Sadaf ul Hassan

Two isomorphous 3-D lanthanide oxalatophosphonate frameworks based on glyphosate: syntheses, crystal structures, and luminescence properties

Two new 3-D isomorphous lanthanide(III) compounds [Eu2(H2L)2(C2O4)2]·2.51H2O (1) and [Tb2(H2L)2(C2O4)2]·2.46H2O (2, H3L = glyphosate), based on glyphosate and oxalate have been successfully synthesized under hydrothermal conditions, and structurally characterized. In the two compounds, tetra-connected glyphosate ligands are coordinated to Ln3+, resulting in the formation of 1-D {Ln2(H2L)2}n double chains along the c direction. Each of the chains is connected to its four neighbors via the O atoms of phosphates of H2L− ligands, resulting in a 3-D (4, 6)-connected framework with 43·58·63·7 topology, which possesses 1-D channels with oxalates and lattice water molecules as troglodytes. The oxalates are stabilized via chelating Ln3+ in the form of 1-D Ln-C2O42− zigzag chains along the c direction. To the best of our knowledge, compounds 1 and 2 represent the first single-crystal structures of lanthanide(III)-glyphosate compounds incorporating second ligands. The luminescent properties of compounds 1 and 2 have been investigated at room temperature. The energy gaps between the triplet excited state of oxalic acid and the lowest excited resonance levels of Eu3+ (5D0) and Tb3+ (5D4) are 7270 cm−1 and 4070 cm−1, respectively, indicating that oxalate is more suitable for the sensitization of Tb3+ luminescence than Eu3+ luminescence.

Polyoxometalate-based layered nano-tubular arrays: facile fabrication and superior performance for catalysis

Keggin-type polyoxoanion PW12O403−-containing one-dimensional nano-tubular arrays, with the structure polyethylenimine/polystyrenesulfonate/(poly(allylammonium)/polystyrenesulfonate)3(poly(allylammonium)/PW12O403−)8, were fabricated as a prototype using a layer-by-layer deposition technique in porous anodic aluminum oxide and polycarbonate templates with a pore diameter of 200 nm, and characterized by IR, UV-vis and SEM. The resulting nano-tubes have a uniform diameter of 180 ± 20 nm and a uniform wall thickness of 30 ± 5 nm. These arrays have shown superior performance in the UV light irradiated photo-degradation of Rhodamine B (selected as a representative dye) under mild conditions with respect to both the catalytic efficiency and operating convenience due to the confinement within the nano-tubes both in the latitudinal and radial direction. Remarkably, the catalytic activity of the nano-tubular arrays could be recovered by means of simple immersion in the polyoxoanion solution when the catalytic reactivity became reduced, which is vital in view of practical applications. The total organic carbon content changes and GC-MS measurements were conducted to identify the degradation products. The hydroxyl radical mechanism was found to be adopted by the photo-degradation reaction.

A general synthesis approach in action: preparation and characterization of polyoxomolybdenum(VI) organophosphonates through oxidative Mo–Mo bond cleavage in {MoV2O4}

Three new tetramolybdenum organophosphonate compounds, (NH4)7{FeIII[MoVI2O6CH3C(O)(PO3)2]2}·10H2O 1, (NH4)4[Na(H2O)6]{CrIII[MoVI2O6CH3C(O)(PO3)2H]2}·7.67H2O 2 and (NH4)8{MnII[MoVI2O6CH3C(O)(PO3)2]2}·9H2O 3 have been successfully synthesized by reacting metal-containing oxidants Fe2(C2O4)3, MnO4− and CrO42− with a simple aqueous solution containing {MoV2O4(H2O)6}2+, respectively, in the presence of (hydroxylethylidene) diphosphonic acid. These compounds are characterized by elemental analyses, spectroscopic methods (IR, UV-Vis, XPS), TG-DTA, single-crystal X-ray diffraction analyses (including bond valence sum calculations) and powder X-ray diffraction analysis. Single crystal X-ray diffraction analyses have revealed that Mo–Mo bonds of {MoV2O4(H2O)6}2+ are cleavaged in the oxidation reaction to form {MoVI2O6} motifs, which are concomitantly stabilized by organophosphate and linked by the resulted metal ions coming from the metal-containing oxidants and bring on the formation of compounds 1–3, whose anions have a general formula {M[MoVI2O6CH3C(O)(PO3)2]2}n−(M = FeIII1; CrIII2; MnII3). It is important that the successful synthesis and characterization of the three new compounds induces a simple yet general strategy which can be utilized for the preparation of polyoxomolybdenum(VI) organophosphonates through oxidative Mo–Mo bond cleavage with various metal-containing oxidants like FeIII, MnVII and CrVI in the presence of various organophosphonates.

Fabrication and notable optical nonlinearities of ultrathin composite films derived from water-soluble Keggin-type polyoxometalates and water-insoluble phthalocyanine

Composite films with the general formula (POM/CuTAPc)n derived from water-soluble Keggin-type polyoxometalates (POMs = H5PMo10V2O40, H4SiW12O40, H3PMo12O40 and H3PW12O40) and water-insoluble 4,9,16,23-copper tetraaminophthalocyanine (denoted CuTAPc) are successfully fabricated by a layer-by-layer self-assembly technique and systematically characterized. The structure of the polyoxometalate anions in the multilayers is kept intact; the deposition amounts of POM and CuTAPc remain constant in every adsorption cycle of the composite film assembly process. The nonlinear optical properties of the composite films were studied by a Z-scan technique at a wavelength of 532 nm and a pulse width of 7 ns. The results not only show that the composite films exhibit notable optical nonlinear self-defocusing behavior and a saturated absorption effect with the nonlinear optical absorption co-efficient β, refractive index n2, and third-order NLO susceptibility χ(3) of the films increasing with the increase in number of layers of the films, but also reveal importantly that the discrepancy of LUMO levels between CuTAPc and POMs is proportional to their third-order NLO response.

Third-order NLO properties of ultrathin films containing cationic phthalocyanine and Keggin polyoxometalates fabricated using layer-by-layer deposition from aqueous solution

Composite films with alternating layers (PAH/PSS)3(AB/POM)n (PAH = polyallylamine hydrochloride, PSS = polystyrene sulfonate) derived from Alcian Blue-tetrakis(methyl-pyridinium) chloride (abbreviated as AB) and Keggin type polyoxometalates (POM = H4SiW12O40, H3PW12O40, H3PMo12O40, H5PMo10V2O40) have been fabricated and characterized. Under laser irradiation at 532 nm with a pulse duration of 6–7 ns, a repetition rate of 10 Hz and the intensity of the light at focus E0 being 10 μJ, the composite films exhibit self-defocusing behavior and saturated absorption effects, and the nonlinear optical absorption coefficient β (m W−1) and refractive index n2 (m2 W−1) of the films are 4–5 times larger than those of pure AB solution in view of their magnitude. Interestingly, it is found that third-order NLO susceptibilities χ(3) of films are in the order of χ(3)(AB/PSS) ELUMO(PW12) > ELUMO(PMo12) > ELUMO(PMo10V2), affirming that the incorporation of different Keggin type POMs of a lower LUMO energy level with phthalocyanine molecules into multilayers could tune the NLO responses of phthalocyanine films. It is concluded that the lower LUMO level of POM than that of the phthalocyanine can stimulate the easier transformation of excited electrons from AB to the POM within the donor–acceptor system (phthalocyanine molecules acted as an electron donor while POMs as an electron acceptor in the composite films) when flashed with the laser, which is thought to be accountable for the profound third-order optical nonlinearity of the composite films.