Calix[4]arene-based Zn2+ complexes as shape- and size-selective catalysts of ester cleavage

[structures: see text] The kinetics of methanolysis of a number of esters endowed with a carboxylate anchoring group have been investigated in the presence of di- and trinuclear Zn2+ complexes of calix[4]arenes functionalized at the upper rim with nitrogen ligands. The results (i) emphasize the importance of a good match between ester size and intermetal distance, (ii) reveal a substrate independent superiority of the 1,2-vicinal dinuclear catalyst 1-Zn2 to its 1,3-distal regioisomer 2-Zn2, and (iii) provide further evidence for the concurrence of the three metal ions of 3-Zn3 in the catalytic mechanism.     

Imidazo[4,5-f][1,10]phenanthroline complexes with Fe2+, Cd2+, Co2+ and Zn2+ ions

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Syntheses,crystal structures and photophysical properties of d10 transition-metal (Ag+, Cu+, Cd2+ and Zn2+) coordination complexes based on a thiophene-containing heterocyclic thioamide

Four d¹⁰ transition-metal coordination complexes 1–4 (1: [Ag₂(TPT)₂(TPTH)₂]; 2: [Cu₆(TPT)₆]·2DMF; 3: [Cd(TPT)₂(TPTH)]·CH₃CH₂OH, 4: [Zn(TPT)₂]_n) have been constructed from a newly designed heterocyclic thioamide ligand, TPTH (TPTH = 4-(thiophen-2-yl)-pyrimidine-2-thiol). All complexes have been structurally elucidated by single crystal X-ray diffraction analyses. Except for 4, which shows a one-dimensional (1-D) chain structure, 1–3 are all discrete coordination complexes featuring dinuclear, hexanuclear and mononuclear entities, respectively. Their photophysical properties have been evaluated in the solid state at room temperature by UV–vis diffuse reflectance and luminescence spectra. Among them, 2 exhibits a strong red luminescence (λ_em = 699 nm) with a remarkable red-shift of the maximum emission compared to that of the TPTH ligand (λ_em = 536 nm). The red emission observed with 2 is ascribed to a LMCT (ligand-to-metal charge transfer) transition which agrees with the DFT calculations.     

Heteroscorpionate-based Co2+, Zn2+, and Cu2+ complexes: coordination behavior, aerobic oxidation, and hydrogen sulfide detection

The coordination behavior and reactivity of the phenol-substituted bis(pyrazolyl)methane ligands, (3,5-(t)Bu(2)-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L1-H) and 2-phenol-bis(3,5-Me(2)-pyrazol-1-yl)methane (L2-H) have been investigated in the metal complexes (L1-H)CoCl(2) (1), (L1-H)ZnCl(2) (2), (L3)CuCl(2) (3), (L2)(2)Co(2)Cl(2) (4) (L2-H)ZnCl(2) (5), and (L2-H)CuCl(2)·H(2)O (6). The mononuclear tetrahedral cobalt complex 1 was isolated and fully characterized by X-ray single crystal diffraction and (1)H NMR spectroscopy and relaxometry. The neutral L1-H is κ(2)-coordinated to the metal center whereas the not coordinated hydroxy-phenyl group is involved in extended intermolecular hydrogen bonds. Aerobic oxidation of L1-H was observed in the reaction of this ligand with CuCl(2) to yield the para-quinone derivative L3 (L3 = 2-(t)Bu-6-(bis(3,5-Me(2)-pyrazol-1-yl)methyl)cyclohexa-2,5-diene-1,4-dione). Upon oxidation L3 resulted κ(2)-coordinated to the tetrahedral Cu(II) metal center, affording 3. The reaction of L2-H with CoCl(2)·6H(2)O produced the elimination of 1 equiv of hydrochloric acid and the formation of the binuclear complex 4 in which one cobalt is in an octahedral environment featuring two κ(3)-coordinated deprotonated ligands whereas the second cobalt center is detected in tetrahedral coordination geometry, bound to the octahedral cobalt via two phenoxo bridging moieties. Interestingly L2-H, (3-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L4-H), or (5-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L5-H) were not oxidized in the reaction with CuCl(2). The reaction of the ligand L2-H with ZnCl(2) and CuCl(2)·2H(2)O yielded the κ(2)-coordinated tetrahedral complex 5 and the square planar complex 6, respectively. The application of the cobalt complex 1 as molecular dosimeter for H(2)S was explored and compared to that of the zinc analogue 2. Density functional theory (DFT) calculations and NMR experiments to assess the possible mechanisms of H(2)S detection by both 1 and 2 are also described.     

Supramolecular structures of Mn2+, Co2+ and Zn2+ complexes containing 1,3-bis(4-pyridyl)propane and aminosalicylate anion

In this study, the synthesis, spectroscopic properties and crystal structures of three new supramolecular compounds named [Mn₂(bpp)₄(H₂O)₄](AS)₄·H₂O (1), [Co₂(bpp)₄(H₂O)₄](AS)₄·H₂O (2) and [Zn(bpp)(AS)₂] (3), have been described, where bpp is 1,3-bis(4-pyridil)propane and AS^?  is aminosalicylate anion. By analysing the similarities between the X-ray powder diffraction results, it has been observed that compounds 1 and 2 are isomorphous, exhibiting an orthorhombic system with space group Pccn; for compound 3, another orthorhombic system was observed, with space group Aba2, which displays coordination between the Zn²⁺ metal ion and the aminosalicylate anion; this can be considered the first case in the literature involving the direct coordination to the metal ion. The vibrational spectra of compounds 1 and 2 are very similar. In the Raman spectra, the main bands are observed at ca. 1625 and 1020 cm^? 1, referring to the ^? O–C = O and CC/CN stretching modes of AS^?  and bpp ligands, respectively.     

Synthesis, crystal structures and spectroscopic properties of two novel oxamido-bridged trinuclear complexes [Cu2M] (M = Cu, Zn)

Based on the complex ligand CuL (H₂L = 2,3-dioxo-5,6:14,15-dibenzo-7,13-diphenyl-1,4,8,12-tetraazacyclo-pentadeca-7,13-diene), two novel oxamido-bridged trinuclear complexes have been prepared. They are of the formula Cu(CuL)₂(ClO₄)₂ · 4C₂H₅OH (1) and [(CuL)₂Zn(C₂H₅OH)₂](ClO₄)₂ · 2C₂H₅OH (2). The crystal structures of the two complexes have been determined by X-ray crystallography. In complex (1), the central Cu is in a complete square-planar environment, bonding to four oxygen atoms of the oxamido macrocyclic ligand, while in complex (2), the Zn center is six-coordinate in an octahedral geometry, the four oxygen donors from macrocyclic ligand form the basal plane and the axial positions are occupied by other oxygen atoms from C₂H₅OH molecules. The spectroscopic properties have been investigated and the EPR spectra have been simulated by WINEPR and SimFonia programs.     

Understanding the inactivation process of organophosphorus herbicides: A DFT study of glyphosate metallic complexes with Zn2+, Ca2+, Mg2+, Cu2+, Co3+, Fe3+, Cr3+, and Al3+

Glyphosate is the active component of one of the top‐selling herbicides, which is also a potent EPSP synthase inhibitor. The herbicide is absorbed by living tissue and translocated via the phloem, to plant roots and rhizomes. When applied directly into the soil it has low activity, due to the high adsorption by soil constituents. Understanding the specific interactions between metals in the soil and glyphosate is the main step in understanding the low activity of the herbicide when applied directly into the ground and not pulverized. We can observe there is a stability order for both tetrahedral and octahedral complexes between glyphosate and metals: Zn>Cu>Co>Fe>Cr>Al>Ca>Mg. © 2012 Wiley Periodicals, Inc.     

CO2 Fixation by Cu2+ and Zn2+ complexes of a terpyridinophane aza receptor. Crystal structures of Cu2+ complexes, pH-metric, spectroscopic, and electrochemical studies

The synthesis of the terpyridinophane-type polyamine 2,6,9,12,16-pentaaza[17]-(5,5' ')-cyclo-(2,2':6',2' ')-terpyridinophane heptahydrobromide tetrahydrate (L.7HBr.4H2O) is described. L presents six protonation constants with values in the range 9.21-3.27 logarithmic units. L interacts with Cu2+ and Zn2+ forming in both cases, neutral, protonated, and hydroxylated mono- and binuclear complexes whose constants have been calculated by potentiometry in 0.15 M NaClO4 at 298.1 K. The crystal structures of the compounds [Cu(HL-carb)(H2O)](ClO4)3.2H2O (1) and [Cu2(H2L)(CO3)]2(ClO4)8.9H2O (2) have been solved by X-ray diffraction. In 1, the metal center presents square pyramidal geometry. The base of the pyramid is formed by the three nitrogen atoms of pyridine and one oxygen atom of a CO2 group which is forming a carbamate bond with the central nitrogen atom of the polyamine chain. The axial position is occupied by a water molecule. In 2, one Cu2+ is bound by the three pyridine nitrogens and the other one by the three central nitrogen atoms of the polyamine chain. The square planar coordination geometry is completed by a carbonate group taken up from the atmosphere that behaves as a bridging mu,mu'-ligand between the two centers. The pH-metric titrations on the ternary Cu2+-L-carbonate and Zn2+-L-carbonate systems show the extensive formation of adduct species which above pH 6 are formed quantitatively in solution. The stoichiometries of the main species formed in solution at pH = 6.8 agree with those found in the crystalline compounds. CO2 uptake by the Zn2+ and Cu2+ 1:1 complexes in aqueous solution has also been followed by recording the variations in the band at ca. 300 nm. The formation of the Zn2+ carbamate moiety has been evidenced by 13C NMR and ESI spectroscopy.     

Homo-and heterodinuclear complexes of the tris(catecholamide) derivative of a tetraazamacrocycle with Fe3+, Cu2+ and Zn2+ metal ions

The new ditopic catecholamide 3,7,11-tris-{N-[3,4-(dihydroxybenzoyl)-aminopropyl]} derivative of a 14-membered tetraazamacrocycle containing pyridine (H(6)L(1)) has been synthesized. The protonation constants of (L(1))(6-) and the stability constants of its mono-, homo- and hetero-dinuclear complexes with Fe(3+), Cu(2+) and Zn(2+) metal ions were determined at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO(3). The large overall basicity of the ligand was ascribed to the very high protonation constants of the catecholate groups, and its acid-base behaviour was correlated with the presence of tertiary nitrogen atoms and secondary amide functions. The UV-vis spectrum of the red solution of [FeL(1)](3-) complex exhibits the LMCT band of catecholate to iron(III), and its EPR spectrum revealed a typical isotropic signal of a rhombic distorted ferric centre in a high-spin state and E/D approximately 0.31, both characteristic of a tris-catecholate octahedral environment. The ligand forms with copper(II) and zinc(II) ions mono- and dinuclear protonated complexes and their stability constants were determined, except for the [ML(1)](4-) complexes as the last proton is released at very high pH. Electronic spectroscopic studies of the copper complexes revealed the involvement of catecholate groups in the coordination to the metal centre in the mono- and dinuclear copper(II) complexes. This information together with the determined stability constants indicated that the copper(II) ion can be involved in both types of coordination site of the ligand with comparable binding affinity. The EPR spectrum of [Cu(2)L(1)](2-) showed a well resolved seven-line hyperfine pattern of copper(II) dinuclear species typical of a paramagnetic triplet spin state with weak coupling between the two metal centres. Thermodynamically stable heterodinuclear complexes, [CuFeH(h)L(1)](h-1) (h = 0-3) and [CuZnH(h)L(1)](h-2) (h = 0-4), were formed as expected from a ditopic ligand having two dissimilar coordination sites. At physiological pH, the [CuFeL(1)](-) complex is formed at approximately 100%. The formation of the [CuFeH(h)L(1)](h-1) complexes in solution was supported by electronic spectroscopic measurements. The data indicated the specific coordination of each metal centre at the dissimilar sites of the ligand, the iron(III) bound to the oxygen donors of the catecholate arms and the copper(II) coordinated to the amine donors of the macrocyclic ring. The two metal centres are weakly coupled, due to the fairly large distance between them.     

Stability constants and thermodynamic parameters of Mn2+, Co2+, Ni2+ Cu2+, Zn2+, Cd2+, UO2(2+), Th4+, Ce3+ and Pr3+-complexes with some Schiff base hydrazones containing the pyrimidine moiety

Proton-ligand dissociation and metal-ligand formation constants of 2-amino-4-chloro-6-[alpha-(phenyl)ethylidenehydrazino]pyrimidine; (AHP) and its p-chloro (ClAHP) and p-methoxy (OMeAHP) derivatives (Str.I&II) with Mn2+, Co2+ Ni2+, Cu2+, Zn2+, Cd2+, UO2(2+), Th4+, Ce3+ and Pr3+ ions have been evaluated potentiometrically in 75% (v/v) dioxane-water and 0.1 mol dm(-3) KNO3. The thermodynamic functions (deltaG, deltaH and deltaS) for the complexation of OMeAHP were evaluated and discussed. The effect of the temperature, dielectric constant of the solvents, mole fraction of dioxane and ionic strength of the medium on the stability of Pr3+-complexes show that the stability of the chelates increases by increasing both the electron repelling property of the substituents and the organic solvent content, and by decreasing the temperature, the ionic strength and the dielectric constant of the medium.     

Synthesis,spectroscopic characterization and study the effect of gamma irradiation on VO2+, Mn2+, Zn2+, Ru3+, Pd2+, Ag+ and Hg2+ complexes and antibacterial activities

Novel complexes of VO²⁺, Mn²⁺, Zn²⁺, Ru³⁺, Pd²⁺, Ag⁺ and Hg²⁺ have been prepared by reacting their metal salts with ligand, named (4-(4-chlorophenyl)-1-(2-(phenylamino) acetyl) thiosemicarbazone). Study of synthesized metal complexes was confirmed by different analytical and spectral techniques (¹H NMR, MS, FT-IR, UV–Vis, EPR and Powder X-ray diffraction), thermogravimetric studies as well as molecular modeling. FT-IR spectra showed that the compound behave as neutral or monobasic tetradentate. In case of complexes of Mn²⁺, Zn²⁺, Ag⁺ and VO²⁺, through (N2H), (CO) or (CO) groups. While, the ligand behave as neutral bidentate in case of complexes with Pd²⁺ and Hg²⁺. X-ray diffraction pattern of Mn²⁺, Pd²⁺ and Ag⁺ complexes before and after irradiation are recorded. XRD studies exhibited that decrease in the crystalline size of sample Mn²⁺ as compared of samples Ag⁺ and Pd²⁺ upon irradiation and irradiation influenced the crystallinity of the complexes. The possible structures of the ligand, Mn²⁺, Pd²⁺ and Hg²⁺complexes have been computed by means of the molecular mechanic calculations using the hyper chem. 8.03 molecular modeling program. The bond length, bond angle, HOMO, LUMO and dipole moment have been studied to verify the geometry of Mn²⁺, Pd²⁺ and Hg²⁺ complexes. The effect of gamma irradiation was investigated by recording the new results of pervious spectroscopic techniques and other measurements. Thermal studies of these chelates before and after γ-irradiation showed that the complexes after γ-irradiation were more thermally stable than before γ-irradiation. The compound and its metal complexes have been experienced for their inhibitory outcome on the growth of microorganisms against gram positive and gram negative. The results proved that the complexes B₁–B₇ have potent antibacterial activity as compared to that of ligand.     

Gas phase ion thermochemistry of tetraaza complexes such as cyclamM2+ with H2O, CH3OH, NH3, and other ligands, where M2+ = Mn2+, Ni2+, Cu2+, and Zn2+

Tetraaza complexes with M(2+) were produced in the gas phase by Electrospray (ESI) of solutions containing salts of M(2+)dinitrates and a tetraaza compound such as cyclam. The complex CyclM(2+) formed in solution and transferred to the gas phase via ESI was introduced into a reaction chamber containing known partial pressures of a ligand L. Equilibria between CyclM(2+) and L establish CyclML(n)(2+) = CyclML(n-1)(2+) + L and the equilibrium constants K(n,n-1) are determined with a mass spectrometer. Determinations at different temperatures lead to not only the DeltaG(0)(n,n-1) values but also the DeltaH(0)(n,n-1) and DeltaS(0)(n,n-1) values. Data for n = 1, 2, and 3 were obtained for L = H(2)O and CH(3)OH. The DeltaG(0)(1,0), DeltaH(0)(1,0) as well as DeltaG(0)(2,1), DeltaH(0)(2,1) values, when M(2+) = Mn(2+) and Zn(2+), were larger than those for Ni(2+) and Cu(2+). The ligand field theory and the Irvine-Williams series predict a reverse order, i.e., stronger bonding with Ni(2+) and Cu(2+) for simple ligand reactions with M(2+). An examination of the differences of the reactions in solution and gas phase provides a rationale for the observed reverse order for the CyclM(2+) + L reactions. Differences between gas phase and solution are found also when M(2+) = Cu(2+), but the tetraaza macrocycle is changed from, 12-ane to 14-ane to 15-ane. The strongest bonding in solution is with the 14-ane while in the gas phase it is with the 15-ane. Bond free energies, DeltaG(0)(1,0), for CyclCu(2+) with L = H(2)O, CH(3)OH, NH(3), C(2)H(5)OH, C(3)H(7)OH, (C(2)H(5))(2)O, and CH(3)COCH(3), are found to increase in the above order. The order and magnitude of the DeltaG(0)(1,0) values is close to DeltaG(0)(1,0) values observed with potassium K(+) and the same ligands. These results show that the cyclam in CyclCu(2+) leads to an extensive shielding of the +2 charge of Cu(2+). Ligands with gas phase basicities that are relatively high, lead to deprotonation of CyclM(2+). The deprotonation varies with the nature of M(2+) and provides information on the extent of electron transfer from the N atoms of the cyclam, to the M(2+) ions.     

Synthesis,characterization and antioxidant,antibacterial activity Zn2+, Cu2+, Ni2+ and Co2+, complexes of ligand [2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole]

New metal complexes of (Zn(II), Co(II), Ni(II) and Cu(II)) based on the ligand 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole] were synthesized, whose structures were determined with the different spectroscopic techniques ¹H NMR,¹³C NMR, FT-IR, UV–Visible and by mass spectrometry. The thermal analysis was performed by TG-DTA. The antioxidant activity of the ligand and its complexes was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) method, in comparison with the synthetic antioxidant, ascorbic acid. The results obtained showed that the antioxidant activity of the ligand and its complexes is moderate and that the copper complex has a high activity that exceeds that of ascorbic acid. Antimicrobial activity of the ligand and its metal complexes was studied against two Gram-positive bacteria: Bacillus subtilis ILP1428B, Staphylococcus aureus CIP543154 and two Gram-negative bacteria: Pseudomonas aeruginosa ATCC27653, Escherichia coli CIP5412 (American Type Culture Collection)the activity data show that the metal complexes are more potent than the free ligand.     

Syntheses, X-ray crystal structures, and magnetic properties of novel linear M2[II]U[IV] complexes (M=Co, Ni, Cu, Zn)

Attempts to prepare heterobimetallic complexes in which 3d and uranium magnetic ions are associated by means of the Schiff bases H(2)L(i) derived from 2-hydroxybenzaldehyde or 2-hydroxy-3-methoxybenzaldehyde were unsuccessful because of ligand transfer reactions between [ML(i)] (M=Co, Ni, Cu) and UCl(4) that led to the mononuclear Schiff base complexes of uranium [UL(i)Cl(2)]. The crystal structure of [UL(3)Cl(2)(py)(2)] [L(3)=N,N'-bis(3-methoxysalicylidene)-ethylenediamine; py=pyridine] was determined. The hexadentate Schiff base ligand N,N'-bis(3-hydroxysalicylidene)-2,2-dimethyl-1,3-propanediamine (L) was useful for the synthesis of novel trinuclear complexes of the general formula [[ML(py)](2)U] (M=Co, Ni, Zn) or [[CuL(py)]M'[CuL]] (M'=U, Th, Zr) by reaction of [M(H(2)L)] with [M'(acac)(4)] (acac=MeCOCHCOMe). The crystal structures of the Co(2)U, Ni(2)U, Zn(2)U, Cu(2)U, and Cu(2)Th complexes show that the two ML fragments are orthogonal, being linked to the central actinide ion by the two pairs of oxygen atoms of the Schiff base ligand. In each compound, the UO(8) core exhibits the same dodecahedral geometry, and the three metals are linear. The magnetic study indicated that the two Cu(2+) ions are not coupled in the Cu(2)Zr and Cu(2)Th compounds. The magnetic behavior of the Co(2)U, Ni(2)U, and Cu(2)U complexes was compared with that of the Zn(2)U derivative, in which the paramagnetic 3d ion was replaced with the diamagnetic Zn(2+) ion. A weak antiferromagnetic coupling was observed between the Ni(2+) and the U(4+) ions, while a ferromagnetic interaction was revealed between the Cu(2+) and U(4+) ions.     

Metal Complexes with Macrocyclic Ligands,V. Formation and dissociation kinetics of the pentaco-ordinated Ni2+, Cu2+, Co2+ and Zn2+ complexes with 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane

The formation and dissociation kinetics of the pentaco-ordinated Cu²⁺, Ni²⁺, Co²⁺ and Zn²⁺ complexes with 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (4-MeCyclam-14) was studied by pH-stat techniques and spectrophotometrically. The rates of the reactions between 4-MeCyclam-14 and each of the four metal ions, although slower than normal complexations by a factor of 10³?10⁴, closely follow the order Cu²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺, found for the rate of water exchange. This implies that beside water exchange an other constant factor plays an important role in the rate determing step. The dissociation of the pentaco-ordinated 4-MeCyclam-14 complexes is acid catalyzed. The limiting rate for acid dissociation is not reached even in 2.5M HNO₃ in the case of Ni(4-MeCyclam-14)²⁺. From the formation and dissociation rates stability constants have been calculated, which do not show any macrocyclic effect.     

Interaction Structure and Affinity of Zwitterionic Amino Acids with Important Metal Cations (Cd2+, Cu2+, Fe3+, Hg2+, Mn2+, Ni2+ and Zn2+) in Aqueous Solution: A Theoretical Study

Heavy metals are non-biodegradable and carcinogenic pollutants with great bio-accumulation potential. Their ubiquitous occurrence in water and soils has caused serious environmental concerns. Effective strategies that can eliminate the heavy metal pollution are urgently needed. Here the adsorption potential of seven heavy metal cations (Cd²⁺, Cu²⁺, Fe³⁺, Hg²⁺, Mn²⁺, Ni²⁺ and Zn²⁺) with 20 amino acids was systematically investigated with Density Functional Theory method. The binding energies calculated at B3LYP-D3/def2TZVP level showed that the contribution order of amino acid side chains to the binding affinity was carboxyl > benzene ring > hydroxyl > sulfhydryl > amino group. The affinity order was inversely proportional to the radius and charge transfer of heavy metal cations, approximately following the order of: Ni²⁺ > Fe³⁺ > Cu²⁺ > Hg²⁺ > Zn²⁺ > Cd²⁺ > Mn²⁺. Compared to the gas-phase in other researches, the water environment has a significant influence on structures and binding energies of the heavy metal and amino acid binary complexes. Collectively, the present results will provide a basis for the design of a chelating agent (e.g., adding carboxyl or a benzene ring) to effectively remove heavy metals from the environment.     

Aminoacid N-substituted 1,4,7-triazacyclononane and 1,4,7,10-tetraazacyclododecane Zn2+, Cd2+ and Cu2+ complexes. A preparative, potentiometric titration and NMR spectroscopic study

The pK(a)s and Zn2+, Cd2+ and Cu2+ complexation constants (K) for 1,4,7-tris[(2'S)-acetamido-2'-(methyl-3'-phenylpropionate)]-1,4,7-triazacyclononane, 1, 1,4,7-tris[(2'S)-acetamido-2'-(1'-carboxy-3'-phenylpropane)]-1,4,7-triazacyclononane, H(3)2, 1,4,7-tris[(2'S)-acetamido-2'-(methyl-3'-(1H-3-indolyl)propionate)]-1,4,7-triazacyclononane, 3, and 1,4,7,10-tetrakis[(2'S)-acetamido-2'-(methyl-3'-phenylpropionate)]-1,4,7,10-tetraazacyclododecane, 4, 1,4,7,10-tetrakis[(2'S)-acetamido-2'-(1'-carboxy-3'-phenylpropane)]-1,4,7,10-tetraazacyclododecane, H(4)5, in 20 : 80 v/v water-methanol solution are reported. The pK(a)s within the potentiometric detection range for H(3)1(3+) = 8.69 and 3.59, for H(6)2(3+) = 9.06, 6.13, 4.93 and 4.52, H(3)3(3+) = 8.79 and 3.67, H(4)4(4+) = 8.50, 5.62 and 3.77 and for H(8)5(4+) = 9.89, 7.06, 5.53, 5.46, 4.44 and 4.26 where each tertiary amine nitrogen is protonated. The complexes of 1: [Zn(1)]2+(9.00), [Cd(1)]2+ (6.49), [Cd(H1)]3+ (4.54) and [Cu(1)]2+ (10.01) are characterized by the log(K/dm3 mol(-1)) values shown in parentheses. Analogous complexes are formed by 3 and 4: [Zn(3)]2+ (10.19), [Cd(3)]2+ (8.54), [Cu(3)]2+ (10.77), [Zn(4)]2+ (11.41) [Cd(4)]2+ (9.16), [Cd(H4)]3+ (6.16) and [Cu(4)]2+ (11.71). The tricarboxylic acid H(3)2 generates a greater variety of complexes as exemplified by: [Zn(2)-] (10.68) [Zn(H2)] (6.60) [Zn(H(2)2)+] (5.15), [Cd(2)](-) (4.99), [Cd(H2)] (4.64), [Cd(H2(2))]+ (3.99), [Cd(H(3)2)]2+ (3.55), [Cu(2)](-) (12.55) [Cu(H2)] (7.66), [Cu(H(2)2)]+ (5.54) and [Cu(2)2](4-) (3.23). The complexes of H(4)5 were insufficiently soluble to study in this way. The 1H and 13C NMR spectra of the ligands are consistent with formation of a predominant Zn2+ and Cd2+ Delta or Lambda diastereomer. The preparations of the new pendant arm macrocycles H(3)2, 3, 4 and H(4)5 are reported.     

Supramolecular motifs and solvatomorphism within the compounds [M(bpy)3]2[NbO(C2O4)(3)]Cl.nH2O (M = Fe2+, Co2+, Ni2+, Cu2+ and Zn2+; n = 11, 12). Syntheses, structures and magnetic properties

Solvatomorphism has been found between two series of complexes of the composition [M(bpy)3]2[NbO(C2O4)3]Cl.nH2O [M = Fe2+ (1, 2), Co2+ (3, 4), Ni2+ (5, 6), Cu2+ (7) and Zn2+ (8, 9); bpy = 2,2'-bipyridine)], crystallizing in the monoclinic space group P2 1/c [3, 5, 8 (n = 11)] or in the orthorhombic space group P21 21 21 [2, 4, 6, 7 (n = 12)]. All the structures contain two symmetry independent [M(bpy)3]2+ cations, one [NbO(C2O4)3]3- anion, one Cl(-) anion, and crystal water molecules. The cations possess a trigonally distorted octahedral geometry, with an additional tetragonal distortion in 7. Analysis of crystal packing reveals a specific type of supramolecular contact comprising four bipyridine ligands from two neighbouring [M(bpy)3]2+ cations--quadruple aryl embrace (QAE) contact. The contact is realized by the alignment of two molecular two-fold rotation axes, preserving the parallel orientation of the molecular three-fold rotation axes. The resulting two-dimensional honeycomb lattices of [M(bpy)3]2+ cations are placed between the hydrogen bonding layers made of [NbO(C2O4)3]3- and Cl(-) anions and the majority of the crystal water molecules. The temperature-dependent magnetic susceptibility measurements (1.8-300 K) show a significant orbital angular momentum contribution for 3 and 4 (high-spin Co2+), the influence of zero-field splitting for 5 and 6(Ni2+) and a substantially paramagnetic Curie behaviour for the Cu2+ compound (7).     

Two Zn(II) coordination polymers constructed by a new tricarboxylate and different N-containing ligands: synthesis,crystal structures,and selective luminescence sensing for Fe3+ in aqueous solution

Two Zn(II) coordination polymers, {[Zn₃(L)₂(bipy)₂(H₂O)₄}_n (1) and {[Zn(HL)(4,4′-bibp)}_n (2), were obtained from Zn(II) nitrate, a tricarboxylate ligand (H₃L) and different N-containing ligands with hydrothermal conditions, where H₃L = 4-((6-carboxynaphthalen-2-yl)oxy)phthalic acid, bipy = 4,4′-bipyridine, and 4,4′-bibp = 4,4′-di(1H-imidazol-1-yl)-1,1′-biphenyl. Single-crystal X-ray analysis reveals that 1 has a 2-D layer framework formed by L^3? and bipy and 2 has an infinite 1-D structure with Zn₂ units built by 4,4′-bibp ligands. The phase purity, IR spectra, thermal stabilities, and fluorescence properties in the solid state of 1 and 2 were investigated. Moreover, 1 and 2 were chosen as fluorescent probes to sense different metal ions, showing selective response to Fe³⁺ ion through luminescence quenching. The possible sensing mechanism to Fe³⁺ ion is also discussed.     

Macrocyclic Cr3+, Mn2+ and Fe3+ complexes of a mimic SOD moiety: Design,structural aspects,DFT, XRD,optical properties and biological activity

A novel SOD-like macrocycle “H₂DPD” and its trivalent chromium, iron and divalent manganese complexes have been isolated and characterized using the conventional tools. The macrocycle was prepared by 2:2 condensation of P-phenylenediamine with 5,5-dimethyl1,3-cyclohexanedione. IR and electronic spectral data suggested that H₂DPD coordinates to the metal ion as N₄ tetradentate donor with two Cl⁻ occupying the remaining two sites of the distorted octahedron. XRD spectrum of Cr³⁺ complex indicated that the complex crystallizes in a face-centered monoclinic structure with lattice parameters: a = 10.9380 Å; b = 12.4870 Å; c = 12.4600 Å, α = γ = 90° and β = 111.430 with space group P 1 21/c 1 (14). The energy gap (E_HOMO-E_LUMO), molecular electrostatic potential map (EPM) of title compounds, bond length, bond angle, as well as global and local reactivity were estimated using DFT method. The E_g values obtained from electronic spectra of Cr³⁺, Mn²⁺ and Fe³⁺ complexes were found to be 1.284, 1.220 and 1.138 eV, respectively which are in accordance with those evaluated by DFT revealing semiconductor nature. Also, the thermal degradation of all title compounds was carried out and the kinetic parameters were evaluated using Coats-Redfern and Horowitz-Metzger equations. Moreover, the compounds have screened for antibacterial as well as superoxide mimic activities. Cr³⁺ complex exhibited the most significant potent activity against all bacterial strains. With respect to SOD-like activity, the macrocycle showed the most remarkable SOD-like activity comparable to the standard drug, ascorbic acid.