Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

Cyanide-bridged [Fe8M6] clusters displaying single-molecule magnetism (M=Ni) and electron-transfer-coupled spin transitions (M=Co)

Cyanide‐bridged metal complexes of [Fe₈M₆(μ‐CN)₁₄(CN)₁₀ (tp)₈(HL)₁₀(CH₃CN)₂][PF₆]₄?n CH₃CN?m H₂O (HL=3‐(2‐pyridyl)‐5‐[4‐(diphenylamino)phenyl]‐1H‐pyrazole), tp^?=hydrotris(pyrazolylborate), 1 : M=Ni with n=11 and m=7, and 2 : M=Co with n=14 and m=5) were prepared. Complexes 1 and 2 are isomorphous, and crystallized in the monoclinic space group P2₁/n. They have tetradecanuclear cores composed of eight low‐spin (LS) Fe^III and six high‐spin (HS) M^II ions (M=Ni and Co), all of which are bridged by cyanide ions, to form a crown‐like core structure. Magnetic susceptibility measurements revealed that intramolecular ferro‐ and antiferromagnetic interactions are operative in 1 and in a fresh sample of 2 , respectively. Ac magnetic susceptibility measurements of 1 showed frequency‐dependent in‐ and out‐of‐phase signals, characteristic of single‐molecule magnetism (SMM), while desolvated samples of 2 showed thermal‐ and photoinduced intramolecular electron‐transfer‐coupled spin transition (ETCST) between the [(LS‐Fe^II)₃(LS‐Fe^III)₅(HS‐Co^II)₃(LS‐Co^III)₃] and the [(LS‐Fe^III)₈(HS‐Co^II)₆] states.     

On the nature of the chemical bond in heterobimetallic palladium(II) complexes with divalent 3<Emphasis Type="Italic">d</Emphasis> metals

The complex Pd(μ-OOCMe)₄Cu(OH₂) · 2Pd₃(μ-OOCMe)₆ was synthesized and characterized by X-ray crystallography. In the heterometallic moiety of this complex, the Pd^II and Cu^II atoms are at an extraordinary short distance (2.521(3) Å). DFT quantum-chemical calculations of the geometric and electronic structure of a series of heterobinuclear paddlewheel complexes Pd^IIM^II(μ-OOCMe)₄L (M = Zn^II, Ni^II, Cu^II, Co^II, Fe^II; L = OH₂ and NCH) and their formate analogues Pd^IIM^II(μ-OOCH)₄L (M = Zn^II, Ni^II, Fe^II) showed that the extraordinary short Pd?M distance in all these complexes is caused only by the tightening effect of carboxylate bridges rather than by the metal-metal bond. The direct Pd-M interaction becomes possible only after removal of electrons from the antibonding orbitals and formation of oxidized complexes of the [Pd^III(μ-OOCMe)₄Ni^III]²⁺ type.     

Synthesis and characterization of complexes of the first transition series cations with 2,2′-biimidazole and 2,2′-biimidazolate

Mononuclear [M(hfacac)₂(H₂biim)] complexes, where M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II or Zn^II, hfacac = hexafluoroacetylacetonate, H₂biim = 2,2-biimidazole; dinuclear K₂[M₂(acac)₄(-biim)] (M = Cu^II or Zn^II) and tetranuclear K₂[M₄(acac)₈( ₄-biim)] (M = Co^II or Ni^II) complexes have been prepared and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r. spectroscopies and by magnetic susceptibility measurements (in the 2–300 K range). Mn^II, Fe^II and Co^II are in a high spin state. The e.p.r. spectra of Cu^II and Mn^II compounds have been recorded.     

Trinuclear Cyanido-Bridged [Cr2Fe] Complexes: To Be or not to Be a Single-Molecule Magnet,a Matter of Straightness

Trinuclear systems of formula [{Cr(L^N3O2Ph)(CN)₂}₂M(H₂L^N3O2R)] (M=Mn^II and Fe^II, L^N3O2R stands for pentadentate ligands) were prepared in order to assess the influence of the bending of the apical M−N≡C linkages on the magnetic anisotropy of the Fe^II derivatives and in turn on their Single-Molecule Magnet (SMM) behaviors. The cyanido-bridged [Cr₂M] derivatives were obtained by assembling trans-dicyanido Cr^III complex [Cr(L^N3O2Ph)(CN)₂]⁻ and divalent pentagonal bipyramid complexes [M^II(H₂L^N3O2R)]²⁺ with various R substituents (R=NH₂, cyclohexyl, S,S-mandelic) imparting different steric demand to the central moiety of the complexes. A comparative examination of the structural and magnetic properties showed an obvious effect of the deviation from straightness of the M−N≡C alignment on the slow relaxation of the magnetization exhibited by the [Cr₂Fe] complexes. Theoretical calculations have highlighted important effects of the bending of the apical C−N−Fe linkages on both the magnetic anisotropy of the Fe^II center and the exchange interactions with the Cr^III units.     

Magnetic and spectroscopic studies of bimetalliciso-propoxides of later 3d metals with aluminium

Summary The structures of the volatile bimetalliciso-propoxides of later 3d metals with the general formula, [M{Al(OPr-i)4}_n] where M=Cr^III, Mn^II, Fe^III, Co^II, Ni^II and Cu^II have been investigated by visible reflectance and electron spin resonance spectroscopy as well as magnetic measurements.     

New complexes of iron(III), cobalt(II), nickel(II) and copper(II) with 2-phenyl-1,2,3-triazole-4-carboxalidene-2-aminophenol

Summary Fe^III, Co^II, Ni^II and Cu^II complexes of a new Schiff base, 2-phenyl-1,2,3-triazole-4-carboxalidene-2-aminophenol (PTCAP), have been synthesized and characterized by elemental analyses, molar conductance and magnetic susceptibility measurements, and by u.v.-vis., i.r. and e.p.r. spectral observations. The studies indicate an octahedral structure for the complexes with the general formula [ML₂] (M = Co^II, Ni^II or Cu^II.; L = PTCAP) or [M′(OH)L₂] (M′ = Fe^III). The i.r. spectra suggest that the ligand acts as a tridentate (NNO) donor towards Co^II, Ni^II and Cu^II, and, in the Fe^III complex, one of the two ligand molecules acts as a bidentate (NO) donor and the other as a tridentate donor. The M?ssbauer spectrum of the Fe^III complex suggests the presence of a spin equilibrium at room temperature. Cyclic voltammograms are also recorded for the Cu^II and Fe^III complexes.     

A Mixed-Valence {Fe13} Cluster Exhibiting Metal-to-Metal Charge-Transfer-Switched Spin Crossover

It is promising and challenging to manipulate the electronic structures and functions of materials utilizing both metal-to-metal charge transfer (MMCT) and spin-crossover (SCO) to tune the valence and spin states of metal ions. Herein, a metallocyanate building block is used to link with a Fe^II-triazole moiety and generates a mixed-valence complex {[(Tp^4-Me)Fe^III(CN)₃]₉[Fe^II₄(trz-ph)₆]}⋅[Ph₃PMe]₂⋅[(Tp^4-Me)Fe^III(CN)₃] ( 1 ; trz-ph=4-phenyl-4H-1,2,4-triazole). Moreover, MMCT occurs between Fe^III and one of the Fe^II sites after heat treatment, resulting in the generation of a new phase, {[(Tp^4-Me)Fe^II(CN)₃][(Tp^4-Me)Fe^III(CN)₃]₈ [Fe^IIIFe^II₃(trz-ph)₆]}⋅ [Ph₃PMe]₂⋅[(Tp^4-Me)Fe^III(CN)₃] ( 1 a ). Structural and magnetic studies reveal that MMCT can tune the two-step SCO behavior of 1 into one-step SCO behavior of 1 a . Our work demonstrates that the integration of MMCT and SCO can provide a new alternative for manipulating functional spin-transition materials with accessible multi-electronic states.     

Derivatives of the 21-tungsto-9-antimonate heteropolyanion. Part 2. Addition of transition metal cations

Ammonium salts of five new heteropolytungstates, [NaSb₉W₂₁O₈₆M₃]^12,9− (M=Mn^II, Fe^III, Co^II, Ni^II, Cu^II) have been prepared and characterized by elemental analysis, visible and i.r. spectroscopy, magnetic susceptibility measurements, and cyclic voltammetry. Evidence for ligand substitution at the M cation centres is presented, and possible binding sites for M on the polyanion surface are discussed.     

Cyano‐Bridged MnIII?MIII Single‐Chain Magnets with MIII=CoIII,FeIII, MnIII,and CrIII

A series of isostructural cyano‐bridged Mn^III(h.s.)–M^III(l.s.) alternating chains, [Mn^III(5‐TMAMsalen)M^III(CN)₆] ? 4H₂O (5‐TMAMsalen^2?=N,N′‐ethylenebis(5‐trimethylammoniomethylsalicylideneiminate), Mn^III(h.s.)=high‐spin Mn^III, M^III(l.s.)=low‐spin Co^III, Mn? Co ; Fe^III, Mn? Fe ; Mn^III, Mn? Mn ; Cr^III, Mn? Cr ) was synthesized by assembling [Mn^III(5‐TMAMsalen)]³⁺ and [M^III(CN)₆]^3?. The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [‐Mn^III‐NC‐M^III‐CN‐] repeating motif, for which the ‐NC‐M^III‐CN‐ motif is provided by the [M^III(CN)₆]^3? moiety adopting a trans bridging mode between [Mn^III(5‐TMAMsalen)]³⁺ cations. The Mn^III and M^III ions occupy special crystallographic positions: a C₂ axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn–Teller axis of the Mn^III(h.s.) ion is perpendicular to the N₂O₂ plane formed by the 5‐TMAMsalen tetradentate ligand. These Jahn–Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn‐N_axis‐C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter‐chain M???M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5‐TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn? Fe and Mn? Mn display intra‐chain ferromagnetic interactions, whereas Mn? Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single‐chain magnet (SCM) behavior of these three systems, whereas Mn? Co is merely paramagnetic with S_Mn=2 and D/k_B=?5.3 K (D being a zero‐field splitting parameter). At low temperatures, the Mn? M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite‐chain and finite‐chain regimes for the SCM behavior. These isostructural hetero‐spin SCMs offer a unique series of alternating [‐Mn‐NC‐M‐CN‐] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits.     

New bis-macrocyclic complexes with transition metal ions

Template condensation of benzidine, formaldehyde, ethylenediamine or 1,3-diaminopropane, metal salt and 1-phenyl-1,3-butanedione or 2,3-butanedione in a 1:4:2:2 molar ratio results in the formation of two new series of binuclear pentaaza macrocyclic complexes: dichloro[1,1-phenylbis(7-methyl-9-phenyl-1,3,6,10,13-pentaazacyclotetradeca-6,9-diene) metal(II)], [M₂LCl₄] (M = Co^II, Cu^II, Fe^III and Zn^II) and dichloro[1,1-phenylbis(8,9-dimethyl-1,3,7,10,14-pentaazacyclopentadeca-7,9-diene) metal(II)], [M₂LCl₄] (M = Ni^II, Co^II, Cu^II and Cd^II). Both series were characterized by i.r., ¹H-n.m.r., u.v.–vis. spectral studies, conductivity and magnetic susceptibility measurements.     

A Mixed‐Valence {Fe13} Cluster Exhibiting Metal‐to‐Metal Charge‐Transfer‐Switched Spin Crossover

It is promising and challenging to manipulate the electronic structures and functions of materials utilizing both metal‐to‐metal charge transfer (MMCT) and spin‐crossover (SCO) to tune the valence and spin states of metal ions. Herein, a metallocyanate building block is used to link with a Fe^II‐triazole moiety and generates a mixed‐valence complex {[(Tp^4‐Me)Fe^III(CN)₃]₉[Fe^II₄(trz‐ph)₆]}?[Ph₃PMe]₂?[(Tp^4‐Me)Fe^III(CN)₃] ( 1 ; trz‐ph=4‐phenyl‐4H‐1,2,4‐triazole). Moreover, MMCT occurs between Fe^III and one of the Fe^II sites after heat treatment, resulting in the generation of a new phase, {[(Tp^4‐Me)Fe^II(CN)₃][(Tp^4‐Me)Fe^III(CN)₃]₈ [Fe^IIIFe^II₃(trz‐ph)₆]}? [Ph₃PMe]₂?[(Tp^4‐Me)Fe^III(CN)₃] ( 1 a ). Structural and magnetic studies reveal that MMCT can tune the two‐step SCO behavior of 1 into one‐step SCO behavior of 1 a . Our work demonstrates that the integration of MMCT and SCO can provide a new alternative for manipulating functional spin‐transition materials with accessible multi‐electronic states.     

Synthesis, structure, and magnetic properties of heterometallic trinuclear complexes {MII��LnIII��MII} (MII = Ni, Cu; LnIII = La, Pr, Sm, Eu, Gd)

Trinuclear heterometallic complexes containing the {M₂Ln(Piv)₆(NO₃)} (M^II = Ni, Cu; Ln^III = Nd, Pr, Sm, Eu, Gd; Piv^? is the anion of pivalic acid) and {Cu₂Ln(Piv)₈)]^? (Ln^III = Eu, Gd) metal cores were synthesized, their structures and magnetic properties were studied. For the most compounds, it was shown that their magnetic properties can be interpreted taking no interaction of the 3d-metal ions and a lanthanide into account. Ferromagnetic exchange interactions were found to exist between the unpaired electrons of the paramagnetic centers in the exchange clusters of the gadolinium-containing heterometallic complexes {M-Gd-M} (M = Ni or Cu).     

Ligational behaviour of two biologically active N−S donors towards cobalt(III), iron(III), iron(II) and rhodium(III)

Summary The chelating behaviour of two biologically active ligands, pyridine-2-carboxaldehyde(4-phenyl) thiosemicarbazone(L₁H) and pyridine-2-carboxaldehyde thiosemicarbazone(LH), towards Fe^III, Co^III, Fe^II and Rh^III has been investigated. The ligands act as tridentate N–N–S donors, resulting in the formation of bis-chelate complexes of the type M^III(A)₂X·nH₂O (A=L₁ or L; X=Cl, ClO₄; M=Co^III, Rh^III, Fe^III), Fe^II(L₁H)₂SO₄·2H₂O and Fe^II(L₁)₂·H₂O. Biological activity of the ligands and the metal complexes in the form ofin vitro antibacterial activities towardsE. coli has been evaluated and the possible reasons for enhancement of the activity of ligands on coordination to metal ion is discussed.     

Cation Coordination of Bisamidopyridine-derived Receptors as Investigated in the Solid-state and in Solution

A bisamidopyridine-type receptor, N,N′-bis(6-methyl-2-pyridyl)pyridine-2,6-dicarboxamide (1), and its Co^III complex were prepared and their X-ray structures were compared to those of N,N′-diphenylpyridine-2,6-dicarboxamide (2) and Co^III(2)². Introduction of the two additional coordinative groups resulted in second-order interactions between the central ion and the nitrogen atoms of the terminal pyridine moieties in the crystalline state. Solution studies in acetonitrile revealed the importance of these interactions for the ligand's metal ion recognition ability. Whereas 2 only binds to Pb^II and Cu^II, 1 yields complexes with a majority of the heavy and transition metal ions studied, Co^II, Ni^II, Cu^II, Zn^II, Fe^III, Fe^II, Hg^II, and Pb^II, respectively. The cation binding properties in solution were investigated by absorption spectroscopy and in the case of 1–M^II/III, the formation of two spectroscopically distinguishable types of complexes was found. Protonation experiments and theoretical considerations helped to gain further insight into possible modes of coordination in solution.     

Syntheses,crystal structures and magnetic properties of two cyano-bridged two-dimensional assemblies [Fe(salpn)]2 [Fe(CN)5NO] and [Fe(salpn)]2[Ni(CN)4]

Two cyano-bridged assemblies, [Fe^III(salpn)]₂[Fe^II(CN)₅NO] (1) and [Fe^III (salpn)]₂[Ni^II(CN)₄] (2) [salpn = N, N-1,2-propylenebis(salicylideneiminato)dianion], have been prepared and structurally and magnetically characterized. In each complex, [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– coordinates with four [Fe(salpn)]⁺ cations using four co-planar CN^– ligands, whereas each [Fe(salpn)]⁺ links two [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– ions in the trans form, which results in a two-dimensional (2D) network consisting of pillow-like octanuclear [—M^II—CN—Fe^III—NC—]₄ units (M = Fe or Ni). In complex (1), the NO group of [Fe(CN)₅NO]^2– remains monodentate and the bond angle of Fe^II—N—O is 180.0°. The variable temperature magnetic susceptibilities, measured in the 5–300 K range, show weak intralayer antiferromagnetic interactions in both complexes with the intramolecular iron(III)iron(III) exchange integrals of –0.017 cm^–1 for (1) and –0.020 cm^–1 for (2), respectively.     

Thermal expansion in 3d-metal Prussian Blue Analogs—A survey study

We present a comprehensive study of the structural properties and the thermal expansion behavior of 17 different Prussian Blue Analogs (PBAs) with compositions M^II₃[(M′)^III(CN)₆]₂·nH₂O and M^II₂[Fe^II(CN)₆]·nH₂O, where M^II=Mn, Fe, Co, Ni, Cu and Zn, (M′)^III=Co, Fe and n is the number of water molecules, which range from 5 to 18 for these compounds. The PBAs were synthesized via standard chemical precipitation methods, and temperature-dependent X-ray diffraction studies were performed in the temperature range between −150 °C (123 K) and room-temperature. The vast majority of the studied PBAs were found to crystallize in cubic structures of space groups Fm3?m, F4?3m and Pm3?m. The temperature dependence of the lattice parameters was taken to compute an average coefficient of linear thermal expansion in the studied temperature range. Of the 17 compounds, 9 display negative values for the average coefficient of linear thermal expansion, which can be as large as 39.7×¹0⁻⁶ K⁻¹ for Co₃[Co(CN)₆]₂·12H₂O. All of the M^II₃[Co^III(CN)₆]₂·nH₂O compounds show negative thermal expansion behavior, which correlates with the Irving–Williams series for metal complex stability. The thermal expansion behavior for the PBAs of the M^II₃[Fe^III(CN)₆]₂·nH₂O family are found to switch between positive (for M=Mn, Co, Ni) and negative (M=Cu, Zn) behavior, depending on the choice of the metal cation (M). On the other hand, all of the M^II₂[Fe^II(CN)₆]·nH₂O compounds show positive thermal expansion behavior.     

Three‐Axis Anisotropic Exchange Coupling in the Single‐Molecule Magnets NEt4[MnIII2(5‐Brsalen)2(MeOH)2MIII(CN)6] (M=Ru,Os)

We have investigated the single‐molecule magnets [Mn^III₂(5‐Brsalen)₂(MeOH)₂M^III(CN)₆]NEt₄ (M=Os ( 1 ) and Ru ( 2 ); 5‐Brsalen=N,N′‐ethylenebis(5‐bromosalicylidene)iminate) by frequency‐domain Fourier‐transform terahertz electron paramagnetic resonance (THz‐EPR), inelastic neutron scattering, and superconducting quantum interference device (SQUID) magnetometry. The combination of all three techniques allows for the unambiguous experimental determination of the three‐axis anisotropic magnetic exchange coupling between Mn^III and Ru^III or Os^III ions, respectively. Analysis by means of a spin‐Hamiltonian parameterization yields excellent agreement with all experimental data. Furthermore, analytical calculations show that the observed exchange anisotropy is due to the bent geometry encountered in both 1 and 2 , whereas a linear geometry would lead to an Ising‐type exchange coupling.     

A Heterometallic FeII–DyIII Single‐Molecule Magnet with a Record Anisotropy Barrier

A record anisotropy barrier (319 cm^?1) for all d‐f complexes was observed for a unique Fe^II‐Dy^III‐Fe^II single‐molecule magnet (SMM), which possesses two asymmetric and distorted Fe^II ions and one quasi‐D_5h Dy^III ion. The frozen magnetization of the Dy^III ion leads to the decreased Fe^II relaxation rates evident in the Mössbauer spectrum. Ab initio calculations suggest that tunneling is interrupted effectively thanks to the exchange doublets.     

Polarographic analysis. I

Summary Reduction of Cu^II in 0.5 M NaOH containing triethanolamine proceeds irreversibly. A similar behaviour is observed in acetate buffer of p_H 6. A reversible wave is obtained in (NH₄)₂CO₃ containing EDTA. The diffusion current measured at the proper voltage is proportional to the Cu^II concentration within a wide range. The waves in 0.5 M NaOH are not well developed being better in acetate buffer and in the presence of EDTA. Ammoniacal solutions containing EDTA can be utilised for the simultaneous estimation of Fe^III and Cu^II. A mixture of Fe^III, Cu^II and U^VI can be fairly well analysed in a medium of (NH₄)₂CO₃ containing EDTA.