A POTENTIOMETRIC STUDY OF METAL CHELATES WITH PENTAETHYLENEHEXAAMINEOCTAACETIC ACID

Abstract

The protonation constants of pentaethylenehexaamineoctaacetic acid, PHOA, were determined by potentiometric titration in aqueous solution at an ionic strength of 0.10 M KNO₃ and at 25°C. The formation constants of various metal-PHOA complexes were also obtained by titrating mixtures of metal to ligand in molar ratios of 1:1 and 2:1. Calculations were performed with the computer program BEST. Individual formation constants are reported for Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) with PHOA as well as their related protonated species. The stabilities of the 1:1 and 2:1 complexes are similar in many respects to complexes formed with tetraethylenepentaamineheptaacetic acid (TPHA). The similarities in the stabilities of both the 1:1 and 2:1 complexes with PHOA and those with TPHA are explained in terms of ligand denticity and steric effects. Mercury(II)-PHOA complexes exhibited the highest formation constants, followed by copper(II)-PHOA complexes which had higher log K _ML's than those for Co(II), Ni(II), Zn(II), Cd(II) and Pb(II).     

A POTENTIOMETRIC STUDY OF METAL CHELATES WITH TETRAETHYLENEPENTAAMINEHEPTA-ACETIC ACID

Abstract

The protonation constants of tetraethylenepentaamineheptaacetic acid, TPHA, were determined by potentiometric titration in aqueous solution at an ionic strength of 0.10 M KNO₃ and at 25°C. The formation constants of various metal-TPHA complexes were also obtained by titrating mixtures of metal to ligand in molar ratios of 1 :1 and 2:1. Calculations were performed with the computer program BEST. Individual stability constants are reported for Co(II). Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) with TPHA as well as their related pro-tonated species. The stabilities of the 1:1 complexes parallel to those of similar complexes with DTPA and TTHA. However the 2: 1 complexes have significantly larger log K _ML's than their TTHA counterparts. The extra stability of the 2:1 metal-TPHA complexes is explained in terms of ligand denticity and steric effects. Mercury(II)-TPHA complexes exhibited the highest formation constants and the copper-TPHA complexes had slightly higher log K _ML's than those for Co(II), Ni(II), Zn(II), Cd(II) and Pb(II).     

Syntheses,crystal structures and characterization of divalent transition metal sulfonate complexes with O-phenanthroline

Two new complexes, [Zn(phen)₂(H₂O)₂]2L·H₂O (1) and [Cu(phen)(L)(H₂O)₂]L·3H₂O (2), where HL?= 4-aminobenzenesulfonic acid and phen = o-phenanthroline, have been synthesized and their crystal structures determined by X-ray diffraction. In the complexes the Cu(II) and Zn(II) atoms revealed two different coordination environments. Complex 1 consists of a cation [Zn(phen)₂(H₂O)₂]²⁺, in which Zn(II) is six-coordinated by four nitrogen atoms from two o-phenanthroline molecules and by two water molecules. Complex 2 has two crystallographically unique Cu(II) ions, where Cu(II) ion is five-coordinate with two nitrogen atoms of o-phenanthroline, two water molecules and one sulfonate oxygen atom. The electrochemical behavior and FT-IR of the two compounds have also been studied in detail.     

Synthesis,structures, and magnetic properties of two pyrazolato-bridged trinuclear copper(II) complexes

One nonlinear and one linear trinuclear copper(II) complex [Cu₃(dien)₂(pdc)₂CH₃OH]₂?·?6CH₃OH (1) and [Cu₃(pdc)₂(CH₃OH)₆(H₂O)₄] (2) were prepared and characterized structurally, where dien is diethylenetriamine and pdc^3? the trianion of 3,5-pyrazoledicarboxylic acid. Both complexes consist of 3,5-pyrazoledicarboxylato-bridged trinuclear copper(II) centers. In 1, copper(II) ions are five-coordinate in distorted square pyramids with bond angles 164.78° for Cu(1)–Cu(2)–Cu(3) and 164.51° for Cu(4)–Cu(5)–Cu(6). In 2, the three copper(II) ions are six-coordinate with elongated octahedral geometry. The trinuclear units of 1 and 2 interact through hydrogen bonds to form 3-D and 2-D supramolecular networks, respectively. Variable temperature magnetic susceptibility measurements show that 1 and 2 are antiferromagnetically coupled with J values of ?11.2 and ?13.3?cm^?1.     

A bifunctional 2,2′:6′,2″-terpyridine-based ligand for ratiometric Cu(II) sensing

Synthesis and characterization of the bifunctional sensor receptor ligand N-([2,2′:6′,2″-terpyridine]-4′-yl)methyl)-N-propylacrylamide (1) and the model ligand N-([2,2′:6′,2″-terpyridine]-4′-yl)methyl)-N-propylisobutyramide (2) are described. Ligand 1 is a receptor for Cu(II) that is copolymerizable with N-isopropylacrylamide giving a ratiometric sensor of weakly bound Cu(II) in environmental waters. Ligand 2 is a model for copolymerized 1 whereby the reactive acrylamide group is replaced by isobutyramide. Solution speciation of complexes of Cu(II) and Zn(II) with 2 were investigated spectroscopically and their solid-state structures were studied through single-crystal X-ray diffraction. Solution UV–vis and fluorescence studies show a preference of 2 toward Cu(II) over Na(I), Zn(II), Cu(II), Co(II), Mn(II), Ni(II), Cd(II), and Pb(II) in accord with the Irving–Williams series and other coordination principles. Solution speciation determined in a weakly coordinating aqueous-organic (60?:?40 DMF/H₂O) medium indicates 1?:?1 Cu(II):2 binding as desired in that formation of [Cu(2)₂]²⁺ would crosslink the polymer sensor. The crystal structures of [Cu(2)(NO₃)₂] and [Zn(2)(NO₃)₂]·MeOH·1/2Et₂O display distorted octahedral geometries where 2 coordinates meridionally and two nitrate groups occupy the remaining sites around the metal center.     

Synthesis,structures and thermal properties of Cu(II) and Ni(II) complexes containing diethylenetriamine and nicotinate ligands

The syntheses and crystal structures of four new divalent transition metal complexes of the types [Cu₂(dien)₂(nic)](ClO₄)₃ · MeOH (nic = anion of nicotinic acid; dien = diethylenetriamine), 1; [Cu(dien)(nic)]₂(nic)₂, 2; [Cu(dien)(nic)]₂(BF₄)₂ · 2MeOH, 3 and [Ni(dien)(nic)(H₂O)]₄(NO₃)₄ · 2MeOH, 4, are reported, which were prepared by the reactions of diethylenetriamine and nicotinic acid with Cu(ClO₄)₂ · 6H₂O, Cu(OAc)₂ · H₂O, Cu(BF₄)₂ · 6H₂O and Ni(NO₃)₂ · 6H₂O in MeOH, respectively. These complexes were characterized by single-crystal X-ray diffraction method and elemental analyses. In the cation of complex 1, one nicotinate ligand bridges two Cu(II) metal centers through the pyridyl nitrogen atom and one of the carboxylate oxygen atoms. The cations of complexes 2 and 3 form the twelve-membered metallocycles, involving two Cu(II) ions that are bridged by two nicotinate ligands. The cation of complex 4 forms a tetranuclear cage with the four Ni(II) metal centers bridged by four nicotinate ligands and each Ni(II) metal center adopts the distorted octahedral geometry. Their thermal properties have been investigated by using differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA).     

SPECTRAL AND MAGNETIC STUDY OF COPPER(II) MEFANAMATES: CRYSTAL AND MOLECULAR STRUCTURE OF BIS(MEFANAMATO)DI(N,N-DIETHYLNICOTINAMIDE)DI(AQUA)COPPER(II)

Abstract

The synthesis and characterization of Cu(II) mefanamate (mef) compounds of composition Cu(mef)₂L (L = water, caffeine, or methyl-3-pyridylcarbamate) and Cu(mef)₂L₂ (L = 3-pyridylcarbinol, nicotinamide, N,N-diethylnicotinamide, 2,6-dimethanol pyridine or nicotine) is reported. Characterizations of the compounds were based on elemental analyses, electronic, infrared and EPR spectra and magnetic susceptibility measurements over a temperature range (80–290 K). The spectral and magnetic properties of Cu(mef)₂L indicate the presence of Cu(II) dimers structurally similar to that of Cu(II) acetate monohydrate. All the Cu(mef)₂L₂ compounds possess octahedral stereochemistry about Cu(II) with differing tetragonal distortion.

An X-ray analysis of Cu(mef)₂(Et₂nia)₂(H₂O)₂was carried out, and it featured tetragonal bipyramidal geometry around the Cu(II) atom. The tetragonal plane is created by mefanamate anions bonded to the Cu(II) atom via the unidentate carboxylate oxygen atoms [Cu-0(2) = 1.936(3)Å] and the pyridine ring nitrogen atoms of the neutral ligand N, N-diethylnicotinamide [Cu-N(l) = 2.027(3)Å] in frans-positions. Axial water molecules [Cu-O(4) = 2.557(3)Å] complete the coordination sphere.     

Thermal Studies of Metal-quinone Complexes Role of Aqua Coligations with Copper(II) in Coordination of 2-hydroxy-1,4-naphthoquinone

Copper(II) complexes of lawsone (2-hydroxy-1,4-naphthaquinone, Lw) with variety of aqua ligation viz. Cu-1, [Cu(Lw)₂(H₂O)]₂; Cu-2, [Cu(Lw)₂(H₂O)₂] and Cu-3, [Cu(Lw)₂(H₂O)₂]₂ have been synthesized. The role of water as counter ligand on coordination propensity of redox active lawsone in naphthoquinone/naphthosemiquinone (NQ/NSQ) forms is quantified by studies of pyrolytic reactions, using non-isothermal TG and DTA techniques, coupled with IR studies. Mixed (NQ) (NSQ) ligation in Cu-1 and Cu-3 required energy of activation, E_a ∼67 kJ mol⁻¹ of (NQ) and ∼41 kJ mol⁻¹ of (NSQ). Comparable energies of aqua ligand (∼43 kJ mol⁻¹) with NSQ ligand in Cu-1 and Cu-3, dictate charge distributions in lawsone coordinations. A large difference between E_a of aqua and p-NQ ligand indicates coordination of lawsone in its fully oxidised quinone form in Cu-2. From thermoanalytical studies schematic oxidative decomposition mechanisms are proposed for Cu-1 and Cu-3. From pyrolytic reactions enthalpies are estimated by DTA technique. This revised version was published online in August 2006 with corrections to the Cover Date.     

PROTONATED METAL COMPLEXES OF DIETHYLENETRIAMINEPENTAACETIC ACID (DTPA)

Abstract

Spectrophotometric studies in acidic solutions with pH between 1.10 and 1.80, show the presence of tetraprotonated complexes, MH₄L, of Co(II), Cu(II) and Fe(III) with DTPA. Under identical conditions, Ni(II) forms the complex NiH₂L.

The effective and overall stability constants of these complexes are determined.     

Syntheses,crystal structures and magnetic properties of heteronuclear bimetallic compounds of [Cu(pdc)2][M(H2O)5]·2H2O [M=Ni(II), Co(II), Mn(II); pdc=2,6-pyridinedicarboxylato]

The complexes [M(H₂O)₅][Cu(pdc)₂]·2H₂O [M=Ni(II) 1, Co(II) 2, Mn(II) 3; pcd=2,6-pyridinedicarboxylato] are prepared and their crystal structures, magnetic susceptibilities and UV-Visible properties reported. In all cases, the Cu(II) ion occupies the chelating site in the pdc ligand, while the M(II) occurs as a pentaaqua ion bridged to the [Cu(pdc)₂] moiety through a carboxylate as demonstrated by both UV-Visible spectroscopy and X-ray diffraction. Single crystal X-ray diffraction shows the three complexes to be isostructural. Weak antiferromagnetic interactions between the metal ions are observed in 1 and 3, while the magnetic behavior of 2 is dominated by single ion anisotropy.     

Synthesis,characterization, DNA-binding,and antioxidant activities of four copper(II) complexes containing N-(3-hydroxybenzyl)-amino amide ligands

Four new substituted amino acid ligands, N-(3-hydroxybenzyl)-glycine acid (HL₁), N-(3-hydroxybenzyl)-alanine acid (HL₂), N-(3-hydroxybenzyl)-phenylalanine acid (HL₃), and N-(3-hydroxybenzyl)-leucine acid (HL₄), were synthesized and characterized on the basis of ¹H NMR, IR, ESI-MS, and elemental analyses. The crystal structures of their copper(II) complexes [Cu(L₁)₂]·2H₂O (1), [Cu(L₂)₂(H₂O)] (2), [Cu(L₃)₂(CH₃OH)] (3), and [Cu(L₄)₂(H₂O)]·H₂O (4) were determined by X-ray diffraction analysis. The ligands coordinate with copper(II) through secondary amine and carboxylate in all complexes. In 2, 3, and 4, additional water or methanol coordinates, completing a distorted tetragonal pyramidal coordination geometry around copper. Fluorescence titration spectra, electronic absorption titration spectra, and EB displacement indicate that all the complexes bind to CT-DNA. Intrinsic binding constants of the copper(II) complexes with CT-DNA are 1.32?×?10^6?M^?1, 4.32?×?10^5?M^?1, 5.00?×?10^5?M^?1, and 5.70?×?10^4?M^?1 for 1, 2, 3, and 4, respectively. Antioxidant activities of the compounds have been investigated by spectrophotometric measurements. The results show that the Cu(II) complexes have similar superoxide dismutase activity to that of native Cu, Zn-SOD.     

Three new binuclear copper(II) complexes with isonicotinic acid N-oxide: syntheses,crystal structures and properties

Three new copper(II) complexes with isonicotinic acid N-oxide (HL) and 1,10-phenanthroline (phen) as ligands, [Cu(L)(phen)(H₂O)]₂(NO₃)₂···2H₂O (1), [Cu(L)(phen)(H₂O)]₂(ClO₄)₂···2H₂O (2), and [Cu(L)(phen)Br]₂- [Cu(L)(phen)(H₂O)]₂Br₂···6H₂O (3) have been synthesized and structurally characterized. The structures of all three complexes feature a Cu₂ dimer formed by two Cu(II) ions interconnected by two bridging ligands. Each copper(II) ion has a distorted square pyramidal coordination geometry with elongated axial coordination by an aqua ligand or halogen anion. The isonicotinic acid N-oxide anion is bidentate, being coordinated to two Cu(II) ions through its N-O oxygen and one of its carboxylate oxygen atoms. Magnetic susceptibility measurements show a Curie–Weiss paramagnetic behavior characteristic of one unpaired electron for a copper(II) ion for all three complexes.     

Copper(II) complexes with pyridine-2,6-dicarboxylic acid from the oxidation of copper(I) iodide

Via an oxidation reaction of Cu(I) iodide with pyridine-2,6-dicarboxylic acid (H₂L) in DMF three copper(II) complexes, [(CH₃)₂NH₂]₂[CuL₂] (1), K₂[CuL₂]?H₂L?H₂O (2) and [Cu(L)(H₂O)]_n (3), were synthesized and characterized. The structures of 1–3 were determined by single crystal X-ray diffraction studies. In-situ DMF decomposition produces dimethylamine base under solvothermal conditions and a proton transfer reaction takes place for the complex formation of 1. 3-D networks are stabilized in 1 and 2 via hydrogen bonds. Complex 3 is a 1-D coordination polymer with Cu-O semi-coordination bonds. Thermal decomposition of the complexes results in the corresponding metal oxides. Also, the electrochemical behavior of 1 was determined to be a metal-centered and diffusion-controlled, one-electron reduction process.     

POTENTIOMETRIC,POLAROGRAPHIC AND SPECTROSCOPIC STUDIES OF THE Cu(II)-D-GLUCOSAMINE-D-LACTOBIONIC ACID TERNARY SYSTEMS

Abstract

Our recent work on Cu(II) and VO(IV) interactions with lactobionic acid have shown^1,2 that this sugar acid has an unusually high ability to coordinate both metal ions. The carboxyl group is not a very effective donor for cupric ions^3,4 and metal interations with the set of the protonated hydroxyl groups should have considerable effects on complex stability. This high stability of the lactobionic acid complexes can lead to the involvement of this ligand in formation of ternary complexes with ligands such as aminosugars.^3–6 Both ligands are important chelating agents for Cu(II) ions in medicine, agriculture and food chemistry.^7–9 Since ternary complexes may play an important role in natural systems we have decided to follow complex formation in solutions containing lactobionic acid and one an aminosugar, D-glucosamine. The anchoring group in D(+)-glucosamine (2-amino-2-deoxy-D-glucose) is an amino group which is much more effective donor than carboxylate which acts as an anchor in sugar acids. Thus in our study we have used excess lactobionic acid to promote the formation of ternary complexes as major species in the solutions studied.     

Syntheses, electrochemistry and crystal structure studies of novel cis-configuration biferrocene trinuclear complexes

The syntheses and characterization of novel biferrocene trinuclear complexes for Schiff base ligand, S-methyl-N-(ferrocenyl-1-methyl-methylidene)dithiocarbazate (hereafter abbreviate as HL), are described. X-ray diffraction studies established the structures of the palladium complex, PdL₂2 and the copper complex, CuL₂3. The geometry of Pd(II) in 2 is close to square planar and in novel cis-configuration with two ferrocene moieties in the same side, while that of Cu(II) in 3 is close to tetrahedral configuration. Electrochemical measurements suggest that the distorted square planar configuration of the Ni(II) and Pd(II) moieties, can effectively transmit the redox effects of the ferrocene moieties, while the distorted tetrahedral configuration of Cu(II) complex can not transmit the redox effects.     

Cu(II)/Cd(II) coordination polymers based on polycarboxylate and 2-(2-pyridyl)benzimidazole

Three polycarboxylate coordination polymers containing 2-(2-pyridyl)benzimidazole as co-ligand, [Cu(Bdc)(2-PyBIm)] _n (1), [Cu(HBtc)(2-PyBIm)] _n (2) and [Cd₂(HBtc)₂(2-PyBIm)₂] _n ·; nH₂O (3) (H₂Bdc?=?1,4-benzenedicarboxylic acid; H₃Btc?=?1,3,5-benzenetricarboxylic acid), have been synthesized and characterized by elemental analyses, IR spectra, TG-DSC and X-ray structural analyses. Complex 1 is a one-dimensional zigzag chain in which the Cu(II) is cis six-coordinated by two chelating carboxyl groups and a 2-PyBIm ligand. Complex 2 is a two-dimensional (4, 4) network in which H₃Btc is partially deprotonated. Complex 3 has a three-dimensional framework in which one Cd(II) is six-coordinate and the other is seven-coordinate. All 2-PyBIm groups are neutral, chelating, bidentate ligands in 1–3. These complexes are quite thermally stable. The luminescence of 3 has also been investigated.     

Synthesis,crystal structure,spectroscopy, thermal properties and carbonic anhydrase activities of new metal(II) complexes with mefenamic acid and picoline derivatives

The mononuclear six metal(II) complexes ([Co(mef)₂(3-pic)₂(CH₃OH)₂] (1), [Ni(mef)₂(3-pic)₂(CH₃OH)₂] (2), [Cu(mef)₂(3-pic)₂] (3), [Co(mef)₂(4-pic)₂] (4), [Ni(mef)₂(4-pic)₂] (5), and [Cu(mef)₂(4-pic)₂] (6) with mefenamic acid and picoline ligands were synthesized, characterized, and their carbonic anhydrase inhibitory activities were evaluated. The six complexes were characterized by elemental analysis, FT-IR spectroscopy, and thermal analyses. The crystal structures of 1, 3, and 6 were determined by X-ray crystallography. The complexes have octahedral geometry. In 1, the mefenamato ligand behaved as monodentate whereas in 3 and 6, the mefenamato ligand acted as a bidentate ligand. Complexes 3 and 6 consist of the mefenamate and 4-picoline ligands. In 1, unlike the other complexes, methanol acted as a ligand and was involved in the coordination. Carbonic anhydrase I and II isoenzymes were purified from human erythrocytes. The in vitro effects of mefenamic acid, 3-picoline, 4-picoline, and the six metal(II) complexes on these isoenzymes were evaluated.     

Synthesis,crystal structures,and characterization of copper(II) carboxylate complexes incorporating 1,10-phenanthroline and bipyridine

A series of Cu(II) carboxylate complexes (carboxylate?=?2-fluorobenzoic acid (2-HFBA) or 4-fluorobenzoic acid (4-HFBA)) containing either one chelating 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy) have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, and thermal analyses. In [Cu(bipy)(H₂O)(2-FBA)₂] (1), [Cu(bipy)(H₂O)(4-FBA)₂] (3), and [Cu(phen)(H₂O)(2-FBA)₂] (4), Cu is five-coordinate in a square pyramidal geometry and four-coordinate in [Cu(phen)(2-FBA)₂] (2). The four complexes are extended into 1-D chains through hydrogen-bonding and π?···?π interactions in 1 and 4, only hydrogen-bonding in 2, and π?···?π interactions in 3. These contacts lead to aggregation and supramolecular self-assembly.     

Thermal,magnetic and spectral studies of metal-quinone complexes. Part II. Media effect on Coligation of Aqua Ligands

Syntheses of phthiocol complexes with Cu(II) in inert media resulted in anhydrous monomer Cu-4: [Cu(NQ)₂] and dimer Cu-5: [Cu(NQ)(NSQ)]₂, however synthesis in air generates polymeric hydrated Cu-6: [Cu(NQ)₂(H₂O)₂]_n. Media and colligation give rise to charge transfers in coordination compounds and lead to different redox ligations of 3-methyl-2-hydroxy-1,4-naphthoquinone. These redox forms are determined from quantitization of activation energies (E _a) of different pyrolytic steps in TG using the rising temperature expression of Coats and Redfern. 'Tyrosinase'-type mechanism is discussed for the redox-type ligation. Characteristic six-line EPR signals of dimeric Cu-5 lead to zero field splitting parameters D=0.01608 cm^-1and E=0.01576 cm^-1. Cu-6 shows molecular association through hydrogen bonding. Variable temperature magnetic measurement data of Cu-6 from 6 to 300 K is fitted to the polymeric expression of Bonner and Fisher model. The best fit was obtained with antiferrromagnetic exchange coupling constantJ=-2 cm^-1, g=2.2 having R=4.2·10^-4. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two copper complexes based on nitronyl nitroxide with different halides: structures and magnetic properties

Complexes based on different halogen-substituted nitronyl nitroxide radicals and Cu(II), Cu₃(hfac)₆(NIT-Ph-F)₂ (1) and Cu₃(hfac)₆(NIT-Ph-Cl)₂ (2) (hfac = hexafluoroacetylacetonate; NIT-Ph-F = 2-(4′-fluorophenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide; NIT-Ph-Cl = 2-(4′-chlorphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), were synthesized and characterized structurally and magnetically. X-ray crystal structure analyses show that 1 and 2 have similar centrosymmetric five-spin structures consisting of three Cu(II) ions bridged by two nitroxide ligands. The Cu(II) is coordinated by six oxygens to form an octahedron, while the five coordination of the terminal Cu(II) ion is square pyramidal. Magnetic measurements reveal strong antiferromagnetic interactions between Cu(II) ions and radicals in 1 (J = ?38.9 cm^?1) and weak antiferromagnetic interactions between Cu(II) ions and radicals in 2 (J = ?1.23 cm^?1), which may be explained by the bond length of the Cu–O_rad (2.468(2) Å) in 1, which is shorter than that (2.514(2) Å) in 2, and the dihedral angle (73.17(1)°) of the plane O7–O8–Cu(2)–O7A–O8A with the moiety O5–N1–C11–N2–O6 in 1 is smaller than (77.82(1)°) in 2.