods and basis sets combinations for the most optimized geometries. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined.     

Spectrophotometric determination of titanium,zirconium and hafnium with pyridoxal 3-hydroxy-2-naphthoylhydrazone

Summary The synthesis, characteristics and analytical applications of pyridoxal 3-hydroxy-2-naphthoylhydrazone are described. The reactions of titanium(IV), zirconium(IV) and hafnium(IV) with this reagent have been studied spectrophotometrically and the stoichiometries of the ternary complexes determined. Photometric methods for the determination of these ions are proposed, and the selectivity of these methods has been established.

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Spektrophotometrische Bestimmung von Titan, Zirkon und Hafnium mit Pyridoxal-3-hydroxy-2-naphthoylhydrazon

Zusammenfassung Synthese, Eigenschaften und analytische Anwendung von Pyridoxal-3-hydroxy-2-naphthoylhydrazon wurden beschrieben. Die Reaktionen von Titan(IV), Zirkon(IV) und Hafnium(IV) mit diesem Reagens wurden untersucht und die Stöchiometrie ihrer ternären Komplexe ermittelt. Photometrische Methoden für die Bestimmung dieser Ionen wurden vorgeschlagen und deren Selektivität untersucht.

     

Extraction and complex formation of niobium(V) with 3-hydroxy-2-methyl-1-(4-tolyl)-4-pyridone

The extraction of niobium(V) from aqueous hydrochloric and sulphuric acid solutions with 3-hydroxy-2-methyl-1-(4-tolyl)-4-pyridone (HY) dissolved in chloroform is described. Niobium(V) can be quantitatively extracted with HY in the form of two different complexes depending on the chloride ion concentration in the aqueous phase. At a low chloride concentration or without chloride in the aqueous phase niobium(V) is extracted with HY in the form of Nb(OH)₃Y₂ and at a high chloride concentration as a mixed Nb(OH)₃ClY complex. Niobium extraction with HY enables the separation of niobium(V) from zirconium(IV) and hafnium(IV). The formation of a mixed chloro-4-pyridone complex is also applicable for the spectrophotometric determination of niobium in the organic phase at the maximum absorption at 350 nm.     

Complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid and related compounds

Summary The complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid as well as with benzoic acid and 4-hydroxybenzoic acid was studied. In aqueous solution weak carboxylic 1 : 1 complexes, are formed in which the carboxyl group is bidentately coordinated to the metal atom. The logarithmic stability constants of these complexes regarding the reaction of the uranyl ion with the single charged anion of the respective ligands are 2.78±0.02, 2.68±0.04, and 2.71±0.04 at an ionic strength of 0.1 mol/l (NaClO₄) and at 25 °C. Bis(4-hydroxy-3-methoxybenzoato)dioxouranium(VI) was obtained as a crystalline compound if the concentrations of the starting components for the synthesis are increased. The monoclinic compound has a reflections-rich X-ray powder diffraction pattern. The lattice constants are a = 13.662(9) ?, b = 21.293(7) ?, c = 11.213(3) ?, b = 107.49(4), and V = 3111(2) ?.³     

双(2-取代-3-羟基-4-吡喃酮)合铜(II)配合物的合成和降血糖作用

合成了双(2-取代-3-羟基-4-吡喃酮)合铜(II)配合物, 采用元素分析、质谱、红外光谱、电子光谱、电子自旋共振谱表征了它们为平面正方型配合物, 中心离子和配体的物质的量比为1∶2. 在STZ-糖尿病小鼠模型上, 其中双(2-乙基-3-羟基-4-吡喃酮)合铜(II)在10 mg/kg的剂量下灌胃给药, 能增加血清胰岛素的合成和分泌、降低糖尿病小鼠的血糖水平, 显示出良好的抗糖尿病的作用. 该配合物毒性低, 对正常小鼠灌胃给药的半数致死量LD₅₀是855.9 mg/kg.     

Crystal Structure of 2-[2-hydroxy-3-methoxyphenyl]-3-[2-hydroxy-3-methoxybenzylamino]-1,2-dihydroquinazolin-4(3H)-one and the Synthesis, Spectral and Thermal Investigation of its Transition Metal Complexes

A new 1,2-dihydroquinazolin-4(3H)-one ligand, 2-[2-hydroxy-3-methoxyphenyl]-3-[2-hydroxy-3-methoxybenzylamino]-1,2-dihydroquinazolin-4(3H)-one (Hmpbaq), formed by the condensation of 2-aminobenzoylhydrazide with 2-hydroxy-3-methoxybenzaldehyde and its copper(II), nickel(II), cobalt(II), manganese(II), zinc(II) and cadmium(II) complexes, have been synthesized. Their structures have been elucidated on the basis of elemental analyses, conductance measurements, magnetic moments, spectral (i.r., ¹H-n.m.r., u.v.–vis., e.p.r. and FAB-mass) and thermal studies. The formation of 1,2-dihydroquinazolin-4(3H)-one rather than hydrazone in the reaction of 2-aminobenzoylhydrazide with 2-hydroxy-3-methoxybenzaldehyde is confirmed by the ¹H-n.m.r. spectra and single crystal X-ray diffraction studies. The tridentate behavior of the ligand was proposed on the basis of spectral studies. X-band e.p.r. spectra of the copper(II) and manganese(II) complexes in the polycrystalline state at room temperature and liquid nitrogen temperature were recorded and their salient features are reported. Thermal stabilities of the manganese(II) and zinc(II) complexes have been studied.     

Synthesis,crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N₂O₂ type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H₂L⁴ and its corresponding complex VOL⁴ were determined by X-ray crystallography.     

Dioxomolybdenum(VI) complexes containing 1-alkyl-2-ethyl-3-hydroxy-4-pyridin-4(1H)-ones

Dioxomolybdenum(VI) complexes derived from ethyl maltol (2-ethyl-3-hydroxy-4-pyrone) and 1-alkyl-2-ethyl-3-hydroxy-4-pyridin-4(1H)-ones have been prepared and characterized using physical methods including ¹H- and ¹³C-n.m.r. spectroscopy, i.r., elemental analysis, and X-ray diffraction for the pyrone and 3-methylpyridine pyridinone derivatives. The octahedral complexes have the general formula cis-MoO₂L₂ where L = the deprotonated pyrone or pyridinone ligand.     

Spectrophotometric and AM1d studies of the equilibria between oxidovanadium(IV) and four isomers of n-propyl-3-azido-2,3-dideoxy-d-hexopyranosides in aqueous solution

Complex formation and stability constants for complexes between isomers of n-propyl-3-azido-2,3-dideoxy-d-hexopyranosides and oxidovanadium(IV) were determined in aqueous solution by the spectrophotometric method. Complexes of 1?:?2 metal-to-ligand stoichiometry were formed. The impact of the structures of the ligands on the complex formation was discussed. The energetically most favorable structures of the complexes were calculated and visualized by the AM1d method at the semi-empirical level of theory.     

Synthetic, structural, and antimicrobial studies of organotin(IV) complexes of semicarbazone, thiosemicarbazone derived from 4-hydroxy-3-methoxybenzaldehyde

Reaction of dibutyltin dichloride, dimethyltin dichloride, and tributyltin chloride with ligands derived from thiosemicarbazone and semicarbazone leads to the formation of a new series of organotin(IV) complexes of general formula R₂SnCl₂·L and R₃SnCl·L (where L ligands derived from the condensation of thiosemicarbazide and semicarbazide with 4-hydroxy-3-methoxybenzaldehyde). The authenticity of these ligands and their metal complexes have been established on the basis of elemental analysis, conductance measurements, molecular weight determinations, infrared, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR, and UV spectral studies. These studies showed that the ligands coordinate to the metal atom in a bidentate. An octahedral structure is proposed for the organotin(IV) complexes. The ligands and its metal complexes are screened for their antimicrobial activities against some Gram-positive and Gram-negative bacteria, and fungus. The studies demonstrated that metalation can increase the antimicrobial activity rather than the free ligands.     

Synthesis,characterization, magnetic,thermal and electrochemical studies of oxidovanadium (IV) picolyl hydrazones as functional catechol oxidase models

The picolyl hydrazone ligands derived from picolonic acid hydrazide and α-pyridyle ketone (L¹, L² and L³), α-acetyl thiophene (L⁴), α-formyl or α-acetyl phenol (L⁵ and L⁶ respectively) and 2-hydroxy-1-naphthaldehyde (L⁷) react with equimolecular amount of vanadyl sulfate in refluxing methanol to yield oxidovanadium (IV) complexes. The structure of the obtained ligands and their oxidovanadium (IV) complexes were characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, thermal analysis (TGA & DTG), IR, electronic absorption and ESR spectral studies. Cyclic voltammeteric behavior of the complexes has also been discussed. Five-coordinate square-pyramidal structure was proposed for all complexes. A monomeric nature was reported for complexes (2), (3), (6), and (7), while dimeric structures were suggested for complexes (1), (4) and (5). The ability of the complexes to catalyze the aerobic oxidation of catechol to the light absorbing o-quinone has been investigated. The results obtained show that all complexes catalyze this oxidation reaction and large variations in the rate were observed. Electrochemical data for most complexes show that there is a linear relationship between their ability to oxidize catechole and their E_1/2 potentials. The most effective catalysts were those complexes which exhibited E_1/2 values approached to the E° value of the natural tyrosinase enzyme isolated from mushroom, while those that largely deviated from that potential exhibited lower oxidase catalytic activity. The probable mechanistic implications of the catalytic oxidation reactions are discussed.