New tripodal N-heterocyclic carbene chelators for small molecule activation

In an effort to develop new tripodal N-heterocyclic carbene (NHC) ligands for small molecule activation, two new classes of tripodal NHC ligands TIME^R and TIMEN^R have been synthesized. The carbon-anchored tris(carbene) ligand system TIME^R (R = Me, t-Bu) forms bi- or polynuclear metal complexes. While the methyl derivative exclusively forms trinuclear 3:2 complexes [(TIME^Me)₂M₃]³⁺ with group 11 metal ions, the tert-butyl derivative yields a dinuclear 2:2 complex [(TIME^t-Bu)₂Cu₂]²⁺ with copper(I). The latter complex shows both “normal” and “abnormal” carbene binding modes and accordingly, is best formulated as a bis(carbene)alkenyl complex. The nitrogen-anchored tris(carbene) ligands TIMEN^R (R = alkyl, aryl) bind to a variety of first-row transition metal ions in 1:1 stoichiometry, affording monomeric complexes with a protected reactivity cavity at the coordinated metal center. Complexes of TIMEN^R with Cu(I)/(II), Ni(0)/(I), and Co(I)/(II)/(III) have been synthesized. The cobalt(I) complexes with the aryl-substituted TIMEN^R (R = mesityl, xylyl) ligands show great potential for small molecule activation. These complexes activate for instance dioxygen to form cobalt(III) peroxo complexes that, upon reaction with electrophilic organic substrates, transfer an oxygen atom. The cobalt(I) complexes are also precursors for terminal cobalt(III) imido complexes. These imido complexes were found to undergo unprecedented intra-molecular imido insertion reactions to form cobalt(II) imine species. The molecular and electronic structures of some representative metal NHC complexes as well as the nature of the metal–carbene bond of these metal NHC complexes was elucidated by X-ray and DFT computational methods and are discussed briefly. In contrast to the common assumption that NHCs are pure σ-donors, our studies revealed non-negligible and even significant π-backbonding in electron-rich metal NHC complexes.     

A voltammetric study of the binding of copper(II) to peptide fragments of prion

Binding of copper to three peptide fragments of prion (Cu²⁺ binding sites: 60–91, 92–96 and 180–193 amino acid residues) was investigated by anodic stripping voltammetry to determine the stoichiometries of Cu²⁺-prion peptide interactions. The method relies on the synthesis of N-terminally acetylated/C-terminally amidated peptide fragments of prion by solid-phase synthesis and direct monitoring of the oxidation current of copper in the absence and presence of each prion fragment. Titration curves of Cu²⁺ with Ac-PHGGGWGQ-NH₂, Ac-GGGTH-NH₂ and Ac-VNITKQHTVTTTT-NH₂ were obtained in concentrations ranging from 8.52 × 10^?7 to 5.08 × 10^?6, 3.95 × 10^?7 to 1.94 × 10^?6 and 7.82 × 10^?8 to 4.51 × 10^?7 M, respectively. The acquired data were used to calculate the stoichiometries (one peptide per Cu²⁺ ion for all the three studied systems) and apparent dissociation constants (K_d = 4.37 × 10^?8–3.50 × 10^?10 M) for the three complexes.     

Mass spectrometric study of the dissociation of Group XI metal complexes with fatty acids and glycerolipids: Ag2H+ and Cu2H+ ion formation in the presence of a double bond

Results of mass spectrometric studies are reported for the collisional dissociation of Group XI (Cu, Ag, Au) metal ion complexes with fatty acids (palmitic, oleic, linoleic and α-linolenic) and glycerolipids. Remarkably, the formation of M₂H⁺ ions (M = Cu, Ag) is observed as a dissociation product of the ion complexes containing more than one metal cation and only if the lipid in the complex contains a double bond. Ag₂H⁺ is formed as the main dissociation channel for all three of the fatty acids containing double bonds that were investigated while Cu₂H⁺ is formed with one of the fatty acids and, although abundant, is not the dominant dissociation channel. Also, Cu(I) and Ag(I) ion complexes were observed with glycerolipids (including triacylglycerols and glycerophospholipids) containing either saturated or unsaturated fatty acid substituents. Interestingly, Ag₂H⁺ ion is formed in a major fragmentation channel with the lipids that are able to form the complex with two metal cations (triacylglycerols and glycerophosphoglycerols), while lipids containing a fixed positive charge (glycerophospocholines) complex only with a single metal cation. The formation of Ag₂H⁺ ion is a significant dissociation channel from the complex ion [Ag₂(L–H)]⁺ where L = Glycerophospholipid (GP) (18:1/18:1). Cu(I) also forms complexes of two metal cations with glycerophospholipids but these do not produce Cu₂H⁺ upon dissociation. Rather organic fragments, not containing Cu(I), are formed, perhaps due to different interactions of these metal cations with lipids resulting from the much smaller ionic radius of Cu(I) compared to Ag(I).     

Influence of redox behavior of copper ions on dielectric and spectroscopic properties of Li2O–MoO3–B2O3: CuO glass system

Li₂O–MoO₃–B₂O₃ glasses mixed with different concentrations of CuO (ranging from 0 to 1.2 mol%) were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Optical absorption, luminescence, ESR, IR and dielectric properties (viz., dielectric constant ?′, loss tan δ and a.c. conductivity σ_ac, over a wide range of frequency and temperature) of these glass materials have been investigated. The results of differential scanning calorimetric studies suggest that the glass forming ability is higher for the glasses containing CuO beyond 0.6 mol%. The analysis of results of the dielectric properties has revealed that the glasses possess high insulating strength when the concentration of CuO is >0.6 mol%. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 0.6 mol%. In the high-temperature region, the a.c. conduction seems to be connected with the mixed conduction viz., electronic conduction and ionic conduction. The optical absorption spectra of these glasses exhibited bands due to Cu⁺ ions in the UV region in addition to the conventional band due to Cu²⁺ ions in the visible region. The ESR spectral studies have indicated that there is a gradual adoption of Cu²⁺ ions from ionic environment to covalent environment as the concentration of CuO increases beyond 0.6 mol% in the glass matrix. The luminescence spectra excited at 271 nm have exhibited an intense yellow emission band centered at about 550 nm and a relatively broad blue emission band at about 450 nm; these bands have been attributed to the ³D₁ → ¹S₀ transition of isolated Cu⁺ ions and ³D₁ → ¹S₀ transition of (Cu⁺)₂ pairs, respectively. The quantitative analysis of the results of all these studies has indicated that as the concentration of CuO is increased beyond 0.6 mol% in the glass matrix, a part of Cu²⁺ ions have been reduced to Cu⁺ ions that have influenced the physical properties of these glasses to a substantial extent.     

Electrochemical characterization of common catalysts and initiators for atom transfer radical polymerization in [BMIm][OTf]

The redox properties of some largely employed ATRP initiators and copper catalysts (Cu/L/X⁻) were investigated in 1-butyl-3-methylimidazolium trifluoromethanesulfonate (L = amine ligand, X = Br or Cl). Both Cu(II) and Cu(I) complexes are stable in the IL and, as required by ATRP, X⁻ stabilizes more Cu(II) than Cu(I). The activation rate constants of initiators by [Cu^ITPMA]⁺ were measured and a good correlation between k_act and the C-X bond dissociation free energy (BDFE) was observed. Overall, the results indicated that [BMIm][OTf] behaves much like organic solvents; the reported data launch the bases for a useful database to select the appropriate catalyst/initiator couple for ATRP in ILs.     

Catalytic cyclopropanation of olefins using copper(I) diphosphinoamines

Catalytic cyclopropanation reactions of olefins with ethyl diazoacetate were carried out using copper(I) diphosphinoamine (PPh₂)₂N(R) (R = ⁱPr, H, Ph and –CH₂–C₆H₄–CHCH₂) complexes at 40 °C in chloroform. High yields of the cyclopropanes were obtained in all cases. The rate of the reaction was influenced by the nuclearity of the complex and the binding mode of the ligand which was either bridging or chelating. Comparison of isostructural complexes shows that the rate follows the order R = ⁱPr > H > Ph, where R is the substituent on the N. However, cyclopropane formation versus dimerization of the carbene, and trans to cis ratios of cyclopropane was similar in all cases. The nearly identical selectivity for different products formed was indicative of a common catalytic intermediate. A labile “copper–olefin” complex which does not involve the phosphine or the counterion is the most likely candidate. The differences in the reaction rates for different complexes are attributed to differences in the concentration of the catalytically active species which are in equilibrium with the catalytically inactive copper–phosphinoamine complex. To test the hypothesis a diphosphinoamine polymer complexed to copper(I) was used as a heterogeneous catalyst. Leaching of copper(I) and deactivation of the catalyst confirmed the proposed mechanism.     

Lithium insertion chemistry of some iron vanadates

Lithium insertion into various iron vanadates has been investigated. Fe₂V₄O₁₃ and Fe₄(V₂O₇)₃ · 3H₂O have discharge capacities approaching 200 mAh g⁻¹ above 2.0 V vs. Li⁺/Li. Although the potential profiles change significantly between the first and subsequent discharges, capacity retention is unexpectedly good. Other phases, structurally related to FeVO₄, containing copper and/or sodium ions were also studied. One of these, β-Cu₃Fe₄(VO₄)₆, reversibly consumes almost 10 moles of electrons per formula unit (ca. 240 mAh g⁻¹) between 3.6 and 2.0 V vs. Li⁺/Li, in a non-classical insertion process. It is proposed that both copper and vanadium are electrochemically active, whereas iron(III) reacts to form LiFe^IIIO₂. The capacity of the Cu₃Fe₄(VO₄)₆/Li system is nearly independent of cycling rate, stabilizing after a few cycles at 120–140 mAh g⁻¹. Iron vanadates exhibit better capacities than their phosphate analogues, whereas the latter display more constant discharge potentials.     

Studies on some ternary complexes of copper(II) involving an amino penicillin drug

Multiple equilibrium studies by pH-metric measurements in the ternary copper(II) complexes with ampicillin(amp) as ligand A and glycine(gly), dl-2-aminobutanoic acid(2aba), dl-3-aminobutanoic acid(3aba), 1,2-diaminopropane(dp), 1,3-diaminopropane(tp), dl-2,3-diaminopropanoic acid(dapa), dl-2,4-diaminobutanoic acid(daba) & dl-2,5-diaminopentanoic acid(ornithine)(orn) as ligands B show the presence of CuABH, CuAB or CuAH?1 B ternary complex species. In the CuAB species the binding of the ligands A and B is similar to their binding in their respective binary complexes. In CuABH_?1 species the deprotonation occurs with amp(A) ligand. The Δlog K values indicate higher stabilities for the ternary complexes than the binary species. The CuAB species with B = gly, 2aba, dapa & orn have been isolated and characterized. The conductivity measurements indicate that the complexes are non-electrolytes. Magnetic susceptibility and electronic spectral data suggest a square pyramidal geometry for CuAB with B = gly/2aba complexes and distorted octahedral geometry for CuAB with B = dapa/orn. The vibrational spectra are interpreted to find the mode of binding of ligand to metal. The TG/DTA studies reveal that the complexes decompose in three steps, indicating non-involvement of hydrated or coordinated water molecules in the complex. The cyclic voltammograms indicate a quasi reversible Cu²⁺/Cu⁺ couple. The antimicrobial activity and CT-DNA cleavage ability of the complexes show higher activity for ternary complexes.     

Comparison of the electrochemical properties of metallic layered nitrides containing cobalt,nickel and copper in the 1 V–0.02 V potential range

We report the first example of an intercalation compound based on the nitrogen framework in which lithium can be intercalated and deintercalated. A comparison of the structural and electrochemical properties of the ternary lithium cobalt, nickel and copper nitrides is performed. Vacancy layered structures of ternary lithium nitridocobaltates Li_3−2xCo_xN and nitridonickelates Li_3−2xNi_xN with 0.10 ⩽ x ⩽ 0.44 and 0.20 ⩽ x ⩽ 0.60, respectively, are proved to reversibly intercalate Li ions in the 1 V–0.02 V potential range. These host lattices can accommodate up to 0.35 Li ion par mole of nitride. Results herein obtained support Li insertion in vacancies located in Li₂N⁻ layers while interlayer divalent cobalt and nickel cations are reduced to monovalent species. No structural strain is induced by the insertion–extraction electrochemical reaction which explains the high stability of the capacity in both cases. For the Li_1.86Ni_0.57N compound, a stable faradaic yield of 0.30 F/mol, i.e. 130 mAh/g, is maintained at least for 100 cycles. Conversely, the ternary copper nitrides corresponding to the chemical composition Li_3−xCu_xN with 0.10 ⩽ x ⩽ 0.40 do not allow the insertion reaction to take place due to the presence of monovalent copper combined with the lack of vacancies to accommodate Li ions. In the latter case, the discharge of the lithium copper nitrides is not reversible.     

Mono- and di-nuclear complexes of thiosemicarbazones with copper(I): Synthesis,spectroscopy and structures

Reactions of copper(I) halides with a series of thiosemicarbazones, namely, benzaldehyde thiosemicarbazone (R¹R²CN–NH–C(S)–NH₂, R¹ = Ph, R² = H; Hbtsc), 2-benzoylpyridine thiosemicarbazone (R¹ = Ph, R² = py; Hbpytsc), and acetone thiosemicarbazone (R¹ = R² = Me; Hactsc), in the presence of PPh₃ has formed dimeric complexes, viz. sulfur bridged [Cu₂(μ-S-Hbtsc)₂Br₂(PPh₃)₂]·2H₂O (1), iodo-bridged [Cu₂(μ-I)₂(η¹-S-Hbtsc)₂(PPh₃)₂] (2), and heterobridged [Cu₂(μ₃-S,N³-Hactsc)(η¹-Br)(μ-Br)(PPh₃)₂] (3), as well as mononuclear complexes [CuX(η¹-S-Hbpytsc)(PPh₃)₂]·CH₃CN (X = Br, 4; Cl, 5). Complexes 1, 2, 4 and 5 involve thiosemicarbazone ligands in η¹-S bonding mode while in compound 3, ligand acts in N³, S-chelation-cum-S-bridging mode (μ₃-S,N³ mode). The intermolecular interactions such as, N²H?X, HN¹H?X (X = S, Br, Cl), CH?π interactions lead to 2D networks. All the complexes have been characterized with the help of elemental analyses, IR, ¹H, and ³¹P NMR spectroscopy, and single crystal X-ray crystallography. The role of a solvent in alteration of nuclearity and bonding modes of complexes has been highlighted.     

Spectroscopic investigation and magnetic properties of Na2Pb1−xCuxP2O7 glasses

Phosphate glasses have several technological interests due to their specific physical properties such as high thermal expansion coefficient, high refractive indice and low melting temperature, that make them suitable for use as conductors, ionic conductors, semiconductors and biomedical materials. The phosphate glasses, in particular the pyrophosphate forms, are not widely studied. In this work we have elaborated the Na₂Pb_1−xCu_xP₂O₇ glasses, with a large range of composition (0 ≤ x ≤ 1), by conventional melting method. Thermal parameters of the glasses were determined using the differential scanning calorimetry. The structure of the glasses was investigated by IR spectroscopy. The local environment of paramagnetic ions Cu²⁺ was analyzed by EPR and magnetic measurements. It was showed that the network structure of the glasses was drastically influenced by the copper content.     

Bonding of copper(II) ions by proctolin analogues modified in fifth position of the peptide chain

The proctolin (Arg–Tyr–Leu–Pro–Thr, RYLPT) analogues modified in fifth position of the peptide chain (RYLPP, RYLPI, RYLP–Dab, where Dab – 2,4-diamminobutyric acid) have been synthesised and their complexes with H⁺ and Cu²⁺ studied by potentiometry and spectroscopy (UV–Vis, CD and EPR) at 25 °C and I = 0.10 mol dm⁻³ (KNO₃). The results obtained support the earlier suggestion on the specific role of a proline residue as a “break-point” in copper complex formation with peptides. The presence of a proline residue into the fourth position of the proctolin analogues (RYLPP, RYLPI) leads in wide pH range of the existence the CuL and CuH₋₁L complexes with expected stabilities. Spectroscopic studies confirm that these are 2N {NH₂, N⁻, CO} and 3N {NH₂, 2N⁻, CO} species, respectively. The amine group of the Dab residue of the RYLP–Dab proctolin analogue, in whole pH range (2.5–10.5) is coordinated to the copper(II) ions, and the deprotonation and coordination of the second amide nitrogen atom to the metal ion is prevented. In solution in wide pH range (5–10.5) the 3N {NH₂, N⁻, CO, NH_2Dab} complex is present. Proctolin and its analogues modified in fifth position contain in the second position of the peptide sequence the Tyr residue and the CD results show that TyrO⁻–Cu²⁺ bonding is present at pH above 8.     

Assembly of two novel Lindqvist polyoxoanion-templated coordination polymers with standard honeycomb cavities

Two novel polyoxometalate(POM)-templated coordination polymers: [Cu₂(phnz)₃][M₆O₁₉] (M = Mo for 1, W for 2; phnz = phenazine), have been hydrothermally synthesized and characterized by routine physical methods and single crystal X-ray diffraction. In the compounds, Lindqvist POMs as templates induce the [Cu₂(phnz)₃] complexes to 2D hexagonal metal-organic framework (MOF), which represents 6³ topologies of dimensions ca. 13.515 × 13.515 × 13.515 Å. Furthermore, the 2D sheets are held together by Lindqvist POMs into 3D supramolecular networks with 1D channel, and Lindqvist POMs site in the channels. The successful syntheses and isolation of two compounds provide a novel example of the utility of POM clusters as templates for self-assembly extended framework with cavities.     

A study of the photodeposition over Ti/TiO2 electrode for electrochemical detection of heavy metal ions

Here we reported that UV light irradiation can significantly enhance sensitivity of Ti/TiO₂ electrode for determination of trace heavy metal ions (such as Cu^2 +, Pb^2 + and Cd^2 +) owing to the photodeposition of metal ions on the surface of electrodes. The sensitivity of heavy metal ions can be selectively enhanced over the Ti/TiO₂ electrode, which is attributed to matching between potential of heavy metal ions and the position of the conduction band of TiO₂.     

Effects of N-heteroaromatic ligands on highly luminescent mononuclear copper(I)–halide complexes

A series of mononuclear Cu(I)–halide complexes, [CuX(PPh₃)₂(L)] (X = Cl⁻, Br⁻, I⁻; PPh₃ = triphenylphosphine; L = pyridine (py), isoquinoline (iq), 1,6-naphthyridine (nap)), were synthesized. The emission color of [CuX(PPh₃)₂(L)] varies from blue to red by changing the L ligands and the halide ions, and all the complexes exhibit high emission quantum yields (0.16–0.99) in the crystals. The emission studies revealed that the emissive states of [CuX(PPh₃)₂(L)] differ depending on the L ligand. Complexes [CuX(PPh₃)₂(py)] and [CuX(PPh₃)₂(nap)] mainly emit from the singlet metal-to-ligand charge transfer mixed with the halide-to-ligand charge transfer (¹(M + X)LCT) state at room temperature. In contrast, emissions from [CuX(PPh₃)₂(iq)] at room temperature originate from both ³(M + X)LCT and ³ππ* states. These results indicate that N-heteroaromatic ligands play an important role in the emission properties of mononuclear Cu(I)–halide complexes.     

Two highly unsymmetrical tetradentate (N3O) Schiff base copper(II) complexes: Template synthesis,structural characterization,magnetic and computational studies

Two new copper(II) complexes, [Cu₂(L¹)₂](ClO₄)₂ (1) and [Cu(L²)(ClO₄)] (2), of the highly unsymmetrical tetradentate (N₃O) Schiff base ligands HL¹ and HL² (where HL¹ = N-(2-hydroxyacetophenone)-bis-3-aminopropylamine and HL² = N-(salicyldehydine)-bis-3-aminopropylamine) have been synthesised using a template method. Their single crystal X-ray structures show that in complex 1 two independent copper(II) centers are doubly bridged through phenoxo-O atoms (O1A and O1B) of the two ligands and each copper atom is five-coordinated with a distorted square pyramidal geometry. The asymmetric unit of complex 2 consists of two crystallographically independent N-(salicylidene)-bis(aminopropyl)amine-copper(II) molecules, A and B, with similar square pyramidal geometries. Cryomagnetic susceptibility measurements (5–300 K) on complex 1 reveal a distinct antiferromagnetic interaction with J = ?23.6 cm^?1, which is substantiated by a DFT calculation (J = ?27.6 cm^?1) using the B3LYP functional. Complex 1, immobilized over highly ordered hexagonal mesoporous silica, shows moderate catalytic activity for the epoxidation of cyclohexene and styrene in the presence of TBHP as an oxidant.     

Mixed-ligand complexes of copper(I) with diimines and phosphines: Effective catalysts for the coupling of phenylacetylene with halobenzene

New copper(I) mixed-ligand complexes 1–4 of the formula Cu(N–N)PR₃X, where N–N = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′dimbpy) and PR₃ = tricyclohexylphosphine, tris(2-cyanoethyl)phosphine and isopropyldiphenylphosphine, have been synthesized. The complexes were characterized by EA, IR, NMR and single crystal X-ray diffraction. The solution fluorescence emission spectra were measured. The single crystal X-ray analysis showed that the copper(I) ion is four-coordinate with a distorted tetrahedral geometry. The complexes catalyze the formation of diphenylacetylene from the coupling of halobenzene with phenylacetylene. The complex Cu(5,5′-dimethylbpy)P{(cyhexyl)₃}I showed the highest catalytic activity. At room temperature all four complexes exhibit, in dichloromethane, emission maxima in the 329–344 nm range, corresponding to intra-ligand excited states.     

Experimental design for copper cementation process in fixed bed reactor using two-level factorial design

This work deals with cementation of copper onto iron grid in a fixed bed reactor. The influence of several parameters is studied, namely: initial concentration of copper [Cu²⁺]₀, temperature and flow rate. Moreover, their influence on the copper cementation reaction is investigated statistically by the experimental design in view of industrial application. The estimation and the comparison of the parameter’s effects are realized by using two-level factorial design. The analysis of these effects permits to state that the most influential factor is initial concentration of copper [Cu²⁺]₀ with an effect of (+2.4566), the second in the order is the temperature with an effect of (+0.18959), the third is the flow rate of the electrolytic solution with an effect of (?0.4226). The significance interactions found by the design of experiments are between initial concentrations of copper ions–flow rate (x₁x₃) with an effect (b₁₃ = +0.6965).     

Electronic structures,photophysical properties,and electrochemistry of ruthenium(II)(bpy)2 pyridylimidazole complexes

The properties of Ru^II complexes involving the imidazole moiety are discussed. Complexes [Ru(bpy)₂(L)]²⁺ [bpy = 2,2′-bipyridine, L = 2-(2′-pyridyl)imidazole (2-pimH) and 4-(2′-pyridyl)imidazole (4-pimH)] have been synthesized and fully characterized. Reduction potentials are 0.76 V vs. Fc⁺/Fc⁰ for both complexes in acetonitrile solution, and the deprotonated complexes undergo irreversible electrochemical oxidation at 0.38 V vs. Fc⁺/Fc⁰. Density functional theory (DFT) calculations suggest that oxidation of the protonated complexes is primarily metal-based and that of the deprotonated complexes is ligand-centered. The pK_a of the 4-pimH complex was found to be 9.7 ± 0.2; the pK_a of the 2-pimH complex is 7.9 ± 0.2. Luminescence lifetimes (L = 4-pimH, 277 ns; 2-pimH, 224 ns; 4pim^?, 40 ns; 2pim^?, 34 ns in 5% methanol/water solution) combined with quantum yield data and acid–base behavior suggest that the non-coordinated imidazole nitrogen tunes deactivation pathways.     

First-principles calculations of the structural and electronic properties of Cu3MN compounds with M = Ni,Cu, Zn,Pd, Ag,and Cd

We have performed accurate ab initio total energy calculations using the full-potential linearized augmented plane wave (FP-LAPW) method to investigate the structural and electronic properties of copper-transition metal nitrides. In its ground state, Cu₃N crystallizes in an anti-ReO₃ type cell and it is a semiconductor material with a small indirect gap. In this paper, we report a study of Cu₃MN compounds with M = Ni, Cu, Zn, Pd, Ag, and Cd. In the calculations, we have used the same anti-ReO₃ type cell of Cu₃N, but with the extra transition metal atom at the center of the cube. In particular, our calculated lattice parameters for copper nitride (a = 3.82 Å) and copper palladium nitride (a = 3.89 Å) are in excellent agreement with the experimental values of a = 3.807 Å and a = 3.86 Å, respectively. In all the cases we have studied, the addition of the transition metal atom modifies the electronic structure of Cu₃N, turning all copper-transition metal nitrides into metals.