Preparation, spectroscopic and structural study of copper(II) complexes derived from bulky pyridine ligands

Three different binuclear tetracarboxylato-bridged copper(II) complexes supported by bulky pyridines ligands [Cu(m-MeCO2)2(dPy)]2 (dPy = 3-phenylpyridine (1), 2-benzylpyridine (2) and 4-acetylpyridine (3)) have been synthesised. These compounds were obtained from reaction of [Cu(MeCO2)2(H2O)]2 with pyridine-derived ligands in methanol at room temperature. All compounds were fully characterized by analytical and spectroscopic methods. The molecular structures were determined by X-ray diffraction analysis. All compounds consist of binuclear units where both Cu(II) atoms are linked by four syn-syn carboxylates bridges, showing a paddle-wheel unit, and exhibit interesting intermolecular interactions in the outer coordination sphere

Mononuclear and binuclear copper(II) bis(1,3-benzodioxole-5-carboxylate) adducts with bulky pyridines

Copper(II) bis(1,3-benzodioxole-5-carboxylate) adducts with bulky pyridines have been prepared from the reaction of copper(II) acetate with 1,3-benzodioxole-5-carboxylic acid (piperonylic acid, HPip) and an excess of pyridine derivatives (3-phenylpyridine, 3-Phpy, 4-phenylpyridine, 4-Phpy, or 4-benzylpyridine, 4-Bzpy). Using 3-Phpy or 4-Bzpy binuclear paddle wheel compounds ([Cu(μ-Pip)2(3-Phpy)]2 (1) and [Cu(μ-Pip)2(4-Bzpy)]2 (3), and mononuclear complexes [Cu(μ-Pip)2(3-Phpy)2(H2O)] (2) and {[Cu(Pip)2(4-Bzpy)2]}{[Cu(Pip)2(4-Bzpy)2](HPip)}·{4A}{4B} have been isolated. Mononuclear 2 can also be produced from 1 in presence of an excess of 3-Phpy, while low thermal treatment of 2 at 70 °C, in absence of solvent, reverts to the formation of 1. On the other hand, 4 presents a singular structure that contains two independent mononuclear units {4A} and {4B}. Working with 4-Phpy yields crystalline binuclear [Cu(μ-Pip)(Pip)(4-Phpy)2]2·4CH3OH (5). In this complex only half of the carboxylate ligands bridge copper atoms, being one of the rare examples of this flat core. Its crystal structure contains a significant fraction of volume filled with methanol that is partly lost simply by exposing the solid to air. However, this process is related to an irreversible structure collapse, showing that the intermolecular interactions after methanol removal are not enough to support a porous structure

Solvent-controlled formation of monomeric and dimeric species containing Cu(II) acetate and 4-phenylpyridine

Three copper(II) acetate complexes with 4-phenylpyridine (4-Phpy), namely [Cu(MeCO2)2(4- Phpy)2(H2O)2] (1), [Cu(MeCO2)2(4-Phpy)2(H2O)1.5] (2) and [Cu(MeCO2)2(4-Phpy)]2 (3), were synthesized and characterized by analytical and spectroscopic methods. Experimental conditions as solvent or temperature determine the species obtained. Crystal and molecular structure of 2 was determined by Xray diffraction. Compound 2 presents a singular structure, containing two crystallographic independent mononuclear units [Cu(MeCO2)2(4-Phpy)2(H2O)2] (2A) and [Cu(MeCO2)2(4-Phpy)2(H2O)] (2B) in its unit cell and each of these forms an independent 1-D chain through H-bonding

Cu(II) 4-phenoxybenzoate dimers and monomer coordinated by pyridines: synthesis and crystal structures

The complexes [Cu(PhOBz)2(dPy)]2 (PhOBz = 4-phenoxybenzoate; dPy = pyridine (1), 3-phenylpyridine (2), 4-benzylpyridine (3) and 4-phenylpyridine (4) and the complex [Cu(PhOBz)2(4-Phpy)2(H2O)] (5) were prepared and fully characterized. X-ray crystal structures of the five complexes have been determined. Complexes 1-4 consist of binuclear units where both Cu(II) are linked by four syn-syn carboxylate bridges, showing a paddle-wheel unit. The compound 5 is mononuclear and the metal center is coordinated to two PhOBz in monodentate form, two 4-Phpy ligands and one H2O molecule with slightly distorted square pyramidal geometry. Finally, the magnetic properties of compounds 3 and 5 have also been studied, confirming the different strength interactions between Cu(II) cations

Modulating p-hydroxycinnamate behavior as a ditopic linker or photoacid in copperth) 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

Diverse Structures and Dimensionalities in Zn(II), Cd(II), and Hg(II) Metal Complexes with Piperonylic Acid

Reaction of M(MeCO2)2 (M = Zn(II), Cd(II), and Hg(II)) with 1,3-benzodioxole-5-carboxylic acid (HPip) in methanol (MeOH) yields four piperonylate compounds, one of Zn(II) ([Zn(Pip)2(H2O)2] (1c)), two of Cd(II) ([Cd(μ-Pip)2(H2O)]n (2) and [Cd3(μ-Pip)6(MeOH)2]n (3)), and one of Hg(II) ([Hg(μ-Pip)2]n (4)). The obtention of compounds 1c and 4 was independent of the M/L ratio. These four compounds were characterized by analytical and spectroscopic techniques. In addition, the thermal stability of 1c, 2, and 4 has been studied, and the structure of all the complexes has been determined by the single crystal X-ray diffraction method. The Zn(II) compound displayed a monomeric structure, while Cd(II) and Hg(II) complexes exhibited three polymeric arrays. The Zn(II) (1c) and Hg(II) (4) centers are four- and eight-coordinated in a tetrahedral or squareantiprism geometry, respectively. Furthermore, the Cd(II) ions are either six- (2) or six- and seven- (3) coordinated in a octahedral or both octahedral and pentagonal bipyramid geometries, respectively. In these compounds, the Pip ligand presents different coordination modes: μ1-η1 (1c); μ2-η1:η1 and μ2-η2:η1 (2); μ2-η1:η1, μ2-η2:η1 and μ3-η2:η1:η1 (3); μ1-η2 and μ2-η2:η1 (4). The extended structures were also analyzed. Their photoluminescence properties have been examined, and the quantum yields have been calculated

Zn(II) and Cd(II) Coordination Dimers Based on Mixed Benzodioxole-Carboxylate and N-Donor Ligands: Synthesis, Characterization, Crystal Structures and Photoluminescence Properties

Four new compounds, formulated as [Zn(m-Pip)2(3-Phpy)]2 (1), [Zn(m-Pip)2(4-Phpy)]2 (2), [Cd(m-Pip)(Pip)(3-Phpy)2]2 (3) and [Cd(m-Pip)(Pip)(4-Phpy)2]2 (4) (HPip=1,3-benzodioxole-5-carboxylic acid; Phpy= phenylpyridine), have been successfully assembled based on rigid carboxylate/pyridine ligands. These four compounds have been fully characterized by analytical and spectroscopic methods. The aim of the present study is to investigate the structural effect and the influence of the size of metal on the class, geometry and type of coordination of the carboxylate ligands (syn-syn, syn-anti) in the final 3D-arrangements of the structures. Finally, luminescence properties of these new four coordination dimers have been investigated

Synthesis, crystal structure and magnetic properties of a Cu(II) paddle-wheel complex with mixed bridges

The synthesis and characterization of a mixed carboxylate paddle-wheel copper complex, with formula [Cu(μ- Pip)(μ-MeCO2)(MeOH)]2 (Pip = piperonylate or 1,3-benzodioxole-5-carboxylate and MeCO2 = acetate), is here reported. The described compound is a binuclear complex, each pair of similar carboxylate ligands occupyingmutually trans bridging positions,while the methanol occupies the apical positions. The dimers are arranged into 2D layers in the bc plane through a network of O-H⋯O hydrogen bonds established between themethanol and the acetate ligand. Magnetic studies showed a strong antiferromagnetic Cu⋯Cu interaction (J = −308 cm−1), in agreement with the presence of four μ-κO-κO′ carboxylates bridging the metallic centers in the binuclear complex

Synthesis and characterization of three new Cu(II) paddle-wheel compounds with 1,3-benzodioxole-5-carboxylic acid

Three different paddle wheel compounds have been synthesized, each one via a different synthetic pathway. The first method is the reaction of Cu(MeCO2)2 H2O with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) in a MeOH solution, yielding [Cu(m-Pip)2(MeOH)]2 (1). The second method is the transformation of the heteroleptic core paddle-wheel compound [Cu(m-MeCO2)(m-Pip)(MeOH)]2 into the homoleptic core paddle-wheel [Cu(m-Pip)2(DMSO)]2 2DMSO (2). Lastly, the third method is the substitution of the solvent molecule (DMF) present in the molecular array [Cu(m-Pip)2(DMF)]2 by 2-benzylpyridine (2-Bzpy) ligand, resulting in [Cu(m-Pip)2(2-Bzpy)]2 2.5MeOH H2O (3a). All compounds are characterized via EA, PXRD, ATR-FTIR, Far-IR and UV-Vis spectroscopy. For all three compounds, the X-ray crystal structure has been determined and their extended structures are discussed. Finally, TG/DTA measurements have been recorded

The challenges and possibilities of reflective learning in higher education. Research focused from the perspective of university students on four different degree courses

Despite an increase in university teaching practices based on reflective learning methodology (RL), only very few studies are found in the context of higher education aimed at determining students? perception of this approach to teaching and learning. The aim of this research was to ascertain the opinions of students on different university degree courses regarding the challenges, difficulties and contributions arising from the application of reflective learning methodology in their learning process so as to propose strategies for improving education. The study was carried out on four Bachelor degree courses at the University of Girona: Social Education, Environmental Sciences, Nursing and Psychology. The research was conducted in two stages. In the first (2011-12 academic year), a questionnaire was administered to 162 students (43 from Social Education; 33 from Environmental Sciences; 31 from Nursing; and 55 from Psychology). One section of the questionnaire was specifically devoted to studying the perceptions of students participating in various RL experiences regarding the main difficulties they faced and the contributions of the RL to their learning process. Among the highlighted difficulties was the fact that RL requires a work process they are not used to and their lack of reflective writing skills. Among the contributions, the students felt that RL results in more complex and selfregulated knowledge, develops greater dynamic capabilities and increases the degree of reflection on learning processes and areas for improvement. In the second stage of the study (2012-13 academic year), four focus groups were held with students who had participated in the previous years? experience with the aim of gaining further insight into their perceptions regarding the challenges and contributions of RL. A total of 20 students participated, all of whom gave informed written consent. The sessions were recorded and transcribed in full and a thematic content analysis was performed. In all four groups the students stated that the experience had allowed them to improve their learning and become aware of their current situation and areas for improvement. As for the challenges, they cited difficulties in understanding the aims and purpose of RL, particularly at the beginning of the experience, together with problems experienced in writing about it, doubts about the level of openness required and uncertainty about how they would be assessed. The research conducted suggested that RL has significant potential to connect academic activity with professional action. It also provided working guidelines for improving experiences carried out on the basis of RL. These include the need to clarify the methodology and present arguments for its use, so that students understand the type of work it will mean for them and the objectives they pursued. Students should also be provided with sufficiently clear guidelines regarding how they will be assessed (in relation to both activities and level of reflection). There is a need to build a group climate based on mutual trust, continuous feedback and the establishment of a support process that maintains this trust throughout the learning process