Supercritical CO2 Synthesis of Porous Metalloporphyrin Frameworks: Application in Photodynamic Therapy.

A series of porous metalloporphyrin frameworks prepared from the 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) linker and four metal complexes, M(hfac)2 M = Cu(II), Zn(II), Co(II), and Ni(II) (hfac: 1,1,1,5,5,5-hexafluoroacetylacetonate), were obtained using supercritical CO2 (scCO2) as a solvent. All the materials, named generically as [M-TPyP] n , formed porous metal-organic frameworks (MOFs), with surface areas of ∼450 m2 g-1. All MOFs were formed through the coordination of the metal to the exocyclic pyridine moieties in the porphyrin linker. For Cu(II), Zn(II), and Co(II), incomplete metal coordination of the inner pyrrole ring throughout the structure was observed, giving place to MOFs with substitutional defects and leading to a certain level of disorder and limited crystallinity. These samples, prepared using scCO2, were precipitated as nano- to micrometric powders. Separately, a layering technique from a mixture of organic solvents was used to crystallize high-quality crystals of the Co(II) based MOF, obtained with the formula [{Co(hfac)2}2H2TPyP] n . The crystal structure of this MOF was elucidated by single-crystal synchrotron X-ray diffraction. The Zn(II)-based MOF was selected as a potential photodynamic therapy drug in the SKBR-3 tumoral cell line showing outstanding performance. This MOF resulted to be nontoxic, but after 15 min of irradiation at 630 nm, using either 1 or 5 µM concentration of the product, almost 70% of tumor cells died after 72 h.

Tuning Photophysical Properties by p-Functional Groups in Zn(II) and Cd(II) Complexes with Piperonylic Acid.

Aggregation between discrete molecules is an essential factor to prevent aggregation-caused quenching (ACQ). Indeed, functional groups capable of generating strong hydrogen bonds are likely to assemble and cause ACQ and photoinduced electron transfer processes. Thus, it is possible to compare absorption and emission properties by incorporating two ligands with a different bias toward intra- and intermolecular interactions that can induce a specific structural arrangement. In parallel, the π electron-donor or electron-withdrawing character of the functional groups could modify the Highest Ocuppied Molecular Orbital (HOMO)-Lowest Unocuppied Molecular Orbital (LUMO) energy gap. Reactions of M(OAc)2·2H2O (M = Zn(II) and Cd(II); OAc = acetate) with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) and 4-acetylpyridine (4-Acpy) or isonicotinamide (Isn) resulted in the formation of four complexes. The elucidation of their crystal structure showed the formation of one paddle-wheel [Zn(µ-Pip)2(4-Acpy)]2 (1); a mixture of one dimer and two monomers [Zn(µ-Pip)(Pip)(Isn)2]2·2[Zn(Pip)2(HPip)(Isn)]·2MeOH (2); and two dimers [Cd(µ-Pip)(Pip)(4-Acpy)2]2 (3) and [Cd(µ-Pip)(Pip)(Isn)2]2·MeOH (4). They exhibit bridged (1, µ2-η1:η1), bridged, chelated and monodentated (2, µ2-η1:η1, µ1-η1:η1 and µ1-η1), or simultaneously bridged and chelated (3 and 4, µ2-η2:η1) coordination modes. Zn(II) centers accommodate coordination numbers 5 and 6, whereas Cd(II) presents coordination number 7. We have related their photophysical properties and fluorescence quantum yields with their geometric variations and interactions supported by TD-DFT calculations.

Single molecule magnets of cobalt and zinc homo- and heterometallic coordination polymers prepared by a one-step synthetic procedure.

The synthesis of 1D cobalt and zinc monometallic and heterometallic coordination polymers (CPs) was carried out applying one-pot synthetic methods by using either supercritical carbon dioxide or ethanol as the solvent. A collection of four 1D CPs were thus obtained by the combination of a metal (or a mixture of metals) with the linker 1,4-bis(4-pyridylmethyl)benzene. The used metallic complexes were zinc and cobalt hexafluoroacetylacetonate, which can easily incorporate pyridine ligands in the coordination sphere of the metal centre. Independently of the used solvent, the precipitated phases involving Zn(ii), i.e., homometallic CP of Zn(ii) and bimetallic CP of Zn(ii)/Co(ii), were isostructural. Contrarily, homometallic CPs of Co(ii) were precipitated as an isostructural phase of Zn(ii) or with a different structure, depending on the used solvent. All the structures were resolved by XRD using synchrotron radiation. In addition, the magnetic properties of the new CPs involving Co(ii) were studied. Remarkably, at low temperatures with the application of an external field, they acted as field-induced single molecule magnets.

Modulating p-hydroxycinnamate behavior as a ditopic linker or photoacid in copper(ii) complexes with an auxiliary pyridine ligand.

The reaction of copper(ii) acetate monohydrate with p-hydroxycinnamic acid (HpOHcinn) and different pyridine derivatives (4-tert-butylpyridine, 4-tBupy; 4-acetylpyridine, 4-Acpy; 3-phenylpyridine, 3-Phpy; 4-phenylpyridine, 4-Phpy) was essayed in methanol solvent at room temperature. The crystal structures of the resulting compounds were elucidated. Their analysis shows that the choice of pyridine ligands determines different coordination modes of the pOHcinn ligand and the Cu(ii) coordination, nuclearity and geometry. The pOHcinn acts as a monodentate carboxylate ligand in combination with 4-tBupy or 4-Phpy, yielding monomers and dimers, associated by hydrogen bonds into supramolecular networks in which the phenol group plays a key role. Conversely, in combination with 4-Acpy or 3-Phpy, the phenol group coordinates directly to the Cu(ii), acting as a ditopic ligand and yielding 2D coordination polymers. The compound containing 3-Phpy shows interesting MeOH-H2O reversible exchange behavior. Not only has the pyridine auxiliary ligand had a tremendous effect on the coordination mode of pOHcinn, but also its reactivity is influenced. Particularly, in the case of the compound containing 4-Phpy, it undergoes a photoinduced process, in which the phenol group deprotonates and coordinates to Cu(ii) as a phenoxy ligand. This yields a coordination polymer in which two different dimers alternate, bridged by the resulting pOcinn ligand. The magneto-structural correlation of this compound is also discussed.

Solution processable titanium dioxide precursor and nanoparticulated ink: application in Dye Sensitized Solar Cells.

Colloidal TiO2 anatase nanoparticles of 4-8 nm diameter capped with 3,6,9-trioxadecanoic acid (TODA) were synthesized at low temperature using water and ethanol as the solvents. ATR-FTIR and (1)H NMR characterization showed the capping acid capability of stabilizing the TiO2 nanoparticles through labile hydrogen bonds. The presence of the capping ligand permitted the further preparation of homogeneous and stable colloidal dispersions of the TiO2 powder in aqueous media. Moreover, after solvent evaporation, the ligand could be easily eliminated by soft treatments, such as UV irradiation or low-temperature thermal annealing. These properties have been used in this work to fabricate mesoporous TiO2 electrodes, which can be applied as photoanodes in Dye Sensitized Solar Cells (DSSCs). For the preparation of the electrodes, the as-synthesized mesoporous TiO2 nanoparticles were mixed with commercial TiO2 (Degussa P25) and deposited on FTO substrates by using the doctor blade technique. A mixture of water and ethanol was used as the solvent. A soft thermal treatment at 140 °C for 2h eliminated the organic compound and produced a sintered mesoporous layer of 6 µm thickness. The photovoltaic performance of the DSSCs applying these electrodes sensitized with the N3 dye resulted in 5.6% power conversion efficiency.

Synthesis and characterization of a novel sodium transition metal oxyfluoride: NaMnMoO3F3·H2O.

NaMnMoO3F3·H2O was precipitated at low temperature from aqueous dissolutions of Na2MoO4·2H2O in aqueous HF (or NaHF2) using either Mn(CH3COO)2·4H2O or MnF2 as manganese precursors. Chemical analysis, IR spectra, and effective paramagnetic moment are in agreement with the proposed formula. Electron microscopy studies indicate that the sample is constituted of very thin plate-like microcrystals. The average crystal structure (a = 3.5947(1), b = 21.246(1), and c = 7.3893(2) Å and Cmcm (No. 63) SG) has been elucidated through powder diffraction methods (synchrotron and neutron). Tiny superstructure peaks are observed that can be indexed with the space group Pbca and cell parameters a = 7.1894(2), b = 21.246(1), and c = 7.3893(2) Å. Electron diffraction confirms the doubling of a parameter. Ordering of O and F is proposed in agreement with Pauling's second crystal rule and bond strength sums for each anionic position. The structure that is formed has a layered stacking arrangement along the b-axis of the MnO4F2 octahedra layers that share corners along a- and c-directions. The large interlayer space contains MoO4F2 octahedra (connected to the layer) together with sodium ions and water molecules, tentatively forming hydrogen bonding with fluorine anions. The origin of the superstructure could not be fully elucidated, but it is presumably related to slight distortions within the MnO4F2 octahedra.

Zirconium-doped and silicon-doped TiO2 photocatalysts synthesis from ionic-liquid-like precursors.

Nanocrystalline titania powders doped with either zirconium or silicon were synthesized at low temperature via destabilization of ionic-liquid-like precursors. Titania materials prepared at low temperature (85 degrees C) consisted of anatase nanocrystals of about 25 nm, according to powder X-ray diffraction and transmission electron microscopy. Dopant incorporation was evaluated using inductively coupled plasma-optical emission spectrometry, and it was found that dopant/titanium ratios in the powder (0.011 for Zr and 0.026 for Si) were lower than those in the precursor (0.11 for both). Low-temperature nitrogen adsorption-desorption isotherms displayed the characteristic hysteresis loop of mesoporous materials. Specific surface areas reached values of 130 and 155 m(2) g(-1) for Zr-doped and Si-doped TiO(2), respectively. The photocatalytic activity of the synthesized nanopowders was tested using methyl orange and 4-chlorophenol as target pollutants.

Hexafluorotitanate salts containing organic cations: use as a reaction medium and precursor to the synthesis of titanium dioxide.

The straightforward modification of commercial hexafluorotitanic acid with organic derivatives containing a tetraalkylammonium cation produced stable precursor solutions with only a small fraction of water, which were then used as a reaction medium for the synthesis of nanocrystalline TiO(2).

Aluminium(III) adsorption: a soft and simple method to prevent TiO2 deactivation during salicylic acid photodegradation.

Deposition of poisoning species on TiO2 during salicylic acid photodegradation can be halted when Al(III) has been previously adsorbed on the catalyst surface; this widens the application of photocatalysis to more concentrated solutions.

How green is a chemical reaction? Application of LCA to green chemistry.

In the present work Life Cycle Assessment (LCA) is used in order to evaluate a chemical reaction from an environmental point of view. The objective is to assess the usefulness of this methodology as an environmental tool to be applied to green chemistry. As an example, two routes of obtaining maleic anhydride are compared using LCA, to ascertain which one is the most environmentally friendly. From the results obtained in this work it can be concluded that LCA seems to be a valuable tool for the environmental assessment of a chemical reaction, because it takes into account all the life cycle stages of the process and discusses the impact of the environmental burdens inventoried according to a diversity of impact categories.

Crystal Structure and Magnetic Behavior of [(C(2)H(5))(4)N](2)Cu(5)Cl(12). A Novel Two-Dimensional Copper(II) Halide Network Derived from the CuCl(2) Structure.

A new chlorocuprate(II), [(C(2)H(5))(4)N](2)Cu(5)Cl(12), was prepared by reaction of CuCl(2).2H(2)O and (C(2)H(5))(4)NCl in 1,1,2-trichloroethane-ethanol followed by water-ethanol evaporation. The crystal structure, solved by single-crystal X-ray diffraction at room temperature, was found to be triclinic, space group P&onemacr;, with cell parameters a = 8.9123(9) Å, b = 11.0690(8) Å, c = 11.2211(9) Å, alpha = 118.766(6) degrees beta = 109.041(8) degrees, gamma = 97.465(7) degrees, and Z = 1, and consists of a two-dimensional network of [(Cu(5)Cl(12))(2)(-)](infinity) parallel to the a, b plane, alternating with layers of the organic cations along c. The anionic sheets are built up by aggregation of infinite zigzag chains of alternating tetranuclear and mononuclear subsequences. This structure can be related to the anhydrous CuCl(2) structure by systematic removal of (Cu(2)Cl(6))(2+) fragments. The magnetic susceptibility of this compound can be described by a simple model, suggested by the structural data, that considers independent contributions of linear tetramers, with antiferromagnetically coupled pairs of copper atoms (J(1)/k = -64(2) K), and almost magnetically isolated Cu(II) centers, that obey a Curie-Weiss law with a Θ = -2.7(8) K.