Paloma Ovejero

Columnar discotic Pt(II) metallomesogens as luminescence multifunctional materials with chemo and thermosensor abilities

A new family of Pt(II) luminescent metallomesogens based on dicatenar pyridylpyrazolate ligands [Pt(pzR(n,n)py)2] (R(n,n) = C6H3(OCnH2n+1)2, n = 4–18) has been prepared, and their mesomorphic and photophysical properties are described. The compounds were isolated as red (n = 4–8) or yellow (n = 10–18) solids at room temperature, but the first ones were converted to yellow crystals by slow evaporation of a chloroform–acetone mixed solution. All of them behave as discotic liquid crystal materials, exhibiting hexagonal columnar mesophases (Colh) in a wide range of temperatures. Photoluminescence studies in the solid state at variable temperatures showed a high emission in the liquid crystalline phase, which was significantly red-shifted with respect to the yellow-green emission of the solid state. This photophysical change was attributed to the formation of aggregates through Pt(dz2)–Pt(dz2) interactions, thereby giving rise to the metal–metal-to-ligand charge transfers (3MMLCT) responsible for the luminescence observed. Taking advantage of these properties we have fabricated polymeric solid supports doped with the platinum complex [Pt(pzR(10,10)py)2], which can be used as temperature sensors for real technological applications. In addition, the Pt–bispyrazolate complexes and their corresponding pyrazole ligands have been proved to be useful as chemosensors towards Pd2+, Zn2+, Cd2+ and Hg2+ metal ions.

Luminescent liquid crystal materials based on unsymmetrical boron difluoride β-diketonate adducts

A strategic design based on the use of asymmetrically 1,3-alkyloxyphenyl substituted β-diketonate ligands towards the BF2 group allowed us to find unsymmetrical compounds that, in addition to a high photoluminescent quantum yield, possess a liquid crystal behaviour, which is related to the presence of the banana-shaped liquid crystal mesophases B1.

Silver pyrazole complexes with tunable liquid crystals and luminescent properties

New silver ionic complexes based on pyrazole ligands of the type [Ag(Hpz2R(n))2][A] (Hpz2R(n) = 3,5-bis(4-alkyloxyphenyl)pyrazole; R = C6H4OCnH2n+1; [A] = CH3-p-C6H4SO3− (PTS), CF3SO3− (OTf)) (type I) are liquid crystal materials exhibiting photoluminescence in the solid state, in solution and in the mesophase. By way of contrast, the related counterparts [Ag(HpzR(n))2][A] (HpzR(n) = 3-(4-alkyloxyphenyl)pyrazole; R = C6H4OCnH2n+1; [A] = CH3-p-C6H4SO3− (PTS), CF3SO3− (OTf)) (type II), containing monosubstituted pyrazole ligands, are not mesomorphic but also behave as luminescent materials. The crystalline structures of 5 and 10, as representative examples of classes I and II, have been solved. Molecular “H” or “Z” shapes, depending on the cis or trans orientation of the NH groups of the pyrazole ligands, were found, respectively. The first type gave rise to a layer-planar network, while a corrugated layer was found for complex 10, these features being related to the mesomorphic behaviour of both kinds of compounds. The mesomorphic and luminescent properties of complexes I and II were compared with those of related compounds containing the less sterically-demanding counteranions PF6−, NO3− and BF4−, described in our previous work. In all cases, the effect of the counteranions, as well as the substitution on the pyrazole groups, were analyzed for their corresponding properties.

Mesomorphism of Four-Coordinated Four-Chained Metal Complexes Based on Pyrazolylpyridine Derivatives

A homologous series of four-chained silver(I) and zinc(II) metal complexes based on the coordination of two N N′-bidentate ligands pzR2py 2-[3,5-bis(4-alkyloxy)phenyl]pyrazol-1-yl]pyridine (R = C6H4OCnH2n+1, n = 16, 18) have been synthesised. All compounds [M(pzR2py)2][A]m (M = Ag, m = 1, n = 16, 18, (1,2), (3,4), CF3 (OTf–) (5,6), (7,8); M = Zn, m = 2, n = 16, 18, (9,10)) exhibit liquid crystal properties showing enantiotropic SmA phases, independently of the starting pzR2py ligands (non-mesomorphism for n = 18 or monotropic liquid crystal for n = 16), as well as the coordination geometry. The silver(I) derivatives [Ag(pzR2py)2]+ containing and as counteranions (1–4) are four-coordinated cationic complexes, but those containing OTf– and (5–8) exhibit a five-coordinated metal environment with distorted base-square pyramidal/trigonal bipyramidal geometry involving the counteranion. For the zinc(II) related compounds [Zn(pzR2py)2][NO3]2 (9–10), the tetrahedral metal environment is also distorted by the presence of coordinative interactions with the groups. Neutral tetrahedral compounds [ZnCl2(pzR2py)] (R = C6H4OCnH2n+1, n = 16 (11), 18 (12), 1 (13)) have also been investigated. Crystal structure of the first member of this series with n = 1, [ZnCl2(pzAn2py)] (13), has been characterised by single crystal X-ray diffraction. The molecules adopt the tetrahedral coordination environment with a planar ZnNNCN core. That structure for the related compounds containing longer alkyloxy chains (11–12) suggests a rod-like molecular shape in agreement with their observed liquid crystal lamellar phases.

Tetrahedral and octahedral metallomesogenic Zn(ii) complexes supported by pyridine-functionalised pyrazole ligands

Pyridylpyrazoles with long-chained alkyloxyphenyl substituents [HpzR(n)py] (R(n) = C6H4OCnH2n+1, n = 12, 14, 16, 18) are versatile ligands for designing new zinc metallomesogens [Zn(HpzR(n)py)m][X]2 (m = 2, X = NO3−; m = 3, X = BF4−) with tetrahedral and octahedral coordination geometry, respectively. Molar conductivity measurements reveal the non-bonding character of the nitrate and tetrafluoroborate anions to Zn(II) and confirm the ionic nature of the complexes in solution. Polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) studies show that all of them are enantiotropic liquid crystals, exhibiting SmA mesophases. A layered packing with interdigitation of the alkyl chains is proposed on the basis of XRD results to explain the organisation in the SmA mesophase. TG experiments indicate that the zinc complexes are stable up to ca. 175 °C, the temperature at which mass loss is observed. On the basis of computational models using hyperchem-7 program the molecular geometry has been examined. The semi-empirical calculations suggest that, in the solid state, the counteranions could be involved in hydrogen bonds, which would contribute to obtaining the stable electronic structure.

Coordination behaviour of new dipyridylpyrazole ligands towards ZnCl2 and PdCl2 fragments. Crystalline structural characterization and multinuclear NMR studies as evidence of linkage and conformational isomers

A series of novel N,N,N-donor pyrazole based ligands of the type pypzR(n)py (R(n) = C6H4OCnH2n+1, n = 1, 12–18) (1–5) bearing two pyridine substituents at the 1- and 3-positions and an alkyloxyphenyl group at the 5-position have been prepared and characterized. The X-ray structure of pypzR(1)py is presented. Coordination of those ligands to MCl2 fragments (M = Zn, Pd) gives rise to complexes of the type [MCl2(pypzR(n)py)] (M = Zn, Pd; R(n) = C6H4OCnH2n+1; n = 1, 12–18) (6–15) which were characterized and studied in the solid state and in solution. In these compounds the ligands were highly versatile as they were metal coordinated in a N,N-bidentate, N,N,N-tridentate fashion or N,N-bidentate fashion with an additional interaction via the third active nitrogen, this different behaviour depending on the metal fragment as well as on the state (solid or in solution) in which the complexes are. The X-ray structures of [ZnCl2(pypzR(1)py)] (6) and [PdCl2(pypzR(1)py)] (11) have also been determined showing distorted trigonal bipyramid and square-planar geometries at the zinc and palladium centres, respectively. In both cases the coordination environment has been confirmed by 13C-and 15N-NMR studies in solid state. In particular, two binuclear M–M stereoisomers “Z”- and “U”-shaped may be established for the Pd derivative. The 1H and 13C-NMR studies in CDCl3 solution of (6) and (11) indicate the presence of monomeric species which exhibit the same or different bidentate coordination of the ligand, respectively, than that observed in solid state. However, DMSO-d6 causes a total dissociation of the ligand in Zn derivatives, while for the related Pd complexes two monomeric linkage isomers (N2,N1′PdCl2 and N2,N1′′PdCl2) were detected.