Amine Nitrogen Atoms Research Articles

Mn(II) azamacrocyclic bromide complexes with different nuclearities

The coordination behaviour of a series of pyridyl azamacrocyclic ligands, some of them containing cyanomethyl and cyanoethyl pendant-arms, towards Mn(II) ion was studied. All the complexes were characterized by microanalysis, LSI mass spectrometry, IR, UV–Vis spectroscopy and magnetic measurements. Crystal structures of [MnL 1 ][MnBr 4 ] ( 1 ), [MnL 3 ][MnBr 4 ] · 2CH 3 CN ( 3 ), [Mn 2 L 5 Br 4 ] · 2CH 3 CN ( 5 ) and [Mn 2 L 6 Br 4 ] ( 6 ) complexes have been determined. The X-ray studies show the presence of an ionic mixed octahedral–tetrahedral complex for 1 and 3 , with the manganese ion of the cation complex, endomacrocyclicly coordinated by the six nitrogen donor atoms from the macrocyclic backbone in a distorted octahedral geometry. Instead, the complexes 5 and 6 are dinuclear, and both manganese ions are coordinated by one pyridinic and two amine nitrogen atoms from the macrocyclic backbone and two bromide ions, being the geometry around the metal better described as distorted square pyramidal. In all cases, the nitrile pendant-arms do not show coordination to the metal ion. The coordination behaviour of a series of pyridyl azamacrocyclic ligands, some of them containing cyanomethyl and cyanoethyl pendant-arms, towards Mn(II) ion was studied. All the complexes were characterized by microanalysis, LSI mass spectrometry, IR, UV–Vis spectroscopy and magnetic measurements. Crystal structures of [MnL 1 ][MnBr 4 ] ( 1 ), [MnL 3 ][MnBr 4 ] · 2CH 3 CN ( 3 ), [Mn 2 L 5 Br 4 ] · 2CH 3 CN ( 5 ) and [Mn 2 L 6 Br 4 ] ( 6 ) complexes have been determined. The X-ray studies show the presence of an ionic mixed octahedral–tetrahedral complex for 1 and 2 , with the manganese ion of the cation complex, endomacrocyclicly coordinated by the six nitrogen donor atoms from the macrocyclic backbone in a distorted octahedral geometry. Instead, the complexes 5 and 6 are dinuclear, and both manganese ions are coordinated by one pyridinic and two amine nitrogen atoms from the macrocyclic backbone and two bromide ions, being the geometry around the metal better described as distorted square pyramidal. In all cases, the nitrile pendant-arms do not show coordination to the metal ion.

Solution Structure and Dynamics, Stability, and NIR Emission Properties of Lanthanide Complexes with a Carboxylated Bispyrazolylpyridyl Ligand

The complexation behavior of the ligand 2,6-bis{3-[N,N-bis(carboxymethyl)aminomethyl]pyrazol-1-yl}-pyridine, L, toward lanthanide cations was investigated throughout the series. Potentiometric titration experiments on L (0.1 M KCl) revealed the presence of four protonation steps in the 2-12 pH domain, associated with the protonation of the two tertiary amine nitrogen atoms and with two of the four carboxylate functions. The stability constants for the formation of the [LnL](-) complexes (Ln = La, Nd, Eu, Ho, and Lu) were determined in water and evidenced a hill-shaped complexation trend along the series, with log K increasing from 14.56(9) (La) to 16.68(2) (Ho) and decreasing to 15.42(2) (Lu). Geometry optimizations showed the [LnL](-) complexes (Ln = La, Nd, Eu, Ho, Yb, and Lu) adopting a C(2) symmetry with the symmetry axis going through the metal atom and the nitrogen atom of the central pyridine ring, leading to the presence of Delta and Lambda helical enantiomers. Analysis of the calculated Ln-O and Ln-N bond lengths showed a marked deviation from the expected values at the end of the series, which accounts for the observed decreased complexation affinity. (1)H and (13)C NMR experiments in D(2)O (room temperature) showed the shortening of the bond distances in [LnL](-) complexes from La to Lu to be accompanied by a rigidification of the structure, leading to a decreased C(2) symmetry for the Lu complex compared to C(2v) for La. This decreased symmetry was attributed to a slow Delta <--> Lambda interconversion that was followed by variable-temperature (13)C NMR experiments on the Lu complex. The activation parameters determined by line broadening analysis for this interconversion process point to an associatively assisted interconversion process. The (1)H NMR spectrum of the paramagnetic [YbL](-) complex was investigated in D(2)O, and a lanthanide induced shift analysis showed good agreement between the observed paramagnetic chemical shifts and those calculated from the DFT optimized structures using a dipolar model, especially when solvent effects are taken into account. The UV-vis absorption and near-infrared luminescence spectra of the Pr, Nd, Er, and Yb complexes were measured in water and showed the complexation pocket provided by the ligand to be well-suited for the protection of the cations, all of them displaying typical Ln-centered emission spectra, the Yb complex having a relatively long lifetime of 3.0 micros in water.

Induction of Cell Death by Ternary Copper(II) Complexes of l-Tyrosine and Diimines: Role of Coligands on DNA Binding and Cleavage and Anticancer Activity

The mononuclear mixed ligand copper(II) complexes of the type [Cu(L-tyr)(diimine)](ClO(4)), where tyr is L-tyrosine and diimine is 2,2'-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (3), and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (4), have been isolated and characterized by analytical and spectral methods. In the X-ray crystal structure 3 Cu(II) possesses a distorted square pyramidal coordination geometry with the two nitrogen atoms of 5,6-dmp ligand and the amine nitrogen and carboxylate oxygen atoms of L-tyrosine located at the equatorial sites and the coordinated water molecule present in the apical position. The electronic absorption and electron paramagnetic resonance (EPR) spectral parameters reveal that the complexes retain their square-based geometries even in solution. All of the complexes display a ligand field band in the visible region (600-700 nm) in Tris-HCl/NaCl buffer (5:50 mM) at pH 7.2 and also axial EPR spectra in acetonitrile at 77 K with g(parallel) > g(perpendicular) indicating a d(x(2)-y(2)) ground state. The g(parallel) and A(parallel) values of 2.230 and (170-180) x 10(-4) cm(-1), respectively, conform to a square-based CuN(3)O coordination chromophore, which is consistent with the X-ray crystal structure of 3. The interaction of the complexes with calf thymus DNA (CT DNA) has been explored by using physical methods to propose modes of DNA binding of the complexes. Absorption (K(b)) and emission spectral studies and viscosity measurements indicate that 4 interacts with DNA more strongly than all of the other complexes through partial intercalation of the extended planar ring of dpq with DNA base stack. Interestingly, complex 3 exhibits a DNA binding affinity that is higher than that of 2, which suggests the involvement of 5,6-dimethyl groups on the phen ring in hydrophobic interaction with DNA surface. In contrast with the increase in relative viscosities of DNA bound to 2-4, the viscosity of DNA bound to 1 decreases, indicating the shortening of the DNA chain length by means of the formation of kinks or bends. All complexes exhibit effective DNA (pUC19 DNA) cleavage at 100 microM complex concentrations, and the order of DNA cleavage ability varies as 3 > 2 > 4 > 1. Interestingly, 3 exhibits a DNA cleavage rate constant that is higher than that of the other complexes only at 100 microM concentration, whereas 4 exhibits the highest cleavage rate constant at 80 microM complex concentration. The oxidative DNA cleavage follows the order 4 > 3 > 2 > 1. Mechanistic studies reveal that the DNA cleavage pathway involves hydroxyl radicals. Interestingly, only 4 displays efficient photonuclease activity upon irradiation with 365 nm light, which occurs through double-strand DNA breaks involving hydroxyl radicals. Furthermore, cytotoxicity studies on the nonsmall lung cancer (H-460) cell line show that the IC(50) values of 2-4 are more or less equal to cisplatin for the same cell line, indicating that they have the potential to act as very effective anticancer drugs in a time-dependent manner. The study of cytological changes reveals the higher induction of apoptosis and mitotic catastrophe for 4 and 3, respectively. The alkaline single-cell gel electrophoresis (comet assay), DNA laddering, and AO/EB and Hoechst 33258 staining assays have also been employed in finding the extent of DNA damage. Flow cytometry analysis shows an increase in the percentage of cells with apoptotic morphological features in the sub-G(0)/G(1) phase for 4, whereas it shows mitotic catastrophe for 3.

Synthesis and Characterization of New Palladium(II) Complexes Containing N-Alkylamino-3,5-diphenylpyrazole Ligands. Crystal Structure of [PdCl(L2)](BF4) {L2 = Bis[2-(3,5-diphenyl-1-pyrazolyl)ethyl]ethylamine}

In this paper, the synthesis of two new N,N′,N-ligands, bis[2-(3,5-diphenyl-1-pyrazolyl)ethyl]amine (L1) and bis[2-(3,5-diphenyl-1-pyrazolyl)ethyl]ethylamine (L2) is reported. These ligands form complexes with the formula [PdCl(N,N′,N)]Cl when reacting with [PdCl2(CH3CN)2] in a 1:1 metal-to-ligand molar ratio. Treatment of these ligands with [PdCl2(CH3CN)2] in a 1:1 metal-to-ligand molar ratio in the presence of AgBF4 or NaBF4 gave [PdCl(N,N′,N)](BF4) complexes. These PdII complexes were characterized by elemental analyses, conductivity measurements, mass spectrometry, and IR, 1H, and 13C{1H} NMR spectroscopies. The X-ray structure of the complex [PdCl(L2)](BF4) has been determined. The metal atom is coordinated by two azine nitrogen atoms and one amine nitrogen atom of the aminopyrazole ligand. The distorted square planar coordination is completed by one chlorine atom. In this complex, intermolecular π–π stacking interactions are present.

Stabilization of Copper(II) Thiosulfonate Coordination Complexes Through Cooperative Hydrogen Bonding Interactions

A series of copper(II) thiosulfonate complexes have been prepared via the reaction of [Cu(Me 3tren)(OH 2)](ClO 4) 2 (Me 3tren = tris(2-methylaminoethyl)amine) with three thiosulfonate ligands (RSO 2S (-), where R = Me, Ph, and MePh) and characterized by microanalysis, FTIR spectroscopy, and X-ray crystallography. In these complexes, the distorted trigonal bipyramidal copper(II) coordination sphere is occupied by four amine nitrogen atoms from the tripodal tetramine ligand and an apically bound sulfur atom from the thiosulfonate ligand. By using the tripodal tetramine ligand the oxidation of the thiosulfonate has been restricted, allowing the isolation of the complexes. The Cu-S distances were found to be similar to those in related thiosulfate complexes, indicating coordinative interactions of similar strength. Two types of intramolecular hydrogen bonding interactions were evident which enhance the binding of the thiosulfonate to the copper(II) center. These interactions, which involve two amine N-H groups and either one or two thiosulfonate oxygens, were found to be weaker than in the corresponding thiosulfate complexes. The complex formation constants for the thiosulfonate complexes (log K f = 0.3-0.7) were found to be two orders of magnitude lower than compared to the thiosulfate analogues. This correlates well with a lower strength of intramolecular hydrogen bonding.

Syntheses and crystal structures of copper mixed-ligand complexes of multidentate enaminones and acetate anions

Reactions of ferrocenoylacetone with 2-(aminomethyl)pyridine and N-(2-hydroxyethyl)-1,2-diaminoethane afford the multidentate enaminones H L 1 and H 3 L 2, respectively. Reactions of copper acetate with the two enaminones generate the corresponding mixed-ligand complexes I and II, which are formulated as [Cu L 1(OAc)] and [Cu(H 2 L 2)(OAc)], respectively. The structures of H L 1, I and II have been determined by single-crystal X-ray crystallography. In complex I, H L 1 acts as a monoanionic tridentate donor via the carbonyl oxygen, deprotonated enamine nitrogen and pyridyl nitrogen atoms, the acetate anion is monodentate and the coordination geometry of the central metal is square planar. In complex II, H 3 L 2 is a monoanionic tetradentate ligand via the carbonyl oxygen, deprotonated enamine nitrogen, secondary amine nitrogen and hydroxy oxygen atoms, the acetate anion is monodentate and the coordination geometry of the central metal is a distorted trigonal bipyramid.

Theoretical study on difunctional electroluminescent molecules containing aromatic heterocycle cores and hole-transporting triphenylamino units

2,2′-difuryl-4,4′-(N,N,N′,N′-tetraphenyl) diaminobiphenyl (FurylBz-Ph4) and 5,5′-bis(4-N,N′- diphenylaminophenyl)-2,2′-bifuryl (PFDA-Ph4) are new light-emitting materials, which are capable of transporting holes. A series of new compounds whose structures were similar to that of FurylBz-Ph4 or PFDA-Ph4, were designed and calculated. The total energies, HOMO and LUMO orbital energies of these compounds at neutral, cationic and anionic states were obtained based on the optimised geometrical structures. The ionization potential ( I p) and electron affinity ( E a) were generated by means of density functional theory (DFT) calculated total energy of neutral, cationic and anionic states. The reorganization energy for the hole transport of compounds 1- 3, FurylBz-Ph4 and PFDA-Ph4 is close to that of TPD at the same level of calculation. For compounds 2, 3 and PFDA-Ph4, the order of I p is 3 > PFDA-Ph4 > 2. It is indicated that the contribution of aryl groups to I p follows the sequence: thienyl > furyl > pyrryl. The absorptions of these compounds had been also investegated by time-dependent density functional theory (TD-DFT) methods with 6-31G(d) basis set. The TD-DFT calculations indicate that the absorption maximum of compounds 2 is blue-shifted from PFDA-Ph4, while the absorption maximum of compounds 3 is red-shifted from PFDA-Ph4. Since the electron-withdrawing strength is in the order pyrryl > thienyl > furyl and PFDA-Ph4 has the longer conjugated length between the two amine nitrogen atoms than that of compound 2 and 3. The different bands of emission and reorganization energy can be obtained by changing the substituents and the site of substitution between two triphenylamino units.

Crystal structure of a new homo trinuclear Ni(II) complex with μ-cyanoacetato bridge

Abstract Ni(II)-Ni(II)-Ni(II) homo-trinuclear linear complex was prepared using bis-N,N′(2-hydroxybenzyl)-1,3-propanediamine in DMF (dimethyl formamide) medium. μ-bridges between metal nuclei are formed using formate, acetate, chloroacetate and benzoate ions. The structure of the homo-trinuclear complex was determined with X-ray diffraction method. It was found that the terminal Ni(II) ions have a N2O4 coordination sphere and central Ni(II) ion has a O6 octahedral coordination sphere. The chelate ring, formed by the coordination of terminal Ni atoms and aminic nitrogen atoms, was found to have a chair conformation. The complexes were elucidated by the use of thermogravimetry and differential thermal analysis method. In acetate, chloroacetate, cyanoacetate and benzoate containing complexes thermal dissociation of DMF took place first while in formate containing complex it was observed that formate bridges and the complex degraded together with the dissociation of DMF moiety. It was observed that the thermal stability of carboxylate μ-bridge affects the thermal stability of the homo-nuclear complex. The average bond energies of coordinated DMF molecules were determined and these coordinative bond energies were found to be in the dimension of that of hydrogen bonds.

The synthesis and structure of trans-di(cyano-κ 1)-( trans-6,13-dimethyl-6,13-bis(propionylamido)-1,4,8,11-tetraazacyclotetradecane-κ 4)cobalt(III) perchlorate dihydrate

trans-Di(cyano-κ 1)-( trans-6,13-dimethyl-6,13-bis(propionylamido)-1,4,8,11-tetraazacyclotetradecane-κ 4)cobalt(III) perchlorate dihydrate, trans-[Co(C 18H 38N 6O 2)(CN) 2)]ClO 4 · 2H 2O, is formed by reaction of trans-[Co(diam)(CN) 2]ClO 4 · 2H 2O (diam = trans-6,13-diamino-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane) with propionic anhydride in DMF. The centrosymmetrical cation has the azamacrocycle in planar coordination by the four secondary amine nitrogen atoms of the azamacrocycle, with Co–N = 1.979(2) and 1.968(2) Å and with trans cyano groups with Co–C = 1.920(2) Å. The propionylamido substituents are axially oriented, with the terminal methyl group disordered over two sites.

The Use of Liquid–Liquid Interface (Biphasic) for the Preparation of Benzenetricarboxylate Complexes of Cobalt and Nickel

AbstractNew metal–organic frameworks (MOFs) [Ni(C12N2H10)(H2O)][C6H3(COO)2(COOH)] (I), [Co2(H2O)6][C6H3(COO)3]2·(C4N2H12)(H2O)2 (II), [Ni2(H2O)6][C6H3(COO)3]2·(C4N2H12)(H2O)2 (III), [Ni(C13N2H14)(H2O)][C6H3(COO)2(COOH)] (IV), [Ni3(H2O)8][C6H3(COO)3] (V) and [Co(C4N2H4)(H2O)][C6H3(COO)3] (VI) {C6H3(COOH)3 = trimesic acid, C12N2H10 = 1,10‐phenanthroline, C4N2H12 = piperazine dication, C13N2H14 = 1,3‐bis(4‐pyridyl)propane and C4N2H4 = pyrazine} have been synthesized by using an interface between two immiscible solvents, water and cyclohexanol. The compounds are constructed from the connectivity between the octahedral M2+ (M = Ni, Co) ions coordinated by oxygen atoms of carboxylate groups and water molecules and/or by nitrogen atoms of the ligand amines and the carboxylate units to form a variety of structures of different dimensionality. Strong hydrogen bonds of the type O–H···O are present in all the compounds, which give rise to supramolecularly organized higher‐dimensional structures. In some cases π···π interactions are also observed. Magnetic studies indicate weak ferromagnetic interactions in I, IV and V and weak antiferromagnetic interactions in the other compounds (II, III and VI). All the compounds have been characterized by a variety of techniques.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis, structure, and physical properties for a series of monomeric iron(III) hydroxo complexes with varying hydrogen-bond networks.

Mononuclear iron(III) complexes with terminal hydroxo ligands are proposed to be important species in several metalloproteins, but they have been difficult to isolate in synthetic systems. Using a series of amidate/ureido tripodal ligands, we have prepared and characterized monomeric Fe (III)OH complexes with similar trigonal-bipyramidal primary coordination spheres. Three anionic nitrogen donors define the trigonal plane, and the hydroxo oxygen atom is trans to an apical amine nitrogen atom. The complexes have varied secondary coordination spheres that are defined by intramolecular hydrogen bonds between the Fe (III)OH unit and the urea NH groups. Structural trends were observed between the number of hydrogen bonds and the Fe-O hydroxo bond distances: the more intramolecular hydrogen bonds there were, the longer the Fe-O bond became. Spectroscopic trends were also found, including an increase in the energy of the O-H vibrations with a decrease in the number of hydrogen bonds. However, the Fe (III/II) reduction potentials were constant throughout the series ( approximately 2.0 V vs [Cp 2Fe] (0/+1)), which is ascribed to a balancing of the primary and secondary coordination-sphere effects.

Synthesis, Structure, and Characterization of Dichloro‐(1‐Benzyl‐4‐Acetato‐1,4,7‐Triazacyclononane)Iron(III)

AbstractThe synthesis, structure and aqueous solution behavior of [FeL1Cl2] (1, L1 = 1‐benzyl‐4‐acetato‐1,4,7‐triazacyclononane) is reported. The X‐ray structure of 1 reveals iron(III) in distorted octahedral geometry bonded to three amine nitrogen atoms and one carboxylate oxygen atom along with two cis chloride atoms. Electrochemical measurements of 1 in acetonitrile indicate that E1/2 = −200 mV vs Ag/AgCl. The stability of the +3 oxidation state is attributed to the hard Namine and carboxylate ligand donors. In acetonitrile, 1 is mononuclear and has an S = 5/2 spin state. The presence of a μ‐oxo bridge upon dissolution of 1 in water is supported by EPR and solution magnetic susceptibility NMR studies. pH‐metric titrations and UV‐vis studies indicate the presence of a total of four acidic protons. At low pH, L1(OH2)Fe‐O‐Fe(OH2)L1 is proposed to be stabilized while at high pH, L1(OH)Fe‐O‐Fe(OH)L1 is suggested to persist.

An Oxidized Tryptophan Facilitates Copper Binding in Methylococcus capsulatus-secreted Protein MopE

Proteins can coordinate metal ions with endogenous nitrogen and oxygen ligands through backbone amino and carbonyl groups, but the amino acid side chains coordinating metals do not include tryptophan. Here we show for the first time the involvement of the tryptophan metabolite kynurenine in a protein metal-binding site. The crystal structure to 1.35 angstroms of MopE* from the methane-oxidizing Methylococcus capsulatus (Bath) provided detailed information about its structure and mononuclear copper-binding site. MopE* contains a novel protein fold of which only one-third of the structure displays similarities to other known folds. The geometry around the copper ion is distorted tetrahedral with one oxygen ligand from a water molecule, two histidine imidazoles (His-132 and His-203), and at the fourth distorted tetrahedral position, the N1 atom of the kynurenine, an oxidation product of Trp-130. Trp-130 was not oxidized to kynurenine in MopE* heterologously expressed in Escherichia coli, nor did this protein bind copper. Our findings indicate that the modification of tryptophan to kynurenine and its involvement in copper binding is an innate property of M. capsulatus MopE*.

Cd(II) complexes with N 8 and N 4O 4 donor macrocyclic ligands

The coordination capability of the octaaza 24-membered (L 1) and the tetraoxotetraaza 28-membered (L 2) macrocycle ligands – with different sizes, nature and number of the donor atoms – has been investigated with nitrate and perchlorate Cd(II) salts. The complexes were prepared in 1:1 and 2:1 Cd:L molar ratio. The characterization by elemental analysis, IR, LSI mass spectrometry, conductivity measurements and 1H NMR spectroscopy, together with the crystal structure of the complexes [CdL 1](NO 3) 2 · 0.5H 2O, [CdL 1](ClO 4) 2 and [CdL 2(CH 3CN) 2](ClO 4) 2 · CH 3CN · H 2O confirms the formation of mononuclear complexes in all cases. The [CdL 1](NO 3) 2 · 0.5H 2O and [CdL 1](ClO 4) 2 present a mononuclear endomacrocyclic structure with the metal ion coordinated by the eight donor nitrogen atoms from the macrocyclic backbone in a square antiprism geometry. The complex [CdL 2(CH 3CN) 2](ClO 4) 2 · CH 3CN · H 2O is also mononuclear, but the cadmium ion is in an octahedral environment coordinated by four amine nitrogen atoms from the macrocyclic framework and two nitrogen atoms from two acetonitrile molecules. The ether oxygen atoms from the ligand are not coordinated.

Syntheses, structures and magnetism of linear tri- and tetra-copper chains containing anions of N,N′-bis(pyrimidine-2-yl)formamidine

Reaction of Kpmf (pmf(-) = anion of N,N'-bis(pyrimidyl-2-yl)formamidine, Hpmf) with divalent copper salt CuX2 afforded the linear trinuclear complexes of the type [Cu3(pmf)4](X)2 (X = BF4, 1; NO3, 2; ClO4, 3), while reaction of Kpmf with monovalent copper salt CuX gave the linear tetranuclear complexes of the type Cu4(pmf)4X2 (X = Cl, 4; Br, 5). The copper atoms of complexes 1-5 are helically bridged by four pmf(-) ligands, resulting in three different coordination modes for the pmf(-) ligands. In complexes 1-3, one pmf(-) ligand adopts a new coordination mode with the two amine nitrogen atoms chelating to the central copper atom, while the other three feature chelation by one pyrimidyl and one adjacent amine nitrogen atoms. The Cu(II)...Cu(II) distances are 2.729(2) and 2.825(2) A for 1, 2.762(1) and 2.832(1) A for 2 and 2.732(1) and 2.827(1) A for 3. In complexes 4 and 5, the pmf(-) ligands are coordinated to the copper atoms in tetradentate fashion with each nitrogen atom coordinating to one Cu atom. The Cu...Cu distances are 2.580(1) and 2.549(1) A for 4 and 2.582(1) and 2.561(1) A for 5. Antiferromagnetic interactions between the copper ions are observed with calculated g and J values of 2.03(1) and -188(2) cm(-1) for 1, 2.09(1) and -268(3) cm(-1) for 2, and 2.09(1) and -486(2) cm(-1) for 5. By comparing the magnetic data it can be shown that the bonding mode of the pmf(-) ligand is one of the important factors in determining the strengths of the Cu...Cu interactions in linear trinuclear and tetranuclear copper complexes.

Crown‐like macrocycle zinc complex derived from β‐diketone ligand for the polymerization of rac‐lactide

AbstractEnolic Schiff base zinc (II) complex 1 was synthesized. XRD revealed 1 was a novel crown‐like macrocycle structure consisted of hexanuclear units of (LZnEt)6 via the coordination chelation between the Zn atom and adjacent amine nitrogen atom. Further reaction of 1 with one equivalent 2‐propanol at RT produced Zn‐alkoxide 2 by in situ alcoholysis. Complex 2 was used as an initiator to polymerize rac‐lactide in a controlled manner to give heterotactic enriched polylactide. Factors that influenced the polymerization such as the polymerization time and the temperature as well as the monomer concentration were discussed in detail in this paper. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 643–649, 2008

Synthesis, spectroscopic, structural and complexation studies of a new tetra-naphthylmethylene pendant-armed macrocyclic ligand

A novel emissive tetra-naphthylmethylene pendant-armed macrocyclic ligand and a series of complexes with monovalent and divalent metal ions have been synthesized. Solid compounds have been isolated as mononuclear (Co(II), Cu(II) and Zn(II)) or dinuclear (Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Ag(I)), complexes, depending on the counterions used. The chemical and photophysical properties of the free ligand, the protonation behavior and its metal complexes have been investigated in solution. UV–Vis spectroscopy has revealed a 1:1 binding stoichiometry for Cu(II), Zn(II), Cd(II), Ni(II) and Co(II), and 2:1 molar ratio for Ag(I). In chloroform, the free ligand presents two emission bands related to the monomer naphthalene emission and a red-shifted band attibutable to an exciplex due to a charge transfer from the nitrogen lone electron pair to the excited chromophore. Upon protonation of the free amines or due to metal complexation, the exciplex band disappears. The crystal structure of [Ag 2 L(NO 3) 2] is also reported. The structure reveals that both metal ions are into the macrocyclic cavity in a distorted square plane {AgN 3O} environment. Each Ag(I) atom interacts with two neighbouring amine nitrogen atoms, one pyridine nitrogen and one oxygen atom from a monodentate nitrate ion.

Structure of aniline-containing Co(III) trans-dioximates with the [ZrF6]2− anion

Two new coordination compounds, trans-octahedral aniline-containing Co(III) dioximates [Co(DH)2(Anil)2]2[ZrF6]·2H2O (I) and [Co(NioxH)2(Anil)2]2[ZrF6]·3H2O (II), where DH− is the dimethylglyoxime monoanion, and NioxH− is the 1,2-cyclohexanedionedioxime monoanion, were synthesized, and their crystal structures were studied by XRD. In I, two centrosymmetric, crystallographically independent [Co(DH)2(Anil)2]+ complex cations (A and B) are linked by a system of hydrogen bonds, the [ZrF6]2− centrosymmetric anion, and the crystallization water molecules into a three-dimensional framework. The coordination polyhedron of the Co3+ atom in I and II is a slightly distorted N6 octahedron formed by four nitrogen atoms of the two dioxime residues and two amine nitrogen atoms of the aniline fragment. The deviation of the cobalt atom from the plane of the metallocycle in II is up to 0.012 A. The [ZrF6]2− outer-spheric anions and crystallization water molecules dominate in the crystal structures.

Pt4S4 Clusters with Functionalized Thiosemicarbazones derived from 5‐Acetylbarbituric Acid

AbstractReaction of K2[PtCl4] with thiosemicarbazones derived from 5‐acetylbarbituric acid led to the isolation of the tetranuclear species [Pt(AcbM)]4 · 2/2DMSO · 2DMSO · 5H2O (1) and [Pt(AcbE)]4 · 4DMSO · 2H2O (2) (H2AcbM = 5‐acetylbarbituric‐4N‐methyl thiosemicarbazone and H2AcbE = 5‐acetylbarbituric‐4N‐ethyl thiosemicarbazone). Both of these compounds feature a Pt4S4 cluster in which some of the Pt–Pt distances suggest the existence of weak metal‐metal interactions. Crystals of these tetranuclear species are stabilized by intermolecular π‐π stacking interactions. The two compounds have almost equivalent molecular structures, differing only in the orientation of the substituent on the amine nitrogen atom of the thiosemicarbazone. The two tetranuclear complexes contain the thiosemicarbazone bonded as a terdentate ligand to the platinum atom through the thiolate sulfur atom, the azomethine nitrogen atom and the alcoholate oxygen atom of the 5‐acetylbarbiturate function.

Dimolybdenum Complex Containing N–H···Mo Interactions. Synthesis and Structure of cis-[Mo2(HDpyF)2(CH3CN)4](BF4)4 and its Transformation to [Mo2(DpyF)2(py)4](BF4)2 [HDpyF = Bis(2-pyridyl)formamidine; py = pyridine

The complex cis-[Mo2(HDpyF)2(CH3CN)4](BF4)4, 1, was prepared by the reaction of Mo2(DpyF)4 with HBF4 in CH3CN, in which new bonding mode of the HDpyF ligand and axial N–H···Mo interactions are observed. Reaction of 1 with pyridine afforded the complex trans-[Mo2(DpyF)2(py)4](BF4)2, 2. In complex 1, the neutral bidentate HDpyF ligands bridge the metal centers through one of the amine nitrogen atoms and the adjacent pyridyl nitrogen atom, resulting in the s-trans-anti-s-trans conformation. The anionic DpyF− ligands of 2 adopt the s-trans,s-trans conformation and are coordinated to the Mo centers in bidentate fashions through the two central nitrogen atoms and the two terminal nitrogen atoms are not coordinated.