Structure and magnetic properties of an unprecedented syn-antiμ-nitrito-1κO:2κO′ bridged Mn(iii)-salen complex and its isoelectronic and isostructural formate analogue

The preparation, crystal structures and magnetic properties of two new isoelectronic and isomorphous formate-and nitrite-bridged 1D chains of Mn(III)-salen complexes, [Mn(salen)(HCOO)](n) (1) and [Mn(salen)(NO2)](n) (2), where salen is the dianion of N,N'-bis(salicylidene)-1,2-diaminoethane, are presented. The structures show that the salen ligand coordinates to the four equatorial sites of the metal ion and the formate or nitrite ions coordinate to the axial positions to bridge the Mn(III)-salen units through a syn-anti mu-1 kappa O:2 kappa O' coordination mode. Such a bridging mode is unprecedented in Mn(III) for formate and in any transition metal ion for nitrite. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 indicate the presence of ferromagnetic exchange interactions with J values of 0.0607 cm(-1) (for 1) and 0.0883 cm(-1) (for 2). The ac measurements indicate negligible frequency dependence for 1 whereas compound 2 exhibits a decrease of chi(ac)' and a concomitant increase of chi(ac)'' on elevating frequency around 2 K. This finding is an indication of slow magnetization reversal characteristic of single-chain magnets or spin-glasses. The mu-nitrito-1 kappa O:2 kappa O' bridge seems to be a potentially superior magnetic coupler to the formate bridge for the construction of single-molecule/-chain magnets as its coupling constant is greater and the chi(ac)' and chi(ac)'' show frequency dependence.

Solvatochromic and lonochromic Effects of Iron(II)bis-(1,10-phenanthroline)dicyano: a Theoretical Study

Solvatochromic and ionochromic effects of the iron(II)bis(1,10-phenanthroline)dicyano (Fe(phen)(2)(CN)(2)) complex were investigated by means of combined DFT/TDDFT calculations using the PBE and B3LYP functionals. Extended solvation models of Fe(phen)(2)(CN)(2) in acetonitrile and aqueous solution, as well as including interaction with Mg(2+), were constructed. The calculated vertical excitation energies reproduce well the observed solvatochromism in acetonitrile and aqueous solutions, the ionochromism in acetonitrile in the presence of Mg(2+), and the absence of ionochromic effect in aqueous solution. The vertical excitation energies and the nature of the transitions were reliably predicted after inclusion of geometry relaxation upon aqueous micro- and global solvation and solvent polarization effect in the TDDFT calculations. The two intense UV-vis absorption bands occurring for all systems studied are interpreted as transitions from a hybrid Fe(II)(d)/cyano N(p) orbital to a phenanthroline pi* orbital rather than a pure metal-to-ligand-charge transfer (MLCT). The solvatochromic and ionochromic blue band shifts of Fe(phen)(2)(CN)(2) were explained with preferential stabilization of the highest occupied Fe(II)(d)/cyano N(p) orbitals as a result of specific interactions with water solvent molecules or Mg(2+) ions in solution. Such interactions occur through the CN(-) groups in the complex, and they have a decisive role for the observed blue shifts of UV-vis absorption bands.

Luminescent nanoparticles of MgAl(2)O(4):Eu, Dy prepared by citrate sol-gel method

MgAl(2)O(4):Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at 600, 700, 800 and 900 degrees C. The trivalent europium ion is partially reduced to the divalent state at 700 and 800 degrees C. Infrared spectra of the phosphors showed bands around 700 and 520 cm(-1) corresponding to the AlO(6) groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900 degrees C indicating the MgAl(2)O(4) spinel phase. Grain size in the range 20-30 nm were observed by measurement of transmission electron microscopy (TEM). The emission spectra of the phosphors show a broadened band at 480 nm assigned to the 4f(G)5d -> 4f(7) ((8)S(7/2)) transition of Eu(2+) ion overlapped to the (4)F(9/2) -> (6)H(15/2) transition of the Dy(3+) ion. Besides, the (4)F(9/2) -> (6)H(13/2) transition (579 nm) of Dy(3+) ion is overlapped with the (5)D(0) -> (7)F(0) (578 nm) and (5)D(0) -> (7)F(1) (595 nm) transitions from the Eu(3+) ion. Excitation spectra of the sample heated at 900 degrees C monitoring the excitation at 615 nm of (5)D(0) -> (7)F(2) transition of Eu(3+) ion exhibit a broad band assigned to the O -> Eu(3+) ligand-to-metal charge-transfer states (LMCT) around 280 nm. The samples present green persistent luminescence after exposure to UV radiation. The chromaticity coordinates were obtained from the luminescence emission spectrum. (C) 2008 Elsevier B.V. All rights reserved.

Synthesis, spectroscopic characterization and radiosensitizing properties of acetato-bridged copper(II) complexes with 5-nitroimidazole drugs

Three novel acetato-bridged dinuclear copper(II) complexes with 5-nitroimidazoles (CuAcNtrim) and the known copper-acetato-metronidazole have been prepared by an environment-friendly route and spectroscopically characterized. The CuAcNtrim compounds of formula [Cu(2)(mu-O(2)CCH(3))(4)Ntrim(2)], where Ntrim = metronidazole (1), secnidazole (2), tinidazole (3) or nimorazole (4), exhibit dimeric copper-acetato paddle-wheel structures with Ntrim axial ligands coordinated to copper(II) ions through the N(3) atoms of the imidazole rings. EPR data indicate antiferromagnetic behavior for this novel series of copper complexes. The constant coupling has been found to decrease along with the increasing of basicity of the Ntrim axial ligand. The CuAcNtrim complexes and the correspondent Ntrim parent drugs have shown radiosensitizer properties for Hep2 (human larynx cancer) cell line in vitro. The best enhancement of radiosensitizer activity upon coordination of the Ntrim drug to copper(II) has been found for the nimorazole compound which has the strongest Cu-Ntrim bond and exhibits the highest lipophilicity within the series of CuAcNtrim complexes. (C) 2010 Elsevier B.V. All rights reserved.

Synthesis, characterization and biological analysis of the complex [VO(Hdhp)(2)] (H(2)dhp=2,3-dihydroxypyridine)

A new vanadium (IV) complex with the monoanion of 2,3-dihydroxypyridine (H(2)dhp), or 3-hydroxy-2(1H)-pyridone, was synthesized, characterized by physicochemical techniques and tested biologically. The EPR data for the [VO(Hdhp)(2)] complex in DMF are: g(x) = 1.9768, g(y) = 1.9768 and g(z) = 1.9390; A values (10(-4) cm(-1)): A(x), 59.4; A(y//), 59.4; A(z), 171.0. The vV=O band in the IR spectrum of the complex is at 986 cm(-1). The complex is paramagnetic, with mu(eff) = 1.65 BM (d(1), spin-only) at 25 degrees C. The irreversible oxidation process [V(V)/V(IV)] of the [VO(Hdhp)(2)] complex, as revealed in a cyclic voltammogram, occurs at 876 mV. The calculated molecular structure of [VO(Hdhp)(2)] shows the vanadium(IV) center in a distorted square pyramidal environment, with the oxo ligand in the apical position and the oxygen donor atoms of the Hdhp ligands in the basal positions. The ability of [VO(Hdhp)(2)] to mimic insulin, and its toxicity to hepato-biliary functions, were investigated in streptozotocin-induced diabetic rats and it was concluded that the length of treatment and the amount of [VO(Hdhp)(2)] administered were effective in reducing experimental diabetes.

Double stranded DNA-binding studies of potential Rhodium(ll) antitumor complexes

In 1952, Dwyer and coworkers began testing a series of metal complexes for potential inhibition of cancer cell proliferation in animals.[l] The complexes tested were unsuitable for such studies due to their high toxicity. Therefore, no further work was done on the project. However, in 1965, Rosenberg and coworkers revisited the possibility of potential metal-based drugs. Serendipitously, they discovered that cis-diamminedichloroplatinum(lI) (cisplatin) inhibits cell division in E. coli.[2] Further studies of this and other platinum compounds revealed inhibition of tumor cell lines sarcoma 180 and leukemia LI2l0 in mice.[l] Cisplatin was approved by the Food and Drug Administration in 1970 as a chemical chemotherapeutic agent in the treatment of cancer. The drug has primarily been used in the treatment of testicular and ovarian cancers, although the powerful chemotherapeutic properties of the compound indicate use against a variety of other cancers.[3] The toxicity of this compound, however, warrants the development of other metal-based potential antitumor agents. The success of cisplatin, a transition-metal-based chemotherapeutic, opened the doors to a host of research on the antitumor effects of other transition-metal complexes. Beginning in the 1970s, researchers looked to rhodium for potential use in antitumor complexes. Dirhodium complexes with bridging equatorial ligands (Figure I) were the primary focus for this research. The overwhelming majority of these complexes were dirhodium(II) carboxylate complexes, containing two rhodium(II) centers, four equatorial ligands in a lantero formation around the metal center, and an axial ligand on either end. The family of complexes in Figure 1 will be referred to as dirhodium(II) carboxylate complexes. The dirhodium centers are each d? with a metal-metal bond between them. Although d? atoms are paramagnetic, the two unpaired electrons pair to make the complex diamagnetic. The basic formula of the dirhodium(lI) carboxylate complexes is Rh?(RCOO)?(L)? with R being methyl, ethyl, propyl, or butyl groups and L being water or the solvent in which the complex was crystalized. Of these dirbodium(II) carboxylate complexes, our research focuses on Rb la and two other similar complexes Rh2 and Rh3 (Figure 2). Rh2 is an activated form of Rhla, with four acetonitrile groups in place of two of the bidentate acetate ligands. Rh3 is similar to Rhla, with trifluoromethyl groups in place of the methyl groups on the acetate ligands.

Crown ethers : applications in inorganic synthesis

The ability of macroheterocyclic compounds to complex with ionic species has led to the synthesis and investigation of many multidentate macroheterocyclic species. The most stable complexes are formed between macrocyclic polyetheral ligands (crown ethers) with alkali or alkaline earth metal iona. There is an excellent correlation of the stability of these complexes with the size of the cation and the site of the cavity in the macrocyclic ligand. Additional factors, such as the basicity of the ligand and the solvating ability of the solvent, also play important roles in the stabilization of the complex. The stability of such complexes has been advantageously used to increase anionic reactivity and has been successfully applied to several organic fluorinations, oxidations, and similar reactions. The use of macrocyclic ligands in inorganic syntheses of otherwise difficult to obtain fluoro compounds has not been reported. O-carborane and m-carborane, C2BlOHl2, are icosahedral cage systems derived from Bl2H122- by replacement of BH with the isoelectronic CH group. These stable molecules exhibit electron-deficient bonding which can best be explained by delocalization of electrons. This delocalization gives rise to stability similar to that found in aromatic hydrocarbons. Crown ether activated potassium fluoride has been successfully employed in the conversion of alkyl, acyl and aryl halides to their respective fluorides. Analogously halide substituted carboranes were prepared, but their fluoro-derivatives were not obtained. The application of crown ethers in the synthesis of transition metal complexes is relatively unexplored. The usual synthesis of fluoro-derivative transition metal complexes involves highly reactive and toxic fluorinating agents such as antimony trifluoride, antimony penta fluoride. bromine trifluoride and hydrogen fluoride, An attempted preparation of the hexafluoroosmate (IV) ion via a crown activated, or naked fluoride~was unsuccessful. Potassium hexafluoroosmate (IV), K208F6. was eventually prepared using bromine trifluoride as a fluorinating and oxidizing agent .

Synthesis, characterization and biological analysis of the complex [VO(Hdhp)(2)] (H(2)dhp=2,3-dihydroxypyridine)

A new vanadium (IV) complex with the monoanion of 2,3-dihydroxypyridine (H(2)dhp), or 3-hydroxy-2(1H)-pyridone, was synthesized, characterized by physicochemical techniques and tested biologically. The EPR data for the [VO(Hdhp)(2)] complex in DMF are: g(x) = 1.9768, g(y) = 1.9768 and g(z) = 1.9390; A values (10(-4) cm(-1)): A(x), 59.4; A(y//), 59.4; A(z), 171.0. The vV=O band in the IR spectrum of the complex is at 986 cm(-1). The complex is paramagnetic, with mu(eff) = 1.65 BM (d(1), spin-only) at 25 degrees C. The irreversible oxidation process [V(V)/V(IV)] of the [VO(Hdhp)(2)] complex, as revealed in a cyclic voltammogram, occurs at 876 mV. The calculated molecular structure of [VO(Hdhp)(2)] shows the vanadium(IV) center in a distorted square pyramidal environment, with the oxo ligand in the apical position and the oxygen donor atoms of the Hdhp ligands in the basal positions. The ability of [VO(Hdhp)(2)] to mimic insulin, and its toxicity to hepato-biliary functions, were investigated in streptozotocin-induced diabetic rats and it was concluded that the length of treatment and the amount of [VO(Hdhp)(2)] administered were effective in reducing experimental diabetes.

Nanoparticles of octakis [3-(3-amino-1,2,4-triazole)propyl] octasilsesquioxane as ligands for Cu(II), Ni(II), Cd(II), Zn(II), and Fe(III) in aqueous solution

Nanoparticles of octakis[3-(3-amino-1,2,4-triazole)propyl]octasilsesquioxane (ATZ-SSQ) were tested as ligands, for transition-metal ions in aqueous solution with a special attention to sorption isotherms, ligand-metal interaction, and determination of metal ions in natural waters. The adsorption potential of the material ATZ-SSQ was compared with related [3(3-amino-1,2,4-triazole)propyl]silica gel (ATZ-SG). The adsorption was performed using a batchwise process and both organofunctionalized surfaces showed the ability to adsorb the metal ions from aqueous solution. The Langmuir model was used to simulate the sorption isotherms. The results suggest that the sorption of these metals on ATZ-SSQ and ATZ-SG occurs mainly by surface complexation. The equilibrium condition is reached at time lower than 3 min for ATZ-SSQ, while for ATZ-SG is only reached at time of 25 min. The maximum metal ion uptake values for ATZ-SSQ were higher than the corresponding values achieved with the ATZ-SG. In order to obtain more information on the ligand-metal interaction of the complexes on the surface of the ATZ-SSQ nanomaterial, ESR study with various degrees of copper loadings was carried out. The ATZ-SSQ was tested for the determination (in flow using a column technique) of the metal ions present in natural waters. (C) 2007 Elsevier B.V. All rights reserved.

Preconcentration and determination of metal ions in commercial ethanol used as fuel for automotive engines

The present investigation reports the synthesis, characterization, and adsorption properties of a new nanomaterial based on organomodified silsesquioxane nanocages. The adsorption isotherms for CuCl,, CoCl2, ZnCl2, NiCl2, and FeCl3 from ethanol solutions were performed by using the batchwise method. The equilibrium condition is reached very quickly (3 min), indicating that the adsorption sites are well exposed. The results obtained in the flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 2 g of the nanomaterial, using 5 mL of 1.0 mol L-1 HCl solution as eluent. The sorption-desorption of the metal ions made possible the development of a method for preconcentration and determination of metal ions at trace level in commercial ethanol, used as fuel for car engines. The values determined by recommended method for plants 1, 2, and 3 indicated an amount of copper of 51, 60, and 78 mu g L-1, and of iron of 2, 15, and 13 mu g L-1, respectively. These values are very close to those determined by conventional analytical methods. Thus, these similar values demonstrated the accuracy of the determination by recommended method.

Estudo teórico QTAIM e DFT dos compostos de coordenação: efeito quelato, titanocenos e ligação química

This work is a study of coordination compounds by quantum theory of atoms in molecules (QTAIM), based on the topological analysis of the electron density of molecular systems, both theoretically and experimentally obtained. The coordination chemistry topics which were studied are the chelate effect, bent titanocene and chemical bond in coordination complexes. The chelate effect was investigated according to topological and thermodynamic parameters. The exchange of monodentate ligands on polydentate ligands from same transition metal increases the stability of the complex both from entropy and enthalpy contributions. In some cases, the latter had a higher contribution to the stability of the complex in comparison with entropy. This enthalpic contribution is explained according to topological analysis of the M-ligand bonds where polidentate complex had higher values of electron density of bond critical point, Laplacian of electron density of bond critical point and delocalization index (number of shared electrons between two atoms). In the second chapter, was studied bent titanocenes with bulky cyclopentadienyl derivative π-ligand. The topological study showed the presence of secondary interactions between the atoms of π-ligands or between atoms of π-ligand and -ligand. It was found that, in the case of titanocenes with small difference in point group symmetry and with bulky ligands, there was an nearly linear relationship between stability and delocalization index involving the ring carbon atoms (Cp) and the titanium. However, the titanocene stability is not only related to the interaction between Ti and C atoms of Cp ring, but secondary interactions also play important role on the stability of voluminous titanocenes. The third chapter deals with the chemical bond in coordination compounds by means of QTAIM. The quantum theory of atoms in molecules so far classifies bonds and chemical interactions in two categories: closed shell interaction (ionic bond, hydrogen bond, van der Waals interaction, etc) and shared interaction (covalent bond). Based on topological parameters such as electron density, Laplacian of electron density, delocalization index, among others, was classified the chemical bond in coordination compounds as an intermediate between closed shell and shared interactions

Development of metal - SiO2 nanocomposites in a single-step process by the polymerizable complex method

This work presents the synthesis and characterization of SiO2:metal (Ni, Co, Ag, and Fe) nanocomposites processed by the polymerizable complex method. The polymeric precursor solutions obtained were characterized by means of FT-Raman and C-13 NMR spectroscopy. The results show the formation of a hybrid polymer with carbon and silicon in the macromolecule chain and the transition metal cation arrested within this polymeric chain. The nanocomposites are formed during the controlled polymeric precursor pyrolysis. The reduction of the metal cation is promoted by the CO/CO2 atmosphere resulting from the pyrolysis of the organic material. Microstructural characterization, performed by TEM and X-ray diffraction (XRD), showed that the nanocomposites are formed by metal nanoparticles embedded in a amorphous matrix formed by SiO2 and carbon. In the SiO2:Fe system, Fe3C was also detected by XRD.

Mono- and dinuclear palladium(II) compounds containing nitrogen ligands. Crystal and molecular structure of [Pd(N,C-dmba)(NCO)(2,3-lut)] and [Pd(H2CCOMe)Cl(2,2 '-bipy)]

The cyanate-bridged cyclopalladated compound [Pd(N,C-dmba)(mu-NCO)](2) (1) (dmba = PhCH2NMe2) reacts in CH2Cl2 with 2,3-lutidine (2,3- lut), 3,4-lutidine (3,4-lut), 2,2'-bipyridine (2,2'-bipy) and 4,4'-bipyridine (4,4'-bipy), to give [Pd(N, C-dmba)(NCO)(2,3-lut)] (2), [Pd(N,C-dmba)(NCO)(3,4-lut)] (3), [{Pd(N,C-dmba)(NCO)}(2)(mu-2,2'-bipy)] .CH2Cl2 (4) and [{Pd(N,C-dmba)(NCO)}(2)(mu-4,4'-bipy)] . CH2Cl2 (5), respectively. The compounds were characterized by elemental analysis, i.r. and n. m. r. spectroscopy and also by t.g.a. The i.r. spectra of (2 - 5) display typical bands of monodentate N-bonded cyanate groups, whereas the n. m. r. data of (4) are consistent with the presence of a bridging 2,2'-bipyridine ligand. Complex (4) decomposes slowly in acetone. One of the products formed, [Pd(H2CCOMe) Cl(2,2'-bipy)] (6), was characterized by X-ray diffraction. As inferred from the t.g.a., the thermal stability decreases in the order: [{Pd(N,C-dmba)(NCO)}(2) (mu-4,4'-bipy)]. CH2Cl2 (5) > [Pd(N,C-dmba)(2,3-lut)( NCO)] (2) = [Pd(N, C-dmba)(3,4-lut)(NCO)] (3) > [{Pd(N,C-dmba)(NCO)}(2)(mu- 2,2'-bipy)] .CH2Cl2 (4). According to thermal analysis and X-ray diffraction patterns compounds (2 - 3) decompose into metallic palladium Pd(0), whereas (4 - 5) decompose with the formation of PdO. The X-ray crystal and molecular structure of [Pd(N, C-dmba)( NCO)(2,3-lut)] (2) was determined. The lutidine unit is perpendicular to the coordination plane.

Trichloro-bridged diruthenium (III,III) complexes: X-ray isomorphous structures of [Ph3X=O center dot center dot center dot H center dot center dot center dot O=XPh3][Ru2Cl7(XPh3)(2)]center dot 0.5(CH2Cl2)(H2O)(X = As or P)

The triply chloro-bridged binuclear complexes [Ph3X=O...H...O=XPh3][Ru2Cl7(XPh3)(2)].0.5(CH2Cl2) (H2O) (X = As or P) were obtained from [RuCl3(XPh3)(2)DMA].DMA (DMA = dimethylacetamide) CH2Cl2/Et2O solution. The structures were characterized by X-ray diffraction studies. The complexes are formed from two Ru atoms bridged by three chloride anions. The two ruthenium atoms are also coordinated to two non-bridging Cl atoms and an AsPh3 or PPh3 ligand respectively. As an interesting feature, the cations of these complexes are protons, trapped in a very short hydrogen bond between two triphenylarsine or triphenylphosphine oxide molecules.

Cleavage of the dimeric cyclopalladated [Pd(N,C-dmba)(mu-X)](2), (dmba = N,N-dimethylbenzylamine; X = SCN and NCO) by diphosphines. Palladium(II) compounds with distinct structures in the solid-state and in solution

The reactions of the pseudohalide-bridged dimer [Pd(N,C-dmba)(mu -SCN)](2) (1) (dmba = N,N-dimethylbenzylamine) with cis-Ph2PCH=CHPPh2 (cis-dppet) (1:1 molar ratio) and of [Pd(N,C-dmba)(mu -NCO)](2) (2) with Ph2PCH2CH2PPh2 (dppe) (1:2 molar ratio) gave mononuclear [Pd(C-dmba)(SCN)(cis-dppet)].H2O (1a) and [Pd(C-dmba)(NCO)(dppe)] (2a), respectively, with the diphosphines acting as chelating ligands. Reaction of (2) with Fe(C5H4PPh2)(2) (dppf) (1:1 molar ratio) yielded [{Pd(N,C-dmba)(NCO)}(2)(mu -dppf)] (2b), a bimetallic species containing two palladium atoms bridged by the diphosphine, whereas reaction in a 1:2 molar ratio gave the mononuclear [Pd(N,C-dmba)(dppf)][NCO]. CH2Cl2 (2c), with the diphosphine acting as a chelating ligand. The compounds have been characterized by elemental analysis, i.r., P-31{H-1}, C-13- and H-1-n.m.r. spectroscopies. Conductivity measurements together with spectroscopic data showed that (1a) and (2a) do not have the same structure in the solid state and in MeCl solution, whereas for compounds (2b) and (2c) no structural changes were observed when the solids were dissolved in MeCl.