A Zn(II) luminescent complex with a Schiff base ligand: solution,computational and solid state studies

Abstract

A new mononuclear complex of zinc(II), [Zn(HL)₂]?2DMF (H₂L = (E)-N′-((E)-(hydroxyimino)butan-2-ylidene)salicyloylhydrazide, DMF = N,N-dimethylformamide), was prepared and characterized. Single-crystal X-ray crystallography revealed a six-coordinate zinc(II) surrounded by nitrogen of the oxime function and oxygen and distal nitrogens of the acylhydrazone group. This entity also exists in solution as demonstrated by ¹H-NMR and potentiometric titrations. The computational analysis showed that the molecular orbitals involved in the main electronic transitions of the complex species in solution are centered on the ligand with negligible contribution of the metal ion. The photophysical properties of the complex were evaluated in solution and in the solid state. Luminescence studies showed that the solid has a strong emission at 550 nm with a large Stokes shift with respect to absorption. The solid state fluorescence emission is ascribed to ligand-centered and/or ligand-to-ligand charge transfer transitions, following the DFT results in solution. A comparison with a previously reported mononuclear [Zn(HL)₂] allowed the investigation of the influence of DMF molecules in the structural packing and the luminescence properties.     

The conjugate base of malonaldehyde as antenna-ligand towards trivalent europium and terbium ions

Coordination compounds having formulae [M(MA)₃] _n and M(MA)(^Me2Tp)₂ (M = Y, Eu, Tb; MA = conjugate base of malonaldehyde; ^Me2Tp = tris(3,5-dimethyl-pyrazol-1-yl)borate) were synthesized and characterized. The photoluminescence features of the europium and terbium derivatives were investigated. By comparing the herein reported photoluminescence data with those relative to analogous nitro- and bromomalonaldehyde derivatives, it appears that the conjugate base of malonaldehyde is a more efficient antenna-ligand for the sensitization of Tb(III) luminescence. The experimental data were rationalized on the basis of DFT calculations. Tb(MA)(^Me2Tp)₂ was used as dopant for the preparation of luminescent plastic materials based on poly(methyl methacrylate).     

RuBisCO‐Inspired CO2 Activation and Transformation by an Iridium(I) Complex

The synthesis of a new iridium(I) complex containing an enamido phosphine anion (dbuP^?) and its unique reactivity with CO₂ is reported. The complex binds two equivalents of CO₂ and initiates a highly selective reaction cascade. The reaction leads to the reversible cleavage of CO₂ and the enamido ligand as well. Computational analysis points to the existence of a relatively stable Ir‐CO₂ complex as a reaction intermediate prior to CO₂ cleavage, which was confirmed experimentally. The observed transformation resembles several aspects of enzymatic CO₂ fixation by RuBisCO.     

A dichotomy in the enantioselective oxidation of aryl benzyl sulfides: A combined experimental and computational work

Pentafluorobenzyl pentafluorophenyl sulfide is oxidised with moderate e.e. value and a low yield by the usually highly successful oxidation protocol based upon tert-butyl hydroperoxide (TBHP) in the presence of a titanium/hydrobenzoin complex. This disappointing result resisted until the present work, in which the switch of the oxidation agent (from TBHP to cumene hydroperoxide), suggested by our previous computations, yielded the enantiopure sulfoxide. This valuable chiral compound was obtained in good yields (76%) without resorting to a chromatographic separation. DFT computations uncovered that this favourable reactivity was originated by a stabilizing π?π?stacking between the phenyl group of the oxidant and the pentafluorophenyl moiety of the substrate.     

A Note on Two-Weight Inequalities for Maximal Functions and Singular Integrals

We deal with weighted inequalities of the type [formula] where: T is either the Hardy–Littlewood maximal operator or asingular integral operator; G is any measurable subset of Rⁿ; f is any measurable function, vanishing outside G, such thatTf is well-defined; v and w are weights, that is, nonnegativelocally integrable functions on G; p, q(1, ). 1991 Mathematics Subject Classification 42B20, 42B25.     

A finiteness theorem for low-codimensional nonsingular subvarieties of quadrics

We prove that there are only finitely many families of codimension two nonsingular subvarieties of quadrics which are not of general type, for and . We prove a similar statement also for the case of higher codimension.

     

Poincaré-Invariant Markov Processes and Gaussian Random Fields on Relativistic Phase Space

We give a complete characterization, including a Lévy–Itô decomposition, of Poincaré-invariant Markov processes on , the relativistic phase space in 1+1 spacetime dimensions. Then, by means of such processes, we construct Poincaré-invariant Gaussian random fields, and we prove a no-go theorem for the random fields corresponding to Brownian motions on .