SYNTHESIS AND CHARACTERIZATION OF DIAQUA(3-pTOLYLIMINO-2-BUTANONE OXIMATO)(3-p-TOLYLIMINO-2-BUTANONE OXIME)NICKEL(II) PERCHLORATE

Abstract

[Ni(L^?1)(HL)(H₂O)₂].ClO₄ with a Schiff base ligand L (HL = 3-p-tolylimino-2-butanone oxime) was prepared and structurally characterized by IR, cyclic voltammetry and X-ray diffraction methods. The nickel atom has distorted octahedral coordination consisting of four nitrogen atoms and two oxygen atoms. The equatorial plane is formed by two oxime nitrogen atoms and two imine nitrogen atoms of two Schiff base ligand (L^?1 and HL) with Ni‐ N bond distances between 2.01(1) and 2.11(1)Å. Water oxygen atoms occupy axial positions with Ni‐ O bond distances of 2.06(1) and 2.15(1) Å. The oxime groups in the Schiff base ligands are coordinated to Ni atom through their nitrogen atoms. One asymmetric intramolecular hydrogen bridge between the two oxime groups is found in the title complex.     

Complexes of a New N3S2 Macrocycle: Synthesis,Structure and Electrospray Mass Spectrometry

The silver(I) complex of a 15-membered macrocyclic ligand with an N₃S₂ donor set (L¹) has been prepared by the reaction of 2,6-diacetylpyridine with 1,8-diamino-3,6-dithiaoctane in the presence of silver(I) ions. A reduced form (L²) of the ligand, in which the imine groups are converted to amines, was prepared by the reduction of the silver(I) complex by sodium borohydride. The ligand L² has been characterised by various spectroscopic techniques and the copper(II) complex has been prepared. The metal complexes of L¹ and L² have been characterised by electrospray mass spectrometry and UV-visible spectroscopy. The copper(II) complex of L¹ has been synthesised from [AgL¹]⁺ via metal exchange. [CuL¹](ClO₄)₂ crystallises in the orthorhombic space group Pna2₁ with a = 14.374(5) Å, b = 12.947(3) Å, c = 11.824(3) Å with Z= 4. The geometry about the metal centre approximates trigonal bipyramidal with the pyridinyl nitrogen and the sulfur donors in the equatorial positions and the imine nitrogen donors in the axial positions. Metal ion exchange and the relative stabilities of metal complexes of the macrocyclic ligands were studied by electrospray mass spectrometry.     

Coordination properties of zinc 5,15-di(<Emphasis Type="Italic">ortho</Emphasis>-aminophenyl)octaalkylporphyrin in reactions with mono- an dibasic nitrogen bases

The coordination properties of zinc 5,15-di(ortho-aminophenyl)octaalkylporphyrin in reactions with mono- and dibasic nitrogen bases in benzene are studied by means of computational modeling and spectrophotometric titration. The stability of molecular zinc porphyrinate complexes in solution is estimated and their structure is determined. The correlation between the coordination properties of the compound under investigation and electronic and conformational factors of the macrocycle is established. The base nature is shown to affect the stability of zinc porphyrinate complexes. The correlations between the calculated σ bond energy of the zinc atom with the nitrogen atom of the base (E _b) and the equilibrium constant of the axial coordination reaction are obtained. It is demonstrated that the reaction is accompanied by an increase in steric hindrance and a change in the type of deformation of the porphyrin ligand.     

Effect of substituants on the structure of dioxouranium(VI) complexes of 7-carboxaldehyde-8-hydroxyquinoline and some of its Schiff bases

Summary A series of dioxouranium(VI) complexes with 7-carboxaldehyde-8hydroxyquinoline (oxine) and with some of its Schiff bases, LH, have been prepared and characterized by elemental analyses, electronic and vibrational spectral studies. All complexes except those of the oxine have the [UO₂L₂] · EtOH, stoichiometry (n=0, 1, 2 or 4). The uranyl complexes of the oxine have the formula [UO₂L₂(LH)]. The i.r. spectra reveal all ligands to be monobasic bidentate chelating agents coordinated to the uranium(VI)via the enolized phenolic OH and aldehydic oxygen or azomethine nitrogen atom. The force constant f_U-o (mdyn Å) and the bond length r_U-o (Å) of the U-O bond are also calculated and related to the electronic properties of thep-substituents.     

Synthesis,characterization, and biological investigation of new mixed-ligand complexes

A novel series of mixed-ligand complexes of 5,5′-{(1E,1E′)-1,4-phenelynebis(diazene-2,1-diyl)}bis(quinolin-8-ol) (H₂L₁) as a primary ligand and 4-aminoantipyrine(L₂) as a secondary ligand with Mn(II) ion were prepared using two general formulae: [Mn₂(H₂L₁)₂(L₂)₂X₄].4Cl (X = OH₂( 1 ), ONO₂⁻( 2 ), Cl=nil; OAc( 3 ), Cl = nil) and [Mn₂(H₂L₁)(L₂)₂(O₂SO₂)₂]( 4 ). Free ligands and their complexes were characterized. Electronic absorption spectra of the mixed-ligand complexes indicate a distorted octahedral geometry around the central metal ion, and the anions X⁻ are in the axial positions for all compounds. The ligands behave in a neutral bidentate manner, through nitrogen atoms and oxygen atoms of the carbonyl group (L₂), whereas H₂L₁ coordinated through nitrogen and OH groups as a neutral bidentate ligand. All complexes do not contain coordinated water molecules, but complex ( 1 ) contains four water molecules. The water molecules are removed in a single step. The complexes exhibited magnetic susceptibility corresponding to five unpaired electrons. The antimicrobial activity of the Mn(II) mixed-ligand complexes ( 1–4 ) against two gram-positive bacteria, three local gram-negative bacteria, and three fungi species was tested. Mn(II) mixed-ligand complex ( 2 ) exhibited significant antibacterial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas sp. Mixed-ligand complex ( 2 ) exhibited a high potential cytotoxicity against the growth of human lung cancer cells.     

Metal Complexes of an Oxatriaza Macrocycle Containing Pyridine: Thermodynamic Stability and Structural Studies

Abstract

A new 14-membered oxatriaza macrocycle containing pyridine has been synthesized, 7-oxa-3,11,17-triazabicyclo[11.3.1]heptadeca-1(17),13,15-triene, L¹. The protonation constants of this compound and stability constants of its complexes with the Mn²⁺ to Zn²⁺, Cd²⁺, and Pb²⁺ were determined by potentiometric methods at 25°C and ionic strength 0.10 Mol dm^?3 in KNO₃. L¹ presents two high values of protonation constants, and the third is very low. Its overall basicity is low because the three basic centres are in close proximity. Only mononuclear complexes were found, and the stability constants with all the metal ions studied are of the same order as those of the corresponding complexes of the oxatriaza macrocycle L² (1-oxa-4,8,12-triazacyclotetradecane), but lower than those of tetraaza macrocycles of similar or lower cavity size. The electronic spectra together with the values of magnetic moments of the cobalt(II) and nickel(II) complexes of L¹ suggest that five co-ordinate species are formed in aqueous solution. The EPR spectroscopy of frozen solutions of the copper(II) complex of L¹ has shown only one species characteristic of rhombic symmetry with elongation of the axial bonds and a d _{x ²-y ²} ground state, and the analysis of the EPR parameters suggests the presence of a bis complex containing two macrocyclic units. The single crystal structure of the complex [CuL¹Cl]ClO₄ 1 was determined. The complex crystallises in the triclinic system, space group P 1, a = 7.4973(9), b = 9.649(2), c = 12.712(2) Å, β = 111.02(2), β = 96.65(1), γ = 90.11(1)°, Z = 2, D_calcd = 1.691 g cm^?3. Final R and R' values of 0.0578 and 0.1454 for 2603 reflections with I>2[sgrave](I) and 0.0782 and 0.1619 for all data were obtained. The complex displays a distorted square pyramidal co-ordination sphere, the three nitrogen atoms of the macrocycle and one chlorine atom determining the basal plane and the apical position occupied by the oxygen atom of the macrocyle. The metal centre is 0.275(2) Å away from the N₃Cl plane towards to the apical ligand giving rise to a Cu-O bond length of 2.247(4) Å. To achieve this geometric arrangement the oxatriaza macrocycle folds about the line defined by the nitrogen atoms contiguous to the pyridine ring leading to a dihedral angle of 72.2(2)°. The single crystal presents a 1-D centrosymmetric supramolecular structure formed by two chains of cations and anions linked by hydrogen bonding via N-H…O and C-H^Δ+δO^Δ? intermolecular interactions.     

Enthalpy and entropy changes associated with mixed ligand chelates of Cu(II) and Ni(II) with 4-methoxy picolinic acid N-oxide and some amino acids in aqueous medium

The stability constants of mixed complexes of Cu(II) and Ni(II) with 4-methoxy picolinic acid N-oxide, and glycine, α-alanine, proline and hydroxy-proline have been determined at various temperatures by the potentiometric method in 0·1 M ionic strength. The formation constants of the mixed complexes have been evaluated and are in good agreement with statistically expected values. The enthalpy and entropy values have been calculated from 1∶1∶1 stability constants temperature coefficient data. From the enthalpy values of the mixed complexes it may be concluded that the bond strengths are not equal to the average of the bond strengths inMA ₂ andMB ₂ type parent complexes. The entropy values have been found to be favourable for ternary complex formation.     

Covalent Bonding and Hyperfine Interactions in Mo(V) Oxo Halide Complexes

Optical and EPR data were used to analyze delocalized bond structures in the antibonding and bonding states of complexes MoOL₅ (L = Cl and Br). Covalent bond parameters were calculated with consideration of charge-transfer states (CTS). The effects of CTS on the components of the g, A, and A ^L tensors were estimated; the third-order corrections for the EPR parameters were calculated. The role of CTSs for interpretation of the parameters of the additional hyperfine interaction was noted.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study. 1. Conformers of arylazacrown ethers and their complexes with Ca2+ cation

Photoinduced recoordination of Ca²⁺ complexes of the photochromic azacrown ethers is studied by the density functional method. The study included model arylazacrown ethers containing various acceptor groups in the aromatic ring in the para position to the azacrown ether moiety and a real azacrown-containing styryl dye. It is found that both free azacrown ethers and their complexes can adopt two types of conformations: (1) axial conformations, in which the aromatic ring axis passing through the crown ether nitrogen N_cr and the opposite atom of the aromatic ring is perpendicular to the root-mean-square (RMS) plane of the crown ether (least-squares fitted plane for all the crown ether atoms), and (2) equatorial conformations, in which the aromatic ring axis only slightly deflects from the RMS plane of the crown ether. In the equatorial conformers, the metal cation is coordinated only to the O atoms of the azacrown ether cycle, the metal—nitrogen bond is broken, and N_cr is conjugated with the aromatic ring. In the axial conformers, the metal cation is additionally coordinated to N_cr. It is found that the presence of an acceptor group bearing a formal positive charge decreases the relative energy of the equatorial conformer and favors metal—nitrogen bond dissociation, which results in the recoordination of the metal cation. However, a long distance between the charged group and N_cr has the reverse effect. The photoinduced recoordination observed in the alkaline-earth metal complexes of the photochromic azacrown ethers is explained by the transitions between the axial and equatorial conformers facilitated by the charge transfer in the excited state of the complex.     

Syntheses,Cytotoxicity and Properties of CO Releasing Molecules Containing Acetyl Salicylamide‐3‐pyridine

A series of CO‐releasing molecules [M(CO)₅L] (M=Cr, W, Mo, L=acetyl salicylamide 3‐pyridine, 1 – 3 ; L=N,N‐dimethyl‐4‐pyridine, 4 – 6 ; L=nicotinamide, 7 – 9 ; L=4‐CHO‐pyridine, 10 – 12 ) were synthesized. And in this paper, we have investigated mainly cytotoxicity and properties of the CO‐releasing molecules containing acetyl salicyamide‐3‐pyridine, namely complexes 1 – 3 . The stability of complexes 1 and 2 was evaluated by means of UV‐Vis spectroscopy and ¹H NMR spectra. The results indicate complexes 1 and 2 were stable in methanol and acidic aqueous solution, but unstable and decayed in basic media (pH 10.0). Among all the complexes, complex 2 was the slowest CO‐releaser, and its half‐life was 73.8 min. Complex 9 containing nicotinamide was the fastest CO‐releaser with half‐life only 6.5 min. In addition, cytotoxic effects of all the complexes on the proliferation of fibroblast line were assayed by MTT. Among all the complexes, the IC₅₀ of complex 1 was 6 µmol/L, revealing complex 1 possessed stronger antiproliferative activity than the control. Analysis by Flow cytometry revealed that complex 1 arrested Hela cells in S phase while complexes 2 and 8 arrested in G2/M phase. Cell apoptosis caused by the complexes mainly occurred in "Late apoptosis".     

Nature of the Chemical Bond and the Mutual Influence of Ligands in Co(III) Dioximinates

The results of MWG calculations of the electronic structures of real Co(III) complexes [Co(HD)₂L¹L²] ⁿ were used to analyze the electron density distribution and to determine the charges on atoms and configurations, where nis the charge of the complex and HD is the acid residue of dimethylglyoxime (H₂D); L¹= NH₃at L²= NH₃, Cl^–, Br^–, or I^–and L¹= L²= Cl^–; and L¹= H₂O or NO^– ₂at L²= NO^– ₂, with self-consistency over all atoms of the system and over d, s, and pconfigurations of cobalt. The mutual influence of the ligands (trans- and cis-) was shown to be determined by the atomic charges and bond orders on the axial coordinate and in the equatorial plane of the complex. The following order of the trans-effect was proposed: I^–> Br^–> Cl^–> NO^– ₂> NH₃> H₂O. The effects of the electronic factors on distorsion and conformational processes in the complexes were discussed.     

Complex Formation Reactions of Divinyltin(IV) Complexes with Amino Acids,Peptides, Dicarboxylic acids and Related Compounds

Complex formation equilibria of divinyltin(IV) with amino acids, peptides, and dicarboxylic acids have been investigated. Stoichiometry and stability constants for the complexes formed were determined at 25°C and ionic strength 0.1 M NaNO₃. The results showed the formation of ML, MLH, and ML₂ (organotin : ligand : hydrogen) complexes with amino acids. Peptides form ML complexes and the corresponding deprotonated amide species MLH_?1. In the latter species the binding with divinyltin(IV) occurs through the terminal amino group, carboxylate oxygen, and the amide nitrogen atoms (CO^? ₂, N^? _amide, NH₂). The results showed the formation of ML and ML₂ complexes with dicarboxylic acids. The concentration distribution of the complexes in solution was evaluated. The bonding sites of the divinyltin(IV) complex in solid state with oxalic acid was investigated by means of elemental analyses, FTIR, and mass spectra. Non-isothermal decomposition of the above complex has been studied and the result was statistically analyzed. The main steps were identified for the thermal decomposition reaction and each step proved to be a first order reaction. The kinetic parameters E _a and A were calculated for each step in the reaction. The thermodynamic functions H, G, and S* were calculated for each step of the reaction.     

Spectrophotometric and Potentiometric Studies on the Binding Abilities of Two Novel Tripodal Imine-Phenol Ligands Towards Al(III) and Ga(III)

The aqueous coordination behavior of two novel tripodal imine-phenol ligands, cis,cis-1,3,5-tris{(2-hydroxybenzilidene)aminomethyl}cyclohexane (TMACHSAL, L¹) and cis,cis-1,3,5-tris{[(2-hydroxyphenyl)ethylidene]aminomethyl}cyclohexane (Me₃- TMACHSAL, L²) with Al³⁺ and Ga³⁺ has been investigated at an ionic strength of 0.1 mol⋅dm⁻³ KCl and 25±1 °C by potentiometric and spectrophotometric methods. Both ligands formed various monomeric metal complex species MLH₃, MLH₂, MLH, ML and MLH₋₁ with Ga(III); and MLH₃, ML and MLH₋₁ with Al(III). The Ga(III) complexes showed higher thermodynamic stability than the Al(III) complexes. Semi-empirical PM6 calculations along with TDDFT/B3LYP/3-21G calculations have been performed to complement the experimental measurements. The calculated structure of the metal complexes predicted a distorted octahedral geometry where favorable ring-flipping from the equatorial conformation in uncomplexed ligands to the axial conformation was observed upon chelation.     

Novel complexes of zirconium and uranium derived from bifunctional azodyes donor ligands containing hydrogen bonds

Novel complexes of zirconium(IV) and uranium(II) with selective azodyes containing nitrogen and oxygen donor ligands have been prepared and characterized by elemental analysis, ¹H NMR and electronic spectral techniques. The important bands in the IR spectra and main ¹H NMR signals are assigned and discussed in relation to the proposed molecular structure of the complexes. The IR data of the azodye ligands suggested a bidentate binding involving azodye nitrogen and C–O/OH oxygen atom of enolic group. They also showed the presence of Cl/OAc coordinating with the metal ion. The prepared complexes of Zr(IV) fall into four types. In the stoichiometric formulae of (1:1), the chelate rings are six-membered/five coordinate; whereas in the (1:2) they are six-membered/six coordinate and all of the complexes possess non-electrolytic properties. The UO₂(II) complex, in the mean time, possesses a planar hexagonal structure with nitrogen and oxygen atoms in the axial position. The stretching vibrations and force constant interactions of the uranyl complexes have been determined and from which the U–O bond distances are calculated. These bond distances as well as the effect of Hamett’s constant are also, in turn, calculated and discussed.     

Regularities of Extra Coordination of Nitrogen-containing Ligands with an Anthracenyl-capped Zinc Porphyrin

3,3'-Dibutyl-4,4'-dimethylpyrrolylmethane was reacted with 9,10-bis(2-formylphenyloxymethyl)anthracene to synthesize a capped porphyrin, and its zinc complex was prepared. The coordination properties of the capped zinc porphyrin in extra coordination with N-methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, and dimethylformamide in o-xylene were studied. A correlation of the stability of the extra complexes and the basicity of the extra ligands was established. A correlation between the stability of the extra complexes and the shifts of their principal electronic absorption bands with respect to those of the zinc porphyrin was found. Deformations of the porphyrin ligand were noted to affect the strengyh of the metalextra ligand bond. The geometric and energetic characteristics of the fivecoordinate zinc porphyrin were obtained by quantum-chemical calculations. A correlation between the calculated energy of interaction of the central metal atom with the nitrogen atom of the extra ligand and the stability of the extra complexes of the capped Zn porphyrin was revealed.     

Synthesis and Analysis of the Structure,Diffusion and Cytotoxicity of Heterocyclic Platinum(IV) Complexes

We have developed six dihydroxidoplatinum(IV) compounds with cytotoxic potential. Each derived from active platinum(II) species, these complexes consist of a heterocyclic ligand (H_L) and ancillary ligand (A_L) in the form [Pt(H_L)(A_L)(OH)₂]²⁺, where H_L is a methyl‐functionalised variant of 1,10‐phenanthroline and A_L is the S,S or R,R isomer of 1,2‐diaminocyclohexane. NMR characterisation and X‐ray diffraction studies clearly confirmed the coordination geometry of the octahedral platinum(IV) complexes. The self‐stacking of these complexes was determined using pulsed gradient stimulated echo nuclear magnetic resonance. The self‐association behaviour of square planar platinum(II) complexes is largely dependent on concentration, whereas platinum(IV) complexes do not aggregate under the same conditions, possibly due to the presence of axial ligands. The cytotoxicity of the most active complex, exhibited in several cell lines, has been retained in the platinum(IV) form.     

Variation–iteration method for one-dimensional two-electron systems

A quantum chemical study of the two low-lying quartet states of seven model compound I iron–porphyrin complexes with varying axial ligands has been carried out using the INDO method. The varying axial ligands included in this study are five that are models for those in the intact enzymes: imidazole and imidazolate (model peroxidase HRP and CCP), CH₃CONH₂ (Gln175 mutant of CCP), PhO^?1 (catalase), CH₃S^?1 (P450), and two that have been used in biomimetics of these enzymes: Cl^?1 (hemin) and PhS^?1 (model P450s). The purpose of these studies was to determine the role of the axial ligands in determining (i) the relative energies of the two nearly degenerate quartet electronic states of compound I, involved either as an a_1u or a_2u porphyrin π cation radical and (ii) the electron and spin distributions in the a_1u and a_2u radical cations of compound I. For most of the model complexes, including both HRP-I and CAT-I, a moderate effect of the axial ligand on the relative energy of these two states was observed and the a_1u radical cation was found to be the ground state. The energy order of these two radical cations, however, was reversed in the P450-I model complexes, indicating an association of the unique property of the Fe?O bond breaking with an a_2u radical cation. The symmetry-allowed overlap between the Fe?O and 3a_2u orbitals may lower the activation energy for the Fe?O bond cleavage in P450-I. However, the calculated electronic and spin properties, including the unpaired spin and net charge on the oxygen and the Fe?O bond overlap density, important determinants of the reactivity of this complex in the ligand–Fe?O region, are very similar for all complexes and in both cation states. © 1992 John Wiley & Sons, Inc.     

Phosphinate Analogues of Ida and Nta with Low Basicity of Nitrogen Atom: Acid-Base and Complexation Properties

Abstract

Analogues of iminodiacetic acid (H₂IDA) and nitrilotriacetic acid (H₃NTA) bearing two (hydroxomethyl)methylphosphinate or (2-carboxyethyl)methylphosphinate groups were synthesized. Their acid-base and coordination properties with divalent metal ions (Cu²⁺, Ni²⁺ and Zn²⁺) were studied by potentiometry. The compounds exhibit very low basicity of the amino groups (pK_a = 6.2–7.6) due to presence of two electron-withdrawing methylphosphinate groups and, consequently, a low stability of the complexes. In the case of IDA-analogues, the low complex stability results in precipitation of metal hydroxides in neutral region. As expected, NTA-analogues form more stable complexes and, thus, they were also studied in the alkaline region. Presence of additional carboxylate in the 2-carboxyethylphosphinic acid groups results in the formation of dinuclear complexes. Solid-state structures of two compounds were determined by X-ray diffraction analysis. The compounds are protonated on the nitrogen atom and the structures are stabilized by rich hydrogen bond network.     

Experimental Evidence for a Valinomycin – Proton Complex

Summary. From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H⁺ (aq) + NaL⁺ (nb) = HL⁺ (nb) + Na⁺ (aq) taking place in the two-phase water-nitrobenzene system (L = valinomycin, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K_ex (H⁺, NaL⁺) = −1.1 ± 0.1. Further, the stability constant of the valinomycin-proton complex in nitrobenzene saturated with water was calculated as log β_nb(HL⁺) = 5.3 ± 0.1. Finally, the stability constants of complexes of some univalent cations with valinomycin were summarized and discussed.     

Some Tribenzyl Tin(IV) Complexes with Thiohydrazides and Thiodiamines. Synthesis,characterization and thermal studies

Tribenzyl tin(IV) chloride complexes of morpholine N-thiohydrazide (L¹), aniline-N-thiohydrazide (L²),N-(morpholine-N-thio)-1,3-propanediamine (L³) and (aniline-N-thio)-1,3-propanediamine (L⁴) of the type (C₆H₅CH₂)₃Sn(L)Cl (where L=L¹, L², L³ and L⁴) have been synthesised in dioxane and in H₂O and acetone mixture. These were characterized by C,H,N-analysis, UV, IR and ¹HNMR spectral studies. In both the complexes ligands act as bidentate, coordinating through sulphur and terminal nitrogen. The complexes are 1:1 metal ligand complexes. Various thermodynamic parameters have been calculated for the decomposition steps using TG/DTA curves in air as well as nitrogen atmosphere. This revised version was published online in July 2006 with corrections to the Cover Date.