Octahedral Copper Research Articles

Well-Defined Highly-Coordinated Copper(III) Iodide and Pincer Tris(trifluoromethyl)copper Complexes.

Copper(III) iodide and bromide complexes representing a unique combination of highly-coordinated metal and soft polarizable anions were synthesized and fully characterized, including X-ray crystallography. Ligand substitution in well-defined highly-coordinated copper complex PyCu(CF3)3 with pincer ligands was achieved to give formally octahedral copper(III) complexes.

Synergistic action of cavity and catalytic sites in etched Pd–Cu2O octahedra to augment the peroxidase-like activity of Cu2O nanoparticles for the colorimetric detection of isoniazid and ascorbic acid

Despite the widespread use of nanozyme-based colorimetric assays in biosensing, challenges such as limited catalytic efficiency, inadequate sensitivity to analytes, and insufficient understanding of the structure-activity relationship still persist. Overcoming these hurdles by enhancing the inherent enzyme-like performance of nanozymes using the unique attributes of nanomaterials is still a significant obstacle. Here, we designed and constructed Pd–Cu2O nanocages (Pd–Cu2O NCs) by selectively etching the vertices of the copper octahedra to enhance the peroxidase-like (POD-like) activity of Cu2O nanoparticles. The improved catalytic activity of Pd–Cu2O NCs was attributed to their high specific surface area and abundant catalytic sites. Mechanistic studies revealed that reactive oxygen species (ROS) intermediates (•OH) were generated through the decomposition of H2O2, resulting in POD-like activity of the Pd–Cu2O NCs. The designed Pd–Cu2O NCs can oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue oxidation product (oxTMB). The oxidation reaction was inhibited and led to a significant bleaching of the blue color in the presence of reducing substances isoniazid (INH) and ascorbic acid (AA). Based on these principles, we developed a colorimetric sensing platform for the detection of INH and AA, exhibiting good sensitivity and stability. This work provided a straightforward approach to the structural engineering of nanomaterials and the enhancement of enzyme-mimicking properties.

Photoelectrocatalytic degradation of wastewater and simultaneous synthesis of NH3 on Fe-CNTs-supported octahedral Cu2O composite nanocatalysts

Fe-core carbon nanotubes (Fe-CNTs) were produced by vapor deposition using coal as a carbon source. Then, octahedral copper oxide nanoparticles (Cu2ONO) (prepared by solvent reduction method) were loaded on Fe-CNTs by hydrothermal method to prepare the composite catalyst Cu2ONO/Fe-CNTs. While characterizing (TEM, XRD, FTIR, XPS, N2-TPD, BET, etc.) the material structure, the performance of Cu2ONO/Fe-CNTs in photoelectrocatalytic (PEC) degradation of cotton pulp black liquor (CPBL an organic wastewater with high CODCr) and simultaneous synthesis of NH3 was studied. The PEC reaction was carried out in an H-type reactor. CPBL was oxidized at the anode to produce H+, CO2, H2O and other small molecules, where H+ passes through a proton exchange membrane and is reduced with N2 to produce NH3 at the cathode. After 4 h of reaction, the CODCr removal rate of CPBL in the anode chamber reached 95.42%, and the yield of NH3 in the cathode chamber reached 9.06 mmol L−1 cm−2. The dual purpose of synthesizing NH3 while degrading wastewater was achieved.

Synthesis, structural characterization, and thermal properties of octahedral diperchlorato complexes of copper(II) with the chelating 2-aminomethylpiperidine and 2-aminomethylpyridine ligands

Two distorted octahedral copper(II) coordination compounds; [Cu(AMPp)2(OClO3)2] (1) and [Cu(AMP)2(OClO3)2] (2) (2-aminomethylpiperidine and 2-aminomethylpyridine) have been synthesized on a SP Sephadex C-25 cation exchanger resin for high purity. Their structures have been determined by single-crystal X-ray diffraction, fourier transform infrared spectroscopy, and also thermal analysis. In both structures, the metal center adopts an elongated octahedral geometry in which two chelating amine ligands occupy the square plane in a trans-position, and two perchlorate ligands occupy the axial sites. The thermal stability of both complexes is relatively high. However, the thermal stability of 2 with the aromatic ring was 12 °C higher, due to intermolecular hydrogen bonds, π⋯π, and π⋯O interactions.

Optimizing Oxidation State of Octahedral Copper for Boosting Electroreduction Nitrate to Ammonia

Optimizing Oxidation State of Octahedral Copper for Boosting Electroreduction Nitrate to Ammonia

Understanding the effect of structural changes on slow magnetic relaxation in mononuclear octahedral copper(II) complexes.

Current advances in molecular magnetism are aimed at the construction of molecular nanomagnets and spin qubits for their utilization as high-density data storage materials and quantum computers. Mononuclear coordination compounds with low spin values of S = ½ are excellent candidates for this endeavour, but knowledge of their construction via rational design is limited. This particularly applies to the single copper(II) spin center, having been only recently demonstrated to exhibit slow relaxation of magnetisation in the appropriate octahedral environment. We have thus prepared a unique organic scaffold that would allow one to gain in-depth insight into how purposeful structural differences affect the slow magnetic relaxation in monometallic, transition metal complexes. As a proof-of-principle, we demonstrate how one can construct two, structurally very similar complexes with isolated Cu(II) ions in an octahedral ligand environment, the magnetic properties of which differ significantly. The differences in structural symmetry effects and in magnetic relaxation are corroborated with a series of experimental techniques and theoretical approaches, showing how symmetry distortions and crystal packing affect the relaxation behaviour in these isolated Cu(II) systems. Our unique organic platform can be efficiently utilized for the construction of various transition-metal ion systems in the future, effectively providing a model system for investigation of magnetic relaxation via targeted structural distortions.

A multifunctional nano-therapeutic platform based on octahedral yolk-shell Au NR@CuS: Photothermal/photodynamic and targeted drug delivery tri-combined therapy for rheumatoid arthritis

Rheumatoid arthritis (RA) is a common chronic autoimmune disease that results from synovial hyperplasia. The hyperplasia of synovium directly degrades cartilage by secreting matrix-degrading enzymes and inducing cartilage degradation and even loss of joint function. In this study, a metal/semiconductor composite, octahedral copper sulfide shell, and gold nanorod core (Au NR@CuS) is designed for, photothermal therapy (PTT), photodynamic therapy (PDT), and chemotherapy (CT) combination therapy for RA to remove hyperplasia of the synovium. Upon laser irradiation, the coupling of the local surface electromagnetic field improves the electromagnetic field of the Au NR core and the absorption of light of the CuS shell, whereby the photothermal effect is enhanced. Due to the Fenton-like reactions and the integration of Au NR and CuS semiconductor photocatalyst inhibits hole recombination and provides a reaction site for photocatalysis, which introduces additional •OH to photodynamics therapy. In addition, the large octahedral void space in Au NR@CuS NPs can be used for loading a high quantity of drugs for chemotherapy, and modified with vasoactive intestinal peptide and hyaluronic acid (HA) formation VIP-HA-Au NR@CuS NPs to target synovial cells in RA. Under combination therapy, VIP-HA-Au NR@CuS NPs were shown to effectively inhibit the synovial cells and the edema degree of the CIA mouse was alleviated apparently. Both in vitro and in vivo studies indicate that the VIP-HA-Au NR@CuS NPs can provide a potential possibility for the treatment of RA.

Dissection of bicapped octahedral copper hydride cluster to form two chiral tetrahedral copper hydride cluster series exhibiting auto deracemization and photoluminescence.

Three series of copper hydride clusters [Cu8H6L6]2+ (1), [Cu4HX2L4]+ where X- = Cl- (2a), Br- (2b), I- (2c), N3- (2d) and SCN- (2e), and [Cu4HX3L3] where X- = Br- (3b) and I- (3c) (L = 2-(diphenylphosphino)pyridine, dppy) were synthesized and characterized by single-crystal X-Ray crystallography and standard spectroscopic techniques. The metal core of 1, Cu8, can be described as a bicapped octahedron, while those of 2 and 3 series adopt tetrahedral structures. The hydride positions were deduced from difference electron density maps and corroborated by NMR and DFT calculations. For 1, there are two μ4-H-, one each in the two tetrahedral cavities of the two capping atoms and four μ3-H- on the six triangular faces around the waist of the octahedron. For [Cu4HX2L4]+ and [Cu4HX3L3] series, the single μ4-H- resides in the center of the Cu4 tetrahedron. It was found that these three series of copper clusters are intimately connected and can convert from one to another under specific reaction conditions. Their transformation pathways were investigated in detail. Spontaneous resolution to form optically pure enantiomeric single crystals was observed for [Cu4H(SCN)2L4]+ (2e) and [Cu4HBr3L3] (3b). Photoluminescence was observed for [Cu4HX2L4]+, as well as [Cu4HX3L3] with strong emissions from green to yellow regions.

Octahedral Copper(II) Carboxylates with 1,10-Phenanthroline: Synthesis, Structural Characterization, DNA-Binding and Anti-Fungal Properties

Two mono-nuclear axially distorted octahedral copper(II) complexes have been prepared and characterized via FT-IR, UV–Visible, elctrochemical, electron spin resonance and powder and single crystal XRD techniques. The complexes consist of a phenanthroline and two carboxylate ligands each bonded in bidentate fashion. Carboxylates are ortho-nitro-2-phenyl acetate (L1) and para-chloro-2-phenyl acetate (L2). Structural study showed that both complexes possess Jahn–Teller distorted octahedral geometry. The bulk purity was assessed from the matching experimental and simulated powder XRD spectra. The results of spectroscopic techniques are consistent with each other. ESR data revealed single electron occupancy of dx2 − y2 orbital with 2B1g as ground state typical of tetragonally distorted octahedral geometry. Electrochemical solution study showed diffusion controlled electron transfer processes with diffusion co-efficient values of 10.323 × 10–8 cm2s–1 and 0.972 × 10–8 cm2s–1 for 1 and 2. Complexes exhibited excellent DNA-binding activity studied via UV–Visible spectroscopy, cyclic voltammetry, florescence spectroscopy and viscometry yielding Kb values of 1.871 × 104 M–1 (1) and 1.577 × 104 M–1 (2), 0.38 × 104 M–1 (1) and 6.39 × 104 M–1 (2) and 2.1 × 106 M–1 (1) and 2.0 × 06 M–1 (2), respectively, for the first three techniques. Complexes possess good antifungal activity against three fungal strains.

Synthesis, characterizations, crystal structures, and theoretical studies of copper(II) and nickel(II) coordination complexes

In the present study, we report synthesis, characterization, structural and theoretical studies of two copper(II) complexes, [Cu(py)2(L1)2] (1) and [Cu(phen)(Ac)2-Cu2(Ac)4]n (2), and a nickel(II) complex, [Ni(bipy)(L)(Ac)] (3), where py = pyridine, L1 = 3,5-dichloro-2-hydroxybenzaldehyde, phen = 1,10-phenanthroline, Ac = acetate ion, bipy = 2,2’-bipyridine and HL = 4-bromo-2-(Z)-(naphthalene-2-ylimino)methyl) phenol. The new complexes were fully characterized using microanalysis, FAB-mas (m/z), FT-IR, UV-Vis and fluorescence spectra, X-band EPR spectroscopy and then by single crystal X-ray diffraction studies. X-ray studies of 1 and 3 revealed distorted octahedral geometries. Complex 2 is a coordination polymer built by an octahedral copper unit Cu(phen)(Ac)2 alternating with paddle wheel species Cu2(Ac)4, located on a crystallographic center of symmetry, where an acetate anion bridges the two crystallographic independent copper ions. The fluorescence intensities and quantum yields of 1 and 2 were found to be more compared to 3. The preliminary tests in the potential application for theoretical biological activities of compounds have also been studied. Furthermore, we also performed quantum chemical calculations to get insights into the structure-property relationships of the synthesized complexes. The quantum chemical calculations were used for theoretical calculations of linear polarizability and third-order nonlinear optical polarizability (γ) for 1, 2 and 3. Besides this, the theoretical calculations, including the analysis of frontier molecular orbitals and electrostatic potential diagrams, are used to highlight the theoretical aspects of metal to ligand charge transfer (MLCT) processes in the studied complexes.

Octahedral copper(ii)-diimine complexes of triethylenetetramine: effect of stereochemical fluxionality and ligand hydrophobicity on CuII/CuI redox, DNA binding and cleavage, cytotoxicity and apoptosis-inducing ability.

Octahedral copper(ii) complexes of the type [Cu(trien)(diimine)](ClO4)2 (1-4), where trien is triethylenetetramine and diimine is 2,2'-bipyridine (1), 1,10-phenanthroline (2), 5,6-dimethyl-1,10-phenanthroline (3), and 3,4,7,8-tetramethyl-1,10-phenanthroline (4), have been isolated. Single crystal X-ray structures of 1 and 2 reveal that the coordination geometry around Cu(ii) is tetragonally distorted octahedral. The stereochemical fluxionality of the complexes illustrates the observed trend in CuII/CuI redox potentials and DNA binding affinity (Kb: 1, 0.030 ± 0.002 < 2, 0.66 ± 0.01 < 3, 1.63 ± 0.10 < 4, 2.27± 0.20 × 105 M-1), determined using absorption spectral titration. All complexes effect oxidative DNA cleavage more efficiently than hydrolytic DNA cleavage. The bpy complex 1 with stereochemical fluxionality lower than its phen analogue 2 shows a higher cytotoxicity against both A549 lung (IC50, 3.3 μM) and MCF-7 human breast (IC50, 3.9 μM) cancer cells, and induces the generation of the highest amount of ROS in A549 cells. Complex 3 with a higher stereochemical fluxionality and higher ligand hydrophobicity exhibits a higher DNA binding and cleavage ability and higher cytotoxicity (IC50, 2.1 μM) towards MCF-7 cells. Complex 4 with a still higher stereochemical fluxionality displays the highest DNA binding and cleavage ability but a lower cytotoxicity towards both A549 and MCF-7 cell lines due to its tendency to form a five-coordinated complex with the uncoordinated amine group. Annexin V.Cy3 staining and immunoblot analysis demonstrate the mechanism of cell death caused by 1 and 2. The finding of the up-regulation of the pro-apoptotic Bax protein and down-regulation of PARP protein in western blot analysis confirms the induction of apoptosis by these complexes.

Crystal structures of two coordination isomers of copper(II) 4-sulfo-benzoic acid hexa-hydrate and two mixed silver/potassium 4-sulfo-benzoic acid salts.

A reaction of copper(II) carbonate and potassium 4-sulfo-benzoic acid in water acidified with hydro-chloric acid yielded two crystalline products. Tetra-aqua-bis-(4-carb-oxy-benzene-sulfonato)-copper(II) dihydrate, [Cu(O3SC6H4CO2H)2(H2O)4]·2H2O, (I), crystallizes in the triclinic space group P with the Cu2+ ions located on centers of inversion. Each copper ion is coordinated to four water mol-ecules in a square plane with two sulfonate O atoms in the apical positions of a Jahn-Teller-distorted octa-hedron. The carboxyl-ate group is protonated and not involved in coordination to the metal ions. The complexes pack so as to create a layered structure with alternating inorganic and organic domains. The packing is reinforced by several O-H⋯O hydrogen bonds involving coordinated and non-coordinated water mol-ecules, the carb-oxy-lic acid group and the sulfonate group. Hexa-aqua-copper(II) 4-carb-oxy-benzene-sulfonate, [Cu(H2O)6](O3SC6H4CO2H)2, (II), also crystallizes in the triclinic space group P with Jahn-Teller-distorted octa-hedral copper(II) aqua complexes on the centers of inversion. As in (I), the carboxyl-ate group on the anion is protonated and the structure consists of alternating layers of inorganic cations and organic anions linked by O-H⋯O hydrogen bonds. A reaction of silver nitrate and potassium 4-sulfo-benzoic acid in water also resulted in two distinct products that have been structurally characterized. An anhydrous silver potassium 4-carb-oxy-benzene-sulfonate salt, [Ag0.69K0.31](O3SC6H4CO2H), (III), crystallizes in the monoclinic space group C2/c. There are two independent metal sites, one fully occupied by silver ions and the other showing a 62% K+/38% Ag+ (fixed) ratio, refined in two slightly different positions. The coordination environments of the metal ions are composed primarily of sulfonate O atoms, with some participation by the non-protonated carboxyl-ate O atoms in the disordered site. As in the copper compounds, the cations and anions cleanly segregate into alternating layers. A hydrated mixed silver potassium 4-carb-oxy-benzene-sulfonate salt dihydrate, [Ag0.20K0.80](O3SC6H4CO2H)·2H2O, (IV), crystallizes in the monoclinic space group P21/c with the Ag+ and K+ ions sharing one unique metal site coordinated by two water mol-ecules and six sulfonate O atoms. The packing in (IV) follows the dominant motif of alternating inorganic and organic layers. The protonated carboxyl-ate groups do not inter-act with the cations directly, but do participate in hydrogen bonds with the coordinated water mol-ecules. (IV) is isostructural with pure potassium 4-sulfo-benzoic acid dihydrate.

MOFs-based coating derived Me-ZIF-67@CuOx materials as low-temperature NO-CO catalysts

To improve the denitrification rate of low-temperature NO-CO selective catalytic reduction (SCR), it is urgent to find new carbon-based materials. In this paper, metal-modified Me-ZIF-67@CuOx (Me = Mn, Fe, Al or Zn) were synthesized by colloidal chemical synthesis and encapsulation method at room temperature as catalysts for low-temperature CO-SCR denitrification. It could be seen that Co ions were replaced by the doping metal ions to form different metal-modified Me-ZIF-67, and Me-ZIF-67@CuOx was loaded by Me-ZIF-67 with regular morphology on octahedral copper oxide derived by Cu-MOF. The test results showed that the catalytic abilities on denitrification rate at low temperature were above 90%. In addition, the ratio of Co2+/Co3+ remained a high value in Me-ZIF-67@CuOx, the denitrification performance of Al-ZIF-67@CuOx was greatly improved, and Mn-ZIF-67@CuOx had the best performance in the sulfur resistance test, indicating that the fine denitrification performance and better sulfur resistance were probably due to the Co-active sites in Me-ZIF-67 loaded on CuOx by metal doping.

Structural Analysis of Polymeric Copper(II)–Pyrazinamide Complexes Prepared from Two Different Copper(II) Salts

In crystal engineering, the presence of different types of anion may alter the structure of transition metal complexes. Thus, the anions may also govern the properties of the metal complexes. Hereby we reported a structural analysis of polymeric copper(II)-pyrazinamide (pza) complexes prepared from copper(II) sulphate and copper(II) chloride. The complexes were crystallised using a bench-top technique with copper(II):pza molar ratio of 1:2 in a layered H2O-CH3OH solvent at room temperature. Single crystal XRD, ATR-IR and melting point apparatus were used to analyse the structure and characterise the complexes. Single crystal XRD analyses reveals that both complexes, [Cu( µ-pza)(SO4)(H2O)2]n (A) and [Cu(pza)2( µ-Cl)2]n (B) forms a 1D polymeric structure with different metal-ligand connectivity around the octahedral copper centre. The copper centres are also linked by different ligand, namely pyrazinamide in A and chloride in B. Thus, the Cu…Cu distances in both complexes are different, 6.719 Å in A and 3.658 Å in B. Unlike in A, the crystal structure of B has two unique copper centres. In addition, crystal structures of A and B were also compared to closely related copper(II)-pza complexes from published literature. As also observed in many metal complexes, crystal structures of copper(II)-pza complex were affected by the anion of the metal salts used in the reaction, in which the anion also involves in the crystal structures.

Metal-organic framework-derived mesoporous octahedral copper oxide/titania composites for high-performance lithium-ion batteries

A mesoporous octahedral copper oxide@titania (CuO/TiO2) composites with core-shelled structure have been successfully fabricated via a facile and cost-effective approach, which involves two main steps: the creation of homogeneous TiO2 shell onto the octahedral Cu-based metal–organic frameworks (MOFs) template and thermal decomposition of the template at controlled temperature in the air. The design of combining CuO with the TiO2 layer within a porous octahedra structure is beneficial to integrate the advantages of different components and address the severe volume change associated with pulverization issue that exists in most metal oxides-based electrodes. When assembled as an anode material for lithium-ion batteries, the as-fabricated mesoporous CuO/TiO2 octahedra can achieve outstanding electrochemical performance in terms of a high reversible capacity (692 mAh g−1 at 100 mA g−1 for over 200 cycles) and exceptional rate capability (441 and 387 mA h g−1 at 1600 and 3200 mA g−1, respectively).

Octahedral copper(II) carboxylate complex: synthesis, structural description, DNA-binding and anti-bacterial studies

Self-assembly of CuSO4, para-methyl-2-phenyl acetate and 1,10-phenanthroline afforded good-quality crystalline complex in quantitative yield. The complex was characterized by FTIR and UV-visible spectroscopy, electrochemistry, and powder and single-crystal XRD studies. Its structure was found to possess axially elongated octahedral symmetry with CuO4N2 chromophore. Its purity was assessed by powder XRD spectrum. Absorption study yielded a broad band corresponding to 2Eg→2T2 g transition. Electrochemical solution study indicated diffusion-controlled irreversible electron transfer process corresponding to Cu(II)/Cu(I) redox couple with diffusion coefficient = 7.89(±0.1)×10−9 cm2s−1. Results of spectroscopic techniques support each other. Complex exhibited excellent DNA-binding ability through UV-visible spectroscopy and cyclic voltammetry yielding Kb values 1.399 × 104 M−1 and 5.81 × 103 M−1, respectively. The complex exhibited significant activity against bacterial strains Escherichia coli, Micrococcus luteus and Staphylococcus aureus and good activity against Bacillus subtilis. These preliminary studies impart good biological relevance on the synthesized complex.

Jahn–Teller distortion in 2-pyridyl-(1,2,3)-triazole-containing copper(ii) compounds

Octahedral copper(ii) compounds, containing two 2-pyridyl-(1,2,3)-triazole ligands as well as two Cl ions, exhibit elongation Jahn–Teller distortion.

Copper(II) complexes of N3O ligands as models for galactose oxidase: Effect of variation of steric bulk of coordinated phenoxyl moiety on the radical stability and spectroscopy

Three N3O tripodal ligands (two pyridines, one phenol) HLMes, HLTRIP and HLNap were synthesized. The phenol ortho substituent is a mesityl, 2,4,6-tri-isopropylphenyl or 2-naphthyl group, respectively. The dinuclear copper(II)-phenolate complexes [μOH-Cu2II(LMes)(HLMes)]2+ and [Cu2II(LNap)2]2+ were isolated as single crystals. In [μOH-Cu2II(LMes)(HLMes)]2+ the two copper centers are bridged by a hydroxo unit. In [Cu2II(LNap)2]2+ two phenolate groups bridge the copper atoms. In the absence of base the mononuclear copper(II)-phenol complexes are formed. The complexes [CuII(HLMes)(CH3CN)]2+ and [CuII(HLNap)(CH3CN)]2+ were structurally characterized, showing a distorted octahedral copper ion. The phenol remains protonated and occupies one axial position, while a counter ion is weakly bound on the opposite position and an acetonitrile molecule completes the coordination sphere. In the presence of pyridine mononuclear copper(II)-phenolate complexes of general formula [CuII(LNap)(Py)]+, [CuII(LMes)(Py)]+ and [CuII(LTRIP)(Py)]+ are obtained. The copper(II)-phenol complexes exhibit a reversible reduction wave in the range −0.27 to −0.29V vs. Fc+/Fc in their CV curve, which corresponds to the CuII/CuI redox couple, as well as an irreversible oxidation wave. In the presence of pyridine a reversible oxidation wave is observed at 0.09–0.13V. It is assigned to the phenoxyl/phenolate redox couple. The one-electron oxidized copper(II)-phenoxyl complexes are mononuclear triplet species, as judged by the ΔMS=2 resonance in their EPR spectra. The |D| value is estimated at 1700MHz (axial ZFS). All these radical species exhibit an intense band at 427nm, which combines the features of both phenoxyl π–π∗ and CT transitions. The stability of the radicals follows the order [CuII(LNap)(Py)]2+>[CuII(LMes)(Py)]2+>[CuII(LTRIP)(Py)]2+. By DFT calculations we show that all the phenoxyl radical species adopt a common trigonal bipyramidal geometry, wherein the phenoxyl moiety coordinates in the trigonal plane. They possess a triplet ground spin state due to the orthogonality between the two SOMOs, which mainly correspond to dz2 and phenoxyl π orbitals.

2 H magic-angle spinning NMR and powder diffraction study of deuterated paramagnetic copper(II) glycinato complexes. Information on crystallographic symmetries, stereo-isomerism, and molecular mobility available from ssNMR spectra

Effects of stereochemistry, polymorphism, crystal packing, and solid phase mobility on the 2H magic-angle spinning (MAS) NMR spectra of the paramagnetic Cu(II) glycinato complexes have been investigated. The reliability of information obtained from the spectra, such as symmetry relations within a molecule, number of chemical sites or molecules found in the asymmetric units, was confirmed by previously published X-ray crystal and molecular structures. From the 2H MAS spectra, complemented with powder diffractograms of the synthetized bis(glycinato-d4)copper(II) complexes, we could identify three solid phases, namely the cis aqua and non-aqua forms and the trans non-aqua crystals. A fourth sample was identified as octahedral copper(II) complex chain with bidentate glycine and NO3 ligands in the octahedral building units. Correlations between the sign and magnitude of the observed paramagnetic shifts and the number of bonds and/or the dihedral angles connecting the actual 2H nucleus and the paramagnetic center, useful in structural assignments, were revealed. The agreement of the 2H MAS NMR spectral information with the available crystal diffraction data forecast their applicability in NMR crystallographic works too.

Thermochemical and electrochemical CO2 reduction on octahedral Cu nanocluster: Role of solvent towards product selectivity

There has been a major interest in the development of efficient catalysts for the electrochemical reduction of CO2 into useful chemicals and fuels. In this work, the thermochemical and electrochemical CO2 reduction pathways are systematically studied on the (111) facet of an octahedral copper (Cu85) nanocluster (NC) using density functional theory (DFT) calculations. An investigation is carried out to understand the catalytic activity of the Cu NC towards CO2 reduction to explore its activity and product selectivity (CH3OH vs. CH4; i.e., six-electron vs. eight-electron reduction reaction). Interestingly, CO2 adsorbs strongly the (111) facet of the Cu NC, as opposed to the previous reports on the periodic Cu(111) surfaces. Furthermore, such NC shows excellent catalytic activity towards direct CO bond dissociation, which is again in contrary to what was reported in the literatures. Besides, the CO2 hydrogenation reaction has been investigated using different proton transfer mechanisms (surface-hydrogenation, water-assisted, and water solvated) with/without the help of a solvent water molecule. We find that the water-assisted H-shuttling mechanism lowers the activation barrier significantly and thus favours the CO2 hydrogenation. However, the direct CO bond dissociation is very competing with respect to indirect CO bond dissociation. Based on our reaction free energy calculations, activation barrier calculations, and simulated Pourbaix calculations, we find that the Cu NC shows excellent catalytic activity and selectivity over any catalysts studied to date. Besides, the Cu NC requires a lower overpotential (0.53V) compared to the periodic Cu(111) surface (0.71V) and thus can be a promising catalyst for CO2 reduction reaction.