Synthesis and characterization of single crystals of the layered copper hydroxide acetate Cu2(OH)3(CH3COO)·H2O

Waste-Derived Copper Flakes for Solvent-Free Reductive Acetamidation of Nitroarenes

Herein, waste-derived copper (Cu) flakes have been used as heterogeneous catalysts for the solvent-free and one-pot reductive acetamidation of nitroarenes. Metallic copper flakes (f-ZCu) were isolated from waste copper Cu scrap/flakes/turnings generated after the grinding and cutting (from the Cu industries). f-ZCu is being used to synthesize acetanilide with a considerable yield (∼82%) in one-step and solvent-free conditions within a reaction time of 6 h. Moreover, the same procedure is also being utilized for producing various substrates (9), including the gram-scale synthesis of the well-known important antipyretic drug, i.e., paracetamol. The plausible mechanism for the reaction was also proposed based on the spectroscopic analyses of spent f-ZCu.

Facile Synthesis of Novel Short-Chain Ligand-Capped Colloidal Metal Oxide Nanoparticles for Printed Flexible Devices

Colloidal metal oxide nanoparticles are key materials for achieving cost-effective and large-scale production of flexible devices, as they enable the formation of functional oxide thin films at low temperatures (<400 °C) through printing techniques such as inkjet printing, gravure coating, and microcontact printing. The conventional solvothermal synthesis of colloidal metal oxide nanoparticles through the thermal decomposition of precursors results in particles with bulky, long-chain ligands on their surfaces, which hinder the formation of dense oxide films when depositing the colloidal metal oxide nanoparticles. Herein, we have developed a simple and versatile method for synthesizing colloidal metal oxide nanoparticles using base-induced hydrolysis and the condensation of metal acetates as precursors. Various binary and ternary colloidal metal oxide nanoparticles (CuO, Mn3O4, Co3O4, CeO2, In2O3, Co1.8Mn1.2O4) were synthesized using short-chain acetate ligands on their surfaces. The thin acetate ligand-containing colloidal Co1.8Mn1.2O4 nanoparticle film exhibited lower resistivity than the same with long-chain oleate ligands. The films coated onto a polyimide substrate formed a flexible negative temperature coefficient thermistor that exhibited the temperature dependence of resistance comparable to bulk materials with a bending durability of up to 5 mm radius. These findings highlight the effectiveness of utilizing colloidal metal oxide nanoparticles with short-chain ligands in flexible devices.

Incorporation of Photo- and Thermoresponsive N-Salicylidene Aniline Derivatives into Cobalt and Zinc Layered Hydroxides

In search of new multifunctional hybrid materials and in order to investigate the influence of chemical modification on the possible synergy between properties, the carboxylate and sulfonate derivatives of photo- and thermochromic N-salicylidene aniline were successfully inserted into Co(II)- and Zn(II)-based layered simple hydroxides, resulting in four novel hybrids: Co-N-Sali-COO, Co-N-Sali-SO3, Zn-N-Sali-COO, and Zn-N-Sali-SO3. All synthesized hybrids adopt a double organic layered configuration, which prevents the cis-trans photoisomerization ability of N-Sali-R molecules in the hybrids. However, the Zn hybrids exhibit fluorescence upon exposure to UV light due to the excited-state intramolecular proton transfer (ESIPT) mechanism. The thermally stimulated keto-enol tautomerization of N-salicylidene aniline in the hybrids was related with the changes in interlamellar spacings observed by temperature-dependent PXRD. This tautomerization process was prominently evident in the Co-N-Sali-SO3 hybrid (about 11% increase in d-spacing upon decreasing the temperature to -180 °C). Finally, the Co-N-Sali-R hybrids exhibit the typical magnetic behavior associated with Co(II)-based LSHs (ferrimagnetic ordering at TN = 6.8 and 7.7 K for Co-N-Sali-COO and Co-N-Sali-SO3, respectively). This work offers insights into isomerization in LSHs and the ESIPT mechanism's potential in new luminescent materials and prospects for designing new multifunctional materials.

Layered Copper Hydroxide Salts as Catalyst for the “Click” Reaction and Their Application in Methyl Orange Photocatalytic Discoloration

The 1,2,3-triazoles are an important class of organic compounds that are found in a variety of biologically active compounds. The most usual and efficient methodology to synthetize these compounds is the Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC), preferably by use of click chemistry principles. Therefore, the development of simple, robust, easily accessible and efficient materials as catalysts for this kind of reaction is highly desirable. In this sense, layered hydroxide salts (LHS) emerge as an interesting alternative for the click reaction. Thus, we describe herein the preparation and characterization of copper (II) layered hydroxide salts and their application as catalysts for the CuAAC reaction under solvent-free conditions. This synthetic methodology of CuAAC reaction is attractive as it follows several concepts of green chemistry, such as being easy to perform, allowing purification without chromatographic column, the process forming no sub-products, affording the desired 1,2,3-traizoles in the specific 1,4-disubstituted position in high yield, and having a short reaction time. Moreover, the photocatalysis for the degradation of methyl orange was also highly efficient using the same catalyst.

Formation of Copper Oxide Nanotextures on Porous Calcium Carbonate Templates for Water Treatment

The necessity of providing clean water sources increases the demand to develop catalytic systems for water treatment. Good pollutants adsorbers are a key ingredient, and CuO is one of the candidate materials for this task. Among the different approaches for CuO synthesis, precipitation out of aqueous solutions is a leading candidate due to the facile synthesis, high yield, sustainability, and the reported shape control by adjustment of the counter anions. We harness this effect to investigate the formation of copper oxide-based 3D structures. Specifically, the counter anion (chloride, nitrate, and acetate) affects the formation of copper-based hydroxides and the final structure following their conversion into copper oxide nanostructures over porous templates. The formation of a 3D structure is obtained when copper chloride or nitrate reacts with a Sorites scaffold (marine-based calcium carbonate template) without external hydroxide addition. The transformation into copper oxides occurs after calcination or reduction of the obtained Cu₂(OH)₃X (X = Cl⁻ or NO₃⁻) while preserving the porous morphology. Finally, the formed Sorites@CuO structure is examined for water treatment to remove heavy metal cations and degrade organic contaminant molecules.

Aggregated manganese complex-nanolayered manganese oxide: a new hybrid molecular-inorganic material

Layered materials such as clays, layered double hydroxides, and layered hydroxides are promising compounds for material science applications because, in addition to their structural and functional properties, the aggregation of these compounds with others results in new structural and functional characteristics. Notably, the aggregation of a metal complex and nanolayered material leads to new structures and properties. Mn oxides and complexes are different compounds, which show promising properties. Herein, a new hybrid molecular-inorganic material was synthesized by the aggregation of a manganese complex with a 2,4,6-tris(2-pyridyl)-1,3,5-triazine ligand and monolayers of Mn oxide. This new hybrid molecular-inorganic material was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, microanalysis, UV-Vis spectroscopy, nitrogen adsorption-desorption isotherm, magnetic properties, and electron paramagnetic resonance spectroscopy. All these methods showed that the aggregation of the manganese complex and layered Mn oxide occurred. A larger extent of aggregation for this hybrid molecular-inorganic material was observed compared to monolayered Mn oxide. The new material constitutes a new family of hybrid molecular-inorganic materials, in which transition metal complexes could be placed in a new environment.

Tracing the Alteration of Verdigris Pigment through Combined Raman Spectroscopy and X-ray Diffraction, Part II: Natural Ageing

This study explores the natural alteration of verdigris, both in the form of neutral verdigris (Cu(II) (CH3COO)2⋅H2O) and basic verdigris (Cu(II) x (CH3COO) y (OH) z ⋅nH2O), through combined Raman spectroscopy and X-ray diffraction investigation of samples created seven to eleven years prior to analysis. The naturally aged paint films of neutral or basic verdigris in gum arabic on paper and parchment provide insight into the pigment’s well-known instability relevant to historical works in aqueous media on maps, prints, books and manuscript materials. The latter historical application is an area that has received far less attention than alteration of verdigris in oil-based paint films. Findings shed new light on alternate pathways for conversion of neutral verdigris to basic verdigris, including the formation of a previously unknown form of verdigris and amorphous material on alkaline paper substrates. Additionally, we demonstrate for the first time that copper hydroxyl chlorides can form in situ from neutral verdigris, in this case on parchment that has a chlorine-rich surface. These results advance our understanding of neutral verdigris alteration, and complement results from our prior artificial ageing study. Both studies point to neutral verdigris as the historically more important form throughout its heyday. Improved understanding of neutral verdigris instability and its alteration pathways are critical for confident identification of the pigment in historical works, leading to better risk assessment of collections of verdigris-containing heritage, such as maps.

Tracing the Alteration of Verdigris Pigment through Combined Raman Spectroscopy and X-ray Diffraction, Part I

This research investigates chemical alteration in the important historical pigment called verdigris, both in the form of neutral verdigris (Cu(II) (CH3COO)2 . H2O) and basic verdigris (Cu(II)x(CH3COO)y(OH)z.nH2O), using reference pigment powders and historically relevant “mock-up” samples exposed to artificial aging. Analytical study of model samples by combined Raman spectroscopy, X-ray diffraction and visible spectroscopy provides new evidence that clarifies and builds on the often conflicting body of literature, first in terms of analytical identification of different forms of verdigris pigment, and second by tracing the alteration of neutral verdigris in systems that link to its behavior in aqueous media on historical types of paper. Results further suggest that the historical importance of neutral verdigris as a pigment is underestimated, since commercially available verdigris throughout its heyday – from before the Renaissance through the eighteenth century – was likely to have been dominated by the more easily manufactured neutral salt. This misunderstanding may arise from pigment alteration, whereby the neutral verdigris converts to basic copper salts, or forms organo-copper complexes.

Crystal structures, and magnetic and thermal properties of basic copper formates with two-dimensional triangular-lattice magnetic networks

Basic copper formate, [Cu₃(OH)₄(HCOO)₂], was selectively prepared by hydrolysis of formate ions in concentrated aqueous solutions of copper formate. This material exhibits a two-dimensional distorted triangular-lattice magnetic network of Cu(ii) ions where S = 1/2. The dominance of antiferromagnetic interactions with J/k_B = 35.7(2) K and a magnetic anomaly at approximately 2.3 K that corresponds to a paramagnetic-to-antiferromagnetic ordering transition were revealed by magnetic measurements. The field dependence of the magnetisation at 2 K corresponds to the 1/3-magnetisation plateau that is commonly observed in a two-dimensional triangular-lattice system. Moreover, heat-capacity measurements found a λ-type anomaly at 2.15 K, which is the magnetic transition temperature. This material may be a good candidate for a geometrical frustration system with novel magnetic phenomena such as spin-liquid states.

Basic copper formate, [Cu₃(OH)₄(HCOO)₂], has a distorted two-dimensional triangular lattice magnetic network and showed antiferromagnetic ordering at 2.15 K.

Mechanisms of the polyol reduction of copper(ii) salts depending on the anion type and diol chain length

Systematic experiments were carried out to identify the main factors influencing the polyol reduction of copper(ii) compounds to elemental copper.

On verdigris, part II: synthesis of the 2-1-5 phase, Cu3(CH3COO)4(OH)2·5H2O, by long-term crystallisation from aqueous solution at room temperature

Long-term crystallisation led to the formation of the 2-1-5 verdigris phase (Cu₃(CH₃COO)₄(OH)₂·5H₂O). The crystal structure, as well as magnetic, thermal and spectroscopic properties, was investigated.

On verdigris, part I: synthesis, crystal structure solution and characterisation of the 1-2-0 phase (Cu3(CH3COO)2(OH)4)

Known synthesis approaches for basic copper(ii) acetates, the main components of historic verdrigis pigments were reinvestigated and revealed to be partially irreproducible. A modification of the reaction conditions led to the successful and reproducible synthesis of the 1-2-0 phase (Cu₃(CH₃COO)₂(OH)₄ = 1Cu(CH₃COO)₂·2Cu(OH)₂·0H₂O). The phase composition was derived from elemental and thermal analysis and confirmed by the crystal structure solution using synchrotron X-ray powder diffraction (XRPD) data. The 1-2-0 phase crystallises in space group Pbca with lattice parameters of a = 20.9742(1) Å, b = 7.2076(1) Å, and c = 13.1220(1) Å. The crystal structure consists of Cu₂(CH₃-COO)₂(OH)_4/3(OH)_2/2^1/3- dimers, which are interconnected by corner sharing Cu(OH)_2/3(OH)_2/2^1/3+ squares forming layers perpendicular to the a-axis. The deep blue color of the solid originates from a reflectance maximum at 472 nm and from an absorbance maximum at 676 nm that is comparable with other historic blue pigments like azurite or Egyptian blue. IR- and Raman-spectroscopic properties of the solid were investigated as well, which demonstrated that the obtained product is identical with a previously synthesised verdigris phase that was obtained by applying historical procedures. Therefore, our reference data for the title compound will help to improve the understanding of the multiphase mixtures occurring in historic verdigris samples. The magnetic properties of the 1-2-0 phase were also investigated. At low temperatures the magnetic susceptibility is well described by a spin-1/2 Heisenberg chain with uniform antiferromagnetic nearest-neighbour spin exchange coupling of only one of three Cu magnetic moments. Due to the very strong antiferromagnetic coupling of the Cu₂(CH₃-COO)₂(OH)_4/3(OH)_2/2^1/3- dimers their contribution to magnetism becomes relevant above ∼140 K, which results in the presence of two distinct temperature regions where Curie-Weiss behaviour of the magnetic susceptibility with different Curie constants and Weiss temperatures is found.

The role of 2D/3D spin-polarization interactions in hybrid copper hydroxide acetate: new insights from first-principles molecular dynamics

The magnetic properties response of the layered hybrid material copper hydroxide acetate Cu₂(OH)₃CH₃COO·H₂O is studied as a function of the applied pressure within first-principles molecular dynamics. We are able to elucidate the interplay between the structural properties of this material and its magnetic character, both at the local (atomic) level and at the bulk level. We performed a detailed analysis of the intralayer spin configurations occurring for each value of the imposed projection along the z-axis for the total spin and of the applied pressure. The transition from an antiferromagnetic to a ferromagnetic state at high pressure (above 3 GPa) goes along with a vanishing difference between the spin polarizations pertaining to each layer. Therefore, at high pressure, copper hydroxide acetate is a ferromagnet with no changes of spin polarization in the direction perpendicular to the inorganic layers.

Confined condensation synthesis and magnetic properties of layered copper hydroxide frameworks

We present a confined condensation technique for the fabrication of layered copper hydroxide frameworks from lamellar copper-organic assemblies with long alkyl chains through the selective introduction of hydroxo bridging ligands. The complete transformations of two different lamellar copper-organic assemblies, Cu(C₁₂H₂₅SO₄)₂·4H₂O (Cu-DS) and Cu₂(C₁₁H₂₃CO₂)₄·2H₂O (Cu-lau), into the corresponding layered copper hydroxide frameworks, Cu₂(OH)₃(C₁₂H₂₅SO₄) (Cu-OH-DS) and Cu₂(OH)_1.8(C₁₁H₂₃CO₂)_2.2 (Cu-OH-lau), were achieved via confined condensation. The magnetic properties of both lamellar copper-organic assemblies, Cu-DS and Cu-lau, and both layered copper hydroxide frameworks, Cu-OH-DS and Cu-OH-lau, were investigated. It was found that drastic changes in the magnetic properties arise as a result of the confined condensation process.

Convenient crystal growth, structural determination and magnetic studies of layered copper hydroxides containing aromatic sulfonates

Single crystals of layered copper hydroxides containing some organic sulfonate anions were obtained by hydrolysis of acetate. Crystal structure determination and magnetic measurements of these materials were carried out.

Non-destructive micro-analytical differentiation of copper pigments in paint layers of works of art using laboratory-based techniques

An unambiguous identification of pigments in paint layers of works of art forms a substantial part of the description of a painting technique, which is essential for the evaluation of the work of art including determination of the period and/or region of its creation as well as its attribution to a workshop or an author. Copper pigments represent a significant group of materials used in historic paintings. Because of their substantial diversity and, on the other hand, similarity, their identification and differentiation is a challenging task. An analytical procedure for unambiguous determination of both mineral-type (azurite, malachite, posnjakite, atacamite, etc.) and verdigris-type (copper acetates) copper pigments in the paint layers is presented, including light microscopy under VIS and UV light, electron microscopy with elemental microanalysis, Fourier transformed infrared micro-spectroscopy (micro-FTIR), and X-ray powder micro-diffraction (micro-XRD). Micro-Raman measurements were largely hindered by fluorescence. The choice of the analytical methods meets the contemporary requirement of a detailed description of various components in heterogeneous and minute samples of paint layers without their destruction. It is beneficial to use the combination of phase sensitive methods such as micro-FTIR and micro-XRD, because it allows the identification of both mineral-type and verdigris-type copper pigments in one paint layer. In addition, preliminary results concerning the study of the loss of crystallinity of verdigris-type pigments in proteinaceous binding media and the effect of lead white and lead tin yellow as highly absorbing matrix on verdigris identification in paint layers are reported.

Preparation, crystal structure, and magnetic properties of a copper hydroxy salt with diamond chain magnetic network

The copper hydroxy salt, α-[Cu₃(OH)₂(CH₃CO₂)₂(H₂O)₄](C₆H₅SO₃)₂, exhibited a distorted diamond chain magnetic network and no magnetic order down to 2 K.