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

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

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

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

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

Syntheses, supramolecular architectures and photoluminescence properties of Zn(II) complexes based on 3,5-dihydroxybenzoic and pyridine/pyrazole derived ligands

Five new coordination compounds [Zn(μ‑3,5‑DHB)2(H2O)2]n (1a), [Zn(μ‑3,5‑DHB)(μ‑OH2) (H2O)2]n·(3,5‑DHB)n·(4H2O)n (1b), [Zn(3,5‑DHB)2(Isna)2]·2H2O (2), [Zn(3,5‑DHB)2(4‑Acpy)2]·3H2O (3) and [Zn (3,5‑DHB)2(3‑Mepz)2]·H2O (4) (3,5‑HDHB=3,5‑dihydroxybenzoic, Isna=isonicotinamide, 4‑Acpy=4‑acetylpyridine and 3‑Mepz=3‑methylpyrazole) were synthesized in water or water-methanol as solvents. All these compounds have been characterized by elemental analysis, FTIR-ATR and 1H NMR spectroscopies and Powder X-ray diffraction (PXRD). For compounds 1b-4, X-ray crystal structures have been determined. In these compounds, 3,5‑DHB ligand displays different coordination modes. Complex 1b is a coordination polymer, while the addition of the pyridine/pyrazole ligands in the reaction provokes the formation of monomeric compounds (2-4). Moreover, the crystal packing indicates that these complexes expand into 2D/ 3D network structures mainly by intermolecular hydrogen bond interactions. Finally, the photoluminescent properties of these complexes in solid state have also been investigated. The strong emission observed for 1b indicates that it may be a good candidate for photoluminescent devices

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

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